The cosmological evolution of the string landscape is expected to consist of multiple stages of old inflation with a large cosmological constant, each of which ends by tunneling. Old inflation has a well-known graceful exit problem as the observable universe becomes empty, devoid of any entropy....

Quintessential inflation is studied using a string modulus as the inflaton–quintessence field. The modulus begins its evolution at the steep part of its scalar potential, which is due to non-perturbative effects (e.g. gaugino condensation). It is assumed that the modulus crosses an enhanced...