# Consistency of Tachyacoustic Cosmology with de Sitter Swampland Conjectures

## TL;DR

This paper explores tachyacoustic cosmology as an alternative to inflation, demonstrating it can align with de Sitter swampland conjectures and potentially fit within a UV-complete theory.

## Contribution

It shows that tachyacoustic models with superluminal sound speed can satisfy swampland conjectures, providing a viable alternative to inflationary cosmology.

## Key findings

- Tachyacoustic models can be consistent with swampland conjectures.
- Derived a general condition for models with superluminal sound speed.
- Established the potential of tachyacoustic cosmology within UV-complete theories.

## Abstract

Recent studies show that there is tension between the de Sitter swampland conjectures proposed by Obeid, et al. and inflationary cosmology. In this paper, we consider an alternative to inflation, `tachyacoustic' cosmology, in light of swampland conjectures. In tachyacoustic models, primordial perturbations are generated by a period of superluminal sound speed instead of accelerating expansion. We show that realizations of tachyacoustic Lagrangians can be consistent with the de Sitter swampland conjectures, and therefore can in principle be consistent with a UV-complete theory. We derive a general condition for models with $c_S > 1$ to be consistent with swampland conjectures.