Modern Physics Letters A

For a charge-monopole pair, we have another definition of the orbital angular momentum, and the transverse part of the momentum including the vector potential turns out to be the so-called geometric momentum that is under intensive study recently. For the charge on the spherical surface with the monopole at the origin, the commutation relations between all components of both the geometric momentum and the orbital angular momentum satisfy the so(3,1) algebra. With construction of the geometrically infinitesimal displacement operator based on the geometric momentum, the so(3,1) algebra implies the Aharonov–Bohm phase shift. The related problems such as charge and flux quantization are also addressed.

We study the motion of massless test particles in a five-dimensional (5D) Myers–Perry black hole spacetime with two-spin parameters. The behavior of the effective potential in view of different values of black hole parameters is discussed in the equatorial plane. The frequency shift of photons is calculated which is found to depend on the spin parameter of black hole and the observed redshift is discussed accordingly. The deflection angle and the strong deflection limit coefficients are also calculated and their behavior with the spin parameters is analyzed in detail. It is observed that the behaviors of both deflection angle and strong field coefficient differs from Kerr black hole spacetime in four dimensions in General Relativity (GR), which is mainly due to the presence of two-spin parameters in higher dimension.

We obtain an analytical expression for the electromagnetic quasinormal (QN) spectrum of the higher-dimensional nearly-extremal Schwarzschild–de Sitter black hole. The WKB method is used to verify the results, and a comparison with known results from previous works is briefly made as well.

Influence of noncommutativity on the motion of composite system is studied in noncommutative phase space of canonical type. A system composed by N free particles is examined. We show that because of the momentum noncommutativity free particles of different masses with the same velocities at the initial moment of time do not move together. The trajectory and the velocity of a free particle in noncommutative phase space depend on its mass. So, a system of the free particles flies away. Also, it is shown that the total momentum defined in the traditional way is not integral of motion in a space with noncommutativity of coordinates and noncommutativity of momenta. We find that in the case when parameters of noncommutativity corresponding to a particle are determined by its mass, the trajectory and the velocity of the free particles are independent of the mass. Also, the total momenta as integrals of motion can be introduced in noncommutative phase space.

In the scenario of an optimal consideration that is, homogeneous and flat spacetime, we study the Black Hole (BH) formation from the gravitational collapse of a spherical symmetric clump of matter in the case of the specific Dark Matter (DM) model interacting with Dark Energy (DE) in the context of the brane world regime. This clump of matter constituted of DM, ${\rho }_M$ and DE, $\rho$. In the present model, we consider anisotropic pressure in the energy–momentum tensor with a polytropic equation of state (EoS), $p_r=k\rho$ and $p_t=\omega \rho$, $(k+2\omega <-1)$. Our results show that the gravitational collapse of an interacting combination of DM and DE leads to the formation of BH in the presence of brane tension. Recent work provides the generalization of isotropic pressure to an-isotropic pressure in the energy–momentum tensor for the specific interacting combination model of DM and DE in a brane world regime.

In this study, we investigate the Bianchi type-I cosmologies with string cloud attached to perfect fluid in f(R) gravity. The field equations and their exact solutions for Bianchi type-I cosmologies with string cloud attached to a perfect fluid are found by using the conformal symmetry properties. The obtained solutions under the varied selection of arbitrary constants indicate three cosmological models. Isotropy conditions for obtained cosmological models are investigated for large value of time. Whether or not the string cloud in conformal symmetric Bianchi type-I universe supports the isotropy condition for the large value of time has been investigated. Also, we examine the contracting and decelerating features of the obtained solutions by using Raychaudhuri equation. Finally, geometrical and physical results of the solutions are discussed.

This work presents an experimental test of Lorentz invariance violation in the infrared (IR) regime by means of an invariant minimum speed in spacetime and its effects on the time when an atomic clock given by a certain radioactive single-atom (e.g. isotope Na${}^{25}$) is a thermometer for an ultracold gas like the dipolar gas Na${}^{23}$K${}^{40}$. So, according to a Deformed Special Relativity (DSR) so-called Symmetrical Special Relativity (SSR), where there emerges an invariant minimum speed V in the subatomic world, one expects that the proper time of such a clock moving close to V in thermal equilibrium with the ultracold gas is dilated with respect to the improper time given in lab, i.e. the proper time at ultracold systems elapses faster than the improper one for an observer in the lab, thus leading to the so-called proper time dilation so that the atomic decay rate of an ultracold radioactive sample (e.g. Na${}^{25}$) becomes larger than the decay rate of the same sample at room temperature. This means a suppression of the half-life time of a radioactive sample thermalized with an ultracold cloud of dipolar gas to be investigated by NASA in the Cold Atom Lab (CAL).