Consistency of Tachyacoustic Cosmology with de Sitter Swampland
  Conjectures
  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.
