Debaprasad Maity

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.

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 red-shift 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, as 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 the Randall–Sundrum braneworld scenario is yet to be understood properly, our work indicates the need for a careful investigation to establish the connection between string-based phenomenological models and the Randall–Sundrum braneworld scenario.

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

Abstract 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 in general 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.

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 backreaction of the scalar field on the geometry is negligibly small. In this paper we reexamine 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 the stabilization of such braneworld models.

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 massless antisymmetric 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.

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 the presence of an 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 the 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. The 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 the Randall–Sundrum braneworld scenario and the presence of the Kalb–Ramond antisymmetric tensor field in the background spacetime.

The role of a higher derivative bulk scalar in stabilizing a warped spacetime

The back-reaction on the Randall?Sundrum warped spacetime is determined in the presence of a scalar field in the bulk. A general condition for the stability of such a model is derived for a bulk scalar field action with non-canonical higher derivative terms. It is further shown that the gauge hierarchy problem can be resolved in such a stabilized scenario by appropriate choice of various parameters of the theory.

Domain walls in a Born-Infeld-dilaton background

We study the dynamics of domain walls in the Einstein-Bom-Infeld-dilaton theory. A dilaton is nontrivially coupled with the Bom-Infeld electromagnetic field. We find three different types of solutions consistent with the dynamic domain walls. For every case, the solutions have singularity. Furthermore, in these backgrounds, we study the dynamics of domain walls. We qualitatively plot various forms of the bulk metrics and the potential encountered by the domain walls. In many cases, depending upon the value of the parameters, the domain walls show a bouncing universe and also undergo an inflationary phase followed by a standard decelerated expansion.

Dynamic domain walls in a Maxwell-dilaton background

Motivated by the well-known Chamblin-Reall solutions of n-dimensional background spacetime in a dilaton gravity and the dynamics of a domain wall in the same backgrounds, we have tried to generalize those solutions by including an electromagnetic field in the bulk. The electromagnetic field is assumed to be coupled with the scalar field in an exponential way. Under the specific relations among the various parameters in our model, we have found five different types of solutions. For every case, the solution has singularity. In these backgrounds, we have also studied the dynamics of the domain wall. The energy densities, which play the role of these interesting dynamics, are known to be induced from the bulk fields through the Israel junction condition. In this more general background field configuration, we have found that static bulk spacetime exists consistently with the dynamic domain wall. In several cases, depending on the values of the parameters, in the early stage of evolution, the domain wall is found to have an inflationary phase for finite period of its proper time followed by usual decelerated expansion.

Engineering holographic phase diagrams

We study how to engineer holographic models with features of a high temperature superconductor phase diagram. We introduce a