736 research outputs found
Electroweak Baryogenesis in a Two-Higgs Doublet Model
Electroweak baryogenesis fails in the SM because of too small CP violation
and the lack of a strong first-order phase transition. It has been shown that
supersymmetric models allow for successful baryogenesis, where the Higgsinos
play an important role in the transport processes that generate the asymmetry.
I will demonstrate that also non-supersymmetric models can provide the observed
baryon asymmetry. The top quark takes the role of the Higgsinos. Focusing on
the two-Higgs doublet model, I will discuss details of the phase transition and
consequences for Higgs physics and EDM searches.Comment: 5 pages, 2 figures. Proceedings of Moriond 2006, Electroweak Session.
11-18 March, La Thuile (Italy
The bubble wall velocity in the minimal supersymmetric light stop scenario
We build on existing calculations of the wall velocity of the expanding
bubbles of the broken symmetry phase in a first-order electroweak phase
transition within the light stop scenario (LSS) of the MSSM. We carry out the
analysis using the 2-loop thermal potential for values of the Higgs mass
consistent with present experimental bounds. Our approach relies on describing
the interaction between the bubble and the hot plasma by a single friction
parameter, which we fix by matching to an existing 1-loop computation and
extrapolate it to our regime of interest. For a sufficiently strong phase
transition (in which washout of the newly-created baryon asymmetry is
prevented) we obtain values of the wall velocity, v_w~0.05, far below the speed
of sound in the medium, and not very much deviating from the previous 1-loop
calculation. We also find that the phase transition is about 10% stronger than
suggested by simply evaluating the thermal potential at the critical
temperature.Comment: 17pages, 3 figure
Baryogenesis at the Electroweak Phase Transition for a SUSY Model with a Gauge Singlet
SUSY models with a gauge singlet easily allow for a strongly first order
electroweak phase transition (EWPT). We discuss the wall profile, in particular
transitional CP violation during the EWPT. We calculate CP violating source
terms for the charginos in the WKB approximation and solve the relevant
transport equations to obtain the generated baryon asymmetry.Comment: 5 pages, 6 figures. To appear in the Proceedings of Strong and
Electroweak Matter 2000 (SEWM2000), Marseilles; a reference adde
Electric dipole moment constraints on minimal electroweak baryogenesis
We study the simplest generic extension of the Standard Model which allows
for conventional electroweak baryogenesis, through the addition of dimension
six operators in the Higgs sector. At least one such operator is required to be
CP-odd, and we study the constraints on such a minimal setup, and related
scenarios with minimal flavor violation, from the null results of searches for
electric dipole moments (EDMs), utilizing the full set of two-loop
contributions to the EDMs. The results indicate that the current bounds are
stringent, particularly that of the recently updated neutron EDM, but fall
short of ruling out these scenarios. The next generation of EDM experiments
should be sufficiently sensitive to provide a conclusive test.Comment: 20 pages, 5 figures; v2: comments added and minor corrections to the
results, published versio
Suppressing lepton flavor violation in a soft-wall extra dimension
A soft-wall warped extra dimension allows one to relax the tight constraints imposed by electroweak data in conventional Randall-Sundrum models. We investigate a setup, where the lepton flavor structure of the standard model is realized by split fermion locations. Bulk fermions with general locations are not analytically tractable in a soft-wall background, so we follow a numerical approach to perform the Kaluza-Klein reduction. Lepton flavor violation is induced by the exchange of Kaluza-Klein gauge bosons. We find that rates for processes such as muon-electron conversion are significantly reduced compared to hard-wall models, allowing for a Kaluza-Klein scale as low as 2 TeV. Accommodating small neutrino masses forces one to introduce a large hierarchy of scales into the model, making pressing the question of a suitable stabilization mechanism
Cosmological signatures of a UV-conformal standard model
Quantum scale invariance in the UV has been recently advocated as an attractive way of solving the gauge hierarchy problem arising in the Standard Model. We explore the cosmological signatures at the electroweak scale when the breaking of scale invariance originates from a hidden sector and is mediated to the Standard Model by gauge interactions (Gauge Mediation). These scenarios, while being hard to distinguish from the Standard Model at LHC, can give rise to a strong electroweak phase transition leading to the generation of a large stochastic gravitational wave background in possible reach of future space-based detectors such as eLISA and BBO. This relic would be the cosmological imprint of the breaking of scale invariance in Nature
Top transport in electroweak baryogenesis
In non-supersymmetric models of electroweak baryogenesis the top quark plays
a crucial role. Its CP-violating source term can be calculated in the WKB
approximation. We point out how to resolve certain discrepancies between
computations starting from the Dirac equation and the Schwinger--Keldysh
formalism. We also improve on the transport equations, keeping the
W-scatterings at finite rate. We apply these results to a model with one Higgs
doublet, augmented by dimension-6 operators, where our refinements lead to an
increase in the baryon asymmetry by a factor of up to about 5.Comment: 17 pages, 3 figures, references adde
Non-Custodial Warped Extra Dimensions at the LHC?
With the prospect of improved Higgs measurements at the LHC and at proposed
future colliders such as ILC, CLIC and TLEP we study the non-custodial
Randall-Sundrum model with bulk SM fields and compare brane and bulk Higgs
scenarios. The latter bear resemblance to the well studied type III
two-Higgs-doublet models. We compute the electroweak precision observables and
argue that incalculable contributions to these, in the form of higher
dimensional operators, could have an impact on the T-parameter. This could
potentially reduce the bound on the lowest Kaluza-Klein gauge boson masses to
the 5 TeV range, making them detectable at the LHC. In a second part, we
compute the misalignment between fermion masses and Yukawa couplings caused by
vector-like Kaluza-Klein fermions in this setup. The misalignment of the top
Yukawa can easily reach 10%, making it observable at the high-luminosity LHC.
Corrections to the bottom and tau Yukawa couplings can be at the percent level
and detectable at ILC, CLIC or TLEP.Comment: 24 pages, 4 figures; v2: Typo in eq.48 fixed, references adde
Gravitational waves from the sound of a first order phase transition
We report on the first three-dimensional numerical simulations of first-order phase transitions in the early Universe to include the cosmic fluid as well as the scalar field order parameter. We calculate the gravitational wave (GW) spectrum resulting from the nucleation, expansion, and collision of bubbles of the low-temperature phase, for phase transition strengths and bubble wall velocities covering many cases of interest. We find that the compression waves in the fluid continue to be a source of GWs long after the bubbles have merged, a new effect not taken properly into account in previous modeling of the GW source. For a wide range of models, the main source of the GWs produced by a phase transition is, therefore, the sound the bubbles make
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