Cosmic microwave background bispectrum and inflation - art. no. 063504

We derive an expression for the non-Gaussian cosmic microwave background (C MB) statistic I-1(3) defined recently by Ferreira, Magueijo, and Gorski in terms of the slow-roll-inflation parameters epsilon and eta. This result sh ows that a nonzero value of I-1(3) in COBE would rule out single-held slow- roll inflation. A sharp change in the slope of the inflaton potential could increase the predicted value of I-1(3), but not significantly. This furthe r suggests that it will be difficult to account for such a detection in mul tiple-field models in which density perturbations are produced by quantum f luctuations in the scalar field driving inflation. An Appendix shows how to evaluate an integral that is needed in our calculation as well as in more general calculations of CMB bispectra.