2,405 research outputs found
The 125 GeV Higgs and Electroweak Phase Transition Model Classes
Recently, the ATLAS and CMS detectors have discovered a bosonic particle
which, to a reasonable degree of statistical uncertainty, fits the profile of
the Standard Model Higgs. One obvious implication is that models which predict
a significant departure from Standard Model phenomenology, such as large exotic
(e.g., invisible) Higgs decay or mixing with a hidden sector scalar, are
already ruled out. This observation threatens the viability of electroweak
baryogenesis, which favors, for example, a lighter Higgs and a Higgs coupled to
or mixed with light scalars. To assess the broad impact of these constraints,
we propose a scheme for classifying models of the electroweak phase transition
and impose constraints on a class-by-class basis. We find that models, such as
the MSSM, which rely on thermal loop effects are severely constrained by the
measurement of a 125 GeV Higgs. Models which rely on tree-level effects from a
light singlet are also restricted by invisible decay and mixing constraints.
Moreover, we find that the parametric region favored by electroweak
baryogenesis often coincides with an enhanced symmetry point with a distinctive
phenomenological character. In particular, enhancements arising through an
approximate continuous symmetry are phenomenologically disfavored, in contrast
with enhancements from discrete symmetries. We also comment on the excess of
diphoton events observed by ATLAS and CMS. We note that although Higgs portal
models can accommodate both enhanced diphoton decay and a strongly first order
electroweak phase transition, the former favors a negative Higgs portal
coupling whereas the latter favors a positive one, and therefore these two
constraints are at tension with one another.Comment: 35 pages, 7 figure
Gravity Waves as a Probe of Hubble Expansion Rate During An Electroweak Scale Phase Transition
Just as big bang nucleosynthesis allows us to probe the expansion rate when
the temperature of the universe was around 1 MeV, the measurement of gravity
waves from electroweak scale first order phase transitions may allow us to
probe the expansion rate when the temperature of the universe was at the
electroweak scale. We compute the simple transformation rule for the gravity
wave spectrum under the scaling transformation of the Hubble expansion rate. We
then apply this directly to the scenario of quintessence kination domination
and show how gravity wave spectra would shift relative to LISA and BBO
projected sensitivities.Comment: 28 pages, 2 figures
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