  We present the first computation of the cosmological perturbations generated
during inflation up to second order in deviations from the homogeneous
background solution. Our results, which fully account for the inflaton
self-interactions as well as for the second-order fluctuations of the
background metric, provide the exact expression for the gauge-invariant
curvature perturbation bispectrum produced during inflation in terms of the
slow-roll parameters or, alternatively, in terms of the scalar spectral $n_S$
and and the tensor to adiabatic scalar amplitude ratio $r$. The bispectrum
represents a specific non-Gaussian signature of fluctuations generated by
quantum oscillations during slow-roll inflation. However, our findings indicate
that detecting the non-Gaussianity in the cosmic microwave background
anisotropies emerging from the second-order calculation will be a challenge for
the forthcoming satellite experiments.
