Friday, 29 May 2015

Planck 2015 Liveblog: Day Four, Session Four

The final session of today is, again, devoted to parallel talks.  I will once again switch between the SUSY and DM sessions.

5:00 pm: "Holomorphic supersymmetric NJL Model for Phenomenology", Otto Kong

MSSM with composite Higgs superfields and dynamical EWSB.  Work in progress.

Physics is only about effective theories.  Not even EFTs, just ETs.  Models have intrinsic and unavoidable cut-off.  SM can be both beautiful, and purely phenomenological.  Obvious comparison for SM Higgs sector is to Ginsburg-Landau theory of superconductivity (this analogy seems to be quite popular all of a sudden).  The question then is where is the BCS theory?

Old candidate: NJL.  Phenomenological problems, so consider a supersymmetric version.  As considering EFT, don't worry too much about things like vacuum stability or renormalisability.

SM is notable in that it is minimal chiral theory with non-trivial anomaly cancellation (given gauge group?) Problem is that gauge group & anomaly cancellation do not constrain the scalar sector of the theory.

Slightly loose statement on naturalness, but better than most I see, indeed have seen here.  Idea here is to have natural dimension-6 operator, by having scale in operator be the cut-off.  In SUSY context, issues with NJL approach as some operators live in superpotential, others Kahler potential.  Using four-superfield term in superpotential, and two Higgses, do not get four-fermion operator but do still get the desired condensate (I think that was what he said...)

SUSY NJL better than non-SUSY NJL because you can use tan β to get a larger top Yukawa for the same top mass.

I've downloaded this paper, I can't quite follow what's going on as is but the idea I think is interesting.  That paper has very few citations; not obvious to me why.

5:25 pm: "Searching for Supersymmetry in Z' Decays at the LHC", Gennaro Corcella

LHC Z' searches so far focused on high-mass dileptons from SSM or GUT models.  Generalise by allowing decays to SUSY partners.  Extending MSSM to include the GUT U(1) requires adding an extra singlet to give that vector a mass.  Extra D-term contribution to sfermion masses.  In realistic model, branching rate to BSM is about 30% maximum.

Also worked with supersymmetric extension of SSM.

EWPT limits?  Don't know off-hand.  (I (AS) think they are not too severe.)
What is likely reach in this channel? Working on backgrounds.

5:50 pm: "Observable Effects of General New Scalar Particles", Jorge De Blas

Try to use a model-independent approach.  EFT with higher-dimensional operators, but this is in a sense too general.  Use "general" UV completions of SM plus new particles.  Prior work considered new quarks, leptons or vectors.  Here consider new scalars.  Assume only need consider terms with single powers of new scalars; will generically provide leading contribution is allowed.  19 possible representations.

Use these to generate EFT terms that are generated when these new scalars are integrated out.  Terms with one scalar lead to dimension 6 operators, again leading terms.  Things, obviously, get rather complicated.

Observable low-energy effects.  Many produce four-fermion interactions.  Some are known terms from e.g. neutrino see-saws.  Also, possible for violation of custodial symmetry.  Lots of options to modify Higgs self-couplings.

Interesting application: constraints can be set on various single-particle extensions.  This type of approach makes it possible to see how robust those approaches are.

Did allow scalars to get VEVs?  Yes, the ones without colour.
How do you place bounds when there are several operators?  Bounds shown in talk for single scalar (correlated operators), discussion of multiple operators shows that cancellations can exist.

6:10 pm: "Stability Constraints in Triplet Extensions of MSSM", Stefano Di Chiara

Triplet contributes (at tree level) to Higgs mass, reducing fine tuning.  Older motivation, can enhance Higgs decay to two photons.  Many aspects of model have been studied, but not its stability.  What are the flat directions in the potential?  Do there exist deeper minima along those directions?

Only two new terms in superpotential over MSSM (as triplet cubed term vanishes).

Be sure to cite the people in the audience!

Flat terms require that each D and F term separately vanish.  Careful choice of VEV ansatz simplifies problem.  End up with only four possible vacua apart from desired one.  This then leads to the stability conditions.  Then proceed to perform a scan incuding one-loop corrections.

Stability strongly prefers lightest chargino below 700 GeV.  Stability also makes fine tuning worse, by about 25%.

Constraints on Higgs bilinears? Prior constraints already derived.
Chargino components?  Higgsino or tripletino, depending on what is going on with the Higgs decay width to photons.
Scale of runnings?  Ran up to 104 TeV on logarithmic scale.  Lowering that scale does provide more viable points.

I've essentially missed a talk because of the different times between sessions.  Unfortunately the talk I missed had some overlap with what follows.

6:50 pm: "Accidental Composite Dark Matter", Oleg Antipin

In SM, all global symmetries are understood as accidental symmetries of renormalisable Lagrangian.  They already leat to one stable particle, the proton.  Take new strong sector (not including Higgs).  Work in terms of underlying theory of hyperquarks, in real representation under SM so do not break SM gauge theory when theyy confine.

Consider SU(N) and SO(N) hypercolour groups.  (SP(N) theories lack stable baryons.)  Also demand that hyperquarks are embeddable in SM SU(5) representations.  Demand no SM Landau poles below Planck sale.  There is an accidental hyperbaryon number.  Also get a species number based on different SM representations; e.g. pions in QCD + QED would be stable, only weak force lets them decay.  Also have a variant of charge conjugation, G-parity.

Demand a DM candidate: stable states neutral under unbroken SM groups.  Scan over possible fermion constraints and identify all possible models.  One difference between SU(N) and SO(N) is due to fundamental: complex and real, respectively.  So hyperbaryons in SO(N) are equal to own anti-particles.

Consider models with only hyperbaryons as stable.  If thermal relic, must be around 100 TeV.  Hope to find in DD through dipole moment interactions.  In SO(N), however, generally have Higgs couplings resulting in mixing of states of different isospin.  Lightest hyperbaryon is then either Majorana fermion or real scalar.

Collider signatures; can these things be seen even at a 100 TeV machine?  Maybe hyperpions.  Looks like main constraint comes from new CP violation.  Many models just beyond current bounds.  Also gravitational wave constraints.

How calculate hyperbaryon masses?  e.g. charged vs neutral components.  Group theory exercise to determine what the represenations of the composite objects.  Typically smallest SM representation will be lighter, due to loop contributions.  Neutral components in multiplets will be lightest for same reasons.
Dark Nucleus?  Possible, but did not consider it here.
More detail on G Parity?  Conider QCD, without hypercharge.  Neutral pion will not decay in this case.

7:10 pm: "Blind Spots for Neutralinos in NMSSM with Light Singlet Scalar", Pawel Szczerbiak 

Blind spot here refers to Direct Detection; evading current and future constraints, which are non-trivial.

Sorry, I kind of got distracted there.

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