Difficulties for field theoretical inflation in string models

Abstract

We consider the possibilities for De Sitter solutions of the gravitational equations of motion in string theory. When the potential for the dilaton field is taken to be zero, no such solution exists. At the tree level when dilaton self-interactions are included we find an approximate De Sitter solution in the limit α′ R⪡1 (exact when α′ = 0). We also solve for exact solutions of the equations of motion leading to linear expansion and comment on conditions necessary to yield a background vacuum energy density.