Closed string tachyon condensation and worldsheet inflation

Abstract

Closed string tachyon condensation in spacetime generates potentials on the worldsheet that model two-dimensional inflationary cosmology. These models illustrate and elucidate a variety of aspects of inflation, in particular the generation of quantum fluctuations and their back-reaction on geometry. We exhibit a class of Liouville gravity models coupled to matter that can exhibit, for example: (a) pure de Sitter gravity; (b) slow-roll inflation; (c) topological inflation; and (d) graceful exit into an FRW phase. The models also provide a quantitative testing ground for ideas about the origin of inflation, such as the various 'no-boundary/tunnelling' proposals, and the 'eternal/chaotic' inflationary scenario. We suggest an alternative mechanism for quantum creation of cosmological spacetimes which, in the context of the model, provides a natural explanation for why the typical FRW cosmology at large scales underwent a period of inflation at small scale.

Decay of type 0 Neveu-Schwarz 5-branes to nothing

“…In [7], it is suggested that condensation of tachyonic twisted modes localized at fixed points of non-supersymmetric orbifolds like C/Z n and C 2 /Z n give rise to deformations of geometries of the background spacetimes. Configurations bringing with localized tachyons are also discussed in many works [8,9,10,11,12,13,14,15,16,17,18].…”

Modeling quantum gravity effects in inflation

“…For completeness, it is worth displaying the full set of equations of motion in the standard 4d parametrization of the metric. This exercise extends to the fluctuations the remarkable parallel between Liouville cosmology in 2d and Einstein cosmology in 4d, observed at the level of homogeneous backgrounds in [2], see equations (2.14). Using the identifications (3.20), the perturbed Hamiltonian and momentum constraint equations for the quadratic effective action (3.7) read…”

“…describes 2d gravity around a de Sitter or anti-deSitter background; coupling to matter, one finds two-dimensional versions of the Friedmann equations of cosmology [2]. Thus we have an ideal setting to investigate the structure of gravitational backreaction at the quantum level -there is enough structure in the single spatial dimension to accommodate the inhomogeneous fluctuations that lead to structure formation, while gravity might be under sufficient control that we can hope to track the quantum back-reaction of the metric on the quantum matter fluctuations.…”

“…Liouville gravity [1] provides a useful substitute, however -especially when it comes to cosmology [2,19]. The Liouville action (for a review and further references, see [20]; our conventions differ slightly so as to conform more closely to Einstein gravity in higher dimensions)…”

“…Models of inflationary cosmology arise if we allow a nontrivial potential for some of the matter fields, dressed by the dynamical metric [2]. A generic parity-symmetric action for scalar matter coupled to Liouville gravity is…”