Secondary CMB temperature anisotropies from magnetic reheating. (arXiv:1904.09121v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Saga_S/0/1/0/all/0/1">Shohei Saga</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ota_A/0/1/0/all/0/1">Atsuhisa Ota</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tashiro_H/0/1/0/all/0/1">Hiroyuki Tashiro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yokoyama_S/0/1/0/all/0/1">Shuichiro Yokoyama</a>
Spatially fluctuating primordial magnetic fields~(PMFs) inhomogeneously
reheat the Universe when they dissipate deep inside the horizon before
recombination. Such an entropy production turns into the additional photon
temperature perturbations, in particular, into the long wavelength ones if
there exists the local form non-Gaussianity in PMFs. We derive the secondary
cosmic microwave background (CMB) temperature anisotropy originated from this
mechanism, which we call {it inhomogeneous magnetic reheating}. We find that
they can bring us the information about the non-linear coupling between PMFs
and primordial curvature perturbations parametrized by $b_{rm NL}$, which
should be important for probing the generation mechanism of PMFs. The null
observations of such an excess of the secondary effect on the CMB temperature
power spectrum put upper bounds on the statistical parameters of PMFs.
Introducing the magnetic field amplitude $B_{lambda}$ by smoothing over
$lambda=$1 Mpc scale, we obtain the upper bound for non-linear coupling as
$log (b_{rm NL} (B_{lambda}/{rm nG})^2) lesssim {-36.5n_{B} – 93.2}$ with
$n_{rm B}$ being the spectral index of the PMF power spectrum. Our constraints
are far stronger than the previous forecast based on the future spectral
distortion anisotropy measurements because the inhomogeneous magnetic reheating
covers a much wider range of the scales, i.e., $1; {rm Mpc}^{-1} lesssim
klesssim 10^{15}; {rm Mpc}^{-1}$.
Spatially fluctuating primordial magnetic fields~(PMFs) inhomogeneously
reheat the Universe when they dissipate deep inside the horizon before
recombination. Such an entropy production turns into the additional photon
temperature perturbations, in particular, into the long wavelength ones if
there exists the local form non-Gaussianity in PMFs. We derive the secondary
cosmic microwave background (CMB) temperature anisotropy originated from this
mechanism, which we call {it inhomogeneous magnetic reheating}. We find that
they can bring us the information about the non-linear coupling between PMFs
and primordial curvature perturbations parametrized by $b_{rm NL}$, which
should be important for probing the generation mechanism of PMFs. The null
observations of such an excess of the secondary effect on the CMB temperature
power spectrum put upper bounds on the statistical parameters of PMFs.
Introducing the magnetic field amplitude $B_{lambda}$ by smoothing over
$lambda=$1 Mpc scale, we obtain the upper bound for non-linear coupling as
$log (b_{rm NL} (B_{lambda}/{rm nG})^2) lesssim {-36.5n_{B} – 93.2}$ with
$n_{rm B}$ being the spectral index of the PMF power spectrum. Our constraints
are far stronger than the previous forecast based on the future spectral
distortion anisotropy measurements because the inhomogeneous magnetic reheating
covers a much wider range of the scales, i.e., $1; {rm Mpc}^{-1} lesssim
klesssim 10^{15}; {rm Mpc}^{-1}$.
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