arXiv subjects

N. Riazi

Publications and source records attributed to N. Riazi.

42 records · Page 3Linked to original sources

arXiv2006

Thermodynamics of rotating solutions in (n+1)-dimensional Einstein-Maxwell-dilaton gravity

We construct a class of charged, rotating solutions of (n+1)-dimensional Einstein-Maxwell-dilaton gravity with Liouville-type potentials and investigate their properties. These solutions are neither asymptotically flat nor (anti)-de Sitter. We find that these solutions can represent black brane, with two inner and outer event horizons, an extreme black brane or a naked singularity provided the parameters of the solutions are chosen suitably. We also compute temperature, entropy, charge, electric potential, mass and angular momentum of the black brane solutions, and find that these quantities satisfy the first law of thermodynamics. We find a Smarr-type formula and perform a stability analysis by computing the heat capacity in the canonical ensemble. We find that the system is thermally stable for alpha <1, while for alpha >1 the system has an unstable phase. This is incommensurate with the fact that there is no Hawking-Page phase transition for black objects with zero curvature horizon.

hep-th↗

arXiv2005

Photometric Observation And Period Study of GO Cygni

Photometric observations of GO Cyg were performed during the July-October 2002, in B and V bands of Johnson system. Based on Wilson's model, the light curve analysis were carried out to find the photometric elements of the system. The O-C diagram which is based on new observed times of minima suggests a negative rate of period variation (dP/dt<0) for the system.

astro-ph↗

arXiv2004

Photometric Observation and Apsidal motion Study of V1143 Cyg

Photometric observations of the eccentric eclipsing binary V1143 Cygni were performed during the August-September 2000 and July 2002, in B and V bands of the Johnson system. The analysis on both light curves was done separately using the 1998 version of Wilson's LC code. In order to find a new observed rate of apsidal motion, we followed the procedure described by Guinan and Maloney (1985). A new observed rate of apsidal motion of 3.72 degrees/100yr was computed which is close to the one reported earlier by Khaliullin (1983), Gimenez and Margrave (1985), and Burns et al.(1996).

astro-ph↗

arXiv2003

Exact String-like Solutions of the Gauged Nonlinear O(3) Model

We show that the least energy conditions in the gauged nonlinear sigma model with Chern-Simons term lead to exact soliton-like solutions which have the same features as domain walls. We will derive and discuss the corresponding solutions, and compute the total energy, charge, and spin of the resulting system.

hep-th↗

arXiv2002

Soliton Decay in Coupled System of Scalar Fields

A system of coupled scalar fields is introduced which possesses a spectrum of massive single-soliton solutions. Some of these solutions are unstable and decay into lower mass stable solitons. Some properties of the solutions are obtained using general principles including conservations of energy and topological charges. Rest energies are calculated via a variational scheme, and the dynamics of the coupled fields are obtained by solving the field equations numerically.

hep-th↗

arXiv2001

Spherical Structures in the Inflationary Cosmology

It has been suggested that wormholes and other non-trivial geometrical structures might have been formed during the quantum cosmological era ($t\sim 10^{-43}$s). Subsequent inflation of the universe might have enlarged these structures to macroscopic sizes. In this paper, spherical geometrical structures in an inflationary RW background are derived from the Einstein equations, using a constraint on the energy-momentum tensor which is an extension of the one expected for inflation. The possibility of dynamical wormholes and other spherical structures are explored in the framework of the solutions.

gr-qc↗