Modern Physics Letters A

We consider Kerr–Newman–AdS–dS black holes near extremality and work out the near-horizon geometry of these near-extremal black holes. We identify the exact U(1)_L×U(1)_R isometries of the near-horizon geometry and provide boundary conditions enhancing them to a pair of commuting Virasoro algebras. The conserved charges of the corresponding asymptotic symmetries are found to be well-defined and nonvanishing and to yield central charges c_L≠0 and c_R = 0. The Cardy formula subsequently reproduces the Bekenstein–Hawking entropy of the black hole. This suggests that the near-extremal Kerr–Newman–AdS–dS black hole is holographically dual to a non-chiral two-dimensional conformal field theory.

It is shown that on the de Sitter spacetime the global behavior of the free Dirac spinors in momentum representation is determined by several phase factors which are functions of momentum with special properties. Such suitable phase functions can be chosen for writing down the free Dirac quantum modes of the spin basis that are well-defined even for the particles at rest in the moving local charts where the modes of the helicity basis remain undefined. Under quantization, these modes lead to a basis in which the one-particle operators keep their usual forms apart from the energy operator which lays out a specific term depending on the concrete phase function one uses.

Approximate analytical solutions of Duffin–Kemmer–Petiau equation are obtained for a vector Hulthén potential. The solutions are reported for any J-state using an elegant approximation and methodology of supersymmetry quantum mechanics.

We show that the equations of motion associated with a complexified sigma-model action do not admit manifest dual SO(n, n) symmetry. In the process we discover new type of numbers which we called "complexoids" in order to emphasize their close relation with both complex numbers and matroids. It turns out that the complexoids allow one to consider the analogue of the complexified sigma-model action but with (1+1)-worldsheet metric, instead of Euclidean-worldsheet metric. Our observations can be useful for further developments of complexified quantum mechanics.

The evolution of electromagnetic and massless Dirac perturbations in the spacetime geometry of Kehagias–Sfetsos (KS) black hole in the deformed Hořava–Lifshitz (HL) gravity is investigated and the associated quasinormal modes (QNMs) are evaluated from time domain integration data. We find a considerable deviation in the nature of field evolution in HL theory from that in the Schwarzschild spacetime and QNM region extends over a longer time in HL theory before the power-law tail decay begins. The dependence of the field evolution on the HL parameter α is also studied. In the time domain picture we find that the length of QNM region increases with α. But the late-time decay of field follows the same power-law tail behavior as in the case of Schwarzschild black hole.

In this paper, we consider spatially homogeneous and anisotropic Bianchi type I universe in the context of F(T) gravity. We construct some corresponding models using conservation equation and equation of state parameter representing different phases of the universe. In particular, we take matter-dominated era, radiation-dominated era, present dark energy phase and their combinations. It is found that one of the models has a constant solution which may correspond to the cosmological constant. We also derive equation of state parameter by using two well-known F(T) models and discuss cosmic acceleration.

We solve vacuum field equations in five-dimensional gravity with cosmological constant to determine the time-dependence of the Robertson–Walker scale factor. We discuss its cosmological implications.