A nonsingular rotating black hole

The spacetime singularities in classical general relativity are inevitable, which are also predicated by the celebrated singularity theorems. However, it is general belief that singularities do not exist in the nature and they are the limitations of the general relativity. In the absence of a well defined quantum gravity, models of regular black holes have been studied. We employ probability distribution inspired mass function $m(r)$ to replace Kerr black hole mass $M$ to present a nonsingular rotating black hole that is identified asymptotically ($r \gg k$, $k>0$ constant) exactly as the Kerr-Newman black hole, and as the Kerr black hole when $k=0$. The radiating counterpart renders a nonsingular generalization of Carmeli's spacetime as well as Vaidya's spacetime, in the appropriate limits. The exponential correction factor changing the geometry of the classic black hole to remove curvature singularity can be also motivated by the quantum arguments. The regular rotating spacetime can also be understood as a black hole of general relativity coupled to nonlinear electrodynamics.Comment: 13 pages, 5 figures, 1 table, several changes, accepted in EPJC (as Letter

Modelling Two-Roton Bound State Formation in Fractional Quantum Hall System

Composite Fermion approach using extensive and parallalized numerical analysis has recently established a two-roton bound state as the lowest energy long wavelength neutral excitation of FQHE for finite particle (N~30) system. By focussing on the "oriented dipole" character of magneto roton, we model the two roton problem and solve it variationally (analytically) to find a two-roton bound state with binding energy which is in good agreement with the composite fermion numerical results.Comment: 4 pages, REVTEX file, 3 figures, Minor changes, Accepted for publication in Physical Review Letter

Rotating black hole in Rastall theory

Rotating black hole solutions in theories of modified gravity are important as they offer an arena to test these theories through astrophysical observation. The non-rotating black hole can be hardly tested since the black hole spin is very important in any astrophysical process. We present rotating counterpart of a recently obtained spherically symmetric exact black hole solution surrounded by perfect fluid in the context of Rastall theory, viz, rotating Rastall black hole that generalize the Kerr-Newman black hole solution. In turn, we analyze the specific cases of the Kerr-Newman black holes surrounded by matter like dust and quintessence fields. Interestingly, for a set of parameters and a chosen surrounding field, there exists a critical rotation parameter ($a=a_{E}$), which corresponds to an extremal black hole with degenerate horizons, while for $a<a_{E}$, it describes a non-extremal black hole with Cauchy and event horizons, and no black hole for $a>a_{E}$ with value $a_E$ is also influenced by these parameters. We also discuss the thermodynamical quantities associated with rotating Rastall black hole, and analyze the particle motion with the behavior of effective potential.Comment: 26 pages, 8 figures. Matched with the published versio

Accretion onto a noncommutative geometry inspired black hole

The spherically symmetric accretion onto a noncommutative (NC) inspired Schwarzschild black hole is treated for a polytropic fluid. The critical accretion rate $\dot{M}$, sonic speed $a_s$ and other flow parameters are generalised for the NC inspired black hole and compared with the results obtained for the standard Schwarzschild black holes. We also derive explicit expressions for gas compression ratios and temperature profiles below the accretion radius and at the event horizon. This analysis is a generalisation of Michel's solution to the NC geometry. Owing to the NC corrected black hole, the accretion flow parameters have also been modified. It turns out that $\dot{M} \approx {M^2}$ is still achievable but $r_s$ seems to be substantially decreased due to NC effects, that in turn does affect the accretion process.Comment: Published in EPJ