Impact of transforming to conformal Fermi coordinates on quasisingle field non-Gaussianity

Abstract

In general relativity, predictions for observable quantities can be expressed in a coordinate independent way. Nonetheless it may be inconvenient to do so. Using a particular frame may be the easiest way to connect theoretical predictions to measurable quantities. For the cosmological curvature bispectrum such frame is described by the conformal Fermi coordinates. In single field inflation it was shown that going to this frame cancels the squeezed limit of the density perturbation bispectrum calculated in global coordinates. We explore this issue in quasisingle field inflation when the curvaton mass and the curvatoninflaton mixing are small. In this case, the contribution to the bispectrum from the coordinate transformation to conformal Fermi coordinates is of the same order as that from the inflaton-curvaton interaction term but does not cancel it.

Light fields during inflation from BOSS and future galaxy surveys

“…The leading physical term is suppressed by O(k 2 1 /k 2 3 ) and is due to the coupling of the short modes at horizon crossing to the curvature of the universe due to long-wavelength modes [69], which is typically proportional to the amplitude of equilateral non-Gaussianity, f eq NL . In the presence of additional fields, the short-scale power can depend on the longwavelength values of these fields and not just derivatives of the metric fluctuations [70]. For an additional massless field, the late-time Newtonian potential Φ may be nonlinearly related JCAP05(2024)090 to a light (isocurvature) field χ during inflation, Φ(⃗ x) = χ(⃗ x) − f loc NL χ 2 (⃗ x).…”