Parity violation in the CMB bispectrum by a rolling pseudoscalar

Abstract

We investigate parity-violating signatures of temperature and polarization bispectra of the cosmic microwave background (CMB) in an inflationary model where a rolling pseudoscalar produces large equilateral tensor non-Gaussianity. By a concrete computation based on full-sky formalism, it is shown that resultant CMB bispectra have nonzero signals in both parity-even $({\ell }_1+{\ell }_2+{\ell }_3=\mathrm{even})$ and parity-odd $({\ell }_1+{\ell }_2+{\ell }_3=\mathrm{odd})$ spaces, and are almost uncorrelated with usual scalar-mode equilateral bispectra. These characteristic signatures and polarization information help to detect such tensor non-Gaussianity. Use of both temperature and E-mode bispectra potentially improves of $400\%$ the detectability with respect to an analysis with temperature bispectrum alone. Considering B-mode bispectrum, the signal-to-noise ratio may be able to increase by 3 orders of magnitude. We present the $1\sigma$ uncertainties of a parameter depending on a coupling constant and a rolling condition for the pseudoscalar expected in the $Planck$ and the proposed PRISM experiments.

Comments: 19 pages, 5 figures. Accepted for publication in JCAP