Embed Size (px)
Citation preview
Inner space meets outer space Subir Sarkar
Rudolf Peierls Centre for Theore6cal Physics
It is likely that further research into "showers" and "bursts" of the cosmic rays may possibly lead to the discovery of still more elementary particles, neutrinos and negative protons, of which the existence has been postulated by some theoretical physicists in recent years. Victor Hess (1936) !
The universe is the poor man’s accelerator … all we have to do is collect the experimental data and interpret them properly Yakob Zel’dovich (1965)
1912: Victor Hess discovers cosmic rays (named so by Millikan in 1927) Nobel Prize 1936
(1928: Paul Dirac predicts the existence of
anH-‐parHcles Nobel Prize 1933)
1932: Carl Anderson discovers the positron in cosmic rays Nobel Prize 1936 … using cloud chamber invented by Charles Wilson Nobel Prize 1927
(1935: Hideki Yukawa predicts the existence
of mesons Nobel Prize 1949)
1937: Seth Neddermeyer & Carl Anderson discover the muon in cosmic rays
1947: Cecil Powell discovers the pion in
cosmic rays Nobel Prize 1950 “for development of the photographic method”
1947: George Rochester & Clifford Butler
discover the kaon
Patrick BlackeA awarded Nobel Prize 1948 (“for development of the Wilson cloud chamber method”)
The birth of astroparticle physics
Per Carlson (Physics Today, Feb 2012)
Bronshtein’s ‘cube of theories’
P
GNc3 1.6 1035m 1.2 1019GeV
After the relativistic quantum theory is created, the task will be to develop the next part of our scheme, that is to unify quantum theory (with its constant h), special relativity (with constant c), and the theory of gravitation (with its G) into a single theory.! Matvei Petrovich Bronshtein (1906-38)!
For an update see: Duff, Okun & Veneziano (arXiv:physics/0110060)
The construc6on of powerful par6cle accelerators and the development of
rela6vis6c quantum field theories of the strong and electro-‐weak interac6ons has led us to the … ‘Standard Model’
… with its last piece now triumphantly in place!
The Standard SU(3)c x SU(2)L x U(1)Y Model (viewed as an effec6ve field theory up to some high energy cut-‐off scale M) accurately describes all of microphysics …
renormalisable!
super-renormalisable!
non-renormalisable!
New physics beyond the SM ⇒ non-‐renormalisable operators suppressed by Mn which ‘decouple’ as M → MP (… so neutrino mass is small, proton decay is slow etc)
But as M is raised, the effects of the super-‐renormalisable operators are exacerbated One solu6on for Higgs mass divergence → ‘soXly broken’ supersymmetry at M ~ 1 TeV !
But the ‘cosmological constant’ is then ~1060 6mes higher than the maximum vacuum energy tolerable today … we do not understand how the SM couples to gravity!
m2H h2
t
162
M2
0dk2 =
h2t
162M2
This provides a candidate for dark maXer – the lightest supersymmetric parHcle (typically the neutralino χ) – as do other extensions beyond the Standard Model e.g.
new dimensions at the TeV scale (the lightest Kaluza-‐Klein par6cle)
Le↵ = F 2 + 6D + + (D)2 + 2
+ M +
M2 + . . .
+M4 +M22
neutrino mass proton decay
hierarchy problem vacuum energy problem
V ()
The standard cosmological model is based on several key assump6ons: maximally symmetric space-‐6me + general rela6vity + ideal fluids
Space-‐Hme metric Robertson-‐Walker
Geometrodynamics Einstein
where :z a0a 1,m m
3H20/8GN
,k ka20H
20,
3H20
ds
2 gµdxµdx
= a
2()d
2 dx
2
The world is indeed a strange place!
Dynamical evidence (assuming GR is valid)
Mainly geometrical evidence: Dark energy is inferred from the ‘cosmic sum rule’: Ωm + Ωk + ΩΛ = 1 Λ ~ O(H0
2), H0 ~ 10-42 GeV
Baryons (no an6-‐baryons)
Both the baryon asymmetry and dark maber require that there be new physics beyond the Standard SU(3)cxSU(2)LxU(1)Y Model … dark energy is even more mysterious (but as yet lacks compelling dynamical evidence)
3He/H p
4He
2 3 4 5 6 7 8 9 101
0.01 0.02 0.030.005
CM
B
BB
N
Baryon-to-photon ratio η × 1010
Baryon density Ωbh2
D___H
0.24
0.23
0.25
0.26
0.27
10−4
10−3
10−5
10−9
10−10
2
57Li/H p
Yp
D/H p
Par6cle accelerators are indeed 6me machines … however to unravel the mysteries of dark maber and dark energy and the Big Bang will need non-‐accelerator experiments
Nucleosynthesis
(Re)combination
In the early universe, radiaHon comes to dominate over non-‐relaHvisiHc maXer and the thermal history can be simply reconstructed assuming adiabaHc expansion
To create the large-‐scale structure observed today, small density perturba6ons must have been generated in the very early universe
… plausibly through quantum fluctua6ons of a nearly massless scalar field in an exponen6ally expanding (De Siber) space-‐6me: ‘Infla6on’
A period of accelerated expansion which blew up the scale-‐factor by > e50-‐60 (~1030) can also explain why causally (apparently) disconnected regions are in fact correlated …
This will also drive the curvature of space to zero … in accordance with observa6ons of the angular scale of characteris6c fluctua6ons in the
Cosmic Microwave Background
The physics is simply that of coherent oscilla6ons in a coupled photon-‐baryon
plasma, which is excited by primordial perturba6ons on super-‐horizon length scales
‘Size’ of the present universe at (re)combination epoch!
By analysing this pabern we can infer the values of the cosmological parameters and test the theory of infla6on
The observed clustering of large-‐scale structure is also understood if the primordial fluctua6ons are adiaba6c and ~scale-‐invariant (as expected in the simplest models of infla6on) and can grow in a sea of dark maber
During infla6on the universe is briefly dominated by the vacuum energy of a scalar field while it evolves towards the minimum of its poten6al … this drives exponen6ally fast expansion and generates small density fluctua6ons on (super-‐horizon) scales as the universe supercools
… aXer reaching its minimum the scalar field oscillates, transferring its stored energy into maber and radia6on, thus ‘rehea6ng’ the universe
We have today a ‘standard’ model of both par6cle physics and cosmology which allows us to extrapolate back from the present day to the very first moments following the Big Bang
While successful in accoun6ng for a wide range of observa6ons, this has raised a new set of more fundamental ques6ons concerning the ‘ini6al condi6ons’ of the universe we live in
None of us can understand why there is a Universe at all, why anything should exist; that’s the ul@mate ques@on. But while we cannot answer this ques@on, we can at least make progress with the next simpler one, of what the Universe as a whole is like.
Dennis Sciama (1978)
