245 research outputs found
Singlet Scalar Dark Matter: monochromatic gamma rays and metastable vacua
We calculate the pair-annihilation cross section of real scalar singlet dark
matter into two mono-energetic photons. We derive constraints on the theory
parameter space from the Fermi limits on gamma-ray lines, and we compare with
current limits from direct dark matter detection. We show that the new limits,
albeit typically relevant only when the dark matter mass is close to half the
Standard Model Higgs mass, rule out regions of the theory parameter space that
are otherwise not constrained by other observations or experiments. In
particular, the new excluded regions partly overlap with the parameter space
where real scalar singlet dark matter might explain the anomalous signals
observed by CDMS. We also calculate the lifetime of unstable vacuum
configurations in the scalar potential, and show that the gamma-ray limits are
quite relevant in regions where the electro-weak vacuum is meta-stable with a
lifetime longer than the age of the universe.Comment: 21 pages, 6 figures; references added, minor additions to text and
figures, version accepted for publication in Phys. Rev.
Cosmological Phase Transitions and their Properties in the NMSSM
We study cosmological phase transitions in the Next-to-Minimal Supersymmetric
Standard Model (NMSSM) in light of the Higgs discovery. We use an effective
field theory approach to calculate the finite temperature effective potential,
focusing on regions with significant tree-level contributions to the Higgs
mass, a viable neutralino dark matter candidate, 1-2 TeV stops, and with the
remaining particle spectrum compatible with current LHC searches and results.
The phase transition structure in viable regions of parameter space exhibits a
rich phenomenology, potentially giving rise to one- or two-step first-order
phase transitions in the singlet and/or directions. We compute several
parameters pertaining to the bubble wall profile, including the bubble wall
width and (the variation of the ratio in Higgs vacuum expectation
values across the wall). These quantities can vary significantly across small
regions of parameter space and can be promising for successful electroweak
baryogenesis. We estimate the wall velocity microphysically, taking into
account the various sources of friction acting on the expanding bubble wall.
Ultra-relativistic solutions to the bubble wall equations of motion typically
exist when the electroweak phase transition features substantial supercooling.
For somewhat weaker transitions, the bubble wall instead tends to be
sub-luminal and, in fact, likely sub-sonic, suggesting that successful
electroweak baryogenesis may indeed occur in regions of the NMSSM compatible
with the Higgs discovery.Comment: 49 pages + 2 appendices, 6 figures. v2: Minor corrections; matches
version published in JHE
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