arXiv subjects

Soumitra SenGupta

Publications and source records attributed to Soumitra SenGupta.

At least 145 records · Page 8Linked to original sources

arXiv2006

Stability analysis of the Randall-Sundrum braneworld in presence of bulk scalar

The stability problem of Randall-Sundrum braneworld is readdressed in the light of stabilizing bulk scalar fields. It is shown that in such scenario the instability persists because of back-reaction even when an arbitrary potential is introduced for a canonical scalar field in the bulk. It is further shown that a bulk scalar field can indeed stabilize the braneworld when it has a tachyon-like action. The full back-reacted metric in such model is derived and a proper resolution of the hierarchy problem (for which the Randall Sundrum scenario was originally proposed) is found to exist by suitable adjustments of the parameters of the scalar potential.

hep-th↗

arXiv2005

Charged black holes in generalized dilaton-axion gravity

We study generic Einstein-Maxwell-Kalb-Ramond-dilaton actions, and derive conditions under which they give rise to static, spherically symmetric black hole solutions. We obtain new asymptotically flat and non-flat black hole solutions which are in general electrically and magnetically charged. They have positive definite and finite quasi-local masses. Existing non-rotating black hole solutions (including those appearing in low energy string theory) are recovered in special limits.

hep-th↗

arXiv2005

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.

hep-th↗

arXiv2005

Spinning Test Particle in Kalb-Ramond background

In this work we explore the geodesic deviations of spinning test particles in a string inspired Einstein-Kalb Ramond background. Such a background is known to be equivalent to a spacetime geometry with torsion. We have shown here that the antisymmetric Kalb-Ramond field has significant effect on the geodesic deviation of a spinning test particle. A search for an observational evidence of such an effect in astrophysical experiments may lead to a better undestanding of the geometry of the background spacetime.

hep-th↗

arXiv2005

Sparticle spectrum and phenomenology in split supersymmetry: some possibilities

We investigate the split supersymmetry (SUSY) scenario recently proposed by Arkani-Hamed and Dimopoulos, where the scalars are heavy but the fermions are within the TeV range. We show that the sparticle spectrum in such a case crucially depends on the specific details of the mechanism underlying the SUSY breaking scheme, and the accelerator signals are also affected by it. In particular, we demonstrate in the context of a braneworld-inspired model, used as illustration in the original work, that a new fermion $ψ_X$, arising from the SUSY breaking sector, is shown to control low-energy phenomenology in several cases. Also, SUSY signals are characterised by the associated production of the light neutral Higgs. In an alternative scenario where the gauginos are assumed to propagate in the bulk, we find that gluinos can be heavy and short-lived, and the SUSY breaking scale can be free of cosmological constraints

hep-th↗

arXiv2004

Cosmic Optical Activity in a Randall-Sundrum Braneworld with Bulk Kalb-Ramond field

Optical activity of electromagnetic waves in a string inspired Kalb-Ramond cosmological background is studied in presence of extra spacetime dimension. The Kalb-Ramond-electromagnetic coupling which originates from the gauge anomaly cancelling Chern-Simons term in a string inspired model, is explicitly calculated following Randall-Sundrum braneworld conjecture. It is shown that the Randall-Sundrum scenario leads to an enormous enhancement of the optical rotation of a plane polarized electromagnetic wave propagating on the visible brane.Absence of any experimental support in favour of such a large rotation in astrophysical experiments on distant galactic radio waves indicates an apparent conflict between Randall-Sundrum brane world scenario and the presence of Kalb-Ramond antisymmetric tensor field in the background spacetime.

hep-th↗

arXiv2004

Parity-violating Kalb-Ramond-Maxwell interactions and CMB anisotropy in a braneworld

Following up on a recent paper by two of us (DM and SS), demonstrating the large enhancement in observable optical activity in radiation from high redshift sources arising from the string-based coupling of bulk Kalb-Ramond field to the Maxwell Chern Simons three-form on the brane in a Randall-Sundrum braneworld, we exhibit here a similar enhancement in parity-violating temperature-polarization correlations, yet unseen, in the CMB anisotropy due to a generalized parity-violating Kalb-Ramond axion-photon interaction proposed earlier by one of us (PM). The non-observation of such correlations in CMB anisotropies would necessitate unnatural fine tuning of the Kalb-Ramond axion parameters. As a stringy realization of Randall-Sundrum braneworld scenario is yet to be understood properly, our work indicates the need of a careful investigation to establish the connection between string-based phenomenological models and the Randall-Sundrum braneworld scenario

hep-th↗

arXiv2004

Parity violation in four and higher dimensional spacetime with torsion

The possibility of parity violation in a gravitational theory with torsion is extensively explored in four and higher dimensions. In the former case,we have listed our conclusions on when and whether parity ceases to be conserved, with both two-and three-index antisymmetry of the torsion field. In the latter, the bulk spacetime is assumed to have torsion, and the survival of parity-violating terms in the four dimensional effective action is studied, using the compactification schemes proposed by Arkani-Hamed-Dimopoulos-Dvali and Randall-Sundrum. An interesting conclusion is that the torsion-axion duality arising in a stringy scenario via the second rank antisymmetric Kalb-Ramond field leads to conservation of parity in the gravity sector in any dimension. However, parity-violating interactions do appear for spin 1/2 fermions in such theories, which can have crucial phenomenological implications.

hep-th↗

arXiv2004

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 $ε^{ABLMN}B_{AB}H_{LMN}$ in a Randall-Sundrum scenario. Such a tensor field $B_{AB}$ (whose rank-3 field strength tensor is $H_{LMN}$), 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.

hep-th↗

arXiv2004

Gravitational Redshift in Einstein-Kalb-Ramond Spacetime and Randall-Sundrum Scenario

It is shown that the gravitational redshift as predicted by Einstein's theory, is modified in presence of second rank antisymmetric tensor (Kalb-Ramond) field in a string inspired background spacetime.In presence of extra dimensions, the Randall-Sundrum brane world scenario is found to play a crucial role in suppressing this additional shift. The bound on the value of the warp factor is determined from the redshift data and is found to be in good agreement with that determined from the requirements of Standard model.

hep-th↗

arXiv2003

Does curvature-dilaton coupling with Kalb Ramond field lead to an accelerating Universe ?

In this work we show that the Universe evolving in a spacetime with torsion (originated from a second rank antisymmetric Kalb-Ramond field) and dilaton is free from any big bang singularity and can have acceleration during the evolution. Both the matter and radiation dominated era have been considered and the role of the dilaton to explain the decelerating phase in the earlier epoch has also been discussed.

hep-th↗

arXiv2002

Static spherisymmetric solutions, gravitational lensing and perihelion precession in Einstein--Kalb--Ramond theory

Static, spherically symmetric solutions of the Einstein--Kalb--Ramond (KR) field equations are obtained. Besides an earlier known exact solution, we also find an approximate, asymptotically flat solution for which the metric coefficients are obtained as an infinte series in $\frac{1}{r}$. Subsequently, we study gravitational lensing and perihelion precession in these spacetimes and obtain explicit formulae which include corrections to these effects in the presence of the KR field.

hep-th↗

arXiv2002

Generation of Neutrino mass in a Kalb-Ramond Background in large extra dimensions

In this paper we investigate whether spacetime torsion induced by a Kalb-Ramond field in a string inspired background can generate a mass for the left-handed neutrino. We consider an Einstein-Dirac-Kalb-Ramond lagrangian in higher dimensional spacetime with torsion generated by the Kalb-Ramond antisymmetric field in the presence of a bulk fermion. We show that such a coupling can generate a mass term for the four dimensional neutrino after a suitable large radius compactification of the extra dimensions.

hep-th↗

arXiv2002

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.

hep-th↗

arXiv2002

Bulk torsion fields in theories with large extra dimensions

We study the consequences of spacetime torsion coexisting with gravity in the bulk in scenarios with large extra dimensions. Having linked torsion with the Kalb-Ramond antisymmetric tensor field arising in string theories, we examine its artifacts on the visible 3-brane when the extra dimensions are compactified. It is found that while torsion would have led to parity violation in a 4-dimensional framework, all parity violating effects disappear on the visible brane when the torsion originates in the bulk. However, such a scenario is found to have characteristics of its own, some of which can be phenomenologically significant.

hep-ph↗

arXiv2001

Cosmic optical activity from an inhomogeneous Kalb-Ramond field

The effects of introducing a harmonic spatial inhomogeneity into the Kalb-Ramond field, interacting with the Maxwell field according to a `string-inspired' proposal made in earlier work are investigated. We examine in particular the effects on the polarization of synchrotron radiation from cosmologically distant (i.e. of redshift greater than 2) galaxies, as well as the relation between the electric and magnetic components of the radiation field. The rotation of the polarization plane of linearly polarized radiation is seen to acquire an additional contribution proportional to the square of the frequency of the dual Kalb-Ramond axion wave, assuming that it is far smaller compared to the frequency of the radiation field.

hep-th↗

arXiv2001

Fermion helicity flip by parity violating torsion

The helicity flip of a spin-1/2 Dirac fermion interacting with a torsion- field endowed with a pseudo-tensorial extension is analysed. Taking the torsion to be represented by a Kalb-Ramond field, we show that there is a finite amplitude for helicity flip for massive fermions. The lowest order contribution is proportional to the pseudo-tensor term.

hep-th↗

arXiv2001

Spacetime torsion and parity violation: a gauge invariant formulation

The possibility of parity violation through spacetime torsion has been explored in a scenario containing fields with different spins. Taking the Kalb-Ramond field as the source of torsion, an explicitly parity violating $U(1)_{EM}$ gauge invariant theory has been constructed by extending the KR field with a Chern-Simons term.

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