2011/08/31 by M. Shiraishi, Maresuke Shiraishi, Daisuke Nitta +3 · 2 citations
Physics and Astronomy · #Amplitude #Bispectrum #Black Holes and Theoretical Physics #Cosmic microwave background #Cosmology and Gravitation Theories #Extra dimensions #Gravitational wave #Graviton #Noncommutative and Quantum Gravity Theories #Parity (physics) #Polarization (electrochemistry) #astro-ph.CO #gr-qc #hep-ph #hep-th
paper · pdf · doi:10.1143/ptp.126.937
published as Prog. Theor. Phys. 126 (2011), 937-959 · 23 pages, 3 figures. Accepted for publication in PTP. Version 3 includes errata in Fig. 2
openalex publication_date 2011/11/01 · arxiv created 2012/02/13 · arxiv updated 2012/02/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We investigate the cosmic microwave background (CMB) bispectra of the intensity (temperature) and polarization modes induced by the graviton non-Gaussianities, which arise from the parity-conserving and parity-violating Weyl cubic terms with time-dependent coupling. By considering the time-dependent coupling, we find that even in the exact de Sitter space time, the parity violation still appears in the three-point function of the primordial gravitational waves and could become large. Through the estimation of the CMB bispectra, we demonstrate that the signals generated from the parity-conserving and parity-violating terms appear in completely different configurations of multipoles. For example, the parity-conserving non-Gaussianity induces the nonzero CMB temperature bispectrum in the configuration with ∑3n=1 ℓn = even and, while due to the parity-violating non-Gaussianity, the CMB temperature bispectrum also appears for ∑3n=1 ℓn = odd. This signal is just good evidence of the parity violation in the non-Gaussianity of primordial gravitational waves. We find that the shape of this non-Gaussianity is similar to the so-called equilateral one and the amplitudes of these spectra at large scale are roughly estimated as |bℓℓℓ| ∼ ℓ-4 × 3.2 × 10−2 (GeV / Λ)2 (r/0.1)4, where Λ is an energy scale that sets the magnitude of the Weyl cubic terms (higher derivative corrections) and r is a tensor-to-scalar ratio. Taking the limit for the nonlinearity parameter of the equilateral type as feqNL < 300, we can obtain a bound as Λ ≳ 3 × 106 GeV, assuming r = 0.1.