Tuesday, 27 August 2013

SUSY 2013 Live Blog: Day Two Session Three

For the first parallel session of the day I'm in the dark matter/cosmology session.

2:30pm: Feng Luo, "Gravitino Decays and the Cosmological Lithium Problem in Light of the LHC Higgs and SUSY Searches"

Success of BBN constrains late decays.  Lithium-7 is exception, a few times larger than expected; can decays ameliorate this?  MSSM framework with neutralino LSP and heavy decaying gravitino, decaying at late times.

Of course, trick is to do this without screwing up what works.

Studied several top-down models; various flavours of cMSSM, also NUHM1 and subGUT models (defined below GUT scale).  Check mHiggs first.  Different benchmark points rather than a scan, based on different DM relic density mechanism (coannihilation, etc.)

Gravitino abundance taken as input parameter.  Generally no constraint at low abundance obviously.  Also no constraints at high mass (decays too soon).

Gravitino decays lead to destruction of Helium, but strongest constraint is not directly Helium but rather the produced deuterium.

Possible to solve problem in narrow region.  Some tension between satisfying Lithium and not violating deuterium.  Still, despite the new parameters the fit has better chi-squared.  All successful models have gravitino mass around 5 TeV, lifetimes 3-4 minutes and abundance 10-10.  This is independent of other details of SUSY spectrum.

2:50pm: Stefano Scopel, "Neutralino Dark Matter and the 125 GeV Higgs boson measured at the LHC"

What are the implications of an SM-like 125 GeV Higgs on light neutralino DM?  Focus is on the ~10 GeV range due to DAMA/CoGeNT/CDMS-Si/CRESST.

Model is low-energy scan over relevant parameters, though keep universal sfermion masses for flavour reasons.  Note cannot have gaugino mass unification due to chargino limits.  Light neutralino has lower bound on DD signal due to need to get low enough relic density.  In rough agreement with DAMA.

Must make squarks, gluinos heavy due to LHC searches.  Higgsino-like chargino at ~few hundred GeV.

Result is that new LHC limits make DD cross section too small compared to the various anomalies.  Model points do still exist.

3:10pm: Alexandre Arbey, "Neutralino dark matter in the MSSM"

DD for neutralinos probes SUSY Higgs sector.  Work is done within pMSSM.  Uses vevacious (from yesterday) to check vacuum stability.

Relic density insensitive to gluino/squark/slepton masses, but does depend on lighter chargino.

XENON-100 excludes 28% of points that fit Higgs data to one sigma.

Looking for DAMA etc. models leads to light bino with nearly-degenerate sbottom as best hope.  Avoid LEP Z-pole constraints by Bino (invisible) and sbottom mixing.

Question: what of the sbottom decays?  Apparently comparable lifetime to b, so possible interesting search.

3:30pm: Krzysztof Turzynski, "Gravitino dark matter with constraints from Higgs boson mass and sneutrino decays"

A main problem with gravitino DM is decay of NLSP, which often happens after BBN.  Want a neutral colourless NLSP to minimise this; low freeze out abundance also helps.  Hence the attention to snuetrinos.  Work in NUHM model, which does give sneutrino NLSP (some of) the time.

Models end up with very long-lived sneutrinos (100 years) if we want  leptogenesis.  Then have constraints from late-time injection of warm dark matter.

Ultimately there is tension between the Higgs mass and thermal leptogenesis.  In the end it looks like the Higgs discovery now disfavours this scenario.

Question: what of less constrictive models?  Better obviously.

No comments:

Post a Comment