Srijit Bhattacharjee

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.

Entropy functionals and c-theorems from the second law

We show that for a general four derivative theory of gravity, only the holographic entanglement entropy functionals obey the second law at linearized order in perturbations. We also derive bounds on the higher curvature couplings in several examples, demanding the validity of the second law for higher order perturbations. For the five-dimensional Gauss-Bonnet theory in the context of AdS/CFT, the bound arising from black branes coincides with there being no sound channel instability close to the horizon. Repeating the analysis for topological black holes, the bound coincides with the tensor channel causality constraint (which is responsible for the viscosity bound). Furthermore, we show how to recover the holographic c-theorems in higher curvature theories from similar considerations based on the Raychaudhuri equation.

Gauge-free electroweak theory: 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.

No hair theorems for a static and stationary reflecting star

We prove the non existence of massive scalar, vector and tensor hairs outside the surface of a static and stationary compact reflecting star. Our result is the extension of the no hair theorem for black holes to horizonless compact configurations with reflecting boundary condition at the surface. We also generalize the proof for spacetimes with a positive cosmological constant.

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 requires, in contrast to our approach, gauge fixing of 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.

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 space-time 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 explicitly calculate the Coleman-Weinberg potential for this theory. 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.

Physical process first law and caustic avoidance for Rindler horizons

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.

Constraining scalar-Gauss-Bonnet inflation by reheating, unitarity, and Planck data

We revisit the inflationary dynamics in detail for theories with Gauss-Bonnet gravity coupled to scalar functions, in light of the Planck data. Considering the chaotic inflationary scenario, we constrain the parameters of two models involving inflaton-Gauss-Bonnet coupling by current Planck data. For non zero inflaton-Gauss-Bonnet coupling

VILKOVISKY-DEWITT EFFECTIVE POTENTIAL REVISITED IN GAUGE-FREE FRAMEWORK

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INFRARED ISSUES IN GRAVITON HIGGS THEORY

, an inflationary analysis provides us a big cosmologically viable region in the space of