Hamidreza Saiedi | Florida Atlantic University (original) (raw)
Address: Boca Raton, Florida, United States
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Homi Bhabha National Institute (HBNI, BARC, MUMBAI)
Università degli Studi di Bergamo (University of Bergamo)
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Papers by Hamidreza Saiedi
Indian Journal of Physics
General Relativity and Gravitation, 2021
In the frame work of Palatini approach to modified f (R) theories of gravity, we attempt to inves... more In the frame work of Palatini approach to modified f (R) theories of gravity, we attempt to investigate the thermodynamic behavior of time-dependent wormhole geometries. By considering an evolving wormhole spacetime, we find the field equations in Palatini f (R) gravity. The energy density and pressure are redefined in order to satisfy the continuity equation. To discuss the thermodynamic behavior, an expression for the variation of total entropy is obtained. Then, we extend our discussions to apparent and event horizons of evolving wormholes. We employ the radius of apparent and event horizons to determine the validity of generalized second law (GSL) of thermodynamics which states that the variation of total entropy is non-negative.
JHEPGC, 2020
In this paper, we review modified f (R) theories of gravity in Palatini formalism. In this framew... more In this paper, we review modified f (R) theories of gravity in Palatini formalism. In this framework, , we use the Raychaudhuri's equation along with the requirement that the gravity is attractive, which holds for any geometrical theory of gravity to discuss the energy conditions. Then, to derive these conditions, we obtain an expression for effective pressure and energy density by considering FLRW metric. To simply express the energy conditions, we write the Ricci scalar and its derivatives in terms of the deceleration (q), jerk (j) and snap (s) parameters. Energy conditions derived in Palatini version of f (R) Gravity differ from those derived in GR. We will see that the WEC (weak energy condition) derived in Palatini formalism has exactly the same expression in its metric approach.
Modern Physics Letters A, 2011
In this work, we construct time-dependent wormhole solutions in the context of f(R) theory of gra... more In this work, we construct time-dependent wormhole solutions in the context of f(R) theory of gravity. The background matter is considered to be traceless. By considering specific shape function and power-law expansion, exact solutions for f(R) are found. The null and the weak energy conditions (NEC and WEC) are checked for wormhole solutions. It is shown that the matter threading the wormhole spacetimes with either accelerated expansion or decelerated expansion satisfies the NEC and WEC.
Read More: http://www.worldscientific.com/doi/abs/10.1142/S0217732311035547?queryID=34%2F1199469
Modern Physics Letters A, 2012
In the context of modified f(R) gravity, we attempt to study the thermodynamic properties of the ... more In the context of modified f(R) gravity, we attempt to study the thermodynamic properties of the evolving Lorentzian wormholes at the apparent horizon. It is shown that the wormhole can be derived from a particular f(R) model in the radiation background. Moreover, it has been shown that the field equations can be cast to a similar form at the apparent horizon for the evolving Lorentzian wormhole. Compared to the case of Einstein's general relativity, an additional term appears here.
Read More: http://www.worldscientific.com/doi/abs/10.1142/S0217732312502203?queryID=39%2F1176472
Indian Journal of Physics
General Relativity and Gravitation, 2021
In the frame work of Palatini approach to modified f (R) theories of gravity, we attempt to inves... more In the frame work of Palatini approach to modified f (R) theories of gravity, we attempt to investigate the thermodynamic behavior of time-dependent wormhole geometries. By considering an evolving wormhole spacetime, we find the field equations in Palatini f (R) gravity. The energy density and pressure are redefined in order to satisfy the continuity equation. To discuss the thermodynamic behavior, an expression for the variation of total entropy is obtained. Then, we extend our discussions to apparent and event horizons of evolving wormholes. We employ the radius of apparent and event horizons to determine the validity of generalized second law (GSL) of thermodynamics which states that the variation of total entropy is non-negative.
JHEPGC, 2020
In this paper, we review modified f (R) theories of gravity in Palatini formalism. In this framew... more In this paper, we review modified f (R) theories of gravity in Palatini formalism. In this framework, , we use the Raychaudhuri's equation along with the requirement that the gravity is attractive, which holds for any geometrical theory of gravity to discuss the energy conditions. Then, to derive these conditions, we obtain an expression for effective pressure and energy density by considering FLRW metric. To simply express the energy conditions, we write the Ricci scalar and its derivatives in terms of the deceleration (q), jerk (j) and snap (s) parameters. Energy conditions derived in Palatini version of f (R) Gravity differ from those derived in GR. We will see that the WEC (weak energy condition) derived in Palatini formalism has exactly the same expression in its metric approach.
Modern Physics Letters A, 2011
In this work, we construct time-dependent wormhole solutions in the context of f(R) theory of gra... more In this work, we construct time-dependent wormhole solutions in the context of f(R) theory of gravity. The background matter is considered to be traceless. By considering specific shape function and power-law expansion, exact solutions for f(R) are found. The null and the weak energy conditions (NEC and WEC) are checked for wormhole solutions. It is shown that the matter threading the wormhole spacetimes with either accelerated expansion or decelerated expansion satisfies the NEC and WEC.
Read More: http://www.worldscientific.com/doi/abs/10.1142/S0217732311035547?queryID=34%2F1199469
Modern Physics Letters A, 2012
In the context of modified f(R) gravity, we attempt to study the thermodynamic properties of the ... more In the context of modified f(R) gravity, we attempt to study the thermodynamic properties of the evolving Lorentzian wormholes at the apparent horizon. It is shown that the wormhole can be derived from a particular f(R) model in the radiation background. Moreover, it has been shown that the field equations can be cast to a similar form at the apparent horizon for the evolving Lorentzian wormhole. Compared to the case of Einstein's general relativity, an additional term appears here.
Read More: http://www.worldscientific.com/doi/abs/10.1142/S0217732312502203?queryID=39%2F1176472