Non-trivial Dilaton Research Articles

Symmetries of cosmological superstring vacua

The concept of discrete scale-factor-duality transformations is extended to a full, continuous O( d, d) group. The action of the group transforms “cosmological” solutions of the low-energy, string-modified Einstein equations (including non-trivial dilaton and antisymmetric tensor fields) into other solutions, thus representing the natural generalization of Narain's construction to time-dependent, not-necessarily-compact manifolds. Possible connections with 2D black holes are also pointed out.

Cosmological string theories and discrete inflation

We catalogue string theories which can be interpreted as Robertson-Walker cosmologies. In the absence of dynamic matter, we find only two discrete classes of such theories: static Einstein universes and linearly expanding Milne universes. These correspond to conformal field theories on group manifolds, with the sizes of the Einstein universes related to the level of the Kac-Moody algebra, and Milne universes also offering a geometrical interpretation of a Goddard-Kent-Olive coset construction. String loop effects or non-perturbative phenomena can generate a non-trivial dilaton potential, in which case string theory admits an inflationary cosmology whose Hubble constant is related to the gauge coupling. Presently known conformal field theories permit only a discrete set of values for the Hubble constant, all of which are O(1) in Planck units.

Compactification of the O(16)×O(16) heterotic string theory

Some aspects of the compactification of the ten-dimensional, non-supersymmetric heterotic string theory with gauge group O(16)×O(16) are discussed. The nonvanishing cosmological constant in ten dimensions can be cancelled by a non-trivial dilaton background field such that the resulting theory in four dimensions has no cosmological constant for a certain value of the radius of the compact manifold. Furthermore, examples of compactifications over homogeneous coset spaces are given.