348 research outputs found
Cosmological constraints on parameters of one-brane models with extra dimension
We study some aspects of cosmologies in 5D models with one infinite extra
dimension. Matter is confined to the brane, gravity extends to the bulk. Models
with positive and negative tension of the brane are considered. Cosmological
evolution of the 4D world is described by warped solutions of the generalized
Friedmann equation. Cosmological solutions on the brane are obtained with the
input of the present-time observational cosmological parameters. We estimate
the age of the Universe and abundance of produced in primordial
nucleosynthesis in different models. Using these estimates we find constraints
on dimensionless combinations of the 5D gravitational scale, scale of the warp
factor and coupling at the 4D curvature term in the action.Comment: 21 pages, 4 figure
Exact Cross Sections for the Neutralino-Slepton Coannihilation
Coannihilation processes provide an important additional mechanism for
reducing the density of stable relics in the Universe. In the case of the
stable lightest neutralino of the MSSM, and in particular the Constrained MSSM
(CMSSM), the coannihilation with sleptons plays a major role in opening up
otherwise cosmologically excluded ranges of supersymmetric parameters. In this
paper, we derive a full set of exact, analytic expressions for the
coannihilation of the lightest neutralino with the sleptons into all two--body
tree--level final states in the framework of minimal supersymmetry. We make no
simplifying assumptions about the neutralino nor about sfermion masses and
mixings other than the absence of explicit CP--violating terms and
inter--family mixings. The expressions should be particularly useful in
computing the neutralino WIMP relic abundance without the approximation of
partial wave expansion. We illustrate the effect of our analytic results with
numerical examples and demonstrate a sizeable difference with approximate
expressions available in the literature.Comment: LaTeX, 46 pages, 8 eps figure
Graviton emission from the brane in the bulk in a model with extra dimension
In a model of 3-brane embedded in 5D space-time we calculate the graviton
emission from the brane to the bulk. Matter is confined to the brane, gravitons
produced in reactions of matter on the brane escape to the bulk. The Einstein
equations which are modified by the terms due to graviton production are solved
perturbatively, the leading order being that without the graviton production.
In the period of late cosmology, in which in the generalized Friedmann equation
the term linear in the energy density of matter in dominant, we calculate the
spectrum of gravitons (of the tower of Kaluza-Klein states) and the collision
integral in the Boltzmann equation. We find the energy-momentum tensor of the
emitted gravitons in the bulk, and using it show that corrections due to
graviton production to the leading-order terms in the Einstein equations are
small, and the perturbative approach is justified. We calculate the difference
of abundances of produced in primordial nucleosynthesis in the models
with and without the graviton production, and find that the difference is a
very small number, much smaller than that estimated previously.Comment: 26 pages, LaTeX Published version with small modification
Superheavy dark matter and ultrahigh energy cosmic rays
The phase of inflationary expansion in the early universe produces superheavy
relics in a mass window between 10^{12} GeV and 10^{14} GeV. Decay or
annihilation of these superheavy relics can explain the observed ultrahigh
energy cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff. We emphasize that
the pattern of cosmic ray arrival directions with energies beyond 20 EeV will
decide between the different proposals for the origin of ultrahigh energy
cosmic rays.Comment: Based on an invited talk given by RD at Theory Canada 1, Vancouver,
June 2-5, 200
Stabilization of internal spaces in multidimensional cosmology
Effective 4-dimensional theories are investigated which were obtained under
dimensional reduction of multidimensional cosmological models with a minimal
coupled scalar field as matter source. Conditions for the internal space
stabilization are considered and the possibility for inflation in the external
space is discussed. The electroweak as well as the Planck fundamental scale
approaches are investigated and compared with each other. It is shown that
there exists a rescaling for the effective cosmological constant as well as for
gravitational exciton masses in the different approaches.Comment: 12 pages, LaTeX2e, to appear in Phys.Rev.D, note adde
Effective CP violation in the Standard Model
We study the strength of effective CP violation originating from the CKM
matrix in the effective action obtained by integrating out the fermions in the
Standard Model. Using results obtained by Salcedo for the effective action in a
general chiral gauge model, we find that there are no CKM CP-violating terms to
fourth order in a gauge-covariant derivative expansion that is non-perturbative
in the Higgs field. The details of the calculation suggest that, at zero
temperature, the strength of CP violation is approximately independent of the
overall scale of the Yukawa couplings. Thus, order of magnitude estimates based
on Jarlskog's invariant could be too small by a factor of about 10^{17}.Comment: 19 pages, no figure
Baryogenesis via lepton number violating scalar interactions
We study baryogenesis through lepton number violation in left-right symmetric
models. In these models the lepton number and CP violating interactions of the
triplet higgs scalars can give rise to lepton number asymmetry through
non-equilibrium decays of the triplet higgs and the right handed
neutrinos. This in turn generates baryon asymmetry during the electroweak
anomalous processes.Comment: 14 pages, UTPT-93-1
Standard Model baryogenesis through four-fermion operators in braneworlds
We study a new baryogenesis scenario in a class of braneworld models with low
fundamental scale, which typically have difficulty with baryogenesis. The
scenario is characterized by its minimal nature: the field content is that of
the Standard Model and all interactions consistent with the gauge symmetry are
admitted. Baryon number is violated via a dimension-6 proton decay operator,
suppressed today by the mechanism of quark-lepton separation in extra
dimensions; we assume that this operator was unsuppressed in the early Universe
due to a time-dependent quark-lepton separation. The source of CP violation is
the CKM matrix, in combination with the dimension-6 operators. We find that
almost independently of cosmology, sufficient baryogenesis is nearly impossible
in such a scenario if the fundamental scale is above 100 TeV, as required by an
unsuppressed neutron-antineutron oscillation operator. The only exception
producing sufficient baryon asymmetry is a scenario involving
out-of-equilibrium c quarks interacting with equilibrium b quarks.Comment: 39 pages, 5 figures v2: typos, presentational changes, references and
acknowledgments adde
Antimatter in the Universe
Cosmological models which predict a large amount of antimatter in the
Universe are reviewed. Observational signatures and searches for cosmic
antimatter are briefly considered. A short discussion of new long range forces
which might be associated with matter and antimatter is presented.Comment: 17 pages + 2 figure
CBR Anisotropy from Primordial Gravitational Waves in Two-Component Inflationary Cosmology
We examine stochastic temperature fluctuations of the cosmic background
radiation (CBR) arising via the Sachs-Wolfe effect from gravitational wave
perturbations produced in the early universe. We consider spatially flat,
perturbed FRW models that begin with an inflationary phase, followed by a mixed
phase containing both radiation and dust. The scale factor during the mixed
phase takes the form , where are
constants. During the mixed phase the universe smoothly transforms from being
radiation to dust dominated. We find analytic expressions for the graviton mode
function during the mixed phase in terms of spheroidal wave functions. This
mode function is used to find an analytic expression for the multipole moments
of the two-point angular correlation function
for the CBR anisotropy. The analytic expression for the multipole
moments is written in terms of two integrals, which are evaluated numerically.
The results are compared to multipoles calculated for models that are {\it
completely} dust dominated at last-scattering. We find that the multipoles
of the CBR temperature perturbations for are
significantly larger for a universe that contains both radiation and dust at
last-scattering. We compare our results with recent, similar numerical work and
find good agreement. The spheroidal wave functions may have applications to
other problems of cosmological interest.Comment: 28 pgs + 6 postscript figures, RevTe
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