196 research outputs found
Transient domain walls and lepton asymmetry in the Left-Right symmetric model
It is shown that the dynamics of domain walls in Left-Right symmetric models,
separating respective regions of unbroken SU(2)_L and SU(2)_R in the early
universe, can give rise to baryogenesis via leptogenesis. Neutrinos have a
spatially varying complex mass matrix due to CP-violating scalar condensates in
the domain wall. The motion of the wall through the plasma generates a flux of
lepton number across the wall which is converted to a lepton asymmetry by
helicity-flipping scatterings. Subsequent processing of the lepton excess by
sphalerons results in the observed baryon asymmetry, for a range of parameters
in Left-Right symmetric models.Comment: v2 version accepted for publication in Phys. Rev. D. Discussion in
Introduction and Conclusion sharpened. Equation (12) corrected. 16 pages, 3
figure files, RevTeX4 styl
Electroweak Baryogenesis in Non-minimal Composite Higgs Models
We address electroweak baryogenesis in the context of composite Higgs models,
pointing out that modifications to the Higgs and top quark sectors can play an
important role in generating the baryon asymmetry. Our main observation is that
composite Higgs models that include a light, gauge singlet scalar in the
spectrum [as in the model based on the symmetry breaking pattern SO(6)/SO(5)],
provide all necessary ingredients for viable baryogenesis. In particular, the
singlet leads to a strongly first-order electroweak phase transition and
introduces new sources of CP violation in dimension-five operators involving
the top quark. We discuss the amount of baryon asymmetry produced and the
experimental constraints on the model.Comment: 15 pages, 7 figure
Magnetic Fields at First Order Phase Transition: A Threat to Electroweak Baryogenesis
The generation of the observed baryon asymmetry may have taken place during
the electroweak phase transition, thus involving physics testable at LHC, a
scenario dubbed electroweak baryogenesis. In this paper we point out that the
magnetic field which is produced in the bubbles of a first order phase
transition endangers the baryon asymmetry produced in the bubble walls. The
reason being that the produced magnetic field couples to the sphaleron magnetic
moment and lowers the sphaleron energy; this strengthens the sphaleron
transitions inside the bubbles and triggers a more effective wash out of the
baryon asymmetry. We apply this scenario to the Minimal Supersymmetric
extension of the Standard Model (MSSM) where, in the absence of a magnetic
field, successful electroweak baryogenesis requires the lightest CP-even Higgs
and the right-handed stop masses to be lighter than about 127 GeV and 120 GeV,
respectively. We show that even for moderate values of the magnetic field, the
Higgs mass required to preserve the baryon asymmetry is below the present
experimental bound. As a consequence electroweak baryogenesis within the MSSM
should be confronted on the one hand to future measurements at the LHC on the
Higgs and the right-handed stop masses, and on the other hand to more precise
calculations of the magnetic field produced at the electroweak phase
transition.Comment: 16 pages, 4 figures. Minor corrections and references added to match
published versio
Electroweak Phase Transition in Two Higgs Doublet Models
We reexamine the strength of the first order phase transition in the
electroweak theory supplemented by an extra Higgs doublet. The
finite-temperature effective potential, , is computed to one-loop
order, including the summation of ring diagrams, to study the ratio
of the Higgs field VEV to the critical temperature. We make a
number of improvements over previous treatments, including a consistent
treatment of Goldstone bosons in , an accurate analytic approximation
to valid for any mass-to-temperature ratios, and use of the
experimentally measured top quark mass. For two-Higgs doublet models, we
identify a significant region of parameter space where is large
enough for electroweak baryogenesis, and we argue that this identification
should persist even at higher orders in perturbation theory. In the case of the
minimal supersymmetric standard model, our results indicate that the extra
Higgs bosons have little effect on the strength of the phase transition.Comment: 18 pp., 5 figures, uses epsf.tex. Corrected matching conditions for
analytic approximation to thermal effective potential, eq. (10), and typos in
eq. (5
Decaying Dark Matter can explain the electron/positron excesses
PAMELA and ATIC recently reported excesses in e+ e- cosmic rays. Since the
interpretation in terms of DM annihilations was found to be not easily
compatible with constraints from photon observations, we consider the DM decay
hypothesis and find that it can explain the e+ e- excesses compatibly with all
constraints, and can be tested by dedicated HESS observations of the Galactic
Ridge. ATIC data indicate a DM mass of about 2 TeV: this mass naturally implies
the observed DM abundance relative to ordinary matter if DM is a quasi-stable
composite particle with a baryon-like matter asymmetry. Technicolor naturally
yields these type of candidates.Comment: 20 pages, 7 figure
Ghost Condensation and a Consistent Infrared Modification of Gravity
We propose a theoretically consistent modification of gravity in the
infrared, which is compatible with all current experimental observations. This
is an analog of Higgs mechanism in general relativity, and can be thought of as
arising from ghost condensation--a background where a scalar field \phi has a
constant velocity, = M^2. The ghost condensate is a new kind of
fluid that can fill the universe, which has the same equation of state, \rho =
-p, as a cosmological constant, and can hence drive de Sitter expansion of the
universe. However, unlike a cosmological constant, it is a physical fluid with
a physical scalar excitation, which can be described by a systematic effective
field theory at low energies. The excitation has an unusual low-energy
dispersion relation \omega^2 \sim k^4 / M^2. If coupled to matter directly, it
gives rise to small Lorentz-violating effects and a new long-range 1/r^2 spin
dependent force. In the ghost condensate, the energy that gravitates is not the
same as the particle physics energy, leading to the possibility of both sources
that can gravitate and antigravitate. The Newtonian potential is modified with
an oscillatory behavior starting at the distance scale M_{Pl}/M^2 and the time
scale M_{Pl}^2/M^3. This theory opens up a number of new avenues for attacking
cosmological problems, including inflation, dark matter and dark energy.Comment: 42 pages, LaTeX 2
Amplification of hypercharge electromagnetic fields by a cosmological pseudoscalar
If, in addition to the standard model fields, a new pseudoscalar field exists
and couples to hypercharge topological number density, it can exponentially
amplify hyperelectric and hypermagnetic fields in the symmetric phase of the
electroweak plasma, while coherently rolling or oscillating. We present the
equations describing the coupled system of a pseudoscalar field and hypercharge
electromagnetic fields in the electroweak plasma at temperatures above the
electroweak phase transition, discuss approximations to the equations, and
their validity. We then solve the approximate equations using assorted
analytical and numerical methods, and determine the parameters for which
hypercharge electromagnetic fields can be exponentially amplified.Comment: 14 pages, 6 figure
First-order cosmological phase transitions in the radiation dominated era
We consider first-order phase transitions of the Universe in the
radiation-dominated era. We argue that in general the velocity of interfaces is
non-relativistic due to the interaction with the plasma and the release of
latent heat. We study the general evolution of such slow phase transitions,
which comprise essentially a short reheating stage and a longer phase
equilibrium stage. We perform a completely analytical description of both
stages. Some rough approximations are needed for the first stage, due to the
non-trivial relations between the quantities that determine the variation of
temperature with time. The second stage, instead, is considerably simplified by
the fact that it develops at a constant temperature, close to the critical one.
Indeed, in this case the equations can be solved exactly, including
back-reaction on the expansion of the Universe. This treatment also applies to
phase transitions mediated by impurities. We also investigate the relations
between the different parameters that govern the characteristics of the phase
transition and its cosmological consequences, and discuss the dependence of
these parameters with the particle content of the theory.Comment: 38 pages, 3 figures; v2: Minor changes, references added; v3: several
typos correcte
Dynamics of Two Higgs Doublet CP Violation and Baryogenesis at the Electroweak Phase Transition
We quantitatively study the charge transport mechanism of electroweak
baryogenesis in a realistic two-Higgs-doublet model, comparing the
contributions from quarks and leptons reflecting from electroweak domain walls,
and comparing the exact profile of the CP-violating phase with a commonly used
ansatz. We note that the phenomenon of spontaneous CP violation at high
temperature can occur in this model, even when there is no CP violation at zero
temperature. We include all known effects which are likely to influence the
baryon production rate, including strong sphalerons, the nontrivial dispersion
relations of the quasiparticles in the plasma, and Debye screening of gauged
charges. We confirm the claim of Joyce, Prokopec and Turok that the reflection
of tau leptons from the wall gives the dominant effect. We conclude that this
mechanism is marginally strong enough to produce the observed baryon asymmetry
of the universe.Comment: 49 pp. latex, 6 figures; section on diffusion expanded and corrected,
published versio
Structure of the Quark Propagator at High Temperature
In the high temperature, chirally invariant phase of QCD, the quark
propagator is shown to have two sets of poles with different dispersion
relations. A reflection property in momentum space relates all derivatives at
zero-momentum of the particle and hole energies, the particle and hole damping
rates, and the particle and hole residues. No use is made of perturbation
theory.Comment: 8 pages, Latex twocolum
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