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We study the development of entropy fluctuations in brane inflation in a warped throat, including the brane–antibrane tachyon as the waterfall field. We find that there is a period at the end of inflation during which the entropy mode associated with the tachyon field increases exponentially. In turn, the induced entropy seeds a contribution to the curvature fluctuation on cosmological scales which grows rapidly and could exceed the primordial curvature perturbation. We identify parameter values for which in the absence of backreaction the induced curvature fluctuations are larger than the primordial adiabatic ones. In the specific model we study, however, backreaction limits the growth of the entropy fluctuations. We discuss situations in which backreaction effects are less constraining. The lesson of our investigation is that the study of the development of entropy fluctuations at the end of the period of inflation can lead to constraints on models of brane inflation and suggests that the curvaton mechanism may contribute significantly to the spectrum of cosmological perturbations. [ABSTRACT FROM AUTHOR]

We argue that many models of inflation in string theory require the usual ten-dimensional compactification geometry to be modified during inflation. Based on arguments from the four-dimensional effective theory, we propose a modified ten-dimensional geometry in which the four-dimensional effective theory is just consistent. We also discuss the implications of the light modes in reheating, following inflation. (Based on work in progress with Anupam Mazumdar and Robert Myers.) [ABSTRACT FROM AUTHOR]