Cosmological disformal invariance

Guillem Domènech, Atsushi Naruko, Misao Sasaki

Research output: Contribution to journalArticlepeer-review

58 Citations (Scopus)


The invariance of physical observables under disformal transformations is considered. It is known that conformal transformations leave physical observables invariant. However, whether it is true for disformal transformations is still an open question. In this paper, it is shown that a pure disformal transformation without any conformal factor is equivalent to rescaling the time coordinate. Since this rescaling applies equally to all the physical quantities, physics must be invariant under a disformal transformation, that is, neither causal structure, propagation speed nor any other property of the fields are affected by a disformal transformation itself. This fact is presented at the action level for gravitational and matter fields and it is illustrated with some examples of observable quantities. We also find the physical invariance for cosmological perturbations at linear and high orders in perturbation, extending previous studies. Finally, a comparison with Horndeski and beyond Horndeski theories under a disformal transformation is made.

Original languageEnglish
Article number067
JournalJournal of Cosmology and Astroparticle Physics
Issue number10
Publication statusPublished - 2015 Oct 30
Externally publishedYes


  • cosmological perturbation theory
  • cosmology of theories beyond the SM
  • inflation

ASJC Scopus subject areas

  • Astronomy and Astrophysics


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