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On non-gaussianities in single-field inflation
We study the impact of higher dimension operators in the inflaton Lagrangian
on the non-gaussianity of the scalar spectrum. These terms can strongly enhance
the effect without spoiling slow-roll, though it is difficult to exceed f_NL ~
1, because the scale which suppresses the operators cannot be too low, if we
want the effective field theory description to make sense. In particular we
explicitly calculate the 3-point function given by an higher derivative
interaction of the form (\nabla\phi)^4, which is expected to give the most
important contribution. The angular dependence of the result turns out to be
quite different from the minimal case without higher dimension operators.Comment: 10 page