(A)symmetric Tachyon Rolling in de Sitter Spacetime: A universe devoid of Planck density

TL;DR

This paper explores symmetric and asymmetric tachyon-driven cosmologies in de Sitter space, showing they can have identical evolution post-initial conditions and that the universe begins at string scale densities, avoiding Planck density.

Contribution

It explicitly demonstrates the equivalence of symmetric and asymmetric tachyon cosmologies after initial conditions and shows the universe starts at string scale densities, not Planck density.

Findings

Universe begins at string scale density (~10^{78} g/cm^3)

Tachyon solutions can produce inflation

Symmetric and asymmetric solutions are equivalent after initial conditions

Abstract

In a recent paper we studied rolling tachyon flat FRW cosmologies, but those admitting only time-reversal asymmetric boundary conditions. The time-reversal symmetric cosmologies have been studied by Sen previously. We show explicitly here that through appropriate choice of initial conditions, the time evolution of the Hubble parameter in these two types of solutions can be made completely identical for $t>0$, except near $t=0$. The rolling tachyon solution also gives rise to necessary inflation. We find that universe does start as a string size object (with string scale $10^{15} GeV$) with a string mass density $\simeq 10^{78} gm. cm^{-3}$ and not with Planck density.