Thermodynamics Of dilaton-axion black holes

Considering a generalised action for Einstein Maxwell theory in four dimensions coupled to scalar and pseudo-scalar fields, the thermodynamic properties of asymptotically flat black holes solutions in such a background are investigated. Bekenstein-Hawking area-entropy law is verified for these class of black holes. From the property of specific heat, it is shown that such black holes can be stable for certain choice of the parameters like charge, mass and the scalar vacuum expectation value. The possibility of a black hole phase transition is discussed in this context.Comment: 7 Pages, Revtex, To appear in Phys.Rev.

Entropy of charged dilaton-axion black hole

Using brick wall method the entropy of charged dilaton-axion black hole is determined for both asymptotically flat and non-flat cases. The entropy turns out to be proportional to the horizon area of the black hole confirming the Beckenstien, Hawking area-entropy formula for black holes. The leading order logarithmic corrections to the entropy are also derived for such black holes.Comment: 7 pages, Revtex, To appear in Physical Review

Slowly Rotating Dilaton Black hole In Anti-de Sitter Spacetime

Rotating dilaton black hole solution for asymptotically anti-de Sitter spacetime are obtained in the small angular momentum limit with an appropriate combination of three Liouville-type dilaton potentials. The angular momentum, magnetic dipole moment and the gyromagnetic ratio of such a black hole are determined for arbitrary values of the dilaton-electromagnetic coupling parameter.Comment: 5 pages, Revtex, To appear in Phys.Rev.

Strong gravitational lensing across dilaton anti-de Sitter black hole

In this work we investigate gravitational lensing effect in strong field region around a dilaton black holes in an anti de Sitter (ADS) space. We also analyse the dependence of the radius of the photon sphere and deflection angle on dilaton coupling and cosmological constant in this black hole space time. Finally the values of minimum impact parameter, the separation between the first and the other images as well as the ratio between the flux of the first image and the flux coming from all the other images are determined to characterize some possible distinct signatures of such black holes.Comment: 8 pages and 3 figures. Accepted in Physical Review

Driven transport of active particles through arrays of symmetric obstacles

We numerically examine the driven transport of an overdamped self-propelled particle through a two-dimensional array of circular obstacles. A detailed analysis of transport quantifiers (mobility and diffusivity) has been performed for two types of channels, {\it channel I} and {\it channel II}, that respectively correspond to the parallel and diagonal drives with respect to the array axis. Our simulation results show that the signatures of pinning actions and depinning processes in the array of obstacles are manifested through excess diffusion peaks or sudden drops in diffusivity, and abrupt jumps in mobility with varying amplitude of the drive. The underlying depinning mechanisms and the associated threshold driving strength largely depend on the persistent length of self-propulsion. For low driving strength, both diffusivity and mobility are noticeably suppressed by the array of obstacles, irrespective of the self-propulsion parameters and direction of the drive. When self-propulsion length is larger than a channel compartment size, transport quantifiers are insensitive to the rotational relaxation time. Transport with diagonal drives features self-propulsion-dependent negative differential mobility. The amplitude of the negative differential mobility of an active particle is much larger than that of a passive one. The present analysis aims at understanding the driven transport of active species like, bacteria, virus, Janus Particle etc. in porous medium.Comment: Accepted for publication in JCP (October 2023

Structure and diffusion of active-passive binary mixtures in a single-file

We numerically study structure and dynamics of single files composed of active particles, as well as, active-passive binary mixtures. Our simulation results show that when the persistent length of self-propelled particles is much larger than the average inter-particle separation and the self-propulsion velocity is larger than the thermal velocity, particles in the file exist as clusters of various sizes. Average cluster size and structures of the file are very sensitive to self-propulsion properties, thermal fluctuations and composition of the mixture. In addition to the variation of file composition, our study considers two sorts of mixture configurations. One corresponds to the uniform distribution of active passive throughout the mixture in the single file. In the other configuration, active particles are on one side of the file. For the both configurations, even a little fraction of active particles produces a large impact on the structure and dynamics of the file

Active diffusion limited reactions

We investigate the one- and two-dimensional diffusion limited reactions A + A → 0 and A + B → 0 with A active Janus particles and B passive particles in thermal equilibrium. We show that by increasing the self-propulsion time of the A particles, the reactant densities decay faster, at least for time transients of potential interest for chemical applications, e.g., to develop smart drug delivery protocols. Asymptotic and transient density decays obey power laws with exponents that depend on the actual annihilation reaction and its dimensionalit