Acceleration from M theory and Fine-tuning

TL;DR

This paper explores how M theory compactification with a time-dependent internal space can cause transient acceleration in the universe, but it predicts a large variation in the fine structure constant that conflicts with observations.

Contribution

It demonstrates that M theory compactification can produce transient acceleration but requires fine-tuning and leads to large, observationally inconsistent variations in fundamental constants.

Findings

Transient acceleration achieved through M theory compactification.

Large variation in fine structure constant conflicts with observational constraints.

Fine-tuning of initial conditions is necessary for acceleration.

Abstract

The compactification of M theory with time dependent hyperbolic internal space gives an effective scalar field with exponential potential which provides a transient acceleration in Einstein frame in four dimensions. Ordinary matter and radiation are present in addition to the scalar field coming from compactification. We find that we have to fine-tune the initial conditions of the scalar field so that our Universe experiences acceleration now. During the evolution of our Universe, the volume of the internal space increases about 12 times. The time variation of the internal space results in a large time variation of the fine structure constant which violates the observational constraint on the variation of the fine structure constant. The large variation of the fine structure constant is a generic feature of transient acceleration models.