The motivation for studying the rolling tachyon and noncommutative inflation comes from string theory. In the tachyon inflation scenario, metric perturbations are created by tachyon field fluctuations during inflation. We drive the exact mode equation for scalar perturbations of the metric and investigate the cosmological perturbations in the commutative and noncommutative inflationary spacetime driven by the tachyon field which have a Born-Infeld Lagrangian. Although at lowest order the predictions of tachyon inflation are no different than those from standard slow-roll inflation, due to the modified inflationary dynamics there exists modifications to the power spectra of fluctuations generated during inflation. In the noncommutative tachyon inflation scenario, the stringy noncommutativity of spacetime results in corrections to the primordial power spectrum that lead to a spectral index that is greater than 1 on large scales and less than 1 on small scales as the first-year results of the Wilkinson Microwave Anisotropy Probe indicate.

• Received 3 February 2004

DOI:https://doi.org/10.1103/PhysRevD.70.123504