588 research outputs found
Leading Gravitational Corrections and a Unified Universe
Leading order gravitational corrections to the Einstein-Hilbert action can
lead to a consistent picture of the universe by unifying the epochs of
inflation and dark energy in a single framework. While the leading local
correction induces an inflationary phase in the early universe, the leading
non-local term leads to an accelerated expansion of the universe at the present
epoch. We argue that both the leading UV and IR terms can be obtained within
the framework of a covariant effective field theory of gravity. The
perturbative gravitational corrections therefore provide a fundamental basis
for understanding a possible connection between the two epochs.Comment: 5 pages, 2 figures. This essay received "Honorable Mention" in the
2016 Gravity Research Foundation Awards for Essays on Gravitation. arXiv
admin note: substantial text overlap with arXiv:1603.0002
On the non-Gaussian correlation of the primordial curvature perturbation with vector fields
We compute the three-point cross-correlation function of the primordial
curvature perturbation generated during inflation with two powers of a vector
field in a model where conformal invariance is broken by a direct coupling of
the vector field with the inflaton. If the vector field is identified with the
electromagnetic field, this correlation would be a non-Gaussian signature of
primordial magnetic fields generated during inflation. We find that the signal
is maximized for the flattened configuration where the wave number of the
curvature perturbation is twice that of the vector field and in this limit, the
magnetic non-linear parameter becomes as large as |b_{NL}| ~ 10^3. In the
squeezed limit where the wave number of the curvature perturbation vanishes,
our results agree with the magnetic consistency relation derived in
arXiv:1207.4187.Comment: 18 pages. V3: some typos fixed, matches version published in JCA
Agronomic and economic performance of organic, conventional and GM-cotton in Central India - First results of a long-term farming systems comparison
Over the past five years the organic cotton production in India has grown many folds. In the conventional cotton arena, the genetically modified cotton is growing at an unprecedented rate. In view of these developments, it was considered necessary to carry out a systematic comparison between the various cotton production systems common in the area. Further, this research attempts to address the larger issues:
• Put the discussion regarding the benefits and drawbacks of organic agriculture on a rational footing;
• Help to identify challenges for organic agriculture that can then be addressed systematically;
• Provide physical reference and meeting points for stakeholders in agricultural research and development and thus support decision-making and agricultural policy dialogue at different levels
Polarographic Investigations of Some 2-Arylazo-2-bromo-5,5-dimethylcydohexane-1,3-diones
Polarographic reduction of 2-arylazo-2-bromo-5,5-dimethylcyclohexane-
1,3-diones takes place in a single step involving two
electrons. Well-defined, diffusion controlled, irreversible waves
are obtained in the pH range 2.0 -11.0. The Ei,2 value shifts
towards more negative potentials with increasing pH. Methyl,
Methoxy, chloro, bromo and ethoxy groups show positive polarographic
ortho shift (~o). The effect of substituents has been interpreted
in terms of the Hammett equation
Generation of scale invariant magnetic fields in bouncing universes
We consider the generation of primordial magnetic fields in a class of
bouncing models when the electromagnetic action is coupled non-minimally to a
scalar field that, say, drives the background evolution. For scale factors that
have the power law form at very early times and non-minimal couplings which are
simple powers of the scale factor, one can easily show that scale invariant
spectra for the magnetic field can arise before the bounce for certain values
of the indices involved. It will be interesting to examine if these power
spectra retain their shape after the bounce. However, analytical solutions for
the Fourier modes of the electromagnetic vector potential across the bounce are
difficult to obtain. In this work, with the help of a new time variable that we
introduce, which we refer to as the --fold, we investigate
these scenarios numerically. Imposing the initial conditions on the modes in
the contracting phase, we numerically evolve the modes across the bounce and
evaluate the spectra of the electric and magnetic fields at a suitable time
after the bounce. As one could have intuitively expected, though the complete
spectra depend on the details of the bounce, we find that, under the original
conditions, scale invariant spectra of the magnetic fields do arise for
wavenumbers much smaller than the scale associated with the bounce. We also
show that magnetic fields which correspond to observed strengths today can be
generated for specific values of the parameters. But, we find that, at the
bounce, the backreaction due to the electromagnetic modes that have been
generated can be significantly large calling into question the viability of the
model. We briefly discuss the implications of our results.Comment: v1: 19 pages, 5 figures; v2: 20 pages, 5 figures, minor revisions, to
appear in JCA
Effective chemical potential in spontaneous baryogenesis
Models of spontaneous baryogenesis have an interaction term
in the Lagrangian, where is the baryonic
current and can be a pseudo-Nambu-Goldstone boson. Since the time
component of this term, , equals for a
spatially homogeneous current, it is usually argued that this term implies a
splitting in the energy of baryons and antibaryons thereby providing an
effective chemical potential for baryon number. In thermal equilibrium, one
{then obtains} . We however argue that a term of
this form in the Lagrangian does not contribute to the single particle energies
of baryons and antibaryons. We show this for both fermionic and scalar baryons.
But, similar to some recent work, we find that despite the above result the
baryon number density obtained from a Boltzmann equation analysis can be
proportional to . Our arguments are very different from that
in the standard literature on spontaneous baryogenesis.Comment: 16 pages, matches with the published versio
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