Saturday, 31 August 2013

SUSY 2013 Live Blog: Day Five Session Four

So It Has Come To This.  The last parallel session of SUSY 2013.  And what better place to sit than the SUSY Phenomenology session.  We have four talks to bring this part of the conference to a close.

4:30pm: Jan Helsig, "Cosmology of long-live stau scenarios in the light of the LHC results"

Serious considerations of SUSY demands the gravitino exists.  The gravitino production in the early universe is proportional to the reheating temperature, which runs into the need for a high reheating temperature if we want to accommodate leptogenesis.  If the gravitino is very light, much below the soft parameters, it can be dark matter but then we do not get leptogenesis.  If it is comparable to the other soft masses, then it may or may not be dark matter; if not, it is long-lived and late decays put an upper limit on the reheating temperature.  If it is very heavy, we get leptogenesis but no dark matter.

The most interesting case is where the gravitino is the dark matter, but comparable in the mass to the other superpartners.  We must worry about late decays of the NLSP spoiling BBN.  We consider the stau as NLSP and look to see what areas fit constraints.

Worth noting that the usual SUSY searches don't really apply; look for heavy stable charged particles, as the stau is stable on collider timescales.

Do a dedicated pMSSM scan using the relevant data sets.  HSCP sets lower limit on stau around 400 GeV.  Higgs bounds make stau annihilations to Higgses suppressed.

Looking at the reheating temperature, there is some tension.  Higgs constraints put upper bound on reheating temperature at a few times 108.  A small handle of points reach 109, all involve stau resonantly annihilating through Higgses.  Also needs the gravitino at a few hundred GeV.

4:50pm: Jonathan da Silva, "The Higgs sector in U(1) extensions of the MSSM"

Worrying: this might impinge on something I've been thinking about.  New U(1) is not dark, i.e. SM fields charged under the U(1).  We extend the Higgs sector with a singlet as in the NMSSM, indeed some similarities in addressing the μ problem.

We have a Z' due to the extra U(1).  It is subject to the usual LHC searches so must be heavy.  Also DM, Higgs measurement constraints.  Use nuisance parameters to address theoretical uncertainties.

Higgs mass raised by new D terms.  Strong dark matter constraints already, even more severe ones to come.

5:10pm: Tanushree Basak, "130 GeV gamma ray line and enhanced Higgs di-photon rate from Triplet-Singlet extended MSSM"

Extending MSSM with triplet has similar motives to the NMSSM.  Adding both because, why not?  Use a scale invariant superpotential so as to avoid the μ-problem.  (Symmetry?)  Triplet scalar couples to Higgses but nor fermions.

T parameter gives usual constraint, that the triplet gets at most a very small VEV.

Higgs mass enhanced by variation of the usual NMSSM approach.

Model must have light charginos to enhance the Higgs width to diphotons; a 130 GeV neutralino and 260 GeV pseudoscalar to get the Fermi gamma ray line; and fit the usual constraints.  Rather than do a scan, pick some benchmark points.  LSP is dominantly Bino but has substantial Higgsino-like.  The pseudoscalar is dominantly triplet-like, suppressing couplings to SM fermions and massive gauge bosons.

Prediction of a moderate enhancement, around 22%, in the Higgs to di-photon channel.  Collider phenomenology to do.

5:30pm: Diego Restrepo, "LSP sneutrino novel decays"

An R-parity violating model, hence the LSP decays.  Single R-partiy violating operator, LHu, so lepton number violated by baryon number conserved.  Focus is on relating to neutrino oscillation data.  Indeed, this fixes all but one of the relevant SUSY parameters.

The interesting decay possibilities are to different-flavour leptons, particularly tau plus either muon or electron.

Gravitino is radiatively decaying dark matter candidate in the range 1 to 10 GeV.