Quantum no-scale regimes and string moduli

TL;DR

This paper reviews how quantum effects in string theory lead to regimes where classical kinetic energies dominate, resulting in stable, expanding universes or collapse depending on the potential's sign, with no gauge instabilities.

Contribution

It introduces the concept of quantum no-scale regimes in string cosmology, analyzing their stability and evolution with quantum corrections at the one-loop level.

Findings

Quantum no-scale regimes can lead to stable, expanding universes.

Positive potentials induce attractor behavior towards QNSRs.

Negative potentials often cause universe collapse unless initial conditions are finely tuned.

Abstract

We review that in perturbative string theory, flat, homogeneous and isotropic cosmological evolutions found in no-scale models at the quantum level can enter into "quantum no-scale regimes" (QNSRs). When this is the case, the quantum effective potential is dominated by the classical kinetic energies of the no-scale modulus, dilaton and moduli not involved in the supersymmetry breaking. As a result, the evolutions approach the classical ones, where the no-scale structure is exact. When the 1-loop potential is positive, a global attractor mechanism forces the initially expanding solutions to enter the QNSR describing a flat, ever-expanding universe. On the contrary, when the potential can reach negative values, the internal moduli induce in most cases some kind of instability of the growing universe. The latter stops expanding and eventually collapses, unless the initial conditions are tuned in a tiny region of the phase space. Finally, in QNSR, no gauge instability takes place, regardless of the details of the potential.