Observational constraints on Tachyon and DBI inflation

Sheng Li*, Andrew R. Liddle

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We present a systematic method for evaluation of perturbation observables in non-canonical single-fi eld inflation models within the slow-roll approximation, which allied with fi eld redefinitions enables predictions to be established for a wide range of models. We use this to investigate various non-canonical inflation models, including Tachyon inflation and DBI inflation. The Lambert W function will be used extensively in our method for the evaluation of observables. In the Tachyon case, in the slow-roll approximation the model can be approximated by a canonical fi eld with a rede fi ned potential, which yields predictions in better agreement with observations than the canonical equivalents. For DBI inflation models we consider contributions from both the scalar potential and the warp geometry. In the case of a quartic potential, we fi nd a formula for the observables under both non-relativistic (sound speed c(s)(2) similar to 1) and relativistic behaviour (c(s)(2) 0, we fi nd consistency with results already in the literature. We present a comparison to the latest Planck satellite observations. Most of the non-canonical models we investigate, including the Tachyon, are better fits to data than canonical models with the same potential, but we find that DBI models in the slow-roll regime have difficulty in matching the data.

Original languageEnglish
Article number044
Number of pages36
JournalJournal of Cosmology and Astroparticle Physics (JCAP)
Issue number3
Publication statusPublished - Mar 2014


  • inflation
  • cosmological parameters from CMBR


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