Late-time Cosmology without Dark Sector but with Closed String Massless Sector

TL;DR

This paper proposes a string theory-based model where the massless closed string sector drives the universe's acceleration, eliminating the need for dark energy and solving the coincidence problem, with predictions matching late-time cosmological data.

Contribution

It introduces a novel cosmological model based on string theory's massless sector that explains acceleration without dark energy, aligning with observational data.

Findings

The model predicts an accelerating universe in string frame.

Observations of supernovae and quasar spectra agree with the model.

Estimated Hubble constant is approximately 71.2 km/s/Mpc.

Abstract

We explore the possibility of solving the dark energy and the coincidence problems by postulating the massless sector of closed strings. This sector constitutes the gravitational multiplet of string theory and, when applied to four-dimensional cosmology, predicts that \textit{the expansion of an open Universe defined in string frame is readily accelerating}. We confront the prediction with the late-time cosmological data of Type Ia supernovae and quasar absorption spectrum, which probe the evolutions of the Hubble parameter and possibly the fine-structure constant. We report that these observations are in admirable agreement with the prediction without any dark sector or coincidence problem. We estimate the Hubble constant, $H_{0}\simeq 71.2\pm 0.2\,\mathrm{km/s/Mpc}$.