200 research outputs found
Parity Violation of Gravitons in the CMB Bispectrum
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 and, while due to the
parity-violating non-Gaussianity, the CMB temperature bispectrum also appears
for . 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 , where is an energy scale that
sets the magnitude of the Weyl cubic terms (higher derivative corrections) and
is a tensor-to-scalar ratio. Taking the limit for the nonlinearity
parameter of the equilateral type as , we can obtain
a bound as , assuming .Comment: 23 pages, 3 figures. Accepted for publication in PTP. Version 3
includes errata in Fig.
CMB Bispectrum from Primordial Scalar, Vector and Tensor non-Gaussianities
We present an all-sky formalism for the Cosmic Microwave Background (CMB)
bispectrum induced by the primordial non-Gaussianities not only in scalar but
also in vector and tensor fluctuations. We find that the bispectrum can be
formed in an explicitly rationally invariant way by taking into account the
angular and polarization dependences of the vector and tensor modes. To
demonstrate this and present how to use our formalism, we consider a specific
example of the correlation between two scalars and a graviton as the source of
non-Gaussianity. As a result, we show that the CMB reduced bispectrum of the
intensity anisotropies is evaluated as a function of the multipole and the
coupling constant between two scalars and a graviton denoted by ;
. By
estimating the signal-to-noise ratio, we find that the constraint as will be expected from the PLANCK experiment.Comment: 19 pages, 4 figures. Accepted for publication in PT
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