50 research outputs found
Bouncing cosmology from warped extra dimensional scenario
From the perspective of four dimensional effective theory on a two brane
warped geometry model, we examine the possibility of "bouncing phenomena"on our
visible brane. Our results reveal that the presence of warped extra dimension
lead to a non-singular bounce on the brane scale factor and hence can remove
the "big-bang singularity". We also examine the possible parametric regions for
which this bouncing is possible.Comment: 7 pages, 3 figure
An asymmetric route to 2,3-epoxy-syn-1,4-cyclohexane diol derivatives using ring closing metathesis (RCM)
An asymmetric route for the synthesis of highly functionalized 2,3-epoxy-syn-1,4-cyclohexane diol derivatives present in some polyketide natural products has been developed. The key step involves RCM of an appropriately constructed 1,7-dienol derived from D-mannitol to cyclohexane-1,4-diol followed by its stereoselective epoxidation
A Critical Analysis of Goldberger-Wise Stabilization in Randall-Sundrum Scenario
The Goldberger-Wise mechanism of stabilizing modulus in the Randall-Sundrum
braneworld,by introducing a bulk scalar field with quartic interaction terms
localized at the 3-branes has been extremely popular as a stabilizing mechanism
when the back-reaction of the scalar field on the geometry is negligibly small.
In this note we re-examine the mechanism by an exact analysis without resorting
to the approximations adopted by Goldberger and Wise. An exact calculation of
the stabilization condition indicates the existence of closely spaced minimum
and a maximum for the potential and also brings out some new features involved
in the context of stabilization of such braneworld models.Comment: 5 pages, Revtex, two figure
Bulk Kalb-Ramond field in Randall Sundrum scenario
We have considered the most general gauge invariant five-dimensional action
of a second rank antisymmetric Kalb-Ramond tensor gauge theory, including a
topological term of the form in a
Randall-Sundrum scenario. Such a tensor field (whose rank-3 field
strength tensor is ), which appears in the massless sector of a
heterotic string theory, is assumed to coexist with the gravity in the bulk.
The third rank field strength corresponding to the Kalb-Ramond field has a
well-known geometric interpretation as the spacetime torsion. The only
non-trivial classical solutions corresponding to the effective four-dimensional
action are found to be self-dual or anti-selfdual Kalb-Ramond fields. This
ensures that the four-dimensional effective action on the brane is
parity-conserving. The massive modes for both cases, lying in the TeV range,
are related to the fundamental parameters of the theory. These modes can be
within the kinematic reach of forthcoming TeV scale experiments. However, the
couplings of the massless as well as massive Kalb-Ramond modes with matter on
the visible brane are found to be suppressed vis-a-vis that of the graviton by
the warp factor, whence the conclusion is that both the massless and the
massive torsion modes appear much weaker than curvature to an observer on the
visible brane.Comment: 15 Pages,2 figures,Late
Observable signals in a string inspired axion-dilaton background and Randall-Sundrum scenario
Rotation angle of the plane of polarization of the distant galactic radio
waves has been estimated in a string inspired axion-dilaton background. It is
found that the axion,dual to the field strength of the second rank
antisymmetric massless Kalb-Ramond field in the string spectrum, produces a
wavelength independent optical rotation which is much larger than that produced
by the dilaton. Detection of such rotation has been reported in some recent
cosmological experiments. The observed value has been compared with our
estimated theoretical value following various cosmological constraints. The
effects of warped extra dimensions in a braneworld scenario on such an optical
rotation have been investigated.Comment: 17 Pages, Latex, article revised, To appear in Physical Review
Cosmological constant, brane tension and large hierarchy in a generalized Randall-Sundrum braneworld scenario
Sherpa Romeo green journal. Open access article. Creative Commons Attribution License (CC BY 4.0) applies.We consider a generalized Randall Sundrum (RS) brane world scenario with a cosmological constant
induced on the visible brane. We show that for
< 0, resolution of the hierarchy problem
requires an upper bound on the magnitude of
. The corresponding tension on the visible brane
can be positive or negative. On the other hand, there is no such bound for
> 0. However, in this
case, the resolution of the hierarchy problem along with the tuning of the value of the cosmological
constant to its observed value closed to +10−124 (in Planck units) naturally lead to the tuning of
the modulus to a small value of inverse Planck length as estimated in the original RS scenario.Ye
Constraining the Randall-Sundrum modulus in the light of recent PVLAS data
Recent PVLAS data put stringent constraints on the measurement of
birefringence and dichroism of electromagnetic waves travelling in a constant
and homogeneous magnetic field. There have been theoretical predictions in
favour of such phenomena when appropriate axion-electromagnetic coupling is
assumed. Origin of such a coupling can be traced in a low energy string action
from the requirement of quantum consistency. The resulting couplings in such
models are an artifact of the compactification of the extra dimensions present
inevitably in a string scenario. The moduli parameters which encode the compact
manifold therefore play a crucial role in determining the axion-photon
coupling. In this work we examine the possible bounds on the value of compact
modulus that emerge from the experimental limits on the coupling obtained from
the PVLAS data. In particular we focus into the Randall-Sundrum (RS) type of
warped geometry model whose modulus parameter is already restricted from the
requirement of the resolution of gauge hierarchy problem in connection with the
mass of the Higgs. We explore the bound on the modulus for a wide range of the
axion mass for both the birefringence and the dichroism data in PVLAS. We show
that the proposed value of the modulus in the RS scenario can only be
accommodated for axion mass \gsim 0.3 eV.Comment: 26 pages, 1 figure, LaTex; added references, typos corrected. Minor
changes in the text, a comment added in the Conclusio
Finite temperature properties of a modified PolyakovNambuJona-Lasinio model
Thermodynamic properties of strongly interacting matter are investigated
using the Polyakov loop enhanced NambuJona-Lasinio model along with some
modifications to include the hadrons. Various observables are shown to have a
close agreement with the numerical data of QCD on lattice. The advantage of the
present scheme over a similar study using a switching function is that here no
extra parameters are to be fitted. As a result the present scheme can be easily
extended for finite chemical potentials.Comment: 9 pages, 8 figure