79 research outputs found
Quantum aspects of antisymmetric tensor field with spontaneous Lorentz violation
We study the quantization of a simple model of antisymmetric tensor field
with spontaneous Lorentz violation in curved spacetime. We evaluate the 1-loop
corrections at first order of metric perturbation, using a general covariant
effective action approach. We revisit the issue of quantum equivalence, and
find that it holds for non-Lorentz-violating modes but breaks down for Lorentz
violating modes.Comment: 20 pages; minor corrections, text improvements, references added;
published versio
Finite Temperature Effects and Axion Cosmology
We investigate the impact of finite temperature effects on axions in the
context of cosmology. The temperature dependence of the decay constant is
modeled analogous to pions. For the two interesting cases considered here, we
find that the temperature effects do lead to changes relevant for detailed and
precise abundance and rate calculations. We also find that the axion decoupling
temperature starts showing large deviations for larger values of the axion
decay constant.Comment: 9 pages, 2 figure
Probing Low-x QCD With Very High Energy Prompt Muons
We explore the possibility of utilizing the prompt muon fluxes at very high
energies in order to discriminate various models/parametrizations of low-x QCD
behaviour of hadronic cross-sections relevant at such energies. We find that
the pair meter technique for measuring high energy prompt muons can be very
efficient in such an endeavor. As a by product, it allows to cleanly probe the
change in composition of the primary cosmic rays expected at high energies.Comment: 5 pages, 2 figure
One-Loop Effective Action for Nonminimal Natural Inflation Model
Recent and upcoming experimental data as well as the possibility of rich
phenomenology has spiked interest in studying the quantum gravitational effects
in cosmology at low (inflation-era) energy scales. While Planck scale physics
is under development, it is still possible to incorporate quantum gravity
effects at relatively low energies using quantum field theory in curved
spacetime, which serves as a low-energy limit of planck scale physics. We use
the Vilkovisky-DeWitt's covariant effective action formalism to study quantum
gravitational corrections to a recently proposed Natural Inflation model with
periodic nonminimal coupling. We present the 1-loop effective action for this
theory valid in the flat-potential region, considering perturbative corrections
upto quadratic order in background scalar fields.Comment: 4 pages; Presented at XXIII DAE-BRNS High Energy Physics Symposiu
Spherically symmetric static solutions, newtonian potential and degrees of freedom of a Nonlocal action
Nonlocal terms in the Einstein Hilbert(EH) action appears as IR corrections
in effective theory of quantum gravity. Here we have considered such an action
keeping the terms which are quadratic in Ricci Scalar. We obtain the solution
for a spherical symmetric. We conduct an analysis for linearised gravity action
and find the Newtonian potentials of linearized gravity action and count the
degrees of freedom. Finally we reproduce the results for few known examples
found in literature.Comment: 16 pages, 6 figure
Inflation and Reheating in f(R,h) theory formulated in the Palatini formalism
A new model for inflation using modified gravity in the Palatini formalism is
constructed. Here non-minimal coupling of scalar field h with the curvature R
as a general function f(R,h) is considered. Explicit inflation models for some
choices of f(R,h) are developed. By writing an equivalent scalar-tensor action
for this model and going over to Einstein frame, slow roll parameters are
constructed. There exists a large parameter space which satisfies values of n_s
and limits on r compatible with Planck 2018 data. Further, we calculate
reheating temperature and the number of e-folds at the end of reheating for
different values of equation of state parameter for all the constructed models.Comment: 20 pages, 17 figure
On the quantum equivalence of an antisymmetric tensor field with spontaneous Lorentz violation
We present an explicit proof that a minimal model of rank-2 antisymmetric
field with spontaneous Lorentz violation and a classically equivalent vector
field model are also quantum equivalent, by calculating quantum effective
actions of both theories. We comment on the issues encountered while checking
quantum equivalence in curved spacetime.Comment: published versio
Anisotropic Bouncing Scenario in model
We investigate the cosmology of a class of model with noncanonical scalar
field and matter in an anisotropic time dependent background. Writing the
Einstein Equations in terms of dimensionless dynamical variables appropriately
defined for bouncing solutions, we find all the fixed points. From the bouncing
conditions and stability of fixed points, solutions describing non singular
bounce are obtained.Comment: 13 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1406.399
Local Scale Invariance and Inflation
We study the inflation and the cosmological perturbations generated during
the inflation in a local scale invariant model. The local scale invariant model
introduces a vector field in this theory. In this paper, for
simplicity, we consider the temporal part of the vector field . We show
that the temporal part is associated with the slow roll parameter of scalar
field. Due to local scale invariance, we have a gauge degree of freedom. In a
particular gauge, we show that the local scale invariance provides sufficient
number of e-foldings for the inflation. Finally, we estimate the power spectrum
of scalar perturbation in terms of the parameters of the theory.Comment: 11 page
Curvature Singularity in f(R) Theories of Gravity
Although modification of late time cosmology is successful in
explaining present cosmic acceleration, it is difficult to satisfy the
fifth-force constraint simultaneously. Even when the fifth-force constraint is
satisfied, the effective scalar degree of freedom may move to a point (close to
its potential minima) in the field space where the Ricci scalar diverges. We
elucidate this point further with a specific example of gravity that
incorporates several viable gravity models in the literature. In
particular, we show that the nonlinear evolution of the scalar field in
pressureless contracting dust can easily lead to the curvature singularity,
making this theory unviable.Comment: 15 pages, 4 figures, 1 table, minor changes in the text, a few
references adde
- …