arXiv subjects

Sayeedul Islam

Publications and source records attributed to Sayeedul Islam.

7 recordsLinked to original sources

arXiv2020

Null Geodesics and QNMs in the field of Regular Black Holes

We analyze the null geodesics of regular black holes. A detailed analysis of geodesic structure both null geodesics and time-like geodesics have been investigated for the said black hole. As an application of null geodecics, we calculate the radius of photon sphere and gravitational bending of light. We also study the shadow of the black hole spacetime. Moreover, we determine the relation between radius of photon sphere~$(r_{ps})$ and the shadow observed by a distance observer. Furthermore, We discus the effect of various parameters on the radius of shadow $R_s$. Also we compute the angle of deflection for the photons as a physical application of null-circular geodesics. We find the relation between null geodesics and quasinormal modes frequency in the eikonal approximation by computing the Lyapunov exponent. It is also shown that~(in the eikonal limit) the quasinormal modes~(QNMs) of black holes are governed by the parameter of null-circular geodesics. The real part of QNMs frequency determines the angular frequency whereas the imaginary part determines the instability time scale of the circular orbit. Next we study the massless scalar perturbations and analyze the effective potential graphically. Massive scalar perturbations also discussed. As an application of time-like geodesics we compute the innermost stable circular orbit~(ISCO) and marginally bound circular orbit~(MBCO) of the regular BHs which are closely related to the black hole accretion disk theory. In the appendix, we calculate the relation between angular frequency and Lyapunov exponent for null-circular geodesics.

gr-qc↗

arXiv2018

Formation of Wormholes by Dark Matter in the Galaxy Dragonfly 44

Recently, ultra diffuse galaxy (UDG) of Dragonfly 44 in the Coma Cluster was observed and observations of the rotational speed suggest that its mass is almost same as the mass of the Milky Way. On the other hand, interestingly, the galaxy emits only 1 \% of the light emitted by the Milky Way. Then, astronomers reported that Dragonfly 44 may be made almost entirely of dark matter. In this study we try to show that the dark matter that constitutes Dragonfly 44 can form the wormhole or not. Two possible dark matter profiles are used, namely, ultra diffuse galaxy King's model and generalized Navarro-Frenk-White (NFW) dark matter profile. We have shown that King's model dark matter profile does not manage to provide wormhole whereas generalized Navarro-Frenk-White (NFW) dark matter profile is managed to find wormholes.

physics.gen-ph↗

arXiv2017

Energy-momentum for a charged nonsingular black hole solution with a nonlinear mass function

The energy-momentum of a new four-dimensional, charged, spherically symmetric and nonsingular black hole solution constructed in the context of general relativity coupled to a theory of nonlinear electrodynamics is investigated, whereby the nonlinear mass function is inspired by the probability density function of the continuous logistic distribution. The energy and momentum distributions are calculated by use of the Einstein, Landau-Lifshitz, Weinberg and M{\o}ller energy-momentum complexes. In all these prescriptions it is found that the energy distribution depends on the mass $M$ and the charge $q$ of the black hole, an additional parameter $\beta$ coming from the gravitational background considered, and on the radial coordinate $r$. Further, the Landau-Lifshitz and Weinberg prescriptions yield the same result for the energy, while in all the aforesaid prescriptions all the momenta vanish. We also focus on the study of the limiting behavior of the energy for different values of the radial coordinate, the parameter $\beta$, and the charge $q$. Finally, it is pointed out that for $r\rightarrow \infty$ and $q = 0$ all the energy-momentum complexes yield the same expression for the energy distribution as in the case of the Schwarzschild black hole solution.

gr-qc↗

arXiv2016

Recovery of hadronic cross section inside the mini black holes at LHC

In curved space time inside the shell of TeV black holes, many gluons and quarks produce due to Unruh effect, interact with each other and create Higgs boson. Studying the Unruh effect, we show that the inside state of the black hole for gluons and quarks can be represented by a maximally entangled two mode squeezed state of inside and matter Hilbert spaces of black hole. Comparing the Higgs boson production outside and inside the shell, we observe that at lower mass, MBH<4 TeV, and at higher mass, MBH>9 TeV, the Higgs boson will not be produced outside the shell of black hole. However this particle can be produced inside the shell for 2.5 TeV 12.5 TeV the black hole can only emit massless gluons. However, inside the shell of black hole is able to produce a quark for 2.5 TeV<MBH<14 TeV. We also find that the micro black hole can be a source for Higgs production at LHC. Finally we calculate the effects of Higgs boson radiation due to inside the shell and outside the shell of mini black holes on hadronic cross section at LHC. We observe that as the order of perturbation theory increases, this effect becomes systematically more effective because at higher orders there exists more channels for Higgs production and their decay of Higgs into massive quark-anti quarks in our calculation. At smaller mass, MBH<2 TeV, the NNLO contribution is large while the cross sections at NLO and at LO are rising and respectively exhibit a turn-over at moderate values of black hole's mass.The peak moves from about 5 TeV to 2.5 TeV. It is concluded that the processes of hadronization inside the event horizon of mini black holes are affected the hadronic cross section outside the event horizon and can be observed at LHC.

hep-ph↗

arXiv2016

Einstein and M{\o}ller energy-momentum complexes for a new regular black hole solution with a nonlinear electrodynamics source

A study about the energy and momentum distributions of a new charged regular black hole solution with a nonlinear electrodynamics source is presented. The energy and momentum are calculated using the Einstein and M{\o}ller energy-momentum complexes. The results show that in both pseudotensorial prescriptions the expressions for the energy of the gravitational background depend on the mass $M$ and the charge $q$ of the black hole, an additional factor $\beta $ coming from the spacetime metric considered, and the radial coordinate $r$, while in both prescriptions all the momenta vanish. Further, it is pointed out that in some limiting and particular cases the two complexes yield the same expression for the energy distribution as that obtained in the relevant literature for the Schwarzschild black hole solution.

gr-qc↗

arXiv2015

Braneworld gravastars admitting conformal motion

In this work, we study the Mazur and Mottola gravastar model within the context of Randall-Sundrum II type braneworld scenario, based on the fact that our four dimensional space-time is a three-brane, embedded in a five dimensional bulk. We present exact solutions of the modified field equations in each of the three regions making up the gravastar, namely, (I) the core, (II) the shell, and (III) the vacuum exterior. The junction conditions at each interface are fulfilled and we further explore interesting physical properties such as length and energy and entropy of the spherical distribution.

gr-qc↗

arXiv2014

Energy distribution of a regular black hole solution in Einstein-nonlinear electrodynamics

In this work a study about the energy-momentum of a new four-dimensional spherically symmetric, static and charged, regular black hole solution developed in the context of general relativity coupled to nonlinear electrodynamics is presented. Asymptotically, this new black hole solution behaves as the Reissner-Nordstr\"om solution only for the particular value {\mu}=4, where {\mu} is a positive integer parameter appearing in the mass function of the solution. The calculations are performed by use of the Einstein, Landau-Lifshitz, Weinberg and M{\o}ller energy-momentum complexes. In all the aforesaid prescriptions, the expressions for the energy of the gravitating system considered depend on the mass M of the black hole, its charge q, a positive integer {\alpha} and the radial coordinate r. In all these pseudotensorial prescriptions the momenta are found to vanish, while the Landau-Lifshitz and Weinberg prescriptions give the same result for the energy distribution. In addition, the limiting behavior of the energy for the cases r tends toward infinity, r=0 and q=0 is studied. The special case {\mu}=4 and {\alpha}=3 is also examined. We conclude that the Einstein and M{\o}ller energy-momentum complexes can be considered as the most reliable tools for the study of the energy-momentum localization of a gravitating system.

gr-qc↗