3,600 research outputs found
A Mechanism for Baryogenesis in Low Energy Supersymmetry Breaking Models
A generic prediction of models where supersymmetry is broken at scales within
a few orders of magnitude of the weak scale and is fed down to the observable
sector by gauge interactions is the existence of superconducting cosmic strings
which carry baryon number. In this paper we propose a novel mechanism for the
generation of the baryon asymmetry which takes place at temperatures much lower
than the weak scale. Superconducting strings act like ``bags'' containing the
baryon charge and protect it from sphaleron wash-out throughout the evolution
of the Universe, until baryon number violating processes become harmless. This
mechanism is efficient even if the electroweak phase transition in the MSSM is
of the second order and therefore does not impose any upper bound on the mass
of the Higgs boson. (13kb)Comment: LaTeX file, 17 pages. One ref. adde
String Theory, Space-Time Non-Commutativity and Structure Formation
A natural consequence of string theory is a non-commutative structure of
space-time on microscopic scales. The existence of a minimal length, and a
modification of the effective field theory are two consequences of this
space-time non-commutativity. I will first explore some consequences of the
modifications of the effective field theory for structure formation in the
context of an inflationary cosmology. Then, I will explore the possibility that
the existence of a minimal length will lead to a structure formation scenario
different from inflation. Specifically, I will discuss recent work on string
gas cosmology.Comment: 12 pages, 2 figures, based on an invited talk at the 21st
Nishinomiya-Yukawa Memorial Symposium, Nov. 11 - 16, 2006, to be publ. in the
proceedings (Prog. Theor. Phys. Suppl.
Matter Bounce in Horava-Lifshitz Cosmology
Horava-Lifshitz gravity, a recent proposal for a UV-complete renormalizable
gravity theory, may lead to a bouncing cosmology. In this note we argue that
Horava-Lifshitz cosmology may yield a concrete realization of the matter bounce
scenario, and thus give rise to an alternative to inflation for producing a
scale-invariant spectrum of cosmological perturbations. In this scenario,
quantum vacuum fluctuations exit the Hubble radius in the pre-bounce phase and
the spectrum is transformed into a scale-invariant one on super-Hubble scales
before the bounce because the long wavelength modes undergo squeezing of their
wave-functions for a longer period of time than shorter wavelength modes. The
scale-invariance of the spectrum of curvature fluctuations is preserved during
and after the bounce. A distinctive prediction of this scenario is the
amplitude and shape of the bispectrum.Comment: 6 pages, 1 figure, a couple of minor wording change
Perturbations in a Bouncing Brane Model
The question of how perturbations evolve through a bounce in the Cyclic and
Ekpyrotic models of the Universe is still a matter of ongoing debate. In this
report we show that the collision between boundary branes is in most cases
singular even in the full 5-D formalism, and that first order perturbation
theory breaks down for at least one perturbation variable. Only in the case
that the boundary branes approach each other with constant velocity shortly
before the bounce, can a consistent, non singular solution be found. It is then
possible to follow the perturbations explicitly until the actual collision. In
this case, we find that if a scale invariant spectrum developed on the hidden
brane, it will get transferred to the visible brane during the bounce.Comment: 15 pages, minor modifications, a few typos correcte
String Gas Baryogenesis
We describe a possible realization of the spontaneous baryogenesis mechanism
in the context of extra-dimensional string cosmology and specifically in the
string gas scenario.Comment: arXiv admin note: substantial text overlap with 0808.0746 by
different autho
Principles, Progress and Problems in Inflationary Cosmology
Inflationary cosmology has become one of the cornerstones of modern
cosmology. Inflation was the first theory within which it was possible to make
predictions about the structure of the Universe on large scales, based on
causal physics. The development of the inflationary Universe scenario has
opened up a new and extremely promising avenue for connecting fundamental
physics with experiment. This article summarizes the principles of inflationary
cosmology, discusses progress in the field, focusing in particular on the
mechanism by which initial quantum vacuum fluctuations develop into the seeds
for the large-scale structure in the Universe, and highlights the important
unsolved problems of the scenario. The case is made that new input from
fundamental physics is needed in order to solve these problems, and that thus
early Universe cosmology can become the testing ground for trans-Planckian
physics.Comment: 8 pages, 8 figures commissioned article for the AAPPS Bulletin,
appeared in 200
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