arXiv subjects

Soumitra SenGupta

Publications and source records attributed to Soumitra SenGupta.

At least 127 records · Page 7Linked to original sources

arXiv2009

Modulus stabilization of generalized Randall Sundrum model with bulk scalar field

We study the stabilization of inter-brane spacing modulus of generalized warped brane models with a nonzero brane cosmological constant. Employing Goldberger-Wise stabilization prescription of brane world models with a bulk scalar field, we show that the stabilized value of the modulus generally depends on the value of the brane cosmological constant. Our result further reveals that the stabilized modulus value corresponding to a vanishingly small cosmological constant can only resolve the gauge hierarchy problem simultaneously. This in turn vindicates the original Randall-Sundrum model where the 3-brane cosmological constant was chosen to be zero.

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arXiv2008

Aspects of warped braneworld models

We review various key issues in connection with the warped braneworld models which provide us with new insights and explanations of physical phenomena through interesting geometrical features of such extra dimensional theories. Starting from the original Randall-Sundrum two brane models, we have discussed the stability, hierarchy and other important issues in connection with such braneworld. The role of higher derivative terms in the bulk for modulus stabilization has been explained. Implications of the existence of various bulk fields have been discussed and it has been shown how a warped braneworld model can explain the invisibility of all antisymmetric bulk tensor fields on our brane. We have also generalised the model for more than one warped dimensions in the form of a multiply warped spacetime. It is shown that such model can offer an explanation to the mass hierarchy among the standard model fermions and the localization of fermions on the standard model brane with a definite chirality.

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arXiv2008

Thermodynamics Of dilaton-axion black holes

Considering a generalised action for Einstein Maxwell theory in four dimensions coupled to scalar and pseudo-scalar fields, the thermodynamic properties of asymptotically flat black holes solutions in such a background are investigated. Bekenstein-Hawking area-entropy law is verified for these class of black holes. From the property of specific heat, it is shown that such black holes can be stable for certain choice of the parameters like charge, mass and the scalar vacuum expectation value. The possibility of a black hole phase transition is discussed in this context.

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arXiv2008

Chiral fermions in a spacetime with multiple warping

In a six dimensional brane world model with multiple $S_1/Z_2$ warping, two of the 4-branes at the boundaries have coordinate dependent brane tensions in order to implement the orbifolded boundary conditions consistently. Such brane tension is shown to be equivalent to a scalar field distribution on the brane [1]. We show that in such a scenario a masslesss left chiral fermion on the 4-brane localizes naturally on the standard model 3-brane located at one edge of the compact manifold while the massless right chiral fermion wave function as well as the wave functions for the massive fermion modes peak away from this brane. This offers a mechanism of obtaining massless chiral fermion with only one of its chiral component present in our brane.

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arXiv2008

Stability and hierarchy problems in string inspired braneworld scenarios

We generalise the RS braneworld model by taking into account a general stringy bulk containing the scalar dilaton field and the two-form Kalb-Ramond field, apart from gravity. Assuming small fluctuations around a RS background, the back-reacted warp factor is obtained. It is shown that the fine tuning problem in connection with the Higgs mass reappears in a new guise and the effective modular potential fails to stabilise the braneworld.

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arXiv2008

Cosmological constant, brane tension and large hierarchy in a generalized Randall-Sundrum braneworld scenario

We consider a generalized Randall Sundrum (RS) brane world scenario with a cosmological constant $Ω$ induced on the visible brane. We show that for $Ω<0$, resolution of the hierarchy problem requires an upper bound on the magnitude of $Ω$. The corresponding tension on the visible brane can be positive or negative. On the other hand, there is no such bound for $Ω>0$. 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.

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arXiv2008

Entropy of charged dilaton-axion black hole

Using brick wall method the entropy of charged dilaton-axion black hole is determined for both asymptotically flat and non-flat cases. The entropy turns out to be proportional to the horizon area of the black hole confirming the Beckenstien, Hawking area-entropy formula for black holes. The leading order logarithmic corrections to the entropy are also derived for such black holes.

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arXiv2008

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.

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arXiv2007

Fermion mass splitting, stability and naturalness problems in warped braneworld models

We generalize the Randall Sundrum warped braneworld model in six and higher dimension and propose a resolution to the mass hierarchy among the standard model fermions. The fine tuning problem in connection with the scalar mass however is shown to reappear in a new guise in five dimensional warped model when the two form antisymmetric tensor fields, a massless string mode, propagates in the bulk. Finally the issue of modulus stabilization is re-examined in presence of a bulk scalar by considering it's back-reaction on the background geometry. The role of higher derivative term of the bulk scalar is shown to be crucial to achieve modulus stabilization.

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arXiv2007

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 $\sim 1/M_P$ 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.

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arXiv2007

Slowly Rotating Dilaton Black hole In Anti-de Sitter Spacetime

Rotating dilaton black hole solution for asymptotically anti-de Sitter spacetime are obtained in the small angular momentum limit with an appropriate combination of three Liouville-type dilaton potentials. The angular momentum, magnetic dipole moment and the gyromagnetic ratio of such a black hole are determined for arbitrary values of the dilaton-electromagnetic coupling parameter.

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arXiv2007

Supergravity can reconcile dark matter with lepton number violating neutrino masses

Supersymmetry offers a cold dark matter candidate, provided that lepton number is {\em not violated by an odd number of units}. On the other hand, lepton number violation by even (two) units gives us an attractive mechanism of neutrino mass generation. Here we offer an explanation of this, in a supergravity framework underlying a supersymmetric scenario, the essential feature being particles carrying lepton numbers, which interact only gravitationally with all other known particles. It is shown that one can have the right amount of $ΔL = 2$ effect giving rise to neutrino masses, whereas the lifetime for $ΔL = 1$ decays of the lightest supersymmetric particle can be prolonged beyond the present age of the universe.

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arXiv2007

Living on the edge in a spacetime with multiple warping

The Randall-Sundrum warped braneworld model is generalised to six and higher dimensions such that the warping has a non-trivial dependence on more than one dimension. This naturally leads to a brane-box like configuration alongwith scalar fields with possibly interesting cosmological roles. Also obtained naturally are two towers of 3 branes with mass scales clustered around either of Planck scale and TeV scale. Such a scenario has interesting phenomenological consequences including an explanation for the observed hierarchy in the masses of standard model fermions.

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arXiv2006

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.

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arXiv2006

The Raychaudhuri equations: a brief review

We present a brief review on the Raychaudhuri equations. Beginning with a summary of the essential features of the original article by Raychaudhuri and subsequent work of numerous authors, we move on to a discussion of the equations in the context of alternate non--Riemannian spacetimes as well as other theories of gravity, with a special mention on the equations in spacetimes with torsion (Einstein--Cartan--Sciama--Kibble theory). Finally, we give an overview of some recent applications of these equations in General Relativity, Quantum Field Theory, String Theory and the theory of relativisitic membranes. We conclude with a summary and provide our own perspectives on directions of future research.

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arXiv2006

Split supersymmetry and the role of a light fermion in a supergravity-based scenario

We investigate split supersymmetry (SUSY) within a supergravity framework, where local SUSY is broken by the F-term of a hidden sector chiral superfield X. With reasonably general assumptions, we show that the fermionic component of X will always have mass within a Tev. Though its coupling to the observable sector superfields is highly suppressed in Tev scale SUSY, we show that it can be enhanced by many orders in split SUSY, leading to its likely participation in accelerator phenomenology.We conclude with a specific example of such a scenario in a string based supergravity model.

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arXiv2006

Randall-Sundrum with Kalb-Ramond field: return of the hierarchy problem?

We show that when the antisymmetric Kalb-Ramond field is included in the Randall-Sundrum scenario, although the hierarchy problem can be solved, it requires an extreme fine tuning of the Kalb-Ramond field (about 1 part in $10^{62}$). We interpret this as the return of the problem in disguise. Further, we show that the Kalb-Ramond field induces a small negative cosmological constant on the visible brane.

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arXiv2006

Readdressing the hierarchy problem in a Randall-Sundrum scenario with bulk Kalb-Ramond background

We re-examine the fine tuning problem of the Higgs mass, when an antisymmetric two form Kalb-Ramond (KR) field is present in the bulk of a Randall-Sundrum (RS) braneworld. Taking into account the back-reaction of the KR field, we obtain the exact correction to the RS metric. The modified metric also warps the Higgs mass from Planck scale (in higher dimension) to TeV scale (on the visible brane) for a range of values of $kr$ exceeding the original RS value (where $k=$ Planck mass and $r=$ size of extra dimension). However, it requires an extraordinary suppression of the KR field density, indicating the re-appearence of the fine tuning problem in a different guise. The new spacetime also generates a small negative cosmological constant on the visible brane. These results are particularly relevant for certain string based models, where the KR field is unavoidably present in the bulk. We further show that such a bulk antisymmetric KR field fails to stabilize the braneworld.

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