1,902 research outputs found
Thermodynamic geometry of black holes in f(R) gravity
In this paper, we consider three types (static, static charged and rotating
charged) of black holes in f(R) gravity. We study the thermodynamical behavior,
stability conditions and phase transition of these black holes. It will be
shown that, the number and type of phase transition points are related to
different parameters, which shows the dependency of stability conditions to
these parameters. Also, we extended our study to different thermodynamic
geometry methods (Ruppeiner, Weinhold and GTD). Next, we investigate the
compatibility of curvature scalar of geothermodynamic methods with phase
transition points of the above balck holes. In addition, we point out the
effect of different values of spacetime parameters on stability conditions of
mentioned black holes.Comment: 45 figures,35 page
Shadow of a Charged Rotating Black Hole in Gravity
We study the shadow of a charged rotating black hole in gravity. This
black hole is characterized by mass, , spin, , electric charge, and
which is proportional to cosmological constant. We analyze the image of
the black hole's shadow in four types 1) at , 2) at
, in vacuum, 3) at , 4) at
, for an observer at the presence of plasma. Moreover, we
investigate the effect of spin, charge and modfication of gravity on the shape
of shadow. In addition, we use two observables, the radius and the
distortion parameter , characterizing the apparent shape. We show
that for all cases, the shadow becomes smaller with increasing electric charge.
Also, by increasing the rotation parameters, circular symmetry of the image of
black hole's shadow will change. Furthermore, in the presence of plasma, plasma
parameter also effects on size of the shadow.Comment: 28 pages,6 tables,43 figure
f(R) Gravity: From the Pioneer Anomaly to the Cosmic Acceleration
We use metric formalism in modified gravity to study the dynamics of
various systems from the solar system to the cosmological scale. we assume an
ansatz for the derivative of action as a function of distance and describe the
Pioneer anomaly and the flat rotation curve of the spiral galaxies. Having the
asymptotic behavior of action, we propose the action of where in galactic and solar system scales it
can recover our desired form. The vacuum solution of this action also results
in a positive late time acceleration for the universe. We fix the parameters of
this model, comparing with the Pioneer anomaly, rotation curve of spiral
galaxies and Supernova Type Ia gold sample data.Comment: 6 pages, 2 figure
Consistency Condition of Spherically Symmetric Solutions in Gravity
In this work we study the spherical symmetric solutions of gravity in
the metric formalism. We show that for a generic gravity, the spherical
symmetric solution is consistent with the modified gravity equations except in
the case of imposing an extra condition for the metric.Comment: 4 pages, accepted in MPL
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