112 research outputs found
Charge asymmetry in two-Higgs doublet models
We discuss the features of a two-Higgs doublet model exhibiting a two stage
phase transition. At finite temperatures electric charge violating stationary
points are developed. In conjunction with {\em CP} violation in the Higgs or
the Yukawa sector, the phase transition to the charge conserving vacuum,
generates a net charge asymmetry , in the presence of heavy leptons,
which may be well above the astrophysical bounds put on unless the
heavy leptons are sufficiently massive. This type of transition may be of
relevance for supersymmetric extensions of the Standard Model, since it shares
the same features, namely two Higgs doublets and similar {\em CP} violating
sources.Comment: 20 pages, LaTeX file, 5 eps figures included using epsfig macro.
Major revisio
Neutralino Relic Density with a Cosmological Constant confronts Electroweak Precision Measurements
We discuss the relic density of the lightest of the supersymmetric particles
({\small LSP}) in view of new cosmological data, which favour the concept of an
accelerating Universe with a non-vanishing cosmological constant. The new bound
on the Cold Dark Matter density, ,
puts stringent constraints on supersymmetry preferring low supersymmetry
breaking scales, in sharp contrast to electroweak precision measurements
favouring large supersymmetry breaking scales. Supersymmetric predictions are
in agreement with cosmological data and electroweak precision data in the
window of the parameter space: m_0<200\GeV, 300\GeV,
putting bounds on sparticle masses, which may be evaded if .Comment: 17 pages, LaTeX, 10 Postscript figures; version to appear in Phys.
Lett.
Dissipative Liouville Cosmology: A Case Study
We consider solutions of the cosmological equations pertaining to a
dissipative, dilaton-driven off-equilibrium Liouville Cosmological model, which
may describe the effective field theoretic limit of a non-critical string model
of the Universe. The non-criticality may be the result of an early-era
catastrophic cosmic event, such as a big-bang, brane-world collision etc. The
evolution of the various cosmological parameters of the model are obtained, and
the effects of the dilaton and off-shell Liouville terms, including briefly
those on relic densities, which distinguish the model from conventional
cosmologies, are emphasised.Comment: 19 pages latex, 11 eps figures incorporate
WMAPing out Supersymmetric Dark Matter and Phenomenology
The recent WMAP data provide a rather restricted range of the Cold Dark
Matter (CDM) density of unprecedented accuracy. We combine
these new data along with data from BNL E821 experiment measuring , the {b\goes s \gamma} branching ratio and the light Higgs
boson mass bound from LEP, to update our analysis of the allowed boundaries in
the parameter space of the Constrained Minimal Supersymmetric Standard Model
(CMSSM). The prospects of measuring Supersymmetry at LHC look like a very safe
bet, and the potential of discovering SUSY particles at a linear collider is enhanced considerably. The implications for
Dark Matter direct searches are also discussed.Comment: 12 pages LaTeX, 5 eps figures included, references adde
Trilinear Gauge Boson Couplings in the MSSM
We study the C and P even WW\gamma and WWZ trilinear gauge boson vertices
(TGV's), in the context of the MSSM assuming that the external W's are on their
mass shell. We find that for energies less than 200 GeV squark and slepton
contributions to the aforementioned couplings are two orders of magnitude
smaller than those of the Standard Model (SM). In the same energy range the
bulk of the supersymmetric Higgs corrections to the TGV's is due to the
lightest neutral Higgs, h_0, whose contribution is like that of a Standard
Model Higgs of the same mass. The contributions of the Neutralinos and
Charginos are sensitive to the input value for the soft gaugino mass M_{1/2},
being more pronounced for values M_{1/2} < 100 GeV. In this case and in the
unphysical region, 0 < \sqrt{s} < 2 M_W , their contributions are substantially
enhanced resulting in large corrections to the static quantities of the W
boson. However, such an enhancement is not observed in the physical region. In
general for 2 M_W < \sqrt{s} < 200 GeV the MSSM predictions differ from those
of the SM but they are of the same order of magnitude. To be detectable
deviations from the SM require sensitivities reaching the per mille level and
hence unlikely to be observed at LEP200. For higher energies SM and MSSM
predictions exhibit a fast fall off behaviour, in accord with unitarity
requirements, getting smaller,in most cases, by almost an order of magnitude
already at energies \sqrt{s} 0.5 TeV.Comment: 16 pages, late
Supersymmetric QCD corrections to the W-boson width
We calculate the one-loop supersymmetric QCD corrections to the width of the
-boson. We find that these are of order , where is the
supersymmetry breaking scale and the tree level hadronic
width for . Due to the appearance of the
suppression factor these are at least two orders of
magnitude smaller than the standard QCD corrections and hence of the order of the two-loop electroweak
effects. Therefore supersymmetric QCD corrections will only be of relevance
once experiments reach that level of accuracy.Comment: 7 pages, LaTeX file with 2 figures, uses epsf macro
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
The soft supersymmetry breaking in D=5 supergravity compactified on S_1/Z_2 orbifolds
We study the origin of the supersymmetry breaking induced by the mediation of
gravity and the radion multiplet from the hidden to the visible brane in the
context of the N=2, D=5 supergravity compactified on S_1/Z_2 orbifolds. The
soft supersymmetry breaking terms for scalar masses, trilinear scalar couplings
and gaugino masses are calculated to leading order in the five dimensional
Newton's constant k_5^2 and the gravitino mass m_{3/2}. These are finite and
non-vanishing, with the scalar soft masses be non-tachyonic, and are all
expressed in terms of the gravitino mass and the length scale R of the fifth
dimension. The soft supersymmetry breaking parameters are thus correlated and
the phenomenological implications are discussed.Comment: 16 pages, 3 figures, 1 Table, final version to appear in Physics
Letters B, slightly shortened, comments added, typos correcte
Role of beam polarization in the determination of and couplings from
We evaluate the constraints on anomalous trilinear gauge-boson couplings that
can be obtained from the study of electron-positron annihilation into pairs
at a facility with either the electron beam longitudinally polarized or both
electron and positron beams transversely polarized. The energy ranges
considered in the analysis are the ones relevant to the next-linear collider
and to LEP~200. We discuss the possibilities of a model independent analysis of
the general conserving anomalous effective Lagrangian, as well as its
restriction to some specific models with reduced number of independent
couplings. The combination of observables with initial and final state
polarizations allows to separately constrain the different couplings and to
improve the corresponding numerical bounds.Comment: 24 pages, LaTeX, 9 figures (available on request from the authors
Low Energy Thresholds and the Renormalization Group in the MSSM
We derive the 1-loop Renormalization Group Equations for the parameters of
the Minimal Supersymmetric Standard Model (MSSM) taking into account the
successive decoupling of each sparticle below its threshold. This is realized
by a step function at the level of each graph contributing to the
Renormalization Group Equations.Comment: 10 pages , Latex, no figure
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