Tuesday, 27 May 2014

Planck 2014 Liveblog: Day Two Session 3

First parallel session of the conference.  I've decided to go with the session on composite Higgs.

2:30 pm: UV description of composite Higgs models without elementary scalars, Tirtha Sankar Ray

Two well-known previous answers to the UV completion of a composite Higgs sector: as the holographic dual to a 5D theory (conformal 4D theory), or through a Seiberg dual to some SUSY theory that is asymptotically free.  Can we extend this: have a UV completion with fermions and gauge bosons in 4D only?

Need to break G/H in the desired way, fermion condensates gain a VEV.  Use NJL framework.  Use SO(6)/SO(5) ~ SU(4)/Sp(4) model (non-minimal for complex G, chiral fermions).  4 identical fermions gives global SU(4) symmetry automatically.  Yang-Mills theory, asymptotically free.  Single meson that has right charge for symmetry breaking.

Problem: 3rd gen. Yukawas demand large anomalous dimensions for bilinear.  This is where four-fermion interactions come in.  Beta function shows existence of UV fixed point.

Yukawas need partial compositeness; top partners considered to be baryonic states.  Require additional preons charged under colour.

Question: role of gauge group?  Doesn't everything come from 4-fermion interactions?  Needed to get top partners, top-partner-Higgs couplings.

2:50 pm: Top FCNC in composite Higgs models, Aleksandr Azatov

Partial compositeness explains fermion mass hierarchy and suppresses FCNC through RS-GIM mechanism.  Top quark mixes most strongly with composite sector; expect large FCNC.  Also responsible for generating Higgs potential; are the two quantitatively related?  Does mh give a prediction for top FCNC?

Flavour anarchy would require partners of light quarks to be not much heavier than top partners.  Use to probe charm sector, e.g. Z-t-c coupling.

3:10 pm: Flavour of 4D composite Higgs, Oleksii Matsedonbskyi

Consider models with flavour symmetries, rather than pure anarchy.  Symmetries can be classified as including (or not) the top, and broken by left or right quarks.

3:30 pm: Dipole Operator constraints on composite Higgs models, Matthias Konig

Dipole operators: b to sgamma, edms.  Emerge from one-loop corrections to fermion-photon couplings.  Consider a number of different fermion implementations (MCHM4, 5 and 10).

Usually to consider 3rd generation only; can exactly diagonalise the mixing.  For 3 generations this is not in general true, but can work in mass insertion approximation.  Leads to unavoidable order-1 uncertainties.

Flavour anarchy has meson mixing problems, hence introduce flavour symmetries.  In particular consider U(2)3 model.  Also model issue about presence or absence of wrong-chirality Yukawas; if present, make flavour constraints much worse.

Use matching to low-energy Wilson coefficients.

Generically, neutron edm seems to be tightest constraint.  Typical bounds, fermion partners heavier than ~ 4 TeV though some room remains.

3:50 pm: Light non-degenerate Composite Partners at the LHC, Thomas Flacke

Searches for partners of first two generations of quarks.  Gain production processes with t-channel Ws, which have light quarks in initial state.  Final states suffer from just having jets rather than taggable t/bs.  Reinterpret old ATLAS/CMS/Tevatron searches.

For moderately large mixing parameters, get better bounds from these searches than the mixing-independent QCD bounds.

Limits on singlet/doublet partners at 300/500 GeV or so.

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