Resolving a Misunderstanding: deltaN formalism and single field consistency relation

علی اکبر ابولحسنی (دانشکده فیزیک دانشگاه صنعتی شریف)

Abstract :  According to equivalence principal, the long wavelength perturbations must not have any dynamical effect on the short scale physics up to O(k_K^2/k_s^2). In particular their only effect is a coordinate transformation as long as single field consistency condition is satisfied. In contrast to the common belief, we show that the deltaN formalism, as it is, when applied carefully give the correct result for the bispectrum of primordial curvature perturbations in the so-called squeezed limit without resorting to in-in formalism or stochastic methods. This is while, previous studies claim that there is some missing intrinsic contribution which cannot captured by applying deltaN formalism for super-horizon scale perturbations. In general, when there is a hierarchy between the scale of the modes in the correlation, e.g when one is interested in the squeezed limit bispectrum of the curvature perturbations, there is some subtleties in using the deltaN formula. The main idea is that the amplitude of  short perturbations get modulated as a result of underlying long perturbations. This simple idea would resolve a long misunderstanding that there is some intrinsic local non-Gaussianity at the time of horizon crossing which deltaN formula is ignorant about it.

یکشنبه 23 اردیبهشت 1397، ساعت 15:00

دانشکده فیزیک، طبقه اول کلاس فیزیک 3