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Register a new userThe bispectra of galactic CMB foregrounds and their impact on primordial non-Gaussianity estimation
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We use the binned bispectrum estimator to determine the bispectra of the dust, free-free, synchrotron, and AME galactic foregrounds using maps produced by the Commander component separation method from Planck 2015 data. We find that all of these peak in the squeezed configuration, allowing for potential confusion with in particular the local primordial shape. Applying an additional functionality implemented in the binned bispectrum estimator code, we then use these galactic bispectra as templates in an $f_mathrm{NL}$ analysis of other maps. After testing and validating the method and code with simulations, we show that we detect the dust in the raw 143 GHz map with the expected amplitude (the other galactic foregrounds are too weak at 143 GHz to be detected) and that no galactic residuals are detected in the cleaned CMB map. We also investigate the effect of the mask on the templates and the effect of the choice of binning on a joint dust-primordial $f_mathrm{NL}$ analysis.
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Tensor non-Gaussianities are a key ingredient to test the symmetries and the presence of higher spin fields during the inflationary epoch. Indeed, the shape of the three point correlator of the graviton is totally fixed by the symmetries of the de Sitter stage and, in the case of parity conservation, gets contributions only from the ordinary gravity action plus a higher derivative term called the (Weyl)$^3$ action. We discuss current and future bounds on the three point tensor contribution from the (Weyl)$^3$ term using cosmic microwave background (CMB) bispectra. Our results indicate that forthcoming experiments, such as LiteBIRD, CMB-S4 and CORE, will detect the presence of the (Weyl)$^3$ term if $M_p^4 L^4 sim 10^{17} r^{-4}$, where $L$ parametrizes the strength of the (Weyl)$^3$ term and $r$ is the tensor-to-scalar ratio, which corresponds to $Lgtrsim 3.2 times 10^5 M_p^{-1}$, while the current upper limit is $M_p^4 L^4 = (1.1 pm 4.0) times 10^{19} r^{-4}$ (68%CL).
We study the impact that uncertainties on assumed relations between galaxy bias parameters have on constraints of the local PNG $f_{rm NL}$ parameter. We focus on the relation between the linear density galaxy bias $b_1$ and local PNG bias $b_phi$ in an idealized forecast setup with multitracer galaxy power spectrum and bispectrum data. We consider two parametrizations of galaxy bias: 1) one inspired by the universality relation where $b_phi = 2delta_cleft(b_1 - pright)$ and $p$ is a free parameter; and 2) another in which the product of bias parameters and $f_{rm NL}$, like $f_{rm NL} b_phi$, is directly fitted for. The constraints on the $f_{rm NL}-p$ plane are markedly bimodal, and both the central value and width of marginalized constraints on $f_{rm NL}$ depend sensitively on the priors on $p$. Assuming fixed $p=1$ in the constraints with a fiducial value of $p=0.55$ can bias the inferred $f_{rm NL}$ by $0.5sigma$ to $1sigma$; priors $Delta p approx 0.5$ around this fiducial value are however sufficient in our setup to return unbiased constraints. In power spectrum analyses, parametrization 2, that makes no assumptions on $b_phi$, can distinguish $f_{rm NL} eq 0$ with the same significance as parametrization 1 assuming perfect knowledge of $b_phi$ (the value of $f_{rm NL}$ is however left unknown). A drawback of parametrization 2 is that the addition of the bispectrum information is not as beneficial as in parametrization 1. Our results motivate strongly the incorporation of mitigation strategies for bias uncertainties in PNG constraint analyses, as well as further theoretical studies on the relations between bias parameters to better inform those strategies.
The CMB polarization promises to unveil the dawn of time measuring the gravitational wave background emitted by the Inflation. The CMB signal is faint, however, and easily contaminated by the Galactic foreground emission, accurate measurements of which are thus crucial to make CMB observations successful. We review the CMB polarization properties and the current knowledge on the Galactic synchrotron emission, which dominates the foregrounds budget at low frequency. We then focus on the S-Band Polarization All Sky Survey (S-PASS), a recently completed survey of the entire southern sky designed to investigate the Galactic CMB foreground.
Cross-correlations between Cosmic Microwave Background (CMB) temperature and polarization anisotropies and $mu$-spectral distortions have been considered to measure (squeezed) primordial scalar bispectra in a range of scales inaccessible to primary CMB bispectra. In this work we address whether it is possible to constrain tensor non-Gaussianities with these cross-correlations. We find that only primordial tensor bispectra with anisotropies leave distinct signatures, while isotropic tensor bispectra leave either vanishing or highly suppressed signatures. We discuss how the kind of anisotropies and the parity state in primordial bispectra determine the non-zero cross-correlations. By employing the so-called BipoSH formalism to capture the observational effects of these anisotropies, we make Fisher-forecasts to assess the detection prospects from $mu T$, $mu E$ and $mu B$ cross-correlations. Observing anisotropies in squeezed $langle gamma gamma gammarangle$ and $langle gamma gamma zetarangle$ bispectra is going to be challenging as the imprint of tensor perturbations on $mu$-distortions is subdominant to scalar perturbations, therefore requiring a large, independent amplification of the effect of tensor perturbations in the $mu$-epoch. In absence of such a mechanism, anisotropies in squeezed $langle zeta zeta gammarangle$ bispectrum are the most relevant sources of $mu T$, $mu E$ and $mu B$ cross-correlations. In particular, we point out that in models where anisotropies in $langle zeta zeta zeta rangle$ leave potentially observable signatures in $mu T$ and $mu E$, the detection prospects of anisotropies in $langle zeta zeta gammarangle$ from $mu B$ are enhanced.
Anisotropies in distortions to the frequency spectrum of the cosmic microwave background (CMB) can be created through spatially varying heating processes in the early Universe. For instance, the dissipation of small-scale acoustic modes does create distortion anisotropies, in particular for non-Gaussian primordial perturbations. In this work, we derive approximations that allow describing the associated distortion field. We provide a systematic formulation of the problem using Fourier-space window functions, clarifying and generalizing previous approximations. Our expressions highlight the fact that the amplitudes of the spectral-distortion fluctuations induced by non-Gaussianity depend also on the homogeneous value of those distortions. Absolute measurements are thus required to obtain model-independent distortion constraints on primordial non-Gaussianity. We also include a simple description for the evolution of distortions through photon diffusion, showing that these corrections can usually be neglected. Our formulation provides a systematic framework for computing higher order correlation functions of distortions with CMB temperature anisotropies and can be extended to describe correlations with polarization anisotropies.
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