Physics Group Meeting

I revisit some alternative mechanisms of gravitational wave production during Inflation and argue that they inevitably produce a large amount of scalar fluctuations. For an appreciable tensor contribution the associated scalar fluctuations completely dominate the zero-point fluctuations of inflaton. The maximum tensor to scalar ratio in these scenarios is suppressed by an extra slow-roll factor r_{max} = 8\epsilon^2. Hence, observable tensor signal requires large slow-roll parameter. Moreover the scalar non-Gaussianity cannot be made arbitrarily small, i.e. f_NL >> 1.