International Atomic Energy Agency

United Nations Educational, Scientific and Cultural Organization

International Centre for Theoretical Phvsics

No. 36137JulyiAugust 1990

Contents

Copley Medal to Abdus Salam I

A Portrait of a Friend:Stig Lundqvist 1

Message from theDirector General of IAEA 3

Honorary Degree

to Abdus Salam 3

Dirac Medats 1990 4

Dirac Medal Award Ceremony 5

String Theory —Some Reminiscences 6Interview with A.N. Matveev 11

Quantum Field Theory andPolitics: Prof. O. Gherman 12

C.V. Raman Prize 13

Fields Medal to E. Wit ten l 4

Maxwell Prize to R.N. Sudan 15

Appointments 15

Visits to ICTP 15

Conferences and Lectures 15

Hot Papers 16

Articles Alert l 6

Activities at ICTPin July-August 1990 l 7

Copley Medalto Abdus Salam

The Council of the Royal Societyhas awarded the Copley Medal 1990 tohofessor Abdus Salam, K.B.E., F.R.S.,in recognition of his work on thesymmetries of the laws of nature, andespecially the unification of theelectromagnetic and weak forces.

Professor Salam has madeoutstanding and influential contributionsto elementary particle theory over aperiod of 40 years. His early workincluded the completion of Dyson'sproof of the renormalization of QuantumElectrodynamics, and his work On parityviolation, dispersion relations and SU(3)invariance. This work contributedgreatly to tle development of elementaryparticle theory, but his majorconuibution was the proposal, inparallel with S. Weinberg, of the elec.tro-weak theory, unifying QuantumElectrodynamics with the weakinteractions between atomic particles.That theory, the first to bring togetherthe theories of the atomic forces,received spectacular confirmationthrough the discovery at CERN in 1983of the Wt and Z" intermediate bosons.

A Portrait of a Friend:Stig Lundqvist

by Hilda Cerdeira

Stig Lundqvist is well known st theICTP for his scientific andorganizational competence and for hiswarm personalily. In this paper, tlildaCerdeira discloses quite unknown traits

of Stig which make him an even morefascinating person. A message from H.Blix, Director General of theInternational Atomic Energy Agency,which was read on the occasion of theSymposium, is also presented.

Professor Stig Lundqvist, Chairmanof the Scientific Council of the ICTP,turned 65 on August 9th. His friendsprepared a short, high-quality meeting inhis honour, under the title "Symposiumon Frontiers in Condensed MatterPhysics in honour of Prof. StigLundqvisl"

During a long chat tlat, I could say,has extended through years, I have cometo know partly this man, whose workwas acknowledged with this event.

In a nutshell, his life can be sum-marized as follows: he was born inGudmudrA, in Northern Sweden, studiedat the University of Uppsala, got marriedduring his student years in 1949, becamean assishnt professor at Uppsala aftergetting his Ph.D. He moved ro theUniversity of Gothenburg in 1961,asanassistant professor, and became fullprofessor in 1963. He started to workwith the Nobel Committee in 1972,which he left officially in 1985, to beappointed as the Chairman of thePhysics Class of the Swedish Academyof Sciences. He has been the Chairmanof the Scientific Council of the ICTPsince 1985.

He comes from a a family with highappreciation for music and reading. AChristmas morning concert in hishometown, played with an organ,inspired him at an early age to staflplaying it, disturbing not only hisfamily but also his classmates. From hisfather he got a special ability to build

News from ICTP - No. 36/37 - July/August 1990

Abdus Salam congratulates Stig Lundqvist for his birthday and for hisaccomplishments. On the left, the Rector of Chalmers University of Technology, Prof.A. Sjdberg.

things, and as many children of his ownage, built model planes that did notwork. But, where most children stop, hekept inquiring the reasons of failure.Whether this was the beginning of hisliking of physics is hard to tell, but hisinterest in physics and music moved him$rough his adolescence.

He started a jazz band at the age of14, which lasted for a yqr . After ttnt hemoved on to play with professionalbands. This helped him to keep his thenhobby of physics, since a good part ofhis income was spent in physics andmathematics books. He played jazz withpeople like Stan HaselgArd, who laterbecame famous as a clarinet in BennyGoodman's band, and later on inCalifornia when he was visiting as ascientist, with Bud Shanks, where heused to give Sunday concerts.

At the age of 2l after his militaryservice, he entered the University ofUppsala. At that time, most Swedishuniversities were not prepared to receivestudents who did not belong to academicfamilies. And it was a shock to find thisLaplander, son of nobody, o make it bysheer stubborness. The Universityteaching was poor at the time due to thearchaic structure. Stig made a lot ofefforts to change the stiffness ofeducation in Swedish universities. Hebecame an assistant professor at the

University of Uppsala in 1955. There hestarted to get interested in many bodytheory, and helped by Jerry Brown, fromCopenhagen, who visited Uppsalafrequently, he went for a semester to theNiels Bohr NORDITA Institute, wherehe could feel the excitement of the NielsBohr years. In 1958, he went to theUSA to work with Keith Bruepkner, andmade some acquaintances that arenowadays some of his best friends.

He became aware of the ICTP whenit was only a dream of Abdus Salam, inthe early sixties. He got involved in theCondensed Matter program from thebeginning. After the first course in thissubject which was held in 1967 and hadbeen organized by J. Ziman, F. Bassaniand himself, he started in 1970 theSummer Workshops with the helP ofPaul Butcher, Federico Garcia Molinerand Norman March. He has made aneffort to present always high qualityactivities at the ICTP, always bringingwhat of new and interesting is around.He has also tried to make the Centre aplace of high quality research. It is inthis area that now, at retirement age,where most people would be thinking ofreceding into a quiet life, that he 'isplanning to put his efforts by spendingmost of his time here.

Two years ago his friends andcolleagues Elias Burstein, PraveenChaudhari, Robert Schrieffer, ErioTosatti and Yu Lu started to organize aconference to celebrate his 65th birthday.

The conference (or birthday party)lasted three days and it was attended bymany of his friends and closeacquaintances, five Nobel laureates —P.W. Anderson, K. von Klitzing, H.Rohrer, AMus Salam and R. Schrieffer— his children and grandchildren, ex-students and many well known

From left to riglt: R. Schrieffer, P.W. Anderson, Abdus Salan, S. Lundqvist and P.Bndinich. Standing behid Profs. Lurdqvist and Budinich are E. Burstein and H. Rohrer.

News from ICTP - No. 36/37 - July/August 1990

physicists who made the conference avery successful evenl

In his own words the most strikingfact of the conference was the"tremendous enthusiasm and momentumgoing on in the frontiers of condensedmatter physics, whose borders arebecoming loose with time. Condensedmatter extends now from atomic andmolecule problems to theory ofcornplexity or that of computation (aspresented by B.A. Huberman). Progressin condensed matter is no longerrestricted to natural materials but toman-made devices in semiconductors,covering wide areas of physics of todayas shown by H. Stormer".

Prof. P. Chaudhari lecturing at theSymposium.

During the ceremony Stig waspresented with the Chalmers Medal bythe Rector of Chalmers University, Prof.Anders Sjdberg, and with the DiracMedal of the ICTP by Prof. AbdusSalam.

Message from theDirector General of IAEA

Dear participants,Dear Stig,

With much regret, I had to declinethe invitation to paticipate with you inthe Symposium on Frontiers inCondensed Matter Physics dedicated tothe 65th anniversary of Stig Lundqvist.

Many know of Stig's impressiveachievements in the Swedish academicscene, but I believe too little is known

about his involvement in theinternational scientific world and in theInternational Centre for TheoreticalPhysics in particular. This involvementhas been exemplary; Stig was one of theDirectors of. the College on CondensedMatter in October-December 1967. Thisfirst course was to have a greatsignificance in the scientific history ofthe Centre because it introduced a newimportant discipline in the curriculum ofthe Centre in addition to elementaryparticle, nuclear and plasma physics, anda branch which was also relevant to theinterests of the IAEA. It is Stig's greatmerit that all potentialities of thisbranch of human knowledge are nowmade available to the scientists andengineers in the developing countries.From the early seventies onwards, Stigand a team of distinguished colleagues— Profs. N. March, P.N. Butcher, F.Garcia-Moliner and others — started !oconsolidate the programme in condensedmatter physics. In a first phase and in aseries of high-level courses, he patientlyrained many young physicists from the

Third World and gave them anopportunity !o exercise their creativity inresearch workshops which became aregular feature of the programme. Iater,he persuaded Ialian colleagues so help insetting up a pennanent research group atthe Centre. This group is nowadayskrnwn as one of the best in the world.

Stig Lundqvist is a convincedinternationalist and wishes to offer thevery best to those who come to work toTrieste. In 1986 he created the AdriaticoResearch Conferences — five to sevenconferences every year — where heinvites the most eminent scientists bothfrom developing and from advancedcountries and where anyone who isgenuinely interested can learn about thelatest developments in a large variety ofopics.

Stig Lundqvist's commitment to thegrowth of science in the developingcoun8ies was the reason he was called oserve on the Scientific Council of theICTP (1982) and as its Chairman since1984. On many occasions, I admired hissharp vision on the role of the ICTP andthe wisdom of his advice. For all theseaccomplishments, we in the IAEA aremost grateful to you, Stig. We hope tocount on your invaluable advice for the

fuhre.I wish you a happy birthday amidst

your friends eud colleagues.To the participants, I wish a very

fruitful conference around Stig who hasdone so much for the success of yourdiscipline.

Honorary Degreeto Abdus Salam

On Thursday 12 July, ProfessorAbdus Salam, Director of theInternational Centre for TheoreticalPhysics and Prresident of the Third WorldAcademy of Sciences, was honouredwith the diploma of Doctor of ScienceHonoris Causa of the University ofGhana. As Abdus Salam could nottravel 0o Ghana the ceremony look placein the Main Lecture Hall of the ICTP.The Vice-Chancellor of the University ofGhana, Prof. A. Sawyerr, wearing thegown of his University, accompanied byHis Excellency the Ambassador ofGhana !o ltaly, Mr. G. Lamptey, and adelegation of Ghanaian personalitieswere the guests of the ICTP for thewhole day. The Vice{hancellor read thecitation for the degree:

"Abdus Salam, born in lhang,Pakistan, on fantary 29,1925, you wereat birth given thc name you still bear,which mcans "Servant of Peace". Youhave infued lived up to lour namc. In1968, the Atoms for Peace Foundationsaw fit to award you the "Atoms forPeace Medal", wMch is only one in along string of awards attesting to alifetime in tlu pwsuit d peace.

"You gave early twtice of academicexcellence wlwn at lw age of 14 youscored tlw higlust marks ever recorded ata Matriculation Examination inPakistan. This was followed bysclnlarships to Government College atiltang, Punj& Universiry in Lalore, andSt. Iohn's College, Cambridge, in acontinuing manifestation of academicextellence.

"You have undertaken a variety ofassignments as a teaclwr and researchcr,and as consultant and adviser togovernmcnts and international bodies,including tlu United Nations. You lavewritten boolcs and published a lnst ofparyrs, runy of which have received

News from ICTP - No. 36/37 - July/August 1990

worldwide acclaim. You have beenappointed to Professorships; elected toFellowships of Learned Academies andSocieties; admiued to DistinguishedOrders; and awarded prizes and otlrcrsymbols in recognition of youroutstanding attainments. All of thisculminated in tlv award to you in 1979of the Nobel Prize for Physics.

"For us in thc Third World, you lnlda special place as much for theseachievements as for your continuingefforts at itnproving the conditions forthe study of science in our deprivedenvironment.

developing countries with what theyneed to sustain and develop theircompetence as scientists, and enhancetlwir contribution to tlv well-being oftluir peoples.

"Nor is that all. In 1984 you, inconcert with otlwrs, founded the ThirdWorld Acdenry of Sciences to continuethe propagation of science on a stillbroader front, with the aim of bringingtln more advanced aspects of sciencecloser to the hitlurto less scientiftcallyfuvebped countries of tlu world.

"In all this, you have given ofyourself totally and without counting the

Abdus Salatn, tlv Vice-Cluncellor of thc University of Gharu A. Smryen and I H.E. tlvAmbassador of Gharu to ltaly Mr. G. Lanptey, at tlrc Horarary Degree Ceremony.

"The International Centre forTheoretical Physics at Trieste, yourbrainchild, which contirutcs to flourishunder your direction, las played lnst tomany a Third World scientist, whosubsequently achieved distinction inscience and public service. Here at theCentre, slart-term concentrated courseson advanced topics in physics areavailable, at little or no cost, to all wlocse to, and ue able to, takc advantage ofthem. This Centre has exposedphysicists from the developing countriesto each other, to physicists of thedeveloped countries, and to tlrc latestdevelopments in a rapidly changingsubject area. Tlllls has the Centre, underyour inspired and inspiring leadership,continued to equip scientists of the

cost, for tlu upliftment of mar*ind."For your serices to mankind many

well-deserved honours have beenbestowed on you already. Beginning in1957, you hary received Innorary Doctorof Science degrees on more than 30different occasions from Universities theworld over. We are proud today to becounted among tlwse institutions whichlave hd the piilege of lwnouring you.

"Abdus Salam, true Messenger ofPeace, teaclrcr, researclur and hwnanist,for your academic achievements, yourpersonal contibution to scientificresearch, your selfless and e*raordinarydevotion to the promotion of sciencethroughout the world for peacefulpurposes, and your insistence on theWrticipation of Third World counties in

the study, and development andapplication of science, tlrc University ofGlana is proud to lwnour you. I feeltruly honoured to invite you to stepforuard to receive tlu fugree of Doctor ofScience, Honoris Causa, of theUniversity of Glana, lcgon."

After receiving the diploma from thehands of the Vice-Chancellor, AbdusSalam also wearing the gown of theUniversity of Ghana, expressed hisgratitude for the distinction beslowed onhim and briefly recounted hisreminiscences of his early and lateracquainance with the Ghanaian scientihcrealitY'

A.M. H anende

Dirac Medals 1990

The 1990 Dirac Medals of theInternational Centre for TheoreticalPhysics (ICTP), Trieste -(Italy), havebeen awarded to Prof. LudwigDmitri ye vich Faddeev (SteklovMathematical Institute, Leningrad,USSR) and Sidney Richard Coleman(Harvard University, Cambridge,Massachusetts, USA).

Ludwig Dmitriyevich Faddeev ishonoured for researches in the area ofquantum field theory and mathematicalphysics. His name is well known intheoretical physics in connection withthe Three Body System (Faddeev'equation). He made decisivecontributions to the quaritization of theYang-Mills and gravitational field. TheFaddeev-Popov covariant prescription ofquantization of non-Abelian gaugetheories discovered in 196G67 has manyessential applications including quantumeffects in the Glashow-Salam-Weinbergmodel of electroweak interactions and inquantum chromodynamics. Faddeev is adisciple of Dirac's ideas in theoreticalphysics. His studies are related with theevolution of the Dirac Hamiltonianinterpretation in the inverse scatteringmethod (1971) and with exact integrablesystems, as well as with quantum theoryof solions (1975). He also clarified thegroup-theoretical origin of anomalies inthe context of cocycles (1984). Hisworks stimulated the wide-spreadapplication of solitons in relativisticquantum field theory. Faddeev's

News from ICTP - No. 35/37 - July/August 1990

contributions to the quantum inversescattering method and 4-matrix theoryinitiated the development of thisdirection which is now known as theQuantum Group Approach. Hisscientific work significantly conributed!o the broad exient of geometrical andalgebraic ideas in modern theuetical andmathematical physics.

Prof. Lndwig Dmitriyevich Faddeevwas born in Leningrad on March 23,1934. He grduted from Leningrad StateUniversity in 1956. He received hisPh-D. in 1956 and degree of doctor ofsciences in 1963 at SteklovMathematical Institute of the USSRAcademy of Sciences. Prof. Faddeevpermanently works at LeningradDepartment of SteHov MathematicalInstitute. He started as a ResearchAssociate (1960), Senior ResearchAssociate (1964), then became kader oftlu Laboratory of Matlwmatical Metlodsof Plrysics (1974) and Depury Directorfor tlre Leningrad Depotment of SteHovInstitute in 1976. He was appointed asProfessor at the Department ofMatlnmartcal and Matlvmatical Physicsin 1967. Ludwig D. Faddeev is aMember of the USSR Academy ofSciences (1976), Member of theAnurican Academy of Scicnce and Art atBoston (1979), President of theInternational Union of Mathematics(1986), Honorary Member of theAcademy of Science of Poland (1987),Doctor Honoris Causa of Universities atNankai and Buenos Aires (1987 and1988), Foreign Member of thc Academyof Science and Literature of Finland(198d). He lw pfiIishcd more tlan 150scientific articles and five books. He isa member of the editorial board ofseveral internatioral jownals. Honoutsbestowed include: USSR State Prize(1971) and Danny Heircmann Prize onMulnmatical Physics (I975).

Sidney Richard Coleman is honouredfor his contributions to quantum fieldtheory and particle physics. His workon quantum field theories has greatlyclarified their structure. This includesthe classification of all possible bosonicsyrimetriesr of S-matrix (with J.Mandula) and the study of somefundamental properties of two-dimensional quantum field theories,including, in particular, the absence of

symmetry breaking and aspects ofboson-fermion equivalence. His study(with E. Weinberg) of the quantumeffective action and the phenomenon ofdimensional transmutation has had animportant influence on the developmentof the subject. Sidney Coleman's workon global aspects of quantum fieldtheories has also been of fundamentalimportance in the development of thesubject. This includes his work on thefate of false vacuum, on the discovery ofQ-balls, and more recently, on thepotentially far-reaching physicalconsequences of wormholes. Thesecontributions are paralleled by theequally important one of teaching theyomger generation of particle physiciststhe modem concepts in quantum fieldtheories through very lucid lectures andpap€rs.

Prof. Coleman was brn on 7 March1937 in Chicago, Illinois, USA. Heobtained ftis 8.Sc. at the lllinoisInstitute of Technology in 1957 ad hisPh.D. at the Califurnia Institute ofTechnology in 1962. He started hiscareer at Hartard University as a CornhgLecturer on and Research Fellow inplrysics (1961-63). He then becameAssistant Professor of Physics (1963-65), AWd Sloan Fellow (1%i4-65), andAssociate Professor of Phyiics from1966 to 1968 at thc sarne Ilniversity.After spending oru year at the Universityof Rome, Italy, as a Visiting Professor,he returncd to Hamard where lw wasappointed as a Professor of Physics in1969. He was visiling Professor oneyear at Prkceton in 1973 and at Statfordin 197930. In 19&, lv was appointedas a Donner Professor of Science atHarvard University. In 1989 he wasagain visiting Professor at Berkeley.Honors bestowed include the BorisPregel Award from the New YorkAcademy of Sciences; the Award forLectures in Physics from the CentoEttore Majorana (International Sclnol ofPlrysics, Erice, Italy); J. Murray LackAward for Scientific Reviewing given bytlv NatioruI Academy of Sciences; andtlu Distinguislrcd Alwnnus Award fromtlu California Institwe of Techrclogy.Prof. Coleman is a Fellow of theAmerican Physical Society, AmericanAcademy of Arts and Sciences andNational Academy of Sciences. He is

the author of 82 papers.

The Dirac Medals of the IntemationalCentre for Theoretical Physics wereinstituted in 1985 in memory of Prof.P.A.M. Dirac, an honoured guest ands0aunch friend of the ICTP. They areawarded every year on Dirac's birthday -8 August - for contributions totheoretical physics. From 1990, theMedalists will also receive a US$10,000 cheque.

In 1985, the Dirac Medals wereawarded to hofessor Yakov Zeldovich(Institute for Space Research, Moscow,USSR) and Prof. Edward Witten@rinceton University, USA), and in1986 to Prof. Yoichiro Nambu @nricoFermi Institute for Nuclear Studies,Chicago University, USA) and Prof.Alexander Polyakov (-andau Instinrte forTheoretical Physics, Moscow, USSR).In 1987, they were awarded to Prof.Bryce DeWitt (University of Texas atAustin, USA) and Prof. Bruno Zumino(University of California at Berkeley,USA). The recipients of the 1988Medals were Prof. David J. Gross(Princeon university, usA) and Prof.Efim S. Fradkin (Lebedev PhysicalInstitute, Moscow, USSR). In 1989,the Medals were awarded to John H.Schwarz (Cdtech, Pasadena, USA) andMichael B. Green (Queen Mary College,London, UK).

The Selection Committee includesProfessors S. Lundqvist, R. Marshak, J.Schwinger, S. Weinber$, E. Witten,Abdus Salam and others. The DiracMedals of the ICTP are not awarded toNobel Laureates or Wolf FoundationPrize winnen.

Dirac Medal AwardCeremony

On July 4, J.H. Schwarz (Caltech,Pasadena, USA) received the 1989 DiracMedal which had been awarded to himlast year. The other of the two Medalsawarded every year on the birthday ofP.A.M. Dirac : 8th August — went toMichael Green from Queen MaryCollege, Inndon, UK.

The ceremony took place in the MainLecture Hall of the ICTP. After anintroduction to the work of J.H. Schwarz

News from ICTP - No. 36/37 - July/August 1990

by Professor AMus Sdlm, Director ofthe ICTP, Prof. P. 'Fasella, a biochemistand Director General of the EuropeanEconomic Community's GeneralDireclorate for Science, Research andDevelopment, read the citation andpresented the Medal to the awardee. HeaMett

"I wish to say what a strongimportance we afirtbue to basic sciencesnot only as the source of tlw knowledgeand know-how which we need to solveour socio<conomic problems but also asa ventwe of mankind itself.

"It is a great lnnour to be associatedwith the presentation of this veryimportant prize and I am very grateful toyou, Professor Salam, and to theInternalional Centre. And, as you say,we are extremely interested in what wedo. We lave started some collaborationand look forwrzrd for more in tlu futwe."

Immediately after, J.H. Schwarzlectured on "Slring Theory — SomeReminiscences".

A.M. Hanende Dirac Medal wiwer J.H. Schwarz and Abdus Salarn.

String Theory —Some Rerniniscences

by IH. Schwarz

I have decided to use the occasion of receiving thiswonderful honor — the Dirrc Medal — to recall some of thehighlights of 'my life as a string theorist.' String theory has arather complex and bizarre history, so it is not possible for meto present a complete and balanced trea0nent. Instead, I havedecided to focus on four specific episodes in which I have beendirectly involved: supersymmetry on the world sheet, stringsfor unification, space-time supersymmery in string theory, andthe 19M superstring revolution. The history of string theoryprior to 1971 is a fascinating story that I will completelyomit.

Supersymmetry on the World SheetThe Veneziano sring theory (or 'dual model), developed in

the period 1968-70, suffered from several unphysical features:the absence of fermions, the presence of a tachyon, and theneed for 2Gdimensional space-time. These facts motivated thesearch for a more realistic string theory. The first significantsuciess was made in January 1971 by Pierre Ramond,l) v6ohad the inspiration of constructing a string analog of the Diracequation.

A bosonic string Xr (o, r) with 0 S o 3 2r has a

momentum density Pp (6, t) = -r-XPio, x), whose zero mode

= +- i P*(o, x)da (l)

is the total momentum of the string. Ramond suggestedinroducipg an analogous -Ae1;tf IT(o, t), whose zero mode

i-ZK

2n

Q(2)

is the usual Dirac matrix. He then defined Fourier modes ofthe product l-.P

2.

*n=T-;* einoTP do. (3)

The zero mode,'FO = T.p + oscilla[or lerms (4)

is an obvious generalization of the Dirac operator, suggesting awave equation of the form

- - l v ) = 0 (5)for a free fermionic ,oi"g:'

By postulating the usual commutation relations for XP andPP as well as

{I1t(o, r), Iv(d,c)} = lTgnPv\(o - d), (6)he discovered the 'super-Virasoro' or W=,1 supercon formal'algebra

= 2Lm+n

| (* ' - ) Sm+n,0

[Lm, (7)

(Lm, Ln] = (m - n)Lm+n * fif*3- m)

generalizing the well-known Virasoro algebra (given by the

News from ICTP - No. 36/37 - July/August 1990

Irr's alone).

While Ramond was doing the work described above, AndrdNeveu and I were working together at Princeton on thedevelopment of a nelv interacting bosonic string theorycontaining a fermionic world-sheet field HP(o, R) satisfying the

. same- anticommutation relations as lv(o, ?), but antiperiodicin o.2) HF therefore has half-integral Fourier modes (A), , ,Z +112) only. The same super-Virasoro algebra arises, butwith half-integrallt moded r * r ? * *

hl e''rc,H .Pdo (replacing the F2's. We thought that our theory came quiteclose to giving a realistic description of nonstrange meso{ls, sowe called it the 'dual pion model.' Nowadays, my viewpoint isquite different, of course. In any case it was clear o me alreadyin 1971 that there is a very rich mathematical structure thatneeds 0o be understood irrespective of any possible physicalinterpreAtion.

Together with Charles Thorn, we figured out how the G7

opemtors .act€d as subsidiary gauge conditions in the interactingtheory.3) The key step *as to redefine the vacuum by i'pichre-changing' operalor. We called the original sring Fockspace F1 and the new one F2. Only in the F2 picture were thesuper-Virasoro conditions realiz€d in a straighdorward way. Atthe same time we began to appreciate the formal similaritybetween our construction and the nork of Ramond. This ledus to conjecture that our model could be extended to includeRamond's fermions. Neveu and I succeeded in finding a vertexoperator describing the emission of a 'pion' from a fermionicsring. We used it to construct amplitudes for two fermionsand any number of pions.4) Two weeks later Charles Thornpresented a paper containing the same resulss) as well as thefirst explicit formulas for fermion emission.

Let me now turn to the question of what all this has to dowith supersymmetry. First of all, it is now understood thatthe Virasoro algebra describes two-dimensional conformaltransformations, which can be regarded as analytic mappings of

a Riemann surface. The infinitesimal generator Ln - -2n+IL

corresponds to z + , a trn*I. The super-Virasoro (orsuperconformal) algebra can be regarded as a generalization to'super-analytic' mappings of a 'super Riemann surface,' withlocal coordinates z and 0, where 0 is a Grassmann number.

Later in 1971, Gervais and Sakita proposed aninterpretation in terms of a npo-dimensional world-sheet actionprinciple.6) Specifically, they described the Xtt(o, z) as freescalars (this was known previously) in supersymmetrymultiplets with free Majorana (2-component) fermions

o, ) . The action is

(9)

where do are world-sheet derivariv* (*, *) and pd are

two-dimensional Dirac matrices. They noted that this rction Sis invariant under the global supenymmetry transformation

(10)where e is a constant infinitesimal Majorana spinor.

When I has periodic boundary conditions (and henceintegrally-labeled Fourier modes) it corresponds to Ramond's

o, t). When it is taken to be antiperiodic, it corresponds to, T). Since Xp is ordinarily periodic, the global

symmefy described above only applies to the Ramond sector.The operators Fn or G7 correspond to Fourier modes of theassociated Noether current, just as L, corresponds to modes ofthe twodimensional energy-momentum tensor.

A deeper understanding of the significance of the super-Virasoro gauge conditions brcame possible following thedevelopment of supergravityJ) That theory involved makingspace-time supersymmetry local, so it was natural to attemptthe same for world-sheet supersymmetry. This was achievedby introducing a two-dimensional 'zweibein' field eS thatdescribes the geometry of the world sheet and a Rarita-Schwinger freld 7o, which is a gauge field for world-sheetsupenymmetry.8)

The discovery of this action was important for severalreasons. First, it exhibits a local Weyl symmetry, a featurethat depends crucially on the two-dimensionality of the worldsheet. There is also an associated local fermionic symmetry.The local symmetries are just sufficient to choose a gauge inwhich eff = fr and I,a = 0 in local coordinate parches. (Ingeneral, there are topological obstructions to doing thisglobally on the world sheet.) In this gauge the XP and VFequations of motion are simply Pa"X' = 0 and Podott = 0, afree wave equation and a free Dirac equation, for which thegeneral solution is easily written down. Also, the To a n d efiequations of motion become the vanishing of the supercurrentand the energy-momentum tensor. This provides a logicalfoundation for ttre super-Virasoro gauge conditions.

A second reason that this formalism proved to be importantis the crucial role it plays in Polyakov's 1981 formulation ofstring amplitudes as a sum over conformally inequivalentworld-sheet geometries.9) Since this viewpoint is sofundamental, many people now refer to S (whether for bosonicor fermionic strings) as the 'Polyakov action.'

Strings for UnificationString theory was origipally developed (by a bizane

sequence of serendipitous events) out of the S matrix programfor understanding the strong interactions. The physical picturethat emerged was one in which hadrons could be pictured asstrings, about a fermi in length, with quarks attached to theends. There was a period of considerable optimism about theprospects for formulating a complete theory of hadrons in suchterms. This program achieved a number of qualitativesuccesses because sring theory amplitudes incorporate severalgeneral features originally identified as properties of hadronssuch as Regge behavior and duality.

After a period of about five years of intense development(1968-73) it became clear to most theorists working on stringtheory that there were severe, perhaps insuperable, difficulties.Some of these were the need for extra dimensions, the

7

News fron ICTP - No. 36/37 - July/August 1990

appeannce of tachyons and massless particles, and the inability!o account for the point-like structre revealed in deep inelasticscattering experiments. The final nail was driven ino thecoffin of string theory when QCD emerged as a successfultheory of the strong nuclear force. String theory was

.abandoned by almost everyone even more quickly than it hadarisen.

A few theorists (such as Polyakov, Gervais, Neveu,...)continued io think about string theories of hadrons drring the1974-U period. In my opinion, it makes good sense to se€k ahadronic string theory, even if one is convinced that QCD iscorrecL QCD describes the srong force in terms of fields tlntcorrespond !o free quanta in the ultraviolet limit. At lowenergies (or long distances) these fields are strongly coupledand analytic calculations are impossible. A sring descriptionshould be a good approximation in the infrared, the free stringmodes bearing close resemblance to the physical mesons.@aryons would arise as skyrmions, as one lno-ws from snadiesof sigma models.)

During the 1973-74 academic year, just at the time thatsring theory was falling out of favor, Jo0l Scherk spent half ayear visiting Caltech. We both felt srongly that string theorywas too beautiful a mathematicd structure !o be completelyirrelevant to nature. After a while it occurred to us that manyof its defecB could be hrrned into virtues if it was used for acompletely different purpose than that for which it wasoriginally developed. One of the nagging problems that hadbugged us for yean was the inevitable occurense of a masslessspin-two state in the closed-sring spectrum. \Me suggestedinterpreting this state as a physical graviton and regardingstring theory as a candidate for a unified theory of allfundamental particles and fcces rather than as a theory ofhadrons.rO) Using a general argument of Weinberg based ongauge invariance,ll) we proved that low-energy gravitoninteractions in string theory agree precisely with generalrelativity. (This argument was also made independently byYoneya.12)

The reinterpretation of string theory as a unified theorycontaining gravity was a radical change in viewpoint. In orderto achieve the correct value of Newion's constant, thefundamental length scale needed to be the Planck length, some20 orders of magnitude smaller than a hadron. Such lengthscales seemed absurd to particle physiciss of the time, sincethey are way beyond anything that can be probedexperimentally. (Grand unified theories, which involvedigances only a few aders of magninde larger, were inrodqcedat about the same time.) As students, we had b€en taught thatgravitational forces are completely negligible in particlephysics. There was a sharply defined division in the sociologyof the profession between the relativists who study gravitation(usually as a classical theory) and partirle physicists who studythe other forces. fircrefore this was not only a difficult stepfor us, but it was a proposal for which there was no readyaudien@.*

* The development of supergravity and Kaluza-Klein theory duringthe subscquent decade produced a generation of young theoristsaccustomed to thinking about gravitation in a particle physics

In addition !o accounting for the graviton, string theory hadseveral other advantages that provided enconagement to Sche*and me. We knew that string theory had much softerultraviolet behavior than point-particle field theories.Therefore we were optimistic that the nonrenormalizabledivergences that plague all attempts to build a point-particlefield theory including gravity could be avoided. Also, ingravity theories the geometry of space-time is dynamical, andso it seemed plausible to us that the extra dimensions could bewrapped up into an invisible ball. In this way the four-dimensional appeararne of space-time could be accounted for.t

The inevitable appearance of gravitons and the goodultraviolet behavior of string theory convinced me that thiswas almost certainly the correct route to unification.Nonetheless, for ten years my best efforts to sell these ideas toothers were rather unsuccessful. Some eminent physicists —such as Murray Gell-Mann and Edward Witten — took themseriously. Almost everyone else did not.

Space-Time Supersymmetry in String TheorySupersymme&y was also discovered independently of the

work on world-sheet supersymmetry that I have described.Gol'fand and Likhtman submitted a paper in March l97l inwhich they formulated the N=1 super-Poirrcard algebra in fourdimensions.l3) wess and Zuminol4) wrote the seminal paperthat made supersymmetry a cottage industry. It states verycleady that their motivation was to construct a four-dimensional analog of the nvo-dimensional symmetry that hadbeen discovered in sring thecy.

Soon after the development of supergravity, Gliozzi,Scherk, and Olive (GSO) wrote an important paper examiningthe possibility of space-time supersymmetry in stringtheory.l5) They observed that since the spectrum of closedsuperstrings contains a massless gravitino in addition to thegraviton, consistency of the theory requires that the entirespectrum form supersymmetry multiplets. As formulated byNeveu and me, this was not quite the case. However, GSOshowed that a simple projection could be introduced toeliminate approximately half the states in ttre specrum. Oncethis was done, they were able to demonstrate that theremaining ten-dimensional open sring spectrum contains anequal number of physical bosons and fermions at each masslevel. This was compelling circumstantial evidence for space-time supersymmetry of the sring theory, although a proof wasstill lacking.

In July 1979 (while visiting CERI$ I began an intense andintellectually exhilarating collaboration with Michael Green.In the six subsequent years we spent a large part of our timeworking together : mostly at Caltech, but also at the AspenCenter for Physics and Queen Mary College in London. Onseveral occasions, Lars Brink also participated in the work.Our first several papers dealt with reformulating superstringtheory in a form that makes space-time supersymmetry

context. Most of these people now work on string theory,t The misleading term 'spontaneous compactification' wasintroduced to describe this possibility. I used to express mymisgivings by saying it was 'spontaneous, but not unrehearsed.'

News lrom ICTP - No. 35/37 - July/August 1990

manifest.l6) In reEospect, it seems strange that it look so longto examine the question of space-time supersymmery in sringtheory. When Mike Green and I returned to the question, ittook abu t a year of hard work to prove that this symmetry isindeed present, both in the particle spectrum and in thejnteracting theory. In those days one could work on thesematters in a leisurely way in complete confidence that no oneelse was doing the same thing — quite a conmst to the prasentsituation!

Following the demonstration of qpace-time supersymmetryf c q e n Cfne D superstrings, we discovered the TWe II closedsring theories with extended space-time supenymmetry.lT)We gave a simple proof at one loop of the vanishing ofarnplinde-s with three or fewer massless external lines (fa bothType I and Type II superstrings), and conjectured that thiswould be true in all higher orders as well ('nonrenormalizationtheorem'). We evaluated four-particle amplitudes,demonstrating their finiteness at one loop. It was argued thatthis too should be rue m all cders. Several Fpers describingsuperstring field theory in the light-cone gauge were alSowritten.l8)

In an atrempt !o obain a deeper understanling of space-timesupersymmetry in string theory, we formulated a covariantworld-sheet action with manifest space-timesupersymmetry.l g) Specifically, we found that the rction

5 = - t J Ot)

••j

l

has N=2 global supersymmetry in ten dimensions:(r2)

In these equations, 4 and # 1A = 1,2) u e Majorana-Weylspinors, r u are tendimensional Dirac mauices, and

n&^djp-ifrrvdee*. (13)This action is sup'posed to describe the same sring physics asthe NSR formulation (with GSO projection) even though irhas no world-sheet fermiqrs or world-sheet supersymmetry.

The equivalence of this action to the NSR one is wellunderstood (by bosonization) in the light-cone gauge.2o)However, covariant quantization of the action given above hasproved to be very challenging, because it contains acomplicated mixtrne of first-class and second-class constraints.There is a large recent litenture devoted to this problem, but itremains to be demonstrarcd that any proposal gives a practicalscheme for evaluating amplinrdes and analyzing ttre theory.

The. 1984 Superstring RevolutionOne issue ,thal surfaced as crucial during the early 1980s

was the need to understand chiral structure (left-rightasymmetry) of the standard model. All the popularsupergravity theories were nonchiral, and it was pretty clearthat a chiral strucqre could not arise spontaneously. Two of

the three known ten-dimensional superstring theories werechiral (ype I and IIB). This was good, because it meant therewas a charrce of accounting for chiral four-dimensional physics.It was also dangerous because it meant the theories werethreatened by gauge anomalies that would make theminconsistent.

The type I supersring theory can be formulated for anyclassical gauge group. The low-energy limit gives ten-dimensional supersymmetric Yang-Mills theory (coupled tosupergravity). It was shown that hexagon diagrams (analogousto triangle diagrams in four dimensions) give a gauge anomalyfor the Yang-Mills theory for every possible choice of gaugegroup. Most experts seemed to believe that string correctionscould not improve matters.

The anomaly problem haunted us throughout the 1980-84period. On several occasions I ried with Mike Green, with mystudent Neil Marcus, or by myself to evaluale the relevanthexagon diagram. However, the calculations always gotbogged dorvn and no clear conclusions could be ilrawn. Some,remarks can be found in my 1982 Physics Reports artide.2l)

The fundamental paper of Alvarez-Gaumd and Witten,entitled 'Gravitational Anomalies,' gave formulas for thecontribution to gauge, graviational, and mixed anomalies ofchiral fermions and self-dual tensor gauge fields in anydimension.22) The most striking example they analyzed wastype IIB supergravity in ten dimensions.23) A priori, it couldhave three distinct types of gravitational anomaliescharacterized by the l2-forms tr R6, tr R2 tN, and 0r n2f.They discovered that the coefficients of each of the three termsvanished as a consequence of remarkable cancellations amongthe various contributions. This made it very plausible that thetype IIB superstring would also be anomaly-free. ( hadexpected ftris to be the case, since Green and I had found thatthe ornJoop sring amplimdes are finite.)

In the summer of 1984,I organized a workshop on 'physicsin higher dimensions' at the Aspen Center for Physics. Manyleading experts on anomalies, such as Bardeen and Zumino,were there. This proved !o be very fortuitous. 'Green and Idiscussed the anomaly problem with Friedan and Shenker.They suggested trying to do the calculation in the old NSRformalism rather than the newer one that we had justdeveloped. This proved to be a gmd idea, because the space-time supersymmetric formalism could only be used in light-cone gauge, which is very awkward for analyzing anomalies.Physically, anomalies correspond to the coupling at one loopof longitudinally polarized gauge particles, which ought o bedecoupled as a oonsequence of gauge invariance. This leads toa breakdown of unitarity at two loops and beyond. In aphysical gauge (such as light-cone gauge) unphysical modesare banished by the formalism from the outset. Therefore theinconsistency must show up elsewhere — namely in abreakdown of Lorentz invariance. Unfortunately, this isextremely difficult to recognize in a formalism that isn'tmanifestly Lorentz invariant in the first place. In the NSRformalism tlre calculation could be done covariantly.

After a period of struggle and confusion, Green and I founda good way of inroducing a regulaor and succeeded in gettinga nonzero result for the planar diagram contribution to the

News from ICTP - No. 35/37 - July/Au gust 1990

hexagon gauge anomaly. At first this didn't make us toohappy, because it confirmed what everyone had said — type Isuperstrings have gauge anomalies. We also calculated theMdbius strip diagram, which gave an anomaly of the sameform.

The next day, just before one of the workshop seminars, Iremarked !o Mike that maybe there is a group for which theplanar and M0bius strip anomalie,s cancel. At the end of theseminar, Mike said to me 'SO(32).' T\en we started gettingexcited. But we were not yet convinced that this wasimportant because there were potentially several distinctgravitational and mixed anomalies, and we had no evidence yetf a their cancellation.

After a while we decided to try to undersand our result interms of a low-energy effective field theory — namelysupergravity coupled to super Yang-Mills theory in tendimensions. I remembered that George Chapline and NickManton had been working on precisely that problem theprevious sutnmer in Aspen,24) so we studied their papercarefully. Drawing on it, the formulas of Alvarez-Gaumd andWitien, and the widom of Bardeen and others, the picturebecame clear p'retty quickly. We showed that for SO(32) allgauge, gravitational, and mixed anomalies could cancel at lowenergy.25) This depended crucially on suing correptions (suchas the Lorentz Chern-Simons term) to the low-energy fieldtheory. Now we were excited! But still, given our previousexperiences, neither of us had any idea of how sudden andenthusiastic the response of the physics world would be.

The next bombshell was the heterotic string of Gross,Harvey, Martinec, and Rohm (often refened to as the Princetonstring quartet) in November 198/'.26) tr,tite Green, PeterWest, and I had been hard at work on many of the essentialideas such as compactification of 16 dimensions on an evenself-dual lacice. Our big mistalre was not to consider tneatingleft-movers and right-movers differently. The irony in this isthat Mike and I had invented the type IIA superstring, whichwas the only previous model with distinct left- and right-moveru. I think that others (including Ed \ilitten and PeterFreund2T)) were also close to discovering the heterotic sring.

Soon thereafter came the wonderful paper of Candelas,Horowitz, Strominger, and Witten.2t) By studying fieldtheory limits, it showed how one could obain remarkablyrealistic four-dimensional models by compactification of theE6 x Eg heterotic sring. It introduced physiciss to manifoldsthey had never heard of (Calabi-Yau spaces) and introducedmany essential ideas — embedding the spin connection in thegauge group, modding out by discrete groups, symmetrybreaking by Wilson lines (following Hosotani), erc. Calabi.Yau compactification of heterotic strings still looks like agood bet for getting realistic physics. Following thesedevelopments, superstring theory became accepted asmainstream physics. Indeed some of the new converts seemedto believe that the end of physics was close at hand, whichseemed to rne a little naive.

Concluding RemarksSince the exciting developments of late 1984 that I have

just described, the study of supersrings has become a very

active and fertile area of research. Many surprising connectionswith various branches of mathematics have turned up. It isvery satisfying to witness the growth of interaction betweenmathematicians and physiciss after a long period of separation.I think it is fair to say that the study of string theory holdsgreat promise for the unification of particles and forces, but ithas already done a great deal o unify disciplines.

References1. P. Ramond, Phys. Rev. D3 (1971) 2415.2. A. Neveu and J.H. Schwarz, Nucl. Phys. B31 (1971) 86.3. A. Neveu, J.H. Schwarz, and C.B. Thorn, Phys. Lett.

3sB (1971) 529.4. A. Neveu and J.H. Schwarz, Phys. Rev. D4 (1971)

r109.5. C.B. Thorn, Phys. Rev. D4 (1971) 1112.6. J.L. Gervais and B. Sakita, Nucl. Phys. B34 (1971') 632.7. D.Z. Freedman, P. Van Nieuwenhuizen, and S. Ferrara,

Phys. Rev. D13 (1976) 3214; S. Deser and B. Zumino,Phys. Len. 628 (1976) 335.

8. L. Brint, P. Di Vecchia, and P. Howe, Phys. Lett. 658(1976\ 471; S. Deser and B. Zumino, Phys. Lett. 65B(re76) 369.

9. A.M. Polyakov, Phys. Lett. 1038 (1981) 207, 211.10. J. Scherk and J.H. Schwarz, Nucl. Phys. B t l (1974)

I18.11. S. Weinberg, Phys. Rev. 135 (J96/) BlMg; Phys.

Rev.138 (1965) 8988.12. T. Yoneya, Prog. Theor. Phys. 51 (1974) L907.13. Yu.A. Gol'fand and E.P. Likhtman, JETP Lett. 13

(r97rr 323.14. J. Wess and B. Zumino, Nucl. Phys. 870 (1974) 39.15. F. Gliozzi, J. Scherk, and D. Olive, Phys. Lett. 6 5 8

(1976) 282; Nucl. Phys. 8122 (1977) 253.16. M.B. Green and J.H. Schwarz, Nucl. Phys. B18f (1981)

502.17. M.B. Green and J.H. Schwarz, Phys. Lett. 1098 (1982)

4M.18. M.B. Green and J.H. Schwarz, Nucl. Phys. 8218 (1983)

43; 8243 (1984) 475; M.B. Green, J.H. Schwarz and L.Brink, Nucl. Phys. 8219 (1983) 437.

19. M.B. Green and J.H. Schwarz, Phys. Lett. 1368 (1984)367; Nucl. Phys. 8243 (1984) 285.

20. E. Witten, p. 395 in "Fourth Workshop on GrandUnification," ed. P. hngrcker et al. @i*hauser, 1983).

21. J.H. Schwarz, Phys. Repors g9 (1982\ 223.22. L. Alvarez-Gaumd and E. Witten, Nucl. Phys. 8234

(1983)269.23. M.B. Green and J.H. Schwarz, Phys. Lett. l22B (1982)

143; J.H. Schwarz and P.C. West, Phys. Lett. t26B(1983) 301; J.H. Schwarz, Nucl. Phys. 8226 (1983)269; P. Howe and P.C. West, Nucl. Phys. B23t (1984)l8r.

24. G.F. Chapline and N.S. Manton, Phys. Lett. 1208(1983) 105; see also: A.H. Chamseddine, Nucl. Phys.Bl85 (1981) 403; E. Bergshoeff. et aI., Nucl. Phys.Bl9s (1982) 97.

l0

News lrom ICTP - No. 35/37 - July/August 1990

25. M.B. Green and J.H. Schwan, Phys. Lett. 1498 (1984)t l 7 .

26. D. Gross, J. Harvey, E. Martinec, and R. Rohm, Phys.Rev. Lett. 54 (1985) 502.

27. P;G.O. Freund, Phys. Lett. 1518 (1985) 387.28. P. Candelas, G. Horowitz, A. Strominger, and E. Witten,

Nucl. Phys. 8258 (1985) 46.

Interview withA.N. Matveev

Prof. A.N. MaMeev, former UnescoAssistant Director General for Scienceand Member of the ICTP ScientificCouncil, was inited by Abdus Salam tospend two weeks at the Centre aftertwenty years from his last :rz.sil. He wasinteniewed by News from ICTP.

Q . Professor Matveev, you were aMember of the Scientific Council of theCentre from 1965 to 1969. The Centrewas very small tlrcn. Wlvn you weresiuing in the meetings of the Council asa high-oficial of Unesco, did you foreseeor expect such a development? Wlatare, according to you, tlw reasons forthis success?

A . My membership to the ScientificCouncil of the Centre resulted fromAbdus Salam's intention to involveUnesco as an equal partner with IAEA inthe running of the Cenfe and from mydesire as Assistant Direcor-General forScience of Unesco to develop in themost effective way Unesco's ScienceProgramme. As a physicist, I knewSalam very well. He was a world-wideknown physicist. But I also knew hisorganizational ability in pushing the ideaof the Centre through IAEA. Thereforeit would have been a serious mistake ofan Assigant Directc-General f c Scienceof Unesco not to involve into UnescoScience Programme such a prospectivefigure as Abdus Salam. For me as aphysicist such a mistake would havebeen like a reachery to the cause ofinternational cooperation in physics.Therefore, from the very beginning,Abdus and I had full mutualunderstanding and unity of action. Weknew very realistically the possibilitiesof all other pafties involved and did notoverestimate thgm. I can say that I didforesee and expect such a developmentwhich had really taken place during thefint stage of the Centre's operation.

But I could not foresee a dale when

Prof. A.N. Matveev talking to Abdus Salarn.

Salam would become Nobel Prizewinner and I could not foresee the Centredevelopment after this event. TheCentre's development after this eventsurpasses all even most imaginativeexpectations. I can only admire all whathas been done in developing the Cenreand what has been and is being done bythe Centre for international scientificcooperation in physics.

The answer to the last part of yourquestion "What are the reasons for thissuccess?", is absolutely clear to me:Salam as the driving force of theCentre's development and the good willof the Italian Government and Triestecommunity.

Q . When you returned to the SovietUnion $ter your tenn with Unesco, didyou remain active in internationalscientific co-operarton through Urcsco?

A . After renrning to the Soviet Union,I remained active in internationalscientific cooperation through Unesco. Iwas a member of the governing board ofthe Unesco Institute of EducationalPlanning for two terms. Also for two

terms I served as a Member of theInternational Commission for PhysicsEducation of the International Union ofPure and Applied Physics which acts inclose cooperation with Unesco. AtUnesco's requests, I took part in variousmissions, studies etc.

Q . Soviet physics and mathematics areftrst class. The Centre has always hadthe co-operation of Soviet scientistseven when the East-West relations werenot as good as they are nowadays. Nowthat the horizon looks wider, how doyou see the collaboration between Sovietscientists with the developing countriesand with the West?

A . Without any doubt, thecollaboration between Soviet scientistswith the developing countries and withthe West will be an important factor offuture international scientific co-operation, but modalities of collab-oration may change in accordance withdevelopments in the Soviet Union.

A -bI. Hanende

l l

News from ICTP - No. 36/37 - July/August 1990

Prof. Alexej Nicolay*ich Mtitveev wasborn in 1922 in Moscow, In 1940, hegraduated from secondary school inMoscow, joincd a military Air Foiceschool and becanu a pilot. He took activepail h World War II as a pilot of the Sovictdiving bomber Pe-2 (Petljalcov-2) afterpiloting for some time the Americanplanes Boston A-208 and Boeing B-25'

He nade aboa 150 conbat military raids.He was shot down several times, waswounded, and paruchuted from his plane.He was owarded five highest militarydecorations.

In 1947, at tte age of 25, he studbd atttv Physics Depafiment of the MoscowState University where he continued towork after graduation in 1952. In 1954, hebecane Ph.D.. and in 1959 Doctor ofScierce. In 1960 le was elected as fullprofessor of Moscow State University,From 1964 untill 1969 he was AssistantDirector-Getural for Science at Unescoafter h.aving spent two years in Egypt as aUnesco upert.

A N. Matveev has published about 150scientifrc papers and is autlpr of 15 books,irrcluding a five-volume textbook ofgeneral physics, accepted h thc USSR as abasb source for teaching physics at theunivercity level He has been horpuredwith the State Prize, the lamonosov Prizeand has other scientific distinctions.Many of his boolcs were translated intoEnglish, Spanish and othcr languages, thefirst translation being his book"Principles of Electromagnetism",published by Reirhold's Publishing Housein USA in 1965.

Quantum Field Theoryand Politics:

Prof. Oliviu Gherman

Professor O. Gherman, Vice-President of tlw Romanian Senate, wasot the ICTP from 16 August to 6September. Prof. Gherman lws visitedth| Centre many times in tlrc past as afield theorist. He was interviewed byNavs from ICTP.

Q . Professor Gherman, you teachquontum tteld theory in Craiova and atthe same time you are Vice-President ofthe Senate of Romania. This is a ratherexceptional situation. Could you tell us

lnw this lappened?

A . With respect to the first part of yourquestion, I hope that my teachingquantum field theory at the University ofCraiova is a natlrral consequence of myinterest (and partially of the publishedpapers) on the subject. My presence assenator is an exceptional situation onlyfor people who did not live incommunist countries and especially inRomania. During the dictatorial regimeof Ceausescu a significant vacuum ofpoliticians has developed. In thosetimes, to be involved in politics wouldmean either to try to become one of hisunconditional servants or to be excludedfrom the society if you opPosed hispolitics (and eventually being Sent in aspecial hospital with a diagnostics ofmental disease!). The people around thedictator were a people of yes-men. Inthe last yqrs I refused any responsibility(head of department, member of theuniversity's senate etc.) but I did nothave the courage to become an opendissident (with all the non negligibleresults). In this respect I considermyself as being guilty.

Immediately after the Revolution, thecountry was faced with tremendousproblems in practically all arBas.' Thepeople with some social prestige andsome ideas about democracy were dividedinto two main groups. Some started todo their best to participate in the effortsof putting the country on the righttracks. Others preferred to criticizeeverything, to show their discontentwith ttre decisions made. As I am deeplyinvolved in all the aspects of theuniversity life, I tried to do my best todirect correctly the activity in ouruniversity. Many of my colleaguesfrom Craiova, Bucharest, CIuj orTimisoara as well as my former studentspersuaded me to run for the RomanianParliament. I was conscious that such astep would mean a host of newresponsibilities, but I considered that inthe period of putting the basis ofdemocracy in our country after a half ofcentury of dictatorship any reserve onmy pafi would mean descrting a patrioticduty. So, I ran, was elected and — tomy surprise — elected as Vice-Presidentof the Senate of Romania. Obviouslymy responsibilities towards the people

who elected me increasedconespondingly.

As I accepted these politicalresponsibilities only for one mandate(this most difficult one, when we mustpave the way to democracy) I asked, andthe Senate was so generous to allow meto mainhin my academic activities inthe University.

As a conclusion, I consider that atleast 70 percent of my colleagues fromthe Chamber and from the Senate arenewcomers in politics in a situationsimilar to mine. I hope that we cancontribute to the elaboration of good,democratic fundamental laws, includingthe constitution.

Professor Oliviu Gherman, Vice-President of the Romanian Senate, andtleoretical physics.

Q . Scientists in the "hard" disciplines"often compilain that their role is notsufficiently understood by politicians(this may not be true in Romania). Doyou share this opinion and if so, do youthink that your work at the RomanianSenate could improve this sination?

A . This problem has been analysedmany times brilliantly by the Director ofthe Centre—Professor Abdus Salam. Ifully agree with his point of view whichis the philosophy of the existence andusefulness of the Centre. Very often,Professor Salam explained that the roleof the fundamental research is essentialin the development of the countries. Asfar as I know, the main scope of theCentre is to help the development of the

12

News lrom ICTP - No. 36/37 - July/August 1990

fundamental research in those countrieswhich are economically less developed.As Professor Salam explained, this isnot a utopiq; on the contrary, this is avital necessity. The opinion of those

,.politicians who encourage the scientificresearches only if these have a directmeasurable effect could be comparedwith the point of view of blind peoplewhose universe ends at the end of theirsticks. In Romania, during Ceausescu'sregime, all the scientists working inresearch institutes had !o cover theirsalary by solving practical (or so-calledpractical) problems under confacts withindusrial production units. Even thestaff of the Universities had to cover3/10 of their salary with such contracts.The beginning of every year meant acalvary to run for obtaining suchcontracts.

Even if occasionally I obtainedimportant results in solving theseconracts I consider that ttre scientific lifeis today so dense, -the tension of aserious scientific activity is so strong,that any disturbance, even a minor one,could be disastrous for the wholeactivity. Therefore, I would try tobecome in our Senate the spokesman ofthe opinions so clearly and powerfullyexpessed by Professor Salam advocatingfor understanding that the main spur to arapid development of a country is theencouragement of fundamental researchwith all possible means and with anational financial effort not last. Forme, it is obvious that the greatestpractical power has the theory deeplyunderstmd.

Q . Romanian physicists andrnatlumartcians wlo lave come to workat the Centre were always excellent.Can you give your opinion on theqwlity of the scientific manpower inyour country and on tlw probkms whichyour scientists lave n face now.

A . It, is not a secret that year by yearour young fellows of the Romaniancolleges won excellent places (recentlythe first ones) in the internationalcompetitions in mathematics; physics,chemistry, bio6gy. So we have and wehad excellent human resources amongour students. Their ambition wasalways !o overtake the results of their

professors, despite the fact that duringthe last fifteen, and even more years,practically no one of those whograduated brilliantly, was promoted inresearch or in a university career. Iconsider this as a miracle and I do notknow if I would have tlreir strength fordisregarding the irresponsible auinrde ofour government and to work so hardwithout any social perspective. Thisexplains their high scientific level. Thisexplains also the fact that among thescientists who have come to work at theCentre there were only few young ones.

I think that pOtrrotially we have inRomania a sufficient scientificmanpower but we have to developprogrammes urgently to recover tlosepromising people who graduated in thelast fifteen years and who were spread inunfruiful activities (teachers, techniciansin factories etc.) and to develop anational progamme for the salvation ofthe scientific activity in general. 'Wesrongly need help in completing ourscientific information, as in the last twodecades we prrctically did not receive anyjournal or book (duplication machinesare essentially in this respect). At thesame time we must encourage researchin fields masterly selected which are inthe forefront of the present scientificactivity but which do not reqiuire hugeexpenses. It is useless !o say that ourexperimental techniques is in at least asa disastrous situation as the scientificinformation. So the good choice of thelines of our scientific activity in theexperimental fields has a national andvital importance. I can say that ourdestiny depends on this choice! TheCentre could help us by helping toparticipate in those international researchprogrammes which considers that wouldbe of the highest relief for our progress.

Q . As you know, the co-operationbetween the Romanian scientificcommunity and the Centre has alwaysbeen good. How do you see thiscollaborarton for the future?

A . I think thqt your appreciation israther generous. The past cooperationwas principally due !o the Centre'sefforts and its finarrcial generosity. Evenif we need morc support from the Centrein the future (participation of Romanian

scientists to the activities of the Centre),I think that the cooperation should beunderstood on much wider basis. Thecooperation should be extended out ofthe traditional fields (physics andmathematics) to other fields of equalimpor0ance, in which we have eminentscientists (chemistry, medicine,engineering, meteorology etc.). On theother side, I think that Romania, inretrun, could offer excellent conditionsfor organizing some of the Centre'sactivities (some workshops, seasonschools, seminars). I think that byorganizing at our expenses, in Romanianclurency, some of the Centres activities(and we can do that in excellentconditions) our cooperation will permitus to work on two legs rather than one,the Centre being able to accept moreRomanian scientists to its ownprogrammes.

Professor Oliviu Gfurttun was born on26th April 1930 in Mihai-Viteazu, CIuj,Romania. He studied at the Faculty ofMathematics and Physics, Cluj andBucharest, from 1948 to 1952. Heobtained his Ph.D. in mathematical-physical scierues in 1956. He workzd asassistant, lecturer, reader at the PhysicsDeparttnent, University of Cluj, and from1966 he has workcd as Professor oftheoretical physics at Craiova University.Between luly 1958 and January 1960 heworkcd as Officer at IAEA in Vbrna. From1965 to 1966 hc was Dean of the Faculty ofPhysics in Cluj and from 1966 to 1968Prorector of the Craiova University. Hehas published works in classicalelectrodynamics, statistical physics andquantr&m ftcld tleory. He is rnarried and lastwo children. He has visited tltc ICTPeleven times.

A-t'{. Hanende

C.V. Raman Prize

The annual ICTP Prize, this timededicated to C.V. Raman, has beenawarded to Professor Jos6 Luis Mordn-L6pez, a solid state physicist, from theUniversidad Autdnoma de San LuisPotosi, Mexico.

Professor AMus Salam, Director ofthe International Centre for TheoreticalPhysics, chaired the award ceremony in

l3

News from ICTP • No. 36/37 - July/August 1990

Iosd Luis Mordn-L6pez receiving tle diplorna of the C.V. Raman Prize from A.N.Matveev. Abdus Salan is in thc middle of the photograph.

the Main Lecture Hall of the Centre on16 July 1990. Prof. A.N. Matveev,former Unesco Assistant DirectorGeneral for Science, read the citation.The most important contribution of J.L.Mor6n-L6pez refers to surfacemagnetism, a domain in which he is oneof the world leading experts. In 1987,he discovered a surface first-order phasetransition in ferromagnets. Morerecently, he investigated quasi-crystalsand Fibonacci chains and high-T"

superconductivity with successfulresults.

Prof. Jos6 Luis Mordn-L6pez wasborn in Charcas (Mexico) on 25 August1950. He obtained his B.Sc. and M.Sc.in San Luis Potosf in 1972 and 1974respectively and his Ph.D. at the FreeUniversity of Berlin in 1977. He was apost-docloral fellow of the NationalCouncil of Science and Technology(Mexico) in 1977-79, a GuggenheimFellow in 1984-85 and a ResearchAssociate of the ICTP from 1985onwards. He has been a VisitingProfessor in Berlin (Free University) in1979, Porto Alegre (Brazil) in 1982, inJiilich (Federal Republic of Germany) in1985 and in Srasburg in 1984-85.

He is the author of l2l papers andeditor of 3 books. He founded theMexican Society of Surface and InterfacePhysics. He was the Vice-President ofthe Mexican Physical Society in 1987-88 and has won two important Mexican

Awads.The ICTP annual Prizes are awarded

to scientists from developing countrieswho have made outstandingcontributions to physics. They arededicated each year to distinguishedscientists. The 1989 Prize was inhonour of Chandrasekhara VenkataRaman, the great Indian scientist whowon the Nobel Prize in 1930 and whodid so much for the advanceiment ofscience in India.

Annual ICTP Prizes were created in1982 by the Scientific Council of theCentre in recognition of outstandingcontributions to physics andmathematics by scientists from andworking in a developing country. Theyconsist in a medal, a certificate and aUS$ l ,m0 cheque. One Prize is awardedeach year.

In the same ceremony, four localpersonalities — politicians DarioRinaldi and Giovanni Di Benedetto, andProf. Guido Gerin and Prof. Giampaolode Ferra who had served in the past asrepresentatives of the Italian Governmentto the International Atomic EnergyAgency of which the Cenne is a part —received ICTP medals from P. Budinich,Deputy Director of the ICTP from 1964.to 1978, in recognition of their activityin favour of the Centre.

AJut. Hanerde

Fields Medalto Edward Witten

On 2I August, one of the fourFields Medals 1990 was awarded toEdward Witten (Institute for AdvancedStudy, School of Natural Sciences,Princeton, NJ, USA) a geat friend of theICTP, for his new ideas in theoreticalphysics, which he applied to

From left to right: Prof. Giarnpaolo deGerk, Dr. Giovawti Di Bercdetto, ProfessorBudinich.

Ferra, Prof. JL. Mordn-L6pez, Prof. GuidoAbdus Salan, Dr. Darb Rinaldi and Prof. P.

t4

News from ICTP - No. 36/37 - July/August 1990

mathematics (supersymmetry, stringtheory and loop spaces).

Prof. Witten has visited the ICTP onmany occasions. He won an ICTP DiracMedal in 1985.

Maxwell Prizeto R.N. Sudan

At its November 1989 meeting inAnaheim, California, the APS divisionof plasma physics presented the JamesClerk Maxwell Prize for Plasma Physicsto Ravindra N. Sudan of CornellUniversity. Sudan received the prize forhis "wide-ranging conributions !o thetheory of plasma stability andturbulence, and pioneering work on thegeneration and propagation of intenseion beams," which have had"considerable impact on iornspheric andmagneospheric physics, on confinementand heating in field-reversed ion rings,and on light-ion-beam drivers for inertialconfirpment fusion."

Sudan received his Ph.D. in elecricalengineering from Imperial College of tlreUniversity of London in 1955. Hejoined the Cornell faculty in 1959 andbecame director of the Laboratory ofPlasma Studies and IBM Professor ofEngineering in 1975.

RN. Sudan was associated with theICTP research group in plamu physicsin 196546 and has come back manytitnes as a lecturer since.

Appointments

News from ICTP welcomescommunications on appointmens andnews on ICTP scientists for publication.

L. LedermanPresident-Elect of AAAS

Leon lrderman, director emerinrs ofFermilab and professor of physics at theUniversity of Chicago, is the newpresident-elect of the AmericanAssociation for the Advancement ofScience.

He has been a Member of the ICTPScientific Council since 1989.

Visits to ICTP

Prof. Paolo Fasella (Italy)Prof. Paolo Fasella, a biochemist and

Director General of the EuropeanEconomic Community's GeneralDirectorate for Science, Research andDevelopment, took part in the DiracMedal Ceremony on 4 July. He haddiscussions with ICTP and TY/ASofficials on future possible avenues ofcollaboration with the EEC.

Austrian Minister for ResearchMr. Ehrard Busek, Austrian Minister

for Research, and several of hiscollaborators, visiled the CenEe on 16July 1990. They were receiVed byAMus Salam, Director of the ICTP andPresident of the Third World Academy ofSciences. After a conversation with theDirector, the group which also includedthe Ausrian Consul in Trieste, Dr.Birbaum, was briefed on the Centre'sprogrammes and on prospects ofcooperation by L. Bertocchi, DeputyDirecor of the ICTP. The collaborationwith the Austrian scientiss is excellent.The Centre welcomes about 30 of themevery year. After the lunch, the AustianDelegation visited other components ofthe "Trieste System": the UNIDOInternational Centre for GeneticEngineering and Biotechnology, and thesite of the future synchrotron light

laboatory.

Minister Kuhanga (Tanzania)The former Vice-Chancellor of the

University of Dar-es-Salaam andMinister of Education, Hon. NicholasKuhanga visited the ICTP on 30 July1990. He is currently Chairman of theNational Committee in charge ofestablishing an Open University inTamann.

Conferences and Lectures

• Prof. Mbaro-Saman Lubuma,Visiting Scientist at ICTP in theMathematics Research Group, presenteda paper on "A Mixed Finite ElementMethod for the Mixed Dirichlet-Neumann Problem for the StokesOperator on a Polygon" at the FourthInternational Congress on Comput-ational and Applied Mathematics,Leuven, Belgium Q3 - 28 July 1990).

• Prof. A. Shkrebtii, VisitingScientist at ICTF in the CondensedResearch Group, presented a paper on"The Atomic Srucnres of ReconstructedSi(110) Surface Phases", written incollaboration with C.M. Beroni, R. DelSole and B. Nesterenko, at the 20thInternational Conference on the Physicsof Semiconductors, Thessaloniki, Greece(6 - l0 August 1990).

Abdus Salatn receives Mr. Elvard Busek, Austrian Minister for Research (at the certreof thc pltotograph) and his collaborator.

t5

News from ICTP - No. 36/37 - July/August 1990

Hot Papers

From "The Scientist",Jurc 11 and Jutc 25, 1990:

Copyright 19.0, "The Scientist".All rights resemed.

Reprinted by permission.

The articles listed below, all lessthan two years old, have received asubstantially great€r number of citationsthan others of the same type and vintage,according !o data frori The ScienceCitation Index of the Institute forScientific Informadon, Philadelphia.Why have these research repcts becomesuch stand-outs? A comment followingeach reference, supplied to Tlre Scientistby one of the authors, attempts toprovide an answer.

PHYSICSM. Biittiker, "Absence of

backscattering in the quantumHall effect in multiprobeconductorsr" Physical Review B,3t, 9375-t9, 15 November1988.

Markus Biittiker (IBM Thomas J.Watson Research Center, YorktownHeights, N.Y.): "Eight years after thediscovery of the quantum Hall effect, mypaper presented a transport theuy, whichis particularly close 0o the setup rctuallyused to measure the effect. Earliertheories that stressed the topologicalnature suggested that the quantum Halleffect is largely independent of theproperties of the sample. In contrast,my discussion showed that the propertiesof the current sourc,e contact and currentsink contact and the properties of thecontacts used 0o measur€ volages are ofimportance for the quantization of theresistance. Fortunately, since thepublication of my paper, a number ofgoups from different parts of the worldhave carried out experiments thatconfirm my p'redictions. Most exciting,it was since discovered that the nonlocaleffects that give rise to deviations fromthe quantum Hall effect persist overmaooscopii distances."

SUPERCONDUCTIYITYC.L. Kane, P.A. Lee, N.

Read, "Motion of a single hole

in a quantum antiferromagnetr"Physical Review B, 39, 6tt0-97, I April 19t9.

Charles Kane (IBM Thomas J.Watson Research Center, YorktownHeighs, N.Y.): "The interplay betweendoping and magnetism is a central issuein current theories of the high-temperature superconductors. Theundoped compounds are genericallyan ti ferromagnetic insulators (such asLa2CuO4), and many of the fascinatingproperties of these materials emergewhen they are doped with holes. Theholes are believed to be the chargecarriers in these materials, and thepresence of superconducting propertiesdepeds crucially on their concentration.In order to understand the normal andultimately superconducting properties ofthese materials, it is therefore importanto undenund the nahre of holes rnovingin an anti ferromagnetic background.

"In this paper we formulate aquasiparticle theory of a single hole in aqwmtum antiferromagnet. we find thatthe mass of a hole is enhanced, since ittends to disturb the antiferromagneticorder as it moves. This quasiparticletheory for a single hole is a usefulstarting point for treating the morecomplicated and realistic problem of afinite density of holes, which would bethe case in a doped antiferromagneticrnaterial."

Articles Alert

From "The Scientist",Jurc I1 ard Jurc 25, IW;

Copyright I9X), "The Sciertist".All rights resemed.

Reprinted by permission.

The Scientist has asked a group ofexperts to comment periodically uponrecent articles that they have foundnoteworthy. Their selections, presentedherein every issue, are neitherendorsements of content n u the result ofsystematic searching. Rather, the listrepresents personal choices of articles thecolumnists believe the scientificcommunity as a whole may also findinteresting. Reprints of any articlescited here may be ordered through TheGenuine Article, 3501 Market St.,

Philadelphia, Pa. 19104, or bYtelephoning Qls) 3864399.

MATERIALS SCIENCEby Theodore Davidson, Institute ofMaterials Science, University ofConnecticut, Storrs.

• Using polymers as Precursors toceramics offers some attractivepossibilities. Polymers can be drawninto fibers or cast as films and thenconverted to ceramic materials. This hasbeen accomplished already with carbonand SiC fibers and coatings. A recentsynthesis of soluble polymers from thesix-membered borazine ring has provideda precursor for boron ninide powder.Subsequent development could producefibers or coatings.

P.J. Fazen, J.S. Beck, A.T. Lynch,E.E. Remsen, L.G. Sneddon,"Thermally induced borazinedehydropolymerization reactions.Synthesis of a new high-yieldpolymeric precursor to boronnitride," Chemistry of Materials, 2(2>, 96-7, 1990. (University ofPennsylvania, Philadelphia)

• In response to the concern overbrittleness in oxide glasses, numeroussfengthening approaches are examined.Surface modifications reduce theinfluence of surface defects, while bulkcomposition, phase separation, and fiberor prticulate reinforcement may irrcreaseboth strength and fractitre toughness.Successes and limitations are evenlypre,sented.

I.W. Donald, "Methods forimproving the mechanical propertiesof oxide glasses," Journal ofMaterials Science, 24, 4177-208,December 1989. (Atomic WeaponsEstablishment, Aldermaston,Be*shire, England)

• Controlling microstructure is aprincipal objective in much of materialsscience. Recently, several approacheshave been taken to selectively place asecond phase "guest" species in anordered array of "host" molecules. Withiron oxychloride (FeOCl) as the hostlasice, intercalation can be achieved withspecies that transfer charge from guest !ohost. .An interesting example involves

16

Ncws from ICTP - No. 36/37 - July/August 1990

aromatic hydrccarbons, such as peryleneand tetracene. When these areintercalated into FeOCl, they raise theelecrical con9uctivity of the host by afactor of 10). The resulting low-dimensional semiconductors have bandgaps near 0.28 electron vols.

J.F. Bringley, B.A. Averill,"Aromatic iron intercalates: synthesisand characterization of ironoxychlcide intercalated with peryleneand tetracene," Chemistry ofMaterials, 2, 180-6, March/April1990. (University of Virginia,Charlottesville)

• In another host-guest situation,narcparticles of cadmium sulfide can besandwiched benveen the headgroups of anordered organic array. Inng-range mderis created by dipping up a Langmuir-Blodgett (L-B) film of dioctadecyl-dimethylammonium chloride, adsorbingthe CdS particles, and closing with asecond L-B film. Measurements by low-energy electron diffraction, absorptionspectroscopy, and scanning tunnelingmicroscopy show that the cadmiumsulfide retains its crystal linity and themultilayer forms a srucnred array.

S. Xu, X.K. Zhao, J.H. Fendler,"Ultrasmall semiconductor particlessandwiched between surfactantheadgroups in Langmuir-Blodgettfilms,' Advanced Materials, 2 (4),183-5, 1990. (Syracuse University,N.Y.)

• The scanning tunneling microscopehas opened new vistas from fundamentalstudies of single crystal surfaces tobiological ultrastructure at themacromolecular level. It has alsoinspired a whole generation of newtechniques in which the spatialresolution is better than the wavelengthused for imaging. There are magneticand electrostatic force microscopies;near-field optical, thermal, and acousticmicroscopies—each with specialcapabilities. These are reviewed—withtheir limiations. And, included in thesame issue are 136 other papers thatwere presented at the FourthInternational Conference on ScanningTunneling Microscopy/Spoctroscopy.

H.K. Wickramasinghe, "Scanningprobe microscopy: qurent status and

future trends," Journal of VacuumScience and Techrclogy, tA, 363-8,January/February 1990. (IBMWatson Research Center, YorktownHeights, N.Y.)

COMPUTATIONAL SCIENCEby Bruce G. Buchanan, Department ofComputer Science, University ofPittsburgh, Pittsburgh.

• Remote procedure calls (RPCs)allow a program running on onecomputer in a network to invoke aprogram on another machine. Thedesign and implementation of parallelRPCs in the Andrew distributedcomputing environment at CarnegieMellon University (CMU) arc reporred,and some of the advantages of thisdesip are analyzed.

M. Satyanarayanan, E.H. Siegel,"Parallel communication in a largedistributed environmenl,," IEEETransactions on Computers, 39,328-48, March 1990. (CMU,Pittsburgh)

• Error-free computation is impossible!o guaranlee, for reasons of failures ineither hardware or software. A re,centsurvey paper reviews the effects ofsoftware on reliability and ddscribes amodel of "resourceful systems." Thesesystems can determine whether or notgoals have been achieved, and, if not,will carry out alternative plans.

R.J. Abbott, "Resourceful systemsfor fault tolerance, reliability, andsafety," ACM Computing surveys,22, 35-68, March 1990. (AerospaceCorp., Los Angeles)

• Circumscription is a technique forformalizing some aspects of commonsense reasoning that introduces arequirement of minimality: If a formula,P, is satisfied, then no proper subset ofP is. Finding ways to expresscircumscription without introducingsecond-order formulas has been an activeresearch area. Results of this researchare extended, and the computationalcomplexity of model checking forcircumscription is analyzed,

P.G. Kolaitis, C.H. Papadiminiou,"Some computational aspects ofcircumscription," fournal of the

Association fo, ComputingMachinery, 37, l-14, January 1990.(University of California, Santa Cruzand San Diego)

• Explanation-based learning is arelatively new technique for abstracting asolution to a specific problem. Thesolution will then be used on laterproblems, based on an explanation ofwhy the solution works. Research isreported that exlends the technique togeneralize over iterative or recursiveprocesses. Results of the BAGGER2learning algdthm are presented.

J.W. Shavlik, "Acquiring recursiveand iterative concepts withexplanation-based learning," MachituLearning,S, 39-70, March 1990.(University of Wisconsin, Madison)

• Computer chess has become an areaof intense interest. Better performanceresults in recent years are due to deepersearches that are allowed by faster andlarger machines. An argument is madethat increasing the amount of lnowledgewill also be necessary for WorldChampionship programs. Several otherarticles about chess programs appearwithin the April issue of ArtificialIntelligence (N).

H. Berliner, G. Goetsch, M.S.Campbell, C. Ebeling, "Measuringthe performance potential of chessprograms," AI, 43, 7-20, Aptil1990. (CMU, Pittsburgh; Universityof Washingon, Seattle),

Activities at ICTPin July-August 1990

Title: MINIWORKSHOP ONSTRONGLY CORRELATEDELECTRON SYSTEMS, l8 June - 27July 1990.

Organizers: Profs. G. Baskaran(Matscience Institute of MathematicalScience, Madras, India), A.E.Ruckenstein (University of California,San Diego, USA), E. Tosatti(International School for AdvancedStudies, ISAS-SISSA, and ICTP,Trieste, Italy) and Yu Lu (AcademiaSinica, Beijing, P.R. China, and ICTP),in collaboration with the InternationalSchool for Advanced Studies (ISAS-

t7

News from ICTP - No. 36/37 - July/August 1990

SISSA, Trieste, Ialy).Lectures: Perturbation theory and

consenring approximations for correlatedfermions. A brief review of NMR:applications. Introduction to low-dimensional magnetism. Opticalproperties of srongly carelated systems.Singlet quasi-particles in multi-bandmodels of the high Tc oxides.Introduction to the l N approach tostrongly correlated systems. Lowtemperature properties of 2-D orbitalantiferromagnets and spin nematics.Approaches to the one dimensionalHubbard model. Cluster simulations ofthe Hubbard model. One particleexcitations in strong couplingsuperconductors. Solution of the five-vertex model. Few electrons in the 2DHubbard model. An inroduction 0o thequantum Hall effect. Spiral phases indoped quantum antiferromagnets. Themean field (Harree-Fock) anyon gas: a(insulating) sheep in wolfs clothing?Numerical approaches to stronglycorrelated systems. Comments onpseudo-gaps in correlated systems.Cumulant expansion study of holes inquantum antiferromagnets. A path-integral approach o the dynamics ofholes and spins in the t-J model.Inroduction 0o anyon superconductivity.Spiral mean field solution in the t-Jmodel. A schematic model for high Ts

superconductivity. Superconductors invery strong magrrctic fields. Infroduction!o Luttinger liquids (in 1-D!). g-ology inI and 2 dimensions. Strong couplingtechniques on the lattice. Dynamics ofdilute holes in quantumantiferromagnets. Pairing with fractionalangular momentum and "spinor" gap.Field theory approach to the fractionalquantum Hall effect. Gauge field theoryof transport properties in stronglycorrelated systems. Introduction !o largeD expansions in strongly conelatedsystems.

The Mini workshop was attended by100 lecturers and participants (32 fromdeveloping countries).

Title: SUMMER SCHOOL INHIGH ENERGY PHYSICS ANDCOSMOLOGY, 18 June - 28 July1990.

Organizers: Prof. J.C. Pati

(University of Maryland, College Park,USA), Dr. S. Randjbar-Daemi (ICTP),Dr. E. Sezgin (Texas A & M University,College Soation, USA) and Prof. Q.Shafi (Bartol Research Institute, Newark,USA), in collaboration with theInternational School for AdvancedStudies (SISSA, Trieste, Italy) and theItalian Institute for Nuclear Physics(INFI.[).

International AdvisoryCommittee: Profs. G. Altarelli(CERN, Geneva, Switzerland), J. Ellis(CERN, Geneva, Switzerland), E.Fradkin (P.N. Lebedev Institute,Moscow, USSR), H. Nicolai(Universit6t Fridericiana Karlsruhe,Federal Republic of Germany) and Dr. J.Straftdee (ICTP).

Lectures: Introduction to conformaland superconformal theories. N = 2supercon formal theories. LandauGinzburg orbifolds. String field theory.N = 2 solitons. Effective field theories in4-dim. N = 2 strings. Quantum groupsand its applications !o conformal fieldtheories. 2-dim. gravity. Quantumchromodynamics. Phenomenologicalsupersymmetry. Beyond the standardmodel. Supersring phenomenology. Anoverview of recent developments inlattice gauge theories. " Chiralperturbation theory and CP violation.Electoweak interactions and applications!o e+e- physics. Standard big bangcosmology and primordial nuclearsynthesis. Anomalous baryon and leponnumber violation in the electroweakmodel. Quantum cosmology. Darkmatter. Cosmic strings,

(Workshop on superstrings andrelated topics): N = 2 strings and Wsymmetry. Background independence ofstring field theory. Topology change instring theuy. W algebras and W gravity.The nucleation model of the Hagedornphase ransition. U(l) Chern-Simons andanyons on a torus. Cancellation of theLorentz anomaly in light-cone gaugesring field theory. 2 4 gravity and relatedmatters. The geometry of the super KPflows. Superstring in curved space:application of Krichever-Novikovformalism. New supersymmetries andhigher spinors.

(lYorkshop on Phenomenology inhigh energy physics and cosmology):Current status of CP violation. Solar

neutrinos. Survey of Calabi-Yausuperstring phenomenology. Heavyflavour physics. Wormholes in thecosmological constant. Results fromVA2. Resu l t s from LEP.Supersymmetry breaking and relatedtopics. Physics at Gran Sasso. 4-dimsuperstring models. Results from CDF,Fermilab.

The School was attended by 273lecturers and participants ( l7l fromdeveloping counries).

Title: ADRIATICO RESEARCHCONFERENCE ON QUANTUMFLUCTUATIONS IN MESOSCOPICAND MACROSCOPIC SYSTEMS, 3 .6 July 1990.

Organizers: Profs. H.A. Cerdeira(UNICAMP, Campinas, Brazil, andICTP), F. Guinea (University ofCalifornia, Santa Barbara, USA) and U.Weiss (Universitdt Stuttgart, FederalRepublic of Germany), with the co-sponsorship of IBM-Italy and theInternational School for AdvancedStudies (SISSA, Trieste, Italy).

Lectures: Change quantizationeffects in small tunnel junctions. Singleelectron effects in tunnel junctions. Thequantum mechanical theory of transportin mesoscopic structures. Criticalbehaviour of dissipative quantumsystems in the dense limit. Periodicorbit theory of dissipative tunneling.Change unbinding transition in junctionarrays. Resistive superconducting groundstate in a very small current biasedJosephson junction. Path integralapproach to the thermodynamics ofquantum anharmonic phonons. Qruntumdiffusion of kinks in dislocations.Current experimental understanding ofl/f noise. The quantum mechanics of amacroscopic variable. Macroscopicquantum tunneling: how quickly mustthe environment react to affect it?Solitons and charging effects usingSTM. Conductance fluctuations andchaotic scattering. Charging effects inultrasmall tunnel junctions. Relaxationtheory of the spectral properties ofdissipative two-state quantum systems.Universality in dissipative two-statesystems. Vortex motion ininhomogeneous superconductors. Chargeordering and transport properties of

18

News lrom ICTP - No. 35/37 - July/August 1990

Josephson arrays and chains. Influencefunctional theory of a heavy particle in aFermi gas. Effect of quantumfluctuations on DC electron mnsport inultrrasmall nnnel junctions. The effect ofcharge fluctuations on Coulombblockade. Quantum dissipation on adisordered lattice: a simple tight-bindingapproach. Dimers, repulsion and theabsence of localization. Classicaleffective XY-coupling constant fordissipative Josephson junction arrays.Aharonov-Bohm oscillations and non-local electronic conduction. Persistentcurrents and thermodynamics ofmesoscopic systems. Coherence andpenistent currents in mesoscopic rings.Transmission through dissipativebarriers. Switching dynamics inJosephson junctions: thermal andquantum behaviour. Traversal time,dynamic polarization and photonemission in tunneling.

The Conference was atlended by 54lecturers and participants (8 fromdeveloping counries).

Title: ADRIATICO RESEARCHCONFERENCE PHYSICS OFSTRONGLY CORRELATEDSYSTEMS, 10-13 July 1990.

O r g a n i z e r s : Professors G.Baskaran (tnstitute for MathematicalScience, Madras, India), A.E.Ruckenstein (Rutgers University,Piscataway, USA), E. Tosatti (SISSAand ICTP, Trieste, Italy) and Yu Lu(Academia Sinica, Beijing, P.R. China,and ICTP), with the co-sponsorship ofIBM-Italy and Consiglio Naziqrale delleRicerche (Ialy).

L e c t u r e s : Overview of theexperimenal shtus of high Ts. Modelstudie,s of ransport in strongly conelatedsystems. Gutzwiller approach to theKondo-lattice problem. Frustration,phase sepration and superconductivity.Finite cluster studies of strongcorrelation models. Quantum Monte-Carlo studies of the Hubbard model.Interrcting fermions in low dimensionsfrom, weak to strong correlation.Eigenfunctions fro 2D square and sripFermi surfaces. Conelation functions ofl-D Hubbard model: zsufield ard finite-field cases 0arge U). Thgory of Ramanscattering in Mott-Hubbard systems.

Finite size scaling and exponents of the.l-D Hubbard model. Landau's theory ofthe Luttinger liquid. Anyonsupercoductivity and frrctianal quanurmHall effect. Orbital ferromagnetism ofanyons. Spin singlet vs. spin polarizedstates in FQHE. Exet statements aboutthe Hubbard model. New large N limitsfor frustrated antiferromagnets andsuperconductivity in the t-J model.Structure of vortices in the classicalGinzburg Landau Chern-Simons theoryof quantum Hall effect. Molecules withsrongly correlated electrons. Exact meanfield theay for fermionic lattice models.Raman scattering in high Tc

superconductors. Phase separation in thet-J model. Pairing of spatially separatedelectrons and holes in high Ts materials.

The Conference was attended by 62lecturefs and participants (19 fromdeveloping cormries).

Title: SYMPOSIUM ONFRONTIERS IN CONDENSEDMATTER PHYSICS, ll-13 Augusr1990.

Organizers: Professors E. Bursiein(University of Pennsylvania,Philadelphia USA), P. Chaudhari (BM,Yorktown Heights, USA), J.R.Schrieffer (University of California,Santa Barbara, USA), E. Tosatti(International School for AdvancedStudies, ISAS-SISSA, and ICTP,Trieste, Italy), and Yu Lu (AcademiaSinica, Beijing, P.R. China, and ICT?,Trieste, Italy).

Lectures: Properties of the blueelecron. Is computing part of the futureof physics? Experimental aprpirorhes tosuperconductivity in oxides. The theoryof high Tg superconductivity: therelation between weak and strongcoupling approaches. Perspectives oflocal probe methods. Single electron

nmneling in ulrasmall nrnnel junctions.Ten years quantum Hall effect.Fractional quantum Hall effect. Thefractional Hall effect and other uses ofhle2. The ecology computation.Superfluidity in neutron stars and itsimplication for the decay of theirmagnetic fields.

The Symposium was anended by 52lecturers and participants (7 from

developing counries).

TitIC: ADRIATTCO RESEARCHCONFERENCE ON DEFECTS INHEXAGONAL CLOSE PACKEDCRYSTALS, 14-17 August 1990.

Organizers: Professors D.J. Bacon(University of Liverpool, UK), W.Frank (Max-Planck-Institut fiirMetallforschung, Stuttgart, FederalRepublic of Germany), E.J. Savino(Comisi6n Nacional de EnergiaAtdmica, Buenos Aires, Argentina), S.Seeger (Max-Planck-Institut f0rMetal lforschung, Stuttgart, FederalRepublic of Germany), M. Tosi(Univenity of Trieste and ICTP, Italy),V. Vitek (University of Pennsylvania,Philadelphia, USA) and C.H. Wop(Atomic Energy of Canada Ltd., Pinawa,Canada), with the co-sponsorship ofAtomic Energy of Canada Ltd. (Canada),CANDU Owners Group (Canada),Commission of the EuropeanCommunities @elgium), IBM-Italy andthe International School for AdvancedSudie.s (ISAS-SISSA, Trieste, Italy).

Lectuies: Collapse of displacementcascades in hexagonal close-packedmetals. Microstructure evolution inhexagonal close-packed metals duringirradiation. Radiation damage and theproperties of vacancies and self-interstitials in Cd and Zn. Defect-complexing and annealing in Cd and Zn.Electrical resistivity measurements incobalt and dilute cobalt alloys followinglow-temperature particle irradiation.Magnetic relaxation measurements ininadiated cobalt. Many body effects oncalculated defect properties of hexagonalclose-packed metals. Point defects inHCP metals—a review. The formationand migration energies of vacancies inboundaries in HCP crystals. Latticedefects in rare earth metals. Self-interstitials, vacancies and diffusionmechanisms in HCP metals. Rate ttreoryanalysis of radiation damage effecs nearsurfaces in hexagonal metals. Pointdefects and sink strength in HCPmaterials. Defects in HCP crystals. Self-diffusion and fast impurity diffusion inthe bulk and in grain boundaries ofhexagonal tianium. Interphase and grainboundary diffusion in a-Zr and Zr-Malloys. Rutherford back scatteringdiffusion studies of Hf in a-Zr. The low-

19

News from ICTP - No. 35/37 • July/August 1990

temperature plasticity of HcP metalsand alloys: the case of titanium-Yalloys. Topological theory ofdiscontinuities in crysals and interfaces:

t o to hexagonal crystals.Deformation twinning in hexagonalclose-prcked meals a d alloys. Stmctureand properties of twinning dislocationsin HCP metals. A study of the stressstate leading o twinning activation inHCP metals. Grain boundary

strengthening associated with 59 nearcoincidence boundary in <10T0> twistZinc bicrystals. Observations of grainboundary structure in zinc. The lowt€mperature plasticity of HCP metalsand alloys: the case of titanium.Prismatic glide in divalent HCP metals.Dislocation core structure in hexagonalclose-prcked metals. Glide mechanism ofU3 <Tt23> (l0Tll dislocatioqs in Tiand k . Deformation of Ti3Al single

crystals. The relative stability of thealpha and omega phases in some Zrbased alloys. Internal friction studies ofhydrogen and hydride precipitation in a-Zr ard a-Ti — a review.

The Conference was attended by 62lecturers and participants (22 fromdeveloping counries).

Symposiwn on Frontiers in Condensed Matter Physics, II-13 August l9A.

International Centre for Theoretical Physicsof IAEA sld UNESCOSuada Costierq l lP.O. Box 58634136 TriesteItaly

Telephone: (40) 22401Cable: CENTRATOMTelex: 450392 ICTP ITelefax: (40) 224163

Bitneu POSTOFFICE@ITSICTP.BITNETDecner V)ilCP1::POSTOFF

Itapac: 022224110125

EDITORIAL NOIE - News from ICTP is not an official document of the International Centre for Theoretical Physics. Its purpose is to keepscientists informed on past and futr"ue activities at the Centre and initiatives in theil home couttries. Suggestions and criticisms shouldbe addressed o Dr. A.M. Hsnende. Scientific Information Officer.

20