21 research outputs found
A Randall-Sundrum scenario with bulk dilaton and torsion
We consider a string-inspired torsion-dilaton-gravity action in a
Randall-Sundrum brane world scenario and show that, in an effective
four-dimensional theory on the visible brane, the rank-2 antisymmetric
Kalb-Ramond field (source of torsion) is exponentially suppressed. The result
is similar to our earlier result in [12], where no dilaton was present in the
bulk. This offers an explanation of the apparent invisibility of torsion in our
space-time. However, in this case the trilinear couplings ~ Tev^{-1} between
dilaton and torsion may lead to new signals in Tev scale experiments, bearing
the stamp of extra warped dimensions.Comment: Accepted for publication in Phys.Rev.D; Manuscript revised;
References update
Bulk antisymmetric tensor fields in a Randall-Sundrum model
We consider bulk antisymmetric tensor fields of various ranks in a
Randall-Sundrum scenario. We show that, rank-2 onwards, the zero-modes of the
projections of these fields on the (3+1) dimensional visible brane become
increasingly weaker as the rank of the tensor increases. All such tensor fields
of rank 4 or more are absent from the dynamics in four dimensions. This leaves
only the zero-mode graviton to have coupling with matter, thus
explaining why the large-scale behaviour of the universe is governed by gravity
only. We have also computed the masses of the heavier modes upto rank-3, and
shown that they are relatively less likely to have detectable accelerator
signals.Comment: 8 Pages, Late
Does a Randall-Sundrum scenario create the illusion of a torsion-free universe?
We consider spacetime with torsion in a Randall-Sundrum (RS) scenario where
torsion, identified with the rank-2 Kalb-Ramond field, exists in the bulk
together with gravity. While the interactions of both graviton and torsion in
the bulk are controlled by the Planck mass, an additional exponential
suppression comes for the torsion zero-mode on the visible brane. This may
serve as a natural explanation of why the effect of torsion is so much weaker
than that of curvature on the brane. The massive torsion modes, on the other
hand, are correlated with the corresponding gravitonic modes and may be
detectable in TeV-scale experiments.Comment: 9 pages, Latex, Equ.(4) added, version to appear in Physical Review
Letter
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
Investigating the Energy-Dependent Temporal Nature of Black Hole Binary System H 1743-322
Black hole X-ray binaries routinely exhibit Quasi Periodic Oscillations
(QPOs) in their Power density spectrum. Studies of QPOs have demonstrated
immense ability to understand these dynamical systems although their
unambiguous origin still remains a challenge. We investigate the
energy-dependent properties of the Type-C QPOs detected for H 1743-322 as
observed with AstroSat in its two X-ray outbursts of 2016 and 2017. The
combined broadband LAXPC and SXT spectrum is well modelled with a soft thermal
and a hard Comptonization component. The QPO exhibits soft/negative lags i.e.
variation in soft band lags the variation in hard band, although the upper
harmonic shows opposite behaviour i.e. hard/positive lags. Here, we model
energy-dependent properties (fractional root mean square and time-lag variation
with energy) of the QPO and its upper harmonic individually with a general
scheme that fits these properties by utilizing the spectral information and
consequently allows to identify the radiative component responsible for
producing the variability. Considering the truncated disk picture of accretion
flow, a simple model with variation in inner disk temperature, heating rate and
fractional scattering with time delays is able to describe the fractional RMS
and time-lag spectra. In this work, we show that this technique can
successfully describe the energy-dependent features and identify the spectral
parameters generating the variability.Comment: 6 Figures, 3 Tables, Accepted for publication in MNRA
Matter-gravity interaction in a multiply warped braneworld,
The role of a bulk graviton in predicting the signature of extra dimensions
through collider-based experiments is explored in the context of a multiply
warped spacetime. In particular it is shown that in a doubly warped braneworld
model, the presence of the sixth dimension, results in enhanced concentration
of graviton Kaluza Klein (KK) modes compared to that obtained in the usual
5-dimensional Randall-Sundrum model. Also, the couplings of these massive
graviton KK modes with the matter fields on the visible brane turn out to be
appreciably larger than that in the corresponding 5- dimensional model. The
significance of these results are discussed in the context of KK graviton
search at the Large Hadron Collider (LHC).Comment: 13 pages, 2 table