Cosmic Birefringence: Cross-Spectra and Cross-Bispectra with CMB Anisotropies. (arXiv:2202.04584v4 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Greco_A/0/1/0/all/0/1">Alessandro Greco</a> (Physics and Astronomy Dept. and INFN, Padova, ITALY), <a href="http://arxiv.org/find/astro-ph/1/au:+Bartolo_N/0/1/0/all/0/1">Nicola Bartolo</a> (Physics and Astronomy Dept. and INFN and INAF, Padova, ITALY), <a href="http://arxiv.org/find/astro-ph/1/au:+Gruppuso_A/0/1/0/all/0/1">Alessandro Gruppuso</a> (INAF and INFN, Bologna, ITALY)
Parity-violating extensions of Maxwell electromagnetism induce a rotation of
the linear polarization plane of photons during propagation. This effect, known
as cosmic birefringence, impacts on the Cosmic Microwave Background (CMB)
observations producing a mixing of $E$ and $B$ polarization modes which is
otherwise null in the standard scenario. Such an effect is naturally
parametrized by a rotation angle which can be written as the sum of an
isotropic component $alpha_0$ and an anisotropic one
$deltaalpha(hat{mathbf{n}})$. In this paper we compute angular power
spectra and bispectra involving $deltaalpha$ and the CMB temperature and
polarization maps. In particular, contrarily to what happens for the
cross-spectra, we show that even in absence of primordial cross-correlations
between the anisotropic birefringence angle and the CMB maps, there exist
non-vanishing three-point correlation functions carrying signatures of
parity-breaking physics. Furthermore, we find that such angular bispectra still
survive in a regime of purely anisotropic cosmic birefringence, which
corresponds to the conservative case of having $alpha_0=0$. These bispectra
represent an additional observable aimed at studying cosmic birefringence and
its parity-violating nature beyond power spectrum analyses. They provide also a
way to perform consistency checks for specific models of cosmic birefringence.
Moreover, we estimate that among all the possible birefringent bispectra,
$langledeltaalpha, TBrangle$ and $langledeltaalpha,EBrangle$ are the
ones which contain the largest signal-to-noise ratio. Once the cosmic
birefringence signal is taken to be at the level of current constraints, we
show that these bispectra are within reach of future CMB experiments, as
LiteBIRD.
Parity-violating extensions of Maxwell electromagnetism induce a rotation of
the linear polarization plane of photons during propagation. This effect, known
as cosmic birefringence, impacts on the Cosmic Microwave Background (CMB)
observations producing a mixing of $E$ and $B$ polarization modes which is
otherwise null in the standard scenario. Such an effect is naturally
parametrized by a rotation angle which can be written as the sum of an
isotropic component $alpha_0$ and an anisotropic one
$deltaalpha(hat{mathbf{n}})$. In this paper we compute angular power
spectra and bispectra involving $deltaalpha$ and the CMB temperature and
polarization maps. In particular, contrarily to what happens for the
cross-spectra, we show that even in absence of primordial cross-correlations
between the anisotropic birefringence angle and the CMB maps, there exist
non-vanishing three-point correlation functions carrying signatures of
parity-breaking physics. Furthermore, we find that such angular bispectra still
survive in a regime of purely anisotropic cosmic birefringence, which
corresponds to the conservative case of having $alpha_0=0$. These bispectra
represent an additional observable aimed at studying cosmic birefringence and
its parity-violating nature beyond power spectrum analyses. They provide also a
way to perform consistency checks for specific models of cosmic birefringence.
Moreover, we estimate that among all the possible birefringent bispectra,
$langledeltaalpha, TBrangle$ and $langledeltaalpha,EBrangle$ are the
ones which contain the largest signal-to-noise ratio. Once the cosmic
birefringence signal is taken to be at the level of current constraints, we
show that these bispectra are within reach of future CMB experiments, as
LiteBIRD.
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