# The Coincidence Problem and the Swampland Conjectures in the Ijjas-Steinhardt Cyclic Model of the Universe

## TL;DR

This paper examines how the cyclic universe model addresses the coincidence problem, showing that scalar fields consistent with Swampland conjectures can naturally produce short cycles that explain the observed matter-dark energy density coincidence.

## Contribution

It demonstrates that scalar field models aligned with Swampland conjectures can resolve the coincidence problem within cyclic universe scenarios.

## Key findings

- Shorter cycle lifetimes naturally solve the coincidence problem.
- Swampland-conforming scalar fields enable finite cycle durations.
- The model aligns cyclic cosmology with string theory constraints.

## Abstract

In the Ijjas-Steinhardt cyclic model, the universe passes through phases dominated by radiation, matter, and a dark energy scalar field, with the value of the scale factor increasing with each cycle. Since each cycle terminates in a finite time, it is straightforward to calculate the fraction of time that the universe spends in a state for which the matter and dark energy densities have comparable magnitudes; when this fraction is large, it can be taken as a solution of the coincidence problem. This solution of the coincidence problem requires a relatively short lifetime for each cycle, but unlike in the case of phantom models, there is no fixed upper bound on this lifetime. However, scalar field models satisfying the Swampland conjectures yield sufficiently short lifetimes to provide a satisfactory resolution of the coincidence problem.