Inflation and Acceleration of the Universe by Nonlinear Magnetic Monopole Fields

Despite impressive phenomenological successes, cosmological models are incomplete without an understanding of what happened at the big bang singularity. Maxwell electrodynamics, considered as a source of the classical Einstein field equations, leads to the singular isotropic Friedmann solutions. In the context of Friedmann-Robertson-Walker (FRW) spacetime, we show that singular behavior does not occur for a class of nonlinear generalizations of the electromagnetic theory for strong fields. A new mathematical model is proposed for which the analytical nonsingular extension of FRW solutions is obtained by using the nonlinear magnetic monopole fields.Comment: two column, 6 pages, 2 figures, final published versio

On a Particular Thin-shell Wormhole

In this paper, using a black hole with scalar hair, we construct a scalar thin-shell wormhole (TSW) in 2+1 dimensions by applying the Visser's famous cut and paste technique. The surface stress, which is concentrated at the wormhole throat is determined by using the Darmois-Israel formalism. By employing the various gas models, we study the stability analysis of the TSW. The region of stability is changed by tuning the parameters of "l" and "u". It is observed that the obtained particular TSW originated from the black hole with scalar hair could be more stable with particular $l$ parameter, however it still needs exotic matter.Comment: 9 pages, accepted for publication in TMPh (Theoretical and Mathematical Physics

Hawking radiation and propagation of massive charged scalar field on a three-dimensional G\"{o}del black hole

In this paper we consider the three-dimensional G\"{o}del black hole as a background and we study the vector particle tunneling from this background in order to obtain the Hawking temperature. Then, we study the propagation of a massive charged scalar field and we find the quasinormal modes analytically, which turns out be unstable as a consequence of the existence of closed time-like curves. Also, we consider the flux at the horizon and at infinity, and we compute the reflection and transmission coefficients as well as the absorption cross section. Mainly, we show that massive charged scalar waves can be superradiantly amplified by the three-dimensional G\"{o}del black hole and that the coefficients have an oscillatory behavior. Moreover, the absorption cross section is null at the high frequency limit and for certain values of the frequency.Comment: 18 pages, 12 figures. Accepted for publication in General Relativity and Gravitatio