Conformal Ricei collineations of static spherically symmetric spacetimes are studied. The general form of the vector fields generating eonformal Rieei eollineations is found when the Rieei tensor is non-degenerate, in...Conformal Ricei collineations of static spherically symmetric spacetimes are studied. The general form of the vector fields generating eonformal Rieei eollineations is found when the Rieei tensor is non-degenerate, in which ease the number of independent eonformal Rieei eollineations is 15, the maximum number for four-dimensional manifolds. In the degenerate ease it is found that the static spherically symmetric spaeetimes always have an infinite number of eonformal Rieei eollineations. Some examples are provided which admit non-trivial eonformal Rieei eollineations, and perfect fluid source of the matter.展开更多
We derive the first law of thermodynamics using the method proposed by Wald.Treating the entropy as Noether charge and comparing with the usual first law of thermodynamics,we obtain explicitly the expression of entrop...We derive the first law of thermodynamics using the method proposed by Wald.Treating the entropy as Noether charge and comparing with the usual first law of thermodynamics,we obtain explicitly the expression of entropy which contains infinitely many non-local terms(i.e.the integral terms).We have proved,in general,that the first law of black hole thermodynamics is violated for f(R,T)gravity.However,there might exist some special cases in which the first law for f(R,T)gravity is recovered.展开更多
Motivated by an earlier study of Sahoo and Singh[Mod.Phys.Lett.A 17(2002)2409],we investigate the time dependence of the Brans–Dicke parameterω(t)for an expanding Universe in the generalized Brans–Dicke Chameleon c...Motivated by an earlier study of Sahoo and Singh[Mod.Phys.Lett.A 17(2002)2409],we investigate the time dependence of the Brans–Dicke parameterω(t)for an expanding Universe in the generalized Brans–Dicke Chameleon cosmology,and obtain an explicit dependence ofω(t)in different expansion phases of the Universe.Also,we discuss how the observed accelerated expansion of the observable Universe can be accommodated in the present formalism.展开更多
文摘Conformal Ricei collineations of static spherically symmetric spacetimes are studied. The general form of the vector fields generating eonformal Rieei eollineations is found when the Rieei tensor is non-degenerate, in which ease the number of independent eonformal Rieei eollineations is 15, the maximum number for four-dimensional manifolds. In the degenerate ease it is found that the static spherically symmetric spaeetimes always have an infinite number of eonformal Rieei eollineations. Some examples are provided which admit non-trivial eonformal Rieei eollineations, and perfect fluid source of the matter.
文摘We derive the first law of thermodynamics using the method proposed by Wald.Treating the entropy as Noether charge and comparing with the usual first law of thermodynamics,we obtain explicitly the expression of entropy which contains infinitely many non-local terms(i.e.the integral terms).We have proved,in general,that the first law of black hole thermodynamics is violated for f(R,T)gravity.However,there might exist some special cases in which the first law for f(R,T)gravity is recovered.
文摘Motivated by an earlier study of Sahoo and Singh[Mod.Phys.Lett.A 17(2002)2409],we investigate the time dependence of the Brans–Dicke parameterω(t)for an expanding Universe in the generalized Brans–Dicke Chameleon cosmology,and obtain an explicit dependence ofω(t)in different expansion phases of the Universe.Also,we discuss how the observed accelerated expansion of the observable Universe can be accommodated in the present formalism.
