In many circumstances the perfect fluid conservation equations can be directly integrated to give a geometric-thermodynamic equation: typically that the lapse N is the reciprocal of the enthalpy h, (N = 1/h). This result is aesthetically appealing as it depends only on the fluid conservation equations and does not depend on specific field equations such as Einstein’s. Here the form of the geome...

In many circumstances the perfect fluid conservation equations can be directly integrated to give a geometric-thermodynamic equation: typically that the lapse N is the reciprocal of the enthalpy h, (N = 1/h). This result is aesthetically appealing as it depends only on the fluid conservation equations and does not depend on specific field equations such as Einstein’s. Here the form of the geome...

Abstract In the present paper we examine a projectively flat spacetime solution of F ( R )-gravity theory. It is seen that once deploy projective flatness in geometry spacetime, matter field has constant energy density and isotropic pressure. We then make condition weaker discuss effects harmonic theory show this case reduces to generalised Robertson-Walker with shear, vorticity, acceleration f...

In this work, we consider a rotating charged black hole surrounded by perfect fluid dark matter. We the system to be immersed in non-magnetised, pressureless plasma. First, evaluate null geodesics order study co-rotating and counter photon orbits. Further, analyse calculate celestial coordinates ($\alpha, \beta$). The are used determine shadow radius ($R_s$). Thereafter, observe effects of spac...

In many circumstances the perfect fluid conservation equations can be directly integrated to give a geometric-thermodynamic equation: typically that the lapse N is the reciprocal of the enthalpy h, (N = 1/h). This result is aesthetically appealing as it depends only on the fluid conservation equations and does not depend on specific field equations such as Einstein’s. Here the form of the geome...

Abstract We apply the Darmois and $C^3$ matching conditions to three different spherically symmetric spacetimes. The exterior spacetime is described by Schwarzschild vacuum solution whereas for interior counterpart we choose perfect fluid solutions with same symmetry. show that are satisfied in all cases not fulfilled. argue this difference due a non-physical behavior of pressure on surface.

The objective of the present paper is to study 4-dimensional almost pseudo Ricci symmetric perfect fluid spacetimes $(APRS)_4$. We show that a Robertson-Walker spacetime $(APRS)_4$ and vice versa under certain condition imposed on its scale factor. Some popular toy models $F(R)$-gravity are also studied current setting various energy conditions investigated.

We compute the exact equation of state of circular strings in the (2+1) dimensional de Sitter (dS) and anti de Sitter (AdS) spacetimes, and analyze its properties for the different (oscillating, contracting and expanding) strings. The string equation of state has the perfect fluid form P = (γ − 1)E, with the pressure and energy expressed closely and completely in terms of elliptic functions, th...

We analyze fermion mixing in the framework of field quantization curved spacetime. compute expectation value energy-momentum tensor mixed fermions on flavor vacuum. consider spatially flat Friedmann-Lema\^{\i}tre-Robertson-Walker metrics, and we show that vacuum is diagonal conserved. Therefore, it can be interpreted as effective a perfect fluid. In particular, assuming fixed de Sitter backgrou...

In scalar-tensor theories of gravity with torsion, the gravitational field is described in terms of a symmetric metric tensor g, a metriccompatible connection ∇ with torsion, and a scalar field φ. The main aim is to explore an interaction of a charged perfect fluid and a scalar field φ in a background electromagnetic and gravitational field described by {g, ∇, φ}. The interaction is based on an...