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Slow-roll corrections to inflaton fluctuations on a brane

Kazuya Koyama·Shuntaro Mizuno·David Wands
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Abstract

Quantum fluctuations of an inflaton field, slow-rolling during inflation are coupled to metric fluctuations. In conventional four dimensional cosmology one can calculate the effect of scalar metric perturbations as slow-roll corrections to the evolution of a massless free field in de Sitter spacetime. This gives the well-known first-order corrections to the field perturbations after horizon-exit. If inflaton fluctuations on a four dimensional brane embedded in a five dimensional bulk spacetime are studied to first-order in slow-roll then we recover the usual conserved curvature perturbation on super-horizon scales. But on small scales, at high energies, we find that the coupling to the bulk metric perturbations cannot be neglected, leading to a modified amplitude of vacuum oscillations on small scales. This is a large effect which casts doubt on the reliability of the usual calculation of inflaton fluctuations on the brane neglecting their gravitational coupling.

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Kazuya Koyama, Shuntaro Mizuno, David Wands. 2005-06-13. Slow-roll corrections to inflaton fluctuations on a brane. https://doi.org/10.1088/1475-7516%2F2005%2F08%2F009

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