Instant Cosmology

TL;DR

This paper explores how Instant Folded Strings (IFSs), which violate the Null Energy Condition, influence cosmology by potentially enabling inflation and bouncing universes, with implications for dark energy and the cosmological constant problem.

Contribution

It introduces the concept of IFSs and analyzes their suppressed NEC violation in expanding universes, proposing new mechanisms for inflation and bouncing cosmologies within string theory.

Findings

NEC violation by IFSs is suppressed in expanding universes.

Dark energy origin includes contributions from the potential and its derivative.

In contracting universes, IFS effects lead to natural bouncing cosmologies.

Abstract

Instant Folded Strings (IFSs) are unconventional light strings that emerge when the string coupling increases with time. A particularly intriguing property of IFSs, especially relevant to cosmology, is that they violate the Null Energy Condition (NEC). In this paper, we begin to explore their cosmological effects. We find that NEC violation by IFSs is significantly suppressed in an expanding universe, leading to a universe that resembles our own, comprising matter, radiation, and dark energy. Upon closer examination, these components exhibit subtle, nonstandard traits that could be experimentally tested in the future. Notably, the origin of dark energy stems not only from the potential, as is usually the case, but also from the derivative of the potential with respect to the dilaton. This paves the way for a new approach to realizing inflation within string theory, addressing the Dine-Seiberg problem associated with dilaton stabilization, and perhaps even hinting at a novel mechanism to tackle the cosmological constant problem. Conversely, in a contracting universe, the effects of IFSs are amplified, making bouncing cosmologies a natural and prevalent outcome.