M. Golmohammadi | Searcharxiv

arXiv2022

(2+1)-dimensional f(R) gravity solutions via Hojman symmetry

In this paper, we use the Hojman symmetry approach to find new $(2+1)$-dimensional $f(R)$ gravity solutions, in comparison to Noether symmetry approach. In the special case of Hojman symmetry vector $X=R$, we recover $(2+1)$-dimensional BTZ black hole and generalized $(2+1)$-dimensional BTZ black hole solutions, obtained by Noether symmetry approach, and the interesting point is that the cosmological constant is appeared as the direct manifestation of Hojman symmetry.

gr-qc↗

arXiv2020

FRW string cosmological solutions via Hojman symmetry

In this paper, we find exact string cosmological solutions for FRW cosmology, by using Hojman symmetry approach. The string cosmology under consideration includes a scalar field $ψ(t)$ with the potential $W(ψ)$, and a totally antisymmetric field strength $H_{μνρ}$ which is specifically defined in terms of the scale factor $a(t)$. We show that for this string cosmology, Hojman conserved quantities exist using which new exact solutions for the scale factor and the scalar field are obtained for specific potentials $W(ψ)$ with some free parameters. The presence of these parameters, together with those of arising from Hojman symmetry, is an important advantage using which one can construct the solutions $a(t)$ and $ψ(t)$ with variety of cosmological behaviors.

gr-qc↗