arXiv subjects

Srijit Bhattacharjee

Publications and source records attributed to Srijit Bhattacharjee.

28 records · Page 2Linked to original sources

arXiv2015

The holographic entropy increases in quadratic curvature gravity

Standard methods for calculating the black hole entropy beyond general relativity are ambiguous when the horizon is non stationary. We fix these ambiguities in all quadratic curvature gravity theories, by demanding that the entropy be increasing at every time, for linear perturbations to a stationary black hole. Our result matches with the entropy formula found previously in holographic entanglement entropy calculations. We explicitly calculate the entropy increase for Vaidya-like solutions in Ricci-tensor gravity to show that (unlike the Wald entropy) the holographic entropy obeys a Second Law.

gr-qc↗

arXiv2014

Physical process first law and caustic avoidance for Rindler horizon

We study the perturbation induced by a slowly rotating massive object as it passes through a Rindler horizon. It is shown that the passage of this object can be approximately modeled as Delta\,function type tidal distortions hitting the horizon. Further, following the analysis presented by Amsel, Marolf and Virmani related to the issue of the validity of physical process first law, we establish a condition on the size of the object so that this law holds for the Rindler horizon.

gr-qc↗

arXiv2014

Standard Model with gauge inert variables

The Standard Model of electroweak interactions has been recast as a gauge free theory where the fields present in the Lagrangian are made inert under $SU(2)_L \times U(1)_Y$ gauge transformations. Furthermore, the residual $U(1)_{em}$ gauge freedom of the dynamical fields are also removed to yield a completely gauge free theory. This formulation thus in turn resolves the issue of gauge dependency of the Standard Model effective potential which plays significant role in determining the instability scale of the electroweak vacuum.

hep-ph↗

arXiv2014

Gravitational Coleman-Weinberg Potential and It's Finite Temperature Counterpart

Coleman-Weinberg (CW) phenomena for the case of gravitons minimally coupled to massless scalar field is studied. The one loop effect completely vanishes if there is no self interaction term present in the matter sector. The one loop effective potential is shown to develop an instability in the form of acquiring an imaginary part, which can be traced to the tachyonic pole in the graviton propagator. The finite temperature counterpart of this CW potential is computed to study the behaviour of the potential in the high and low temperature regimes with respect to the typical energy scale of the theory. Finite temperature contribution to the imaginary part of gravitational CW potential exhibits a damped oscillatory behaviour; all thermal effects are damped out as the temperature vanishes, consistent with the zero-temperature result. Possibility of symmetry restoration at high temperature is also depicted.

hep-th↗

arXiv2013

Gauge-free Coleman-Weinberg Potential

The gauge-dependence of the one loop Coleman-Weinberg effective potential in scalar electrodynamics is resolved using a gauge-free approach not requiring any gauge-fixing of quantum fluctuations of the photon degrees of freedom. This leads to a unique dynamical ratio at one loop of the Higgs mass to the photon mass. We compare our approach and results with those obtained in geometric framework of DeWitt and Vilkovisky, which maintains invariance under field redefinitions as well as invariance under background gauge transformations, but {\it requires}, in contrast to our approach, gauge fixing of {\it fluctuating} photon fields. We also discuss possible modifications of the Coleman-Weinberg potential if we adapt the DeWitt-Vilkovisky method to our gauge-free approach for scalar QED.

hep-th↗

arXiv2013

Infrared Issues in Graviton Higgs Theory

We investigate the one-loop infrared behaviour of the effective potential in minimally coupled graviton Higgs theory in Minkowski background. The gravitational analogue of one loop Coleman Weinberg effective potential turns out to be complex, the imaginary part indicating an infrared instability. This instability is traced to a tachyonic pole in the graviton propagator for constant Higgs fields. Physical implications of this behaviour are studied. We also discuss physical differences between gauge theories coupled to Higgs fields and graviton Higgs theory.

gr-qc↗

arXiv2012

Vilkovisky-DeWitt Effective Potential Revisited in Gauge-Free Framework

An alternative approach to scalar quantum electrodynamics has been proposed where the usual gauge redundancy of the theory do not manifest. The gauge-dependence of Coleman- Weinberg effective potential is resolved using gauge-free approach leading to a unique scalar to vector mass ratio. The gauge-free result is compared with the one obtained in Vilkovisky-DeWitt geometric framework and it is shown that it differs from the standard result reported earlier. It is also shown that for reparametrization invariance of the Coleman-Weinberg potential one must combine the Vilkovisky-DeWitt method with the gauge-free approach.

hep-th↗

arXiv2010

Gauge invariant coupling of fields to torsion: a string inspired model

In a consistent heterotic string theory, the Kalb-Ramond field, which is the source of spacetime torsion, is augmented by Yang-Mills and gravitational Chern-Simons terms. When compactified to 4-dimensions and in the field theory limit, such additional terms give rise to interactions with interesting astrophysical predictions like rotation of plane of polarization for electromagnetic and gravitational waves. On the other hand, if one is also interested in coupling 2 or 3-form (Abelian or non-Abelian) gauge fields to torsion, one needs another class of interaction. In this paper, we shall study this interaction and offer some astrophysical and cosmological predictions. We also comment on the possibility of such terms in loop quantum gravity where, if the Barbero-Immirzi parameter is promoted to a field, acts as a source for torsion.

hep-th↗

arXiv2010

Gauge-free Electrodynamics

We propose a reformulation of electrodynamics in terms of a {\it physical} vector potential entirely free of gauge ambiguities. Quantizing the theory leads to a propagator that is gauge invariant by construction in this reformulation, in contrast to the standard photon propagator. Coupling the theory to a charged Abelian Higgs field leads at the quantum level to a one loop effective potential which realizes the Coleman-Weinberg mechanism of mass generation, thus resolving the issue of its gauge dependence. We relate our results to recent work by Niemi et. al. and Faddeev, where similar strategies are adopted in a version of the electroweak theory. Other theories with linear Abelian gauge invariance, like the linearized spin 2 theory of gravity or the antisymmetric tensor field, which may all be reformulated in terms of physical vector or tensor potentials without gauge ambiguities, are also discussed briefly.

hep-th↗

arXiv2010

Electroweak Theory without a Higgs potential: Radiative Effects

We examine the one loop effective potential in a recently proposed (by Chernodub et. al.) alternative approach to mass generation in the Higgs-gauge sector of the electroweak theory, which does not make use of a classical Higgs potential. We show that the interpretation given by these authors, of the Higgs boson as the conformal degree of freedom in a background conformal gravity theory, is invalidated because genuine one loop radiative effects cancel the local functional measure of the Higgs field taken to be the basis of this interpretation. Functional evaluation of the one loop effective Higgs potential leads to a minimum away from the origin, thereby providing yet another radiative mass generation scheme for weak gauge bosons. In arriving at the one loop effective potential we make use of the gauge free formulation of electrodynamics introduced by us earlier, which obviates any need for gauge fixing.

hep-ph↗