27 research outputs found
Parity breaking at high temperature and density
We investigate the question of parity breaking in three-dimensional Euclidean
SU(2) gauge-Higgs theory by Monte Carlo simulations. We observe no sign of
spontaneous parity breaking in the behaviour of both local and non-local gauge
invariant operators. However, the presence of parity odd terms in the action
can induce a phase transition to a parity odd ground state which is
characterized by a Chern-Simons like condensate. The implications for various
proposed scenarios of fermion number non-conservation is discussed.Comment: 20 pages, 13 figures not included, sorr
Vector field localization and negative tension branes
It is shown that negative tension branes in higher dimensions may lead to an
effective lower dimensional theory where the gauge-invariant vector fields
associated with the fluctuations of the metric are always massless and
localized on the brane. Explicit five-dimensional examples of this phenomenon
are provided. Furthermore, it is shown that higher dimensional gauge fields can
also be localized on these configurations with the zero mode separated from the
massive tower by a gap.Comment: 16 pages, LaTeX style; to appear in Phys. Rev.
Refining the predictions of supersymmetric CP-violating models: A top-down approach
We explore in detail the consequences of the CP-violating phases residing in
the supersymmetric and soft SUSY breaking parameters in the approximation that
family flavour mixings are ignored. We allow for non-universal boundary
conditions and in such a consideration the model is described by twelve
independent CP-violating phases and one angle which misaligns the vacuum
expectation values (VEVs) of the Higgs scalars. We run two-loop renormalization
group equations (RGEs), for all parameters involved, including phases, and we
properly treat the minimization conditions using the one-loop effective
potential with CP-violating phases included. We show that the two-loop running
of phases may induce sizable effects for the electric dipole moments (EDMs)
that are absent in the one-loop RGE analysis. Also important corrections to the
EDMs are induced by the Higgs VEVs misalignment angle which are sizable in the
large tanb region. Scanning the available parameter space we seek regions
compatible with accelerator and cosmological data with emphasis on rapid
neutralino annihilations through a Higgs resonance. It is shown that large
CP-violating phases, as required in Baryogenesis scenarios, can be tuned to
obtain agreement with WMAP3 cold dark matter constraints, EDMs and all
available accelerator data, in extended regions of the parameter space which
may be accessible to LHC.Comment: 41 pages, 22 eps figures. A reference added and a typo corrected;
version to appear in JHE
Electroweak phase diagram at finite lepton number density
We study the thermodynamics of the electroweak theory at a finite lepton
number density. The phase diagram of the theory is calculated by relating the
full 4-dimensional theory to a 3-dimensional effective theory which has been
previously solved using nonperturbative methods. It is seen that the critical
temperature increases and the value of the Higgs boson mass at which the first
order phase transition line ends decreases with increasing leptonic chemical
potential.Comment: 16 pages, 14 figures, RevTex4, v2: references added, minor
corrections, v3: small changes, references added, published in Phys. Rev.
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 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
On initial conditions for the Hot Big Bang
We analyse the process of reheating the Universe in the electroweak theory
where the Higgs field plays a role of the inflaton. We estimate the maximal
temperature of the Universe and fix the initial conditions for
radiation-dominated phase of the Universe expansion in the framework of the
Standard Model (SM) and of the nuMSM -- the minimal extension of the SM by
three right-handed singlet fermions. We show that the inflationary epoch is
followed by a matter dominated stage related to the Higgs field oscillations.
We investigate the energy transfer from Higgs-inflaton to the SM particles and
show that the radiation dominated phase of the Universe expansion starts at
temperature T_r~(3-15)*10^{13} GeV, where the upper bound depends on the Higgs
boson mass. We estimate the production rate of singlet fermions at preheating
and find that their concentrations at T_r are negligibly small. This suggests
that the sterile neutrino Dark Matter (DM) production and baryogenesis in the
nuMSM with Higgs-driven inflation are low energy phenomena, having nothing to
do with inflation. We study then a modification of the nuMSM, adding to its
Lagrangian higher dimensional operators suppressed by the Planck scale. The
role of these operators in Higgs-driven inflation is clarified. We find that
these operators do not contribute to the production of Warm Dark Matter (WDM)
and to baryogenesis. We also demonstrate that the sterile neutrino with mass
exceeding 100 keV (a Cold Dark Matter (CDM) candidate) can be created during
the reheating stage of the Universe in necessary amounts. We argue that the
mass of DM sterile neutrino should not exceed few MeV in order not to overclose
the Universe.Comment: 41 pages, 5 figures. Journal version accepted in JCA
Brane Induced Gravity, its Ghost and the Cosmological Constant Problem
"Brane Induced Gravity" is regarded as a promising framework for addressing
the cosmological constant problem, but it also suffers from a ghost instability
for parameter values that make it phenomenologically viable. We carry out a
detailed analysis of codimension > 2 models employing gauge invariant variables
in a flat background approximation. It is argued that using instead a curved
background sourced by the brane would not resolve the ghost issue, unless a
very specific condition is satisfied (if satisfiable at all). As for other
properties of the model, from an explicit analysis of the 4-dimensional
graviton propagator we extract a mass, a decay width and a momentum dependent
modification of the gravitational coupling for the spin 2 mode. In the flat
space approximation, the mass of the problematic spin 0 ghost is instrumental
in filtering out a brane cosmological constant. The mass replaces a background
curvature that would have had the same function. The optical theorem is used to
demonstrate the suppression of graviton leakage into the uncompactified bulk.
Then, we derive the 4-dimensional effective action for gravity and show that
general covariance is spontaneously broken by the bulk-brane setup. This
provides a natural realization of the gravitational Higgs mechanism. We also
show that the addition of extrinsic curvature dependent terms has no bearing on
linearized brane gravity.Comment: v2: LaTeX, JHEP style, 41 pages, 3 eps figures. Partly rewritten to
improve presentation, results unchanged, published versio
Supersymmetric Large Extra Dimensions and the Cosmological Constant Problem
This article briefly summarizes and reviews the motivations for - and the
present status of - the proposal that the small size of the observed Dark
Energy density can be understood in terms of the dynamical relaxation of two
large extra dimensions within a supersymmetric higher-dimensional theory.Comment: Talk presented to Theory Canada I, Vancouver, June 2005. References
added in V
A photon mass on the brane
We discuss the impact of a bulk photon mass in a Dvali-Gabadadze-Porrati type
brane model with Maxwell terms both on the brane and in the bulk, as proposed
by Dvali, Gabadadze and Shifman. The motivation to include the bulk photon mass
is to suppress radiation loss into the bulk. We point out that this modifies
the photon propagator in such a way that it generates a small photon mass on
the brane. Compatibility with present bounds on a photon mass imply that the
transition to five-dimensional distance laws for the electromagnetic potentials
would appear only at super-horizon length scales, thus excluding any direct
detection possibility of a transition from four-dimensional to five-dimensional
distance laws in electromagnetic interactions. We also include results on
fermion propagators with Dirac terms on the brane and in the bulk.Comment: 9 page