Non-singularcosmological models in string gravity with constant dilaton andsecond-order curvature corrections

Abstract

We investigate FRW cosmological solutions in the theory ofamodulus field coupled to gravity through a Gauss-Bonnet term.The explicit analytical forms of non-singular asymptotics arepresented for power-law and exponentially steep modulus couplingfunctions. We study the influence ofa modulus field potential onthese asymptotic regimes and find some forms of the potentialwhich do not destroy the non-singular behaviour. In particular, weobtain that exponentially steep coupling functions arising fromthe string theory do not allow non-singular past asymptoticunlessthe modulus field potential tends to zero fora modulus fieldψ→±∞. Finally, the modification of the chaoticdynamics in the closed FRW universe due to presence of theGauss-Bonnet term is discussed.