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Vectorlike Confinement and its Signatures at the LHC
Can Kılıçwork done with Takemichi Okui and Raman Sundrum
arXiv: 0906.0577
Introduction
• LHC coming, expectations shaped by the hierarchy problem.
• Known solutions constrained by experiment. Possible scenarios.
• Concept of meso-tuning. Impact on discovery potential at the LHC. Part of NP may be accessible. Need guiding principle.
• Theoretical simplicity / safety from PO at low energy. (rich phenomenology at higher energies)
• Define Vectorlike Confinement: – new vectorlike fermions– a new strong gauge force – (very weak interactions relevant for decay)
• LHC phenomenology dominated by hyperhadrons.
Attractive features
• Precedent: Analogy to QED + low energy QCD. Signatures: pair production, resonance. can decay, is stable up to weak interactions. Mirrored in VC.
• Safety: “Gauge-mediation” is flavor blind. Mass scale set by confinement, separated from EWSB.
• Rich phenomenology: A minimal theory naturally gives rise to an array of distinct collider signatures (multi GB, CHAMPs, other exotica), some new features.
Deja-Vu?
• Not TC. Different motivation / structure / signatures.
• TC must have chiral fermions for EWSB, which impacts PEW.
• Generating masses leads to flavor problems in TC.
• Connected in the bigger picture?
• Can use same tools (analog computer)
• VC as a strawman model
Outline
• Theoretical Structure• Phenomenological Lagrangian• Representative Case Studies
– A subtlety in the minimal model– CHAMPs and EW gauge bosons– Multijets– R Hadrons– DM, cascades, other possibilities
• Conclusion
A Brief History of QCD
• Begin by strongest interactions (u,d only)• Focus on ,ρ• Confinement, flavor symmetry
• (Pseudo) Goldstones:
transform in adjoint of flavor group. ’s and baryons stable• ρ lightest state, decays to
2 , becomes special once we add U(1)em
A Brief History of QCD
Consequences of turning on U(1)em
(qu = 2/3 , qd = -1/3)
• ρ is the lightest meson which can be interpolated by – ρ/γ mixing– resonant production
• charges–
• anomalous,
• Both up and down number still conserved, stable, turn on weak interactions. (4-fermion operators)
• Up and down numbers no longer conserved, baryon number still conserved.
• Need light particles for to decay, introduce non-strongly interacting particles.
induces as well as neutron decay (proton stable)
A Brief History of QCD
Could Lightning Strike Twice?From a simple UV theory to rich IR Physics
• Hypercolor: SU(N) gauge theory with F vectorlike flavors in the fundamental representation. Scale ΛHC.
(F chosen such that theory confines) • Flavor symmetry
Conserved number for each flavor. • (Pseudo)Goldstones:
we consider• and baryons stable at this point• is the lightest meson, decays
to 2 , becomes special as we turn on SM.
Could Lightning Strike Twice?From a simple UV theory to rich IR Physics
• Turn on
hyperfermions charged under SM. • SM breaks many of the flavor numbers, introduce
“species” of hyperfermions. (e.g. color triplet)• Changes running of SM couplings,
for one species in to avoid QCD Landau-pole in the UV.
• interpolated by can mix with SM gauge bosons, resonant production.
• charges. • Radiative masses for• Anomaly of can decay with zero species
number ( - short)• Species number unbroken. Leads to stable .
Could Lightning Strike Twice?From a simple UV theory to rich IR Physics
• - long stable, SM charged. UV physics analogous to weak interactions can decay them to non-hypercolored particles (SM).
or
breaks species numbers.• Straightforward to break hyperbaryon
number as well. Model dependent.• Models constrained, there must exist
a SM final state with matching quantum numbers. (simple choice: GUT-like representations)
Constraints (I)
• Vectorlike fermions: Confinement preserves vector part of flavor symmetry, SM unaffected. Choose quantum numbers such that Yukawa terms with the SM Higgs forbidden, PEW safe.
• “Gauge mediation” means that flavor violating effects from renormalizable part of the VC theory suppressed relative to the SM by loop factor.
• Nonrenormalizable operators can induce flavor violating SM operators. For generic coefficients, need M ~ O(104) TeV. For special flavor structure, M can be anything consistent with EFT description.
Phenomenological Lagrangian The
• Not literal EFT. Large N estimates.• Mixing/production:
where• Shift induces• Production from gluons• Dominant decay
from where• Rare decays
Phenomenological LagrangianMasses
Three sources of mass:
• SM gauge groups break the flavor symmetry
• Fundamental hyperquark masses
• From EWSB
Phenomenological Lagrangian-short and -long
• Chiral anomalies induce
those with no net species numbers decay to a pair
of gauge bosons. Here
• Higher dimensional operators decay with nonzero species number.
Phenomenological Lagrangian-long Decay Length
• Current-current decays suppressed by fermion masses
• Scalar-scalar decays are less suppressed
• Prospects for visibility tied to flavor structure.
Phenomenological LagrangianOverview
Constraints (II)• Many exotic states with SM charges. Ocean bottom searches
for charged particles:Plenty of room between bounds from cosmology and flavor.
• Fermion compositeness:
worst case is eeqq , OK as long as• -short decays at the Tevatron OK as long as • Resonant production and decay to SM: electroweak has
too small cross section/branching fraction, color is interesting – search strategy in a few slides.
• Singlet are axions. Forwe have (safe for SN cooling, beam dump)
decay not observablenot observable (BF too small)
A Few Simple ModelsSU(2) Doublet
• representation• Spectrum contains
with• , bleak collider phenomenology• There is a special that could keep the from decaying
because axial current is odd:• MDM candidate?• If decays, adding a singlet gives more generic structure,
without losing any features.
A Few Simple ModelsWhat a Singlet Can Do
• SM charge assignment:• The singlet as “strange”
• Masses (singlet is axion):
• After EWSB:
• -strahlung at LEP?
A Few Simple ModelsWhat a Singlet Can Do
• Resonances:
• Short-lived pions:
Lepton-rich, very good reconstruction in the channel.• Long lived pions
decays through the current operator (heavier states preferred).
When suppression scale is low, prompt or displaced same-sign tau-pair +MET as well as , otherwise CHAMP pairs.
too softto see
• Triggers like a muon.
• Experimental handles: curvature, dE/dx,ToF
• Tevatron Limits dictate
• Distributions
• more advanced
analysis by
Chen & Adams
(200 pb-1 at 10 TeV)
A Few Simple ModelsCHAMPs
• Associated production gives mode.(BF ~35% in CN)
• Resonant as well as nonresonant channels. (~65% in CC)
(GMSB searches) – work in progress. (~32% in CN)
• Distributions
• Hyperbaryon decay
A Few Simple ModelsMulti-photons
A Few Simple ModelsSU(3) Triplet
• Color triplet gives rise to color octet , .• Without any electroweak charges, can be as light as
300GeV. Possibly in Tevatron data, not excluded, discoverable. still easy at LHC, harder.
A Few Simple ModelsSU(3) Triplet + Singlet
• Add a singlet• Spectrum
• Decay modes
• Axion mode interesting but unobservable
A Few Simple ModelsR-Hadrons
• Triplet collider stable or decays through current-current operator, 3rd generation leptoquark
• R-hadrons will be charged with O(1) probability. Resonance easier to observe compared to EW model.
• 4 R-hadrons (leptoquarks) if g’ pair produced – fb cross section
• Hyperbaryon decay
A Few Simple ModelsSpectators
• DM candidates generic in VC models.• Exotic species have a much harder time decaying• and make up DM candidate• can decay to
“Squark” pair production with subsequent decay to “LSP”• More general cascades
Conclusions
• VC: New confining gauge interactions with vectorlike matter are theoretically simple and generic.
• “Gauge-mediated” setup with vectorlike matter ensures safety from low energy precision tests.
• Vector states can be resonantly produced, decay to naturally light PGB’s.
• Scalars have short-lived and collider stable species. – Short-lived scalars decay to a pair of SM gauge bosons. 4 GB
final states can be spectacular.– Long lived scalars appear as CHAMPs / R-hadrons. Resonance
reconstruction possible. Decays into heavy flavors can be preferred. (leptoquarks, di-taus, di-tops…)
• Unbroken species number or spectators can give DM candidates. Cascades possible.
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