Patchy screening of the CMB from dark photons

Multifield inflation models and non-Bunch–Davies vacuum initial conditions both predict sizeable non-Gaussian primordial perturbations and anisotropic μ-type spectral distortions of the cosmic microwave background (CMB) blackbody. While CMB anisotropies allow us to probe non-Gaussianity at wavenumbers $k\simeq 0.05\, {\rm Mpc^{-1}}$, μ-distortion anisotropies are related to non-Gaussianity of primordial perturbation modes with much larger wavenumbers, $k\simeq 740\, {\rm Mpc^{-1}}$. Through cross-correlations between CMB and μ-distortion anisotropies, one can therefore shed light on the aforementioned inflation models. We investigate the ability of a future CMB satellite imager like LiteBIRD to measure μT and μE cross-power spectra between anisotropic μ-distortions and CMB temperature and E-mode polarization anisotropies in the presence of foregrounds, and derive LiteBIRD forecasts on ${f_{\rm NL}^\mu (k\simeq 740\, {\rm Mpc^{-1}})}$. We show that μE cross-correlations with CMB polarization provide more constraining power on $f_{\rm NL}^\mu$ than μT cross-correlations in the presence of foregrounds, and the joint combination of μT and μE observables adds further leverage to the detection of small-scale primordial non-Gaussianity. For multifield inflation, we find that LiteBIRD would detect ${f_{\rm NL}^\mu }=4500$ at 5σ significance after foreground removal, and achieve a minimum error of ${\sigma (f_{\rm NL}^\mu =0) \simeq 800}$ at 68 per cent CL by combining CMB temperature and polarization. Due to the huge dynamic range of wavenumbers between CMB and μ-distortion anisotropies, such large $f^\mu _{\rm NL}$ values would still be consistent with current CMB constraints in the case of very mild scale dependence of primordial non-Gaussianity. Anisotropic spectral distortions thus provide a new path, complementary to CMB B-modes, to probe inflation with LiteBIRD.

Measurements of the cosmic microwave background (CMB) spectral distortions (SDs) will open a new window on the very early universe, providing new information complementary to that gathered from CMB temperature and polarization anisotropies. In this paper, we study their synergy as a function of the characteristics of the considered experiments. In particular, we examine a wide range of sensitivities for possible SD measurements, spanning from FIRAS up to noise levels 1000 times better than PIXIE, and study their constraining power when combined with current or future CMB anisotropy experiments such as Planck or LiteBIRD plus CMB-S4. We consider a number of different cosmological models such as the ΛCDM, as well as its extensions with the running of the scalar spectral index, the decay or the annihilation of dark matter (DM) particles. While upcoming CMB anisotropy experiments will be able to decrease the uncertainties on inflationary parameters such as As and ns by about a factor 2 in the ΛCDM case, we find that an SD experiment 100 times more sensitive than PIXIE (comparable to the proposed Super-PIXIE satellite) could potentially further contribute to constrain these parameters. This is even more significant in the case of the running of the scalar spectral index. Furthermore, as expected, constraints on DM particles decaying at redshifts probed by SDs will improve by orders of magnitude even with an experiment 10 times worse than PIXIE as compared to CMB anisotropies or Big Bang Nucleosynthesis bounds. On the contrary, DM annihilation constraints will not significantly improve over CMB anisotropy measurements. Finally, we forecast the constraints obtainable with sensitivities achievable either from the ground or from a balloon.

To reliably detect the cosmic microwave background (CMB) anisotropy is of great importance in understanding the birth and evolution of the Universe. One of the difficulties in CMB experiments is the domination of measured CMB anisotropy maps by the Doppler dipole moment from the motion of the antenna relative to the CMB. For each measured temperature the expected dipole component has to be calculated separately and then subtracted from the data. A small error in dipole direction, antenna pointing direction, sidelobe pickup contamination, and/or timing synchronism, can raise significant deviation in the dipole cleaned CMB temperature. After a full-sky observational scan, the accumulated deviations will be structured with a pattern closely correlated to the observation pattern with artificial anisotropies on large scales, including artificial quadrupole, octopole etc in the final CMB map. Such scan-induced anisotropies on large scales can be predicted by the true dipole moment and observational scan scheme. Indeed, the expected scan-induced quadrupole pattern of the WMAP mission is perfectly in agreement with the published WMAP quadrupole. With the scan strategy of the Planck mission, we predict that scan-induced anisotropies will also produce an artificially aligned quadrupole. The scan-induced anisotropy is a common problem for all sweep missions and, like the foreground emissions, has to be removed from observed maps. Without doing so, CMB maps from COBE, WMAP, and Planck as well, are not reliable for studying the CMB anisotropy.

We study the complementarity between the cosmological information obtainable with the Planck Surveyor and the large-scale structure (LSS) redshift surveys in Λ cold+hot dark matter (ΛCHDM) cosmologies. We compute the initial full phase-space neutrino distribution function for ΛCHDM models by using numerical simulations. As initial conditions, we adopt the HDM density fluctuation power spectrum normalized on the basis of the analysis of the local cluster X-ray temperature function and derive the initial neutrino phase-space distribution at each spatial wavenumber k by using the Zel'dovich approximation. These initial neutrino phase-space distributions are implemented in the CMBFAST code for the integration of the coupled linearized Einstein, Boltzmann, and fluid equations in k-space. We find that the relative bias between the cosmic microwave background (CMB) temperature fluctuations and the underlying matter density fluctuation power spectrum in COBE Differential Microwave Radiometer normalization is given by the CDM component normalized according to the abundance of rich clusters at the present time. We use the Fisher information matrix approximation to constrain a multidimensional parameterization of the ΛCHDM model by jointly considering CMB and large-scale structure data according to the Planck and the Sloan Digital Sky Survey experimental specifications and by taking into account redshift distortions and nonlinear effects on the matter power spectrum. We found that, although the CMB anisotropy and polarization measurements tend to dominate the constraints on most of the cosmological parameters, the additional small-scale LSS data help to break the parameter degeneracies. This work has been done in the framework of the Planck Low Frequency Instrument activities.

One of the major goals of future cosmic microwave background (CMB) B-mode polarization experiments is the detection of primordial gravitational waves through an unbiased measurement of the tensor-to-scalar ratio r. Robust detection of this signal will require mitigating all possible contamination to the B-mode polarization from astrophysical origins. One such extragalactic contamination arises from the patchiness in the electron density during the reionization epoch. Along with the signature on CMB polarization, the patchy reionization can source secondary anisotropies on the CMB temperature through the kinetic Sunyaev–Zeldovich (kSZ) effect. In order to study the impact of this foreground for the upcoming CMB missions, we present a self-consistent framework to compute the CMB anisotropies based on a physically motivated model of reionization. We show that the value of r can bias towards a higher value if the secondary contribution from reionization is neglected. However, combining small-scale kSZ signal, large-scale E-mode polarization, and B-mode polarization measurements, we can put constraints on the patchiness in electron density during reionization and can mitigate its impact on the value of r. CMB missions such as CMB-S4 and PICO may experience a bias of >0.17σ which can go as high as ∼0.73σ for extreme reionization models allowed by the Planck and SPT CMB measurements. As future experiments target to measure r at 5σ, this is likely to affect the measurement significance and hence possibly affect the claim of detection of r, if not mitigated properly by using joint estimations of different reionization observables.

Astrophysical magnetic fields decay primarily via two processes, namely ambipolar diffusion and turbulence. Constraints on the strength and the spectral index of nonhelical magnetic fields have been derived earlier in the literature through the effect of the above-mentioned processes on the cosmic microwave background (CMB) radiation. A helical component of the magnetic field is also produced in various models of magnetogenesis, which can explain larger coherence length magnetic field. In this study, we focus on studying the effects of post-recombination decay of maximally helical magnetic fields through ambipolar diffusion and decaying magnetic turbulence and the impact of this decay on CMB. We find that helical magnetic fields lead to changes in the evolution of baryon temperature and ionization fraction which in turn lead to modifications in the CMB temperature and polarization anisotropy. These modifications are different from those arising due to nonhelical magnetic fields with the changes dependent on the strength and the spectral index of the magnetic field power spectra.

We examine the Planck 2015 cosmic microwave background (CMB) anisotropy data by using a physically consistent energy density inhomogeneity power spectrum generated by quantum-mechanical fluctuations during an early epoch of inflation in the non-flat XCDM model. Here dark energy is parameterized using a fluid with a negative equation of state parameter but with the speed of fluid acoustic inhomogeneities set to the speed of light. We find that the Planck 2015 data in conjunction with baryon acoustic oscillation distance measurements are reasonably well fit by a closed-XCDM model in which spatial curvature contributes a percent of the current cosmological energy density budget. In this model, the measured non-relativistic matter density parameter and Hubble constant are in good agreement with values determined using most other data. Depending on cosmological parameter values, the closed-XCDM model has reduced power, relative to the tilted, spatially flat ΛCDM case, and can partially alleviate the low multipole CMB temperature anisotropy deficit and can help partially reconcile the CMB anisotropy and weak lensing σ 8 constraints, at the expense of somewhat worsening the fit to higher multipole CMB temperature anisotropy data. However, the closed-XCDM inflation model does not seem to improve the agreement much, if at all, compared to the closed ΛCDM inflation case, even though it has one additional free parameter.

A primordial magnetic field (PMF) would be expected to manifest itself in the cosmic microwave background (CMB) temperature and polarization anisotropies, and also in the formation of large scale structure(LSS). In this article, we demonstrate how the PMF is an important cosmological physical process on small scales as follows, We also report the newest constraints on the PMF amplitude Bλ and the power spectral index nB which have been deduced from the available CMB observational data by using our computational framework and the Markov chain Monte Carlo method. In particular we find that |Bλ|<2.10(68%CL) nG and < 2.98(95%CL) nG and nB<−1.19(68%CL) and <−0.25(95%CL) at a present scale of 1 Mpc.

Any neutral boson such as a dark photon or dark Higgs that is part of a non-standard sector of particles can mix with its standard model counterpart. When very weakly mixed with the Standard Model, these particles are produced in the early Universe via the freeze-in mechanism and subsequently decay back to standard model particles. In this work, we place constraints on such mediator decays by considering bounds from Big Bang nucleosynthesis and the cosmic microwave background radiation. We find both nucleosynthesis and CMB can constrain dark photons with a kinetic mixing parameter between log ϵ ∼ −10 to −17 for masses between 1 MeV and 100 GeV . Similarly, the dark Higgs mixing angle ϵ with the Standard Model Higgs is constrained between log ϵ ∼ −6 to −15. Dramatic improvement on the bounds from CMB spectral distortions can be achieved with proposed experiments such as PIXIE.

We use wavelet and curvelet transforms to extract signals of cosmic strings from simulated cosmic microwave background (CMB) temperature anisotropy maps, and to study the limits on the cosmic string tension which various ongoing CMB temperature anisotropy experiments will be able to achieve. We construct sky maps with size and angular resolution corresponding to various experiments. These maps contain the signals of a scaling solution of long string segments with a given string tension G μ, the contribution of the dominant Gaussian primordial cosmological fluctuations, and pixel by pixel white noise with an amplitude corresponding to the instrumental noise of the various experiments. In the case that we include white noise, we find that using curvelets we obtain lower bounds on the string tension than with wavelets. For maps with Planck specification, we obtain bounds comparable to what was obtained by the Planck collaboration [1]. Experiments with better angular resolution such as the South Pole Telescope third generation (SPT-3G) survey will be able to yield stronger limits. For maps with a specification of SPT-3G we find that string signals will be visible down to a string tension of G μ = 1.4 × 10−7.

New physics has traditionally been expected in the high-$p_T$ region at high-energy collider experiments. If new particles are light and weakly-coupled, however, this focus may be completely misguided: light particles are typically highly concentrated within a few mrad of the beam line, allowing sensitive searches with small detectors, and even extremely weakly-coupled particles may be produced in large numbers there. We propose a new experiment, ForwArd Search ExpeRiment, or FASER, which would be placed downstream of the ATLAS or CMS interaction point (IP) in the very forward region and operated concurrently there. Two representative on-axis locations are studied: a far location, $400~\text{m}$ from the IP and just off the beam tunnel, and a near location, just $150~\text{m}$ from the IP and right behind the TAN neutral particle absorber. For each location, we examine leading neutrino- and beam-induced backgrounds. As a concrete example of light, weakly-coupled particles, we consider dark photons produced through light meson decay and proton bremsstrahlung. We find that even a relatively small and inexpensive cylindrical detector, with a radius of $\sim 10~\text{cm}$ and length of $5-10~\text{m}$, depending on the location, can discover dark photons in a large and unprobed region of parameter space with dark photon mass $m_{A'} \sim 10~\text{MeV} - 1~\text{GeV}$ and kinetic mixing parameter $\epsilon \sim 10^{-7} - 10^{-3}$. FASER will clearly also be sensitive to many other forms of new physics. We conclude with a discussion of topics for further study that will be essential for understanding FASER's feasibility, optimizing its design, and realizing its discovery potential.

It is now well known that mode-coupling effects associated with certain secondary effects generate higher order correlations in cosmic microwave background (CMB) temperature anisotropies, beyond the two-point function. In order to extract such a non-Gaussian signal at the three-point level, we suggest a two-point statistic in the form of an angular power spectrum involving correlations between squared temperature and temperature anisotropies. This power spectrum contains compressed information from the bispectrum and can be easily measured in data with the same techniques that have been considered for the measurement of the usual temperature-temperature anisotropy power spectrum. We study the proposed power spectrum resulting from the non-Gaussian signal generated by correlations involved with gravitational lensing angular deflections in CMB and the Sunyaev-Zel’dovich (SZ) effect due to large scale pressure fluctuations. Using the Planck frequency cleaned CMB and SZ maps, the CMB2-SZ power spectrum provides a direct estimate of the cross-power between lensing angular deflections and the SZ effect. Through an optimal filter applied to the squared CMB map, the proposed statistic allows one to obtain all information from the lensing-SZ bispectrum. The observational measurement of the lensing-SZ cross-correlation is useful to understand the relation between large scale structure pressure and dark matter fluctuations.

Dark matter (DM) could be a pseudo-Dirac thermal relic with a small mass splitting that is coupled off diagonally to a kinetically mixed dark photon. This model, particularly in the sub-GeV mass range, is a key benchmark for accelerator searches and direct detection experiments. Typically, the presence of even a tiny fraction of pseudo-Dirac DM in the excited state around the time of recombination would be excluded by DM annihilation bounds from the cosmic microwave background (CMB); thus, viable thermal histories must typically feature an exponential suppression of the excited state. We revisit assumptions about the thermal history in the resonant regime, where the dark photon mass is slightly more than twice the DM mass (to within ∼10%), leading to an s-channel resonance in the annihilation cross section. This resonance substantially reduces the couplings required for achieving the observed relic abundance, implying that in much of the parameter space, the DM kinetically decouples from the Standard Model well before the final DM relic abundance is achieved. We find that the excited state is not thermally depopulated in this regime. In spite of this, we find that the presence of the excited state does violate CMB bounds, even for arbitrarily small mass splittings. The present-day abundance of the excited state opens up the possibility of signatures that are usually not relevant for pseudo-Dirac DM, including indirect detection, direct detection, and self-interacting DM signatures. Published by the American Physical Society 2024

In this note we investigate the effects of perturbations in a dark energy component with a constant equation of state on large scale cosmic microwave background anisotropies. The inclusion of perturbations increases the large scale power. We investigate more speculative dark energy models with w<-1 and find the opposite behaviour. Overall the inclusion of perturbations in the dark energy component increases the degeneracies. We generalise the parameterization of the dark energy fluctuations to allow for an arbitrary const ant sound speeds and show how constraints from cosmic microwave background experiments change if this is included. Combining cosmic microwave background with large scale structure, Hubble parameter and Supernovae observations we obtain w=-1.02+-0.16 (1 sigma) as a constraint on the equation of state, which is almost independent of the sound speed chosen. With the presented analysis we find no significant constraint on the constant speed of sound of the dark energy component.

The primordial B-modes component of the cosmic microwave background (CMB) polarization is a promising experimental dataset to probe the inflationary paradigm. B-modes are indeed a direct consequence of the presence of gravitational waves in the early universe. However, several secondary effects in the low redshift universe will produce \textit{non-primordial} B-modes. In particular, the gravitational interactions of CMB photons with large-scale structures will distort the primordial E-modes, adding a lensing B-mode component to the primordial signal. Removing the lensing component ("delensing") will then be necessary to constrain the amplitude of the primordial gravitational waves. Here we examine the role of current and future large-scale structure surveys in a multi-tracers approach to CMB delensing. We find that, in general, galaxy surveys should be split into tomographic bins as this can increase the reduction of lensing B-modes by $\sim 25\%$ in power in the most futuristic case. Ongoing or recently completed CMB experiments (CMB-S2) will particularly benefit from large-scale structure tracers that, once properly combined, will have a better performance than a CMB internal reconstruction. With the decrease of instrumental noise, the lensing B-modes power removed using CMB internal reconstruction alone will rapidly increase. Nevertheless, optical galaxy surveys will still play an important role even for CMB S4. In particular, an LSST-like survey can a achieve a delensing performance comparable to a 3G CMB experiment but with entirely different systematics. This redundancy will be essential to demonstrate the robustness against systematics of an eventual detection of primordial B-modes.