arXiv subjects

Subhajit Barman

Publications and source records attributed to Subhajit Barman.

23 records · Page 2Linked to original sources

arXiv2019

The Hawking effect and the bounds on greybody factor for higher dimensional Schwarzschild black holes

In this work, we have considered a $n-$dimensional Schwarzschild-Tangherlini black hole spacetime with massless minimally coupled free scalar fields in its bulk and $3-$brane. The bulk scalar field equation is separable using the higher dimensional spherical harmonics on $(n-2)-$sphere. First, using the Hamiltonian formulation with the help of the recently introduced near-null coordinates we have obtained the expected temperature of the Hawking effect, identical for both bulk and brane localized scalar fields. Second, it is known that the spectrum of the Hawking effect as seen at asymptotic future does not correspond to a perfect black body and it is properly represented by a greybody distribution. We have calculated the bounds on this greybody factor for the scalar field in both bulk and $3-$brane. Furthermore, we have shown that these bounds predict a decrease in the greybody factor as the spacetime dimensionality $n$ increases and suggest that for a large number of extra dimensions the Hawking quanta is mostly emitted in the brane.

gr-qc↗

arXiv2019

Perturbative approach to the entanglement entropy and the area law in Fock and polymer quantization

The area dependence of entanglement entropy of a free scalar field is often understood in terms of coupled harmonic oscillators. In Schrodinger quantization, the Gaussian nature of ground state wave-function for these oscillators is sufficient to provide the exact form of the reduced density matrix and its eigenvalues, thus giving the entanglement entropy. However, in polymer quantization, the ground state is not Gaussian and the formalism which can provide the exact analytical form of the reduced density matrix is not yet known. In order to address this issue, here we treat the interaction between two coupled harmonic oscillators in the perturbative approach and evaluate the entanglement entropy in Schrodinger and polymer quantization. In contrary to Schrodinger quantization, we show that in high frequency regime the entanglement entropy decreases for polymer quantization keeping the ratio of coupling strength to the square of individual oscillator frequency fixed. Furthermore, for a free scalar field, we validate the area dependence of entanglement entropy in Fock quantization and demonstrate that polymer quantization produces a similar area law.

gr-qc↗

arXiv2018

Consistent derivation of the Hawking effect for both non-extremal and extremal Kerr black holes

It is believed that extremal black holes do not emit Hawking radiation as understood by taking extremal limits of non-extremal black holes. However, it is debated whether one can make such conclusion reliably starting from an extremal black hole, as the associated Bogoliubov coefficients which relate ingoing and outgoing field modes do not satisfy the required consistency condition. We address this issue in a canonical approach firstly by presenting an exact canonical derivation of the Hawking effect for non-extremal Kerr black holes. Subsequently, for extremal Kerr black holes we show that the required consistency condition is satisfied in the canonical derivation and it produces zero number density for Hawking particles. We also point out the reason behind the reported failure of Bogoliubov coefficients to satisfy the required condition.

gr-qc↗

arXiv2017

The Hawking effect is short-lived in polymer quantization

It is widely believed that the Hawking effect might hold clues to the possible, yet unknown, trans-Planckian physics. On the other hand, one could ask whether the effect itself might be altered by such trans-Planckian physics. We seek an answer to this question within a framework where matter field is quantized using polymer quantization, a canonical quantization technique employed in loop quantum gravity. We provide an exact derivation of the Hawking effect using canonical formulation by introducing a set of near-null coordinates which allows one to overcome the challenges posed by a Hamiltonian-based derivation of the Hawking effect. Subsequently, we show that in polymer quantization the Hawking effect is short-lived and it eventually disappears for an asymptotic future observer. Such an observer finds the duration of the Hawking effect to be few milliseconds for a solar mass black hole whereas it is few years for an ultra-massive black hole. Consequently, it provides a new way to resolve the so-called information loss paradox.

gr-qc↗

arXiv2017

An exact derivation of the Hawking effect in canonical formulation

The Hawking effect is one of the most extensively studied topics in modern physics. Yet it remains relatively under-explored within the framework of canonical quantization. The key difficulty lies in the fact that the Hawking effect is principally understood using the relation between the ingoing modes which leave past null infinity and the outgoing modes which arrive at future null infinity. Naturally, these modes are described using advanced and retarded null coordinates instead of the usual Schwarzschild coordinates. However, null coordinates do not lead to a true Hamiltonian that describes the evolution of these modes. In order to overcome these hurdles in a canonical formulation, we introduce here a set of near-null coordinates which allows one to perform an exact Hamiltonian-based derivation of the Hawking effect. This derivation opens up an avenue to explore the Hawking effect using different canonical quantization methods such as polymer quantization.

gr-qc↗