$O(d,d)$-Covariant String Cosmology

TL;DR

This paper demonstrates that the $O(d,d)$ symmetry in string cosmology remains intact even with bulk string matter, enabling a reduction to first-order equations and revealing non-zero viscosity in stringy fluids.

Contribution

It shows the preservation of $O(d,d)$ symmetry with matter and derives simplified equations, highlighting non-ideal fluid behavior in string cosmology.

Findings

$O(d,d)$ symmetry is preserved with bulk matter.

Equations reduce to first-order differential equations.

Stringy fluids generally have non-zero viscosity.

Abstract

The recently discovered $O(d,d)$ symmetry of the space of slowly varying cosmological string vacua in $d+1$ dimensions is shown to be preserved in the presence of bulk string matter. The existence of $O(d,d)$ conserved currents allows all the equations of string cosmology to be reduced to first-order differential equations. The perfect-fluid approximation is not $O(d,d)$-invariant, implying that stringy fluids possess in general a non-vanishing viscosity.