A bridge between unified cosmic history by f(R)-gravity and BIonic system

Abstract

Recently, the cosmological deceleration-acceleration transition redshift in $f(R)$ gravity has been considered in order to address consistently the problem of cosmic evolution. It is possible to show that the deceleration parameter changes sign at a given redshift according to observational data. Furthermore, a $f(R)$ gravity cosmological model can be constructed in brane-antibrane system starting from the very early universe and accounting for the cosmological redshift at all phases of cosmic history, from inflation to late time acceleration. Here we propose a $f(R)$ model where transition redshifts correspond to inflation-deceleration and deceleration-late time acceleration transitions starting froma BIon system. At the point where the universe was born, due to the transition of $k$ black fundamental strings to the BIon configuration, the redshift is approximately infinity and decreases with reducing temperature ($z\sim T^{2}$). The BIon is a configuration in flat space of a universe-brane and a parallel anti-universe-brane connected by a wormhole. This wormhole is a channel for flowing energy from extra dimensions into our universe, occurring at inflation and decreasing with redshift as $z\sim T^{4+1/7}$. Dynamics consists with the fact that the wormhole misses its energy and vanishes as soon as inflation ends and deceleration begins. Approaching two universe branes together, a tachyon is originated, it grows up and causes the formation of a wormhole. We show that, in the framework of $f(R)$ gravity, the cosmological redshift depends on the tachyonic potential and has a significant decrease at deceleration-late time acceleration transition point ($z\sim T^{2/3}$). As soon as today acceleration approaches, the redshift tends to zero and the cosmological model reduces to the standard $\Lambda$CDM cosmology.