69,659 research outputs found
Magnetic Fields from the Electroweak Phase Transition
I review some of the mechanisms through which primordial magnetic fields may
be created in the electroweak phase transition. I show that no magnetic fields
are produced initially from two-bubble collisions in a first-order transition.
The initial field produced in a three-bubble collision is computed. The
evolution of fields at later times is discussed.Comment: Talk presented at the International Workshop on Particle Physics and
the Early Universe (COSMO--97) in Ambleside, England, 15-19 Sept 1997. To
appear in the proceedings (World Scientific). LaTeX, 5 page
Particle creation in a toroidal universe
We calculate the particle production rate in an expanding universe with a
three-torus topology. We discuss also the complete evolution of the size of
such a universe. The energy density of particles created through the nonzero
modes is computed for selected masses. The unique contribution of the zero mode
and its properties are also analyzed.Comment: 9 pages, 11 figure
A New Source for Electroweak Baryogenesis in the MSSM
One of the most experimentally testable explanations for the origin of the
baryon asymmetry of the universe is that it was created during the electroweak
phase transition, in the minimal supersymmetric standard model. Previous
efforts have focused on the current for the difference of the two Higgsino
fields, , as the source of biasing sphalerons to create the baryon
asymmetry. We point out that the current for the orthogonal linear combination,
, is larger by several orders of magnitude. Although this increases
the efficiency of electroweak baryogenesis, we nevertheless find that large
CP-violating angles are required to get a large enough baryon
asymmetry.Comment: 4 pages, 2 figures; numerical error corrected, which implies that
large CP violation is needed to get observed baryon asymmetry. We improved
solution of diffusion equations, and computed more accurate values for
diffusion coefficient and damping rate
Quintessence and effective AdS brane geometries
A geometric torsion dynamics leading to an effective curvature in a second
order formalism on a D4-brane is revisited with a renewed interest. We obtain
two effective brane geometries on a vacuum created pair of -brane. One of them is shown to describe an AdS Schwarzschild spinning
black hole and the other is shown to describe a spinning black hole bound
state. It is argued that a D-instanton in a vacuum created anti D3-brane within
a pair may describe a quintessence. It may seen to incorporate a varying vacuum
energy density in a brane universe. We consider the effective curvature scalar
on to analyze torsion-less geometries on a vacuum created pair
of -brane. The emergent brane is shown to describe a
Schwarzschild and a Reissner-Nordstrom (RN) geometries in presence of extra
dimension(s).Comment: 20 pages, expanded discussion and added referenc
Global Cosmological Parameters Determined Using Classical Double Radio Galaxies
A sample of 20 powerful extended radio galaxies with redshifts between zero
and two were used to determine constraints on global cosmological parameters.
Data for six radio sources were obtained from the VLA archive, analyzed, and
combined with the sample of 14 radio galaxies used previously by Guerra & Daly
to determine cosmological parameters. The results are consistent with our
previous results, and indicate that the current value of the mean mass density
of the universe is significantly less than the critical value. A universe with
of unity is ruled out at 99.0% confidence, and the best fitting
values of in matter are and
assuming zero space curvature and zero cosmological
constant, respectively. Note that identical results obtain when the low
redshift bin, which includes Cygnus A, is excluded; these results are
independent of whether the radio source Cygnus A is included. The method does
not rely on a zero-redshift normalization.
The radio properties of each source are also used to determine the density of
the gas in the vicinity of the source, and the beam power of the source. The
six new radio sources have physical characteristics similar to those found for
the original 14 sources. The density of the gas around these radio sources is
typical of gas in present day clusters of galaxies. The beam powers are
typically about .Comment: 39 pages includes 21 figures, accepted to Ap
Cosmic structure formation in Hybrid Inflation models
A wide class of inflationary models, known as Hybrid Inflation models, may
produce topological defects during a phase transition at the end of the
inflationary epoch. We point out that, if the energy scale of these defects is
close to that of Grand Unification, then their effect on cosmic structure
formation and the generation of microwave background anisotropies cannot be
ignored. Therefore, it is possible for structure to be seeded by a combination
of the adiabatic perturbations produced during inflation and active
isocurvature perturbations produced by defects. Since the two mechanisms are
uncorrelated the power spectra can be computed by a weighted average of the
individual contributions. We investigate the possible observational
consequences of this with reference to general Hybrid Inflation models and also
a specific model based on Supergravity. These mixed perturbation scenarios have
some novel observational consequences and these are discussed qualitatively.Comment: 22 Page
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