Measuring chiral gravitational waves in Chern-Simons gravity with CMB bispectra

Nicola Bartolo; Giorgio Orlando; Maresuke Shiraishi

doi:10.1088/1475-7516/2019/01/050

paper

Measuring chiral gravitational waves in Chern-Simons gravity with CMB bispectra

arXiv:1809.11170 · doi:10.1088/1475-7516/2019/01/050

Abstract

Chern-Simons gravity coupled to the scalar sector through a generic coupling function $f (ϕ)$ can be tested at the very high energies of the inflationary period. In 1706.04627, we computed the theoretical parity breaking signatures of the $⟨ γ γ ζ ⟩$ primordial bispectrum which mixes two gravitons and one scalar curvature perturbation. We defined a parameter $Π$ which measures the level of parity breaking of the corresponding bispectrum. In this work we forecast the expected $1 σ$ error on $Π$ using the cosmic microwave background (CMB) angular bispectra. We find that, given the angular resolution of an experiment like $P l an c k$ , $Π \sim 1 0^{6}$ is detectable via the measurement of $B B T$ or $B B E$ angular bispectra if the tensor-to-scalar ratio $r = 0.01$ . We also show that, from the theoretical point of view, $Π$ can be greater than $1 0^{6}$ . Thus, our conclusion is that $B B T$ or $B B E$ CMB angular bispectra can become an essential observable for testing Chern-Simons gravity in the primordial universe.

arXiv comment16 pages, 1 figure; version matching publication in JCAP

Measuring chiral gravitational waves in Chern-Simons gravity with CMB bispectra

Abstract

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