81 research outputs found
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
Phase Transitions and Gauge Artifacts in an Abelian Higgs Plus Singlet Model
While the finite-temperature effective potential in a gauge theory is a
gauge-dependent quantity, in several instances a first-order phase transition
can be triggered by gauge-independent terms. A particularly interesting case
occurs when the potential barrier separating the broken and symmetric vacua of
a spontaneously broken symmetry is produced by tree-level terms in the
potential. Here, we study this scenario in a simple Abelian Higgs model, for
which the gauge-invariant potential is known, augmented with a singlet real
scalar. We analyze the possible symmetry breaking patterns in the model, and
illustrate in which cases gauge artifacts are expected to manifest themselves
most severely. We then show that gauge artifacts can be pronounced even in the
presence of a relatively large, tree-level singlet-Higgs cubic interaction.
When the transition is strongly first order, these artifacts, while present,
are more subtle than in the generic situation.Comment: 19 pages, 4 figures. Added comparisons with a gauge-independent
formalism (which necessitated removing the counterterms from the original
model), and fixed a computational error in the effective potential. Figures
2, 3, and 4 are changed, along with much of section 3. The qualitative
results remain the sam
Supersymmetric Electroweak Baryogenesis Via Resonant Sfermion Sources
We calculate the baryon asymmetry produced at the electroweak phase
transition by quasi-degenerate third generation sfermions in the minimal
supersymmetric extension of the Standard Model. We evaluate constraints from
Higgs searches, from collider searches for supersymmetric particles, and from
null searches for the permanent electric dipole moment (EDM) of the electron,
of the neutron and of atoms. We find that resonant sfermion sources can in
principle provide a large enough baryon asymmetry in various corners of the
sfermion parameter space, and we focus, in particular, on the case of large
, where third-generation down-type (s)fermions become relevant. We
show that in the case of stop and sbottom sources, the viable parameter space
is ruled out by constraints from the non-observation of the Mercury EDM. We
introduce a new class of CP violating sources, quasi-degenerate staus, that
escapes current EDM constraints while providing large enough net chiral
currents to achieve successful "slepton-mediated" electroweak baryogenesis.Comment: 35 pages, 9 figures; v2: several revisions, but conclusions
unchanged. Matches version published in PR
- …