Primordial perturbations and non-Gussianity in DBI inflation

Inflationary scenario was proposed to address several problems on initial conditions in big bang cosmology. Recently, because of the development of the observational technique, making use of the information of the primordial perturbations, we have become able to investigate the physics behind the inflation. On the other hand, among the inflation models, Dirac-Born-Infeld (DBI) model which is constructed within string theory is known to generate primordial perturbations with interesting properties. Therefore, in this talk, after briefly summarizing how primordial perturbations and non-Gaussianity are generated in general inflation models, we show the theoretical predictions on these quantities in single-field and multi-field DBI inflation based on our previous works. If there is sufficient time, we also mention about theoretical extension to include Galileon interaction as well as recent observational constraints. Reference: F. Arroja, S. Mizuno and K. Koyama, ``Non-gaussianity from the bispectrum in general multiple field inflation,'' JCAP 0808 (2008) 015 F. Arroja, S. Mizuno, K. Koyama and T. Tanaka, ``On the full trispectrum in single field DBI-inflation,'' Phys. Rev. D80 (2009) 043527 S. Mizuno, F. Arroja and K. Koyama, ``On the full trispectrum in multi-field DBI inflation,'' Phys.\ Rev. D80 (2009) 083517 S. Mizuno and K. Koyama, ``Primordial non-Gaussianity from the DBI Galileons,'' Phys. Rev. D82 (2010) 103518 S. Renaux-Petel, S. Mizuno and K. Koyama, ``Primordial fluctuations and non-Gaussianities from multifield DBI Galileon inflation,'' JCAP 1111 (2011) 042