173 research outputs found
Supersymmetric Singlet Majorons and Cosmology
We examine cosmological constraints on the lepton number breaking scale in
supersymmetric singlet majoron models. Special attention is drawn to the model
dependence arising from the particular choice of a certain majoron extension
and a cosmological scenario. We find that the bounds on the symmetry breaking
scale can vary substantially. Large values of this scale can be allowed if the
decoupling temperature of smajoron and majorino exceeds the reheating
temperature of inflation. In the opposite case an upper bound depending on the
majoron model can be obtained which, however, is unlikely to be much larger
than GeV.Comment: 14 pages, 2 figures, IC/94/40, SNUTP 94-15, TUM - TH - 164/9
Discrete Gauge Symmetries in Axionic Extensions of the SSM
We examine discrete gauge symmetries in axionic extensions of the SSM which
provide a solution of the -problem. Automatic-PQ symmetry and proton
stability are shown to be guaranteed by certain discrete symmetries. Focusing
on the L-violating discrete symmetries we discuss two sources of neutrino
masses and their relevance for the solar neutrino problem.Comment: 13 pages, TUM-TH-150/92, MPI-Ph/92-7
Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials
We investigate the cosmological evolution of the tachyon and phantom-tachyon
scalar field by considering the potential parameter () as a function of another potential parameter
(), which correspondingly extends the
analysis of the evolution of our universe from two-dimensional autonomous
dynamical system to the three-dimension. It allows us to investigate the more
general situation where the potential is not restricted to inverse square
potential and .One result is that, apart from the inverse square potential,
there are a large number of potentials which can give the scaling and dominant
solution when the function equals for one or some
values of as well as the parameter satisfies
condition Eq.(18) or Eq.(19). We also find that for a class of different
potentials the dynamics evolution of the universe are actually the same and
therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal
C(2010), online first,
http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=
Big bang of the brane universe
Big bang of the Friedmann-Robertson-Walker (FRW)-brane universe is studied.
In contrast to the spacelike initial singularity of the usual FRW universe, the
initial singularity of the FRW-brane universe is point-like from the viewpoint
of causality including gravitational waves propagating in the bulk. Existence
of null singularities (seam singuralities) is also shown in the flat and open
FRW-brane universe models.Comment: LaTeX, 11 pages, 3 EPS figure
Aspects of Tachyonic Inflation with Exponential Potential
We consider issues related to tachyonic inflation with exponential potential.
We find exact solution of evolution equations in the slow roll limit in FRW
cosmology. We also carry out similar analysis in case of Brane assisted
tachyonic inflation. We investigate the phase space behavior of the system and
show that the dust like solution is a late time attractor. The difficulties
associated with reheating in the tachyonic model are also indicated.Comment: New References added. To appear in Phys. Rev.
Observational constraints on braneworld chaotic inflation
We examine observational constraints on chaotic inflation models in the
Randall-Sundrum Type II braneworld. If inflation takes place in the high-energy
regime, the perturbations produced by the quadratic potential are further from
scale-invariance than in the standard cosmology, in the quartic case more or
less unchanged, while for potentials of greater exponent the trend is reversed.
We test these predictions against a data compilation including the WMAP
measurements of microwave anisotropies and the 2dF galaxy power spectrum. While
in the standard cosmology the quartic potential is at the border of what the
data allow and all higher powers excluded, we find that in the high-energy
regime of braneworld inflation even the quadratic case is under strong
observational pressure. We also investigate the intermediate regime where the
brane tension is comparable to the inflationary energy scale, where the
deviations from scale-invariance prove to be greater.Comment: 5 pages RevTeX4 file with three figures incorporated. Minor changes
to match version accepted by Physical Review
The effect of extra dimensions on gravity wave bursts from cosmic string cusps
We explore the kinematical effect of having extra dimensions on the gravity
wave emission from cosmic strings. Additional dimensions both round off cusps,
and reduce the probability of their formation. We recompute the gravity wave
burst, taking into account these two factors, and find a potentially
significant damping on the gravity waves of the strings.Comment: 33 pages, 8 figures, published versio
Cosmological Evolution of Brane World Moduli
We study cosmological consequences of non-constant brane world moduli in five
dimensional brane world models with bulk scalars and two boundary branes. We
focus on the case where the brane tension is an exponential function of the
bulk scalar field, . In the limit , the model reduces to the two-brane model of Randall-Sundrum, whereas larger
values of allow for a less warped bulk geometry. Using the moduli
space approximation, we derive the four-dimensional low-energy effective action
from a supergravity-inspired five-dimensional theory. For arbitrary values of
, the resulting theory has the form of a bi-scalar-tensor theory. We
show that, in order to be consistent with local gravitational observations,
has to be small (less than ) and the separation of the branes
must be large. We study the cosmological evolution of the interbrane distance
and the bulk scalar field for different matter contents on each branes. Our
findings indicate that attractor solutions exist which drive the moduli fields
towards values consistent with observations. The efficiency of the attractor
mechanism crucially depends on the matter content on each branes. In the
five-dimensional description, the attractors correspond to the motion of the
negative tension brane towards a bulk singularity, which signals the eventual
breakdown of the four-dimensional description and the necessity of a better
understanding of the bulk singularity.Comment: 18 pages, 10 figures, typos and factor of 2 corrected, version to
appear in Physical Review
Stable, Time-Dependent, Exact Solutions for Brane Models with a Bulk Scalar Field
We derive two classes of brane-world solutions arising in the presence of a
bulk scalar field. For static field configurations, we adopt a time-dependent,
factorizable metric ansatz that allows for radion stabilization. The solutions
are characterized by a non-trivial warping along the extra dimension, even in
the case of a vanishing bulk cosmological constant, and lead to a variety of
inflationary, time-dependent solutions of the 3D scale factor on the brane. We
also derive the constraints necessary for the stability of these solutions
under time-dependent perturbations of the radion field, and we demonstrate the
existence of phenomenologically interesting, stable solutions with a positive
cosmological constant on the brane.Comment: 24 pages, latex, 4 eps figur
Inflation in Realistic D-Brane Models
We find successful models of D-brane/anti-brane inflation within a string
context. We work within the GKP-KKLT class of type IIB string vacua for which
many moduli are stabilized through fluxes, as recently modified to include
`realistic' orbifold sectors containing standard-model type particles. We allow
all moduli to roll when searching for inflationary solutions and find that
inflation is not generic inasmuch as special choices must be made for the
parameters describing the vacuum. But given these choices inflation can occur
for a reasonably wide range of initial conditions for the brane and antibrane.
We find that D-terms associated with the orbifold blowing-up modes play an
important role in the inflationary dynamics. Since the models contain a
standard-model-like sector after inflation, they open up the possibility of
addressing reheating issues. We calculate predictions for the CMB temperature
fluctuations and find that these can be consistent with observations, but are
generically not deep within the scale-invariant regime and so can allow
appreciable values for as well as predicting a potentially
observable gravity-wave signal. It is also possible to generate some admixture
of isocurvature fluctuations.Comment: 39 pages, 21 figures; added references; identified parameters
combining successful inflation with strong warping, as needed for consistency
of the approximation
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