Cosmic Microwave Background Spectrum Research Articles

Indefinitely flat rotation curves from Mpc sized charged cocoons

Abstract Weak lensing exhibits that rotation curves of isolated galaxies remain flat up to Mpc scale (Mistele et al, 2024). Recently we proposed that dark matter is a combination of electrostatic and vacuum energy in standard physics. In this theory, isolated galaxies may be embedded in ``charged cocoons'', spheres with $\pm 1/r^2$ charge density. The related circular rotation curves decay at the Mpc scale. The analytic solution is extended to the early Universe. A peak in the cosmic microwave background spectrum is expected at the arcsec scale. The induced nanometer size of the cocoons at the Big Bang makes the initial state inhomogeneous.

Enhanced monochromatic photon emission from millicharged co-interacting dark matter

We study a millicharged co-interacting dark matter scenario, where the primary dark matter constituent is the dark photon A′ and the secondary component is the fermion χ. In this model, χ interacts with A′ via a U(1)′ interaction while being millicharged with respect to normal photons. Our investigation focuses on the oscillation of A′ dark matter into photons within the background of χ particles, revealing that the A′ − χ scattering rate benefits from a Bose enhancement of the A′ final state. As the oscillation production rate is directly linked to the scattering rate, the conversion of A′ dark matter into monochromatic photons experiences significant amplification owing to this Bose enhancement, especially when the scattering rate Γsca approaches the dark photon mass mA′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_{A^{\\prime }} $$\\end{document}. These converted monochromatic photons are detectable through radio telescopes and can induce distortions in the Cosmic Microwave Background (CMB) spectrum. We find that the sensitivity of radio telescopes and the constraints imposed by CMB distortion on the kinetic mixing parameter are notably heightened compared to scenarios without the subdominant millicharged dark matter.

Cutting corners: hypersphere sampling as a new standard for cosmological emulators

Cosmological emulators of observables such as the Cosmic Microwave Background (CMB) spectra and matter power spectra commonly use training data sampled from a Latin hypercube. This method often incurs high computational costs by covering less relevant parts of the parameter space, especially in high dimensions where only a small fraction of the parameter space yields a significant likelihood. In this paper, we make use of hypersphere sampling, which instead concentrates sample points in regions with higher likelihoods, significantly enhancing the efficiency and accuracy of emulators. A novel algorithm for sampling within a high-dimensional hyperellipsoid aligned with axes of correlation in the cosmological parameters is presented. This method focuses the distribution of training data points on areas of the parameter space that are most relevant to the models being tested, thereby avoiding the computational redundancies common in Latin hypercube approaches. Comparative analysis using the connect emulation tool demonstrates that hypersphere sampling can achieve similar or improved emulation precision with more than an order of magnitude fewer data points and thus less computational effort than traditional methods. This was tested for both the ΛCDM model and a 5-parameter extension including Early Dark Energy, massive neutrinos, and additional ultra-relativistic degrees of freedom. Our results suggest that hypersphere sampling holds potential as a more efficient approach for cosmological emulation, particularly suitable for complex, high-dimensional models.

A new solution for the observed isotropic cosmic birefringence angle and its implications for the anisotropic counterpart through a Boltzmann approach

Abstract Cosmic Birefringence (CB) is a phenomenon in which the polarization of the Cosmic Microwave Background (CMB) radiation is rotated as it travels through space due to the coupling between photons and an axion-like field. We look for a solution able to explain the result obtained from the Planck Public Release 4 (PR4), which has provided a hint of detection of the CB angle, α = (0.30 ± 0.11)∘. In addition to the solutions, already present in the literature, which need a non-negligible evolution in time of the axion-like field during recombination, we find a new region of the parameter space that allows for a nearly constant time evolution of such a field in the same epoch. The latter reinforces the possibility to employ the commonly used relations connecting the observed CMB spectra with the unrotated ones, through trigonometric functions of the CB angle. However, if the homogeneous axion field sourcing isotropic birefringence is almost constant in time during the matter-dominated era, this does not automatically imply that the same holds also for the associated inhomogeneous perturbations. For this reason, in this paper we present a fully generalized Boltzmann treatment of this phenomenon, that is able, for the first time to our knowledge to deal with the time evolution of anisotropic cosmic birefringence (ACB). We employ this approach to provide predictions of ACB, in particular for the set of best-fit parameters found in the new solution of the isotropic case. If the latter is the correct model, we expect an ACB spectrum of the order of (10-15 ÷ 10-32) deg2 for the auto-correlation, and (10-7 ÷ 10-17) μK·deg for the cross-correlations with the CMB T and E fields, depending on the angular scale.

GeV-scale dark matter with p -wave Breit-Wigner enhanced annihilation

We consider a light scalar dark matter candidate with mass in the GeV range whose p-wave annihilation is enhanced through a Breit-Wigner resonance. The annihilation actually proceeds in the s-channel via a dark photon mediator whose mass is nearly equal to the masses of the incoming particles. We compute the temperature at which kinetic decoupling between dark matter and the primordial plasma occurs and show that including the effect of kinetic decoupling can reduce the dark matter relic density by orders of magnitude. For typical scalar masses ranging from 200 MeV to 5 GeV, we determine the range of values allowed for the dark photon couplings to the scalar and to the standard model particles after requiring the relic density to be in agreement with the value extracted from cosmological observations. We then show that μ and y-distortions of the cosmic microwave background spectrum and x-ray data from XMM-Newton strongly constrain the model and rule out the region where the dark matter annihilation cross section is strongly enhanced at small dispersion velocities. Constraints from direct detection searches and from accelerator searches for dark photons offer complementary probes of the model. Published by the American Physical Society 2024

CMB spectrum in unified EFT of dark energy: scalar-tensor and vector-tensor theories

We study the cosmic microwave background (CMB) radiation in the unified description of the effective field theory (EFT) of dark energy that accommodates both scalar-tensor and vector-tensor theories. The boundaries of different classes of theories are universally parameterised by a new EFT parameter αV characterising the vectorial nature of dark energy and a set of consistency relations associated with the global/local shift symmetry. After implementing the equations of motion in a Boltzmann code, as a demonstration, we compute the CMB power spectrum based on the wCDM background with the EFT parameterisation of perturbations and a concrete Horndeski/generalised Proca theory. We show that the vectorial nature generically prevents modifications of gravity in the CMB spectrum. On the other hand, while the shift symmetry is less significant in the perturbation equations unless the background is close to the ΛCDM, it requires that the effective equation of state of dark energy is in the phantom region w DE<-1. The latter is particularly interesting in light of the latest result of the DESI+CMB combination as the observational verification of w DE>-1 can rule out shift-symmetric theories including vector-tensor theories in one shot.

Antenna Design for Absolute Sky Measurements at Gigahertz Frequencies—a First Step toward Detecting CMB Spectral Distortions from Recombination

There exist inevitable deviations in the cosmic microwave background spectrum from that of a blackbody. The additive distortions from photons emitted over the epoch of recombination are one such deviation. We present a novel scalable broadband antenna design motivated by detecting these spectral distortions in the 2.5–4 GHz band. This antenna is capable of maintaining the spectral quality of the measured sky spectrum to 1 part in 103 over the full band and outperforms conventional broadband antennas by at least an order of magnitude. While this is not sufficient to make a direct detection of the cosmological recombination radiation, it meets the baseline design criteria for an experiment that can make an absolute measurement of the sky spectrum at the millikelvin level, thereby making it capable of improving foreground models to global signal detection experiments (including those from cosmic dawn and the epoch of reionization) and addressing the problem of the excess radio background at 3.3 GHz reported by the ARCADE2 experiment.

Analysis of the Composition and Characteristics of Dark Matter

Today, astronomers use different methods to study the structure and evolution of the universe. However, they will all be affected by other factors such as light or electromagnetic radiation. It is impossible to accurately observe the structure of the universe in the distant past. To find objects that fit the criteria, the existence of dark matter was assumed. It only has a gravitational effect and will be less affected. The composition and characteristics of dark matter are important research foundations. In this paper, the Cosmic Microwave Background (CMB) and power spectrum are used to study the status of dark matter in the universe. The search found Weakly Interacting Massive Particles (WIMPs) to be a candidate in the dark matter component. The three types of dark matter are cold dark matter, warm dark matter, and hot dark matter. Comparing their respective characteristics, it is concluded that cold dark matter (CDM) is the condition for observing large-scale structures. The result is that dark matter constitutes the second largest component of the universe. WIMPs are more suitable candidates than Neutrinos. CDM is best suited for studying large-scale structures over time. Eventually, it will be discovered that dark matter has strong stability, which will help astronomers find the process of universe evolution. Dark matter is also an important player that is best used to study the structure and evolution of the universe.

Integrating Cosmic Microwave Background Readings with Celestial Navigation to Enhance Deep Space Navigation.

This research unveils a cutting-edge navigation system for deep space missions that utilizes cosmic microwave background (CMB) sensor readings to enhance spacecraft positioning and velocity estimation accuracy significantly. By exploiting the Doppler-shifted CMB spectrum and integrating it with optical measurements for celestial navigation, this approach employs advanced data processing through the Unscented Kalman Filter (UKF), enabling precise navigation amid the complexities of space travel. The simulation results confirm the system's exceptional precision and resilience in deep space missions, marking a significant advancement in astronautics and paving the way for future space exploration endeavors.

Angular correlations of cosmic microwave background spectrum distortions from photon diffusion

ABSTRACT During cosmic recombination, charged particles bind into neutral atoms and the mean free path of photons rapidly increases, resulting in the familiar diffusion damping of primordial radiation temperature variations. An additional effect is a small photon spectrum distortion, because photons arriving from a particular sky direction were originally in thermal equilibrium at various spatial locations with different temperatures; the combination of these different blackbody temperature distributions results in a spectrum with a Compton y-distortion. Using the approximation that photons had zero mean free path prior to their second-to-last scattering, we derive an expression for the resulting y-distortion, and compute the angular correlation function of the diffusion y-distortion and its cross-correlation with the square of the photon temperature fluctuation. Detection of the cross-correlation is within reach of existing arcminute-resolution microwave background experiments such as the Atacama Cosmology Telescope and the South Pole Telescope.

Minkowski Functionals in 𝖲𝖮(3) for the spin-2 CMB polarisation field

The study of the angular power spectrum of Cosmic Microwave Background (CMB) anisotropies, both in intensity and in polarisation, has led to the tightest constraints on cosmological parameters. However, this statistical quantity is not sensitive to any deviation from Gaussianity and statistical isotropy in the CMB data. Minkowski Functionals (MFs) have been adopted as one of the most powerful statistical tools to study such deviations, since they characterise the topology and geometry of the field of interest. In this paper, we extend the application of MFs to CMB polarisation data by introducing a new formalism, where we lift the spin 2 polarisation field to a scalar function in a higher-dimensional manifold: the group of rotations of the sphere, SO(3). Such a function is defined as f = Q cos(2ζ) - U sin(2ζ). We analytically obtain the expected values for the MFs of f in the case of Gaussian isotropic polarisation maps. Furthermore, we present a new pipeline which estimates these MFs from input HEALPix polarisation maps. We apply it to CMB simulations in order to validate the theoretical results and the methodology. The pipeline is to be included in the publicly available Python package Pynkowski .

Warm Dark matter constraints from the joint analysis of CMB, Ly α, and global 21 cm data

ABSTRACT With the help of our previously built MCMC (Markov chain Monte Carlo)-based parameter estimation package cosmoreionmc, we investigate in detail the potential of 21 cm global signal, when combined with cosmic microwave background (CMB) and observations related to the Quasar (QSO) absorption spectra, to constraint the mass of warm dark matter (WDM) particle. For the first time, we simultaneously vary all the free parameters (mass of WDM particle, cosmological parameters, and astrophysical parameters) in a joint analysis with CMB, observations related to the QSO absorption spectra and 21 cm global signal, to address the long-overlooked issue of the possible degeneracies between the dark matter particle mass mX and cosmological/astrophysical parameters. From the existing CMB and QSO absorption spectra data, we can rule out mX &amp;lt; 2.8 keV at 95 per cent confidence level. Including a mock 21 cm global signal in the redshift range z = 25−5 expected to be observed with upcoming instruments designed for global signal, the forecasted constraint is found to be much tighter mX &amp;gt; 7.7 keV, assuming that the true dark matter model is the usual cold dark matter. In case the mock 21 cm signal is constructed for dark matter particles having mX = 7 keV, our forecasts indicate that (mX/keV)−1 is in the range [0.1, 0.2] (95 per cent confidence level). This implies that the future 21 cm data should allow detection of the WDM particle mass if mX ∼ 7 keV.

Ruling out strongly interacting dark matter–dark radiation models from joint observations of cosmic microwave background and quasar absorption spectra

ABSTRACT The cold dark matter paradigm provides a remarkably good description of the Universe’s large-scale structure. However, some discrepancies exist between its predictions and observations at very small sub-galactic scales. To address these issues, the consideration of a strong interaction between dark matter particles and dark radiation emerges as an intriguing alternative. In this study, we explore the constraints on those models using joint observations of cosmic microwave background and quasars absorption spectra with our previously built parameter estimation package cosmoreionmc. At 2σ confidence limits, this analysis rules out the strongly interacting dark matter–dark radiation models within the recently proposed effective theory of structure formation framework, representing the most stringent constraint on those models to the best of our knowledge. Future research using a 21-cm experiment holds the potential to reveal stronger constraints or uncover hidden interactions within the dark sector.

(Slow-)twisting inflationary attractors

We explore in detail the dynamics of multi-field inflationary models. We first revisit the two-field case and rederive the coordinate independent expression for the attractor solution with either small or large turn rate, emphasizing the role of isometries for the existence of rapid-turn solutions.Then, for three fields in the slow-twist regime we provide elegant expressions for the attractor solution for generic field-space geometries and potentials and study the behaviour of first order perturbations. For generic 𝒩-field models, our method quickly grows in algebraic complexity. We observe that field-space isometries are common in the literature and are able to obtain the attractor solutions and deduce stability for some isometry classes of 𝒩-field models. Finally, we apply our discussion to concrete supergravity models. These analyses conclusively demonstrate the existence of 𝒩 > 2 dynamical attractors distinct from the two-field case, and provide tools useful for future studies of their phenomenology in the cosmic microwave background and stochastic gravitational wave spectrum.

Back to the features: assessing the discriminating power of future CMB missions on inflationary models

Future Cosmic Microwave Background (CMB) experiments will deliver extremely accurate measurements of the E-modes pattern of the CMB polarization field. Given the sharpness of the E-modes transfer functions, such surveys make for a powerful detector of high-frequency signals from primordial features that may be lurking in current data sets. With a handful of toy models that increase the fit to the latest Planck data, but are of marginal statistical significance, we use a state-of-the-art forecast pipeline to illustrate the promising prospects to test primordial features in the next decade. Not only will future experiments allow us to detect such features in data, but they will also be able to discriminate between models and narrow down the physical mechanism originating them with high statistical significance. On the other hand, if the anomalies in the currently measured CMB spectra are just statistical fluctuations, all the current feature best fit candidates will be ruled out. Either way, our results show that primordial features are a clear target of forthcoming CMB surveys beyond the detection of tensor modes.

One μ to rule them all: CMB spectral distortions can probe domain walls, cosmic strings and low scale phase transitions

We present a new probe of purely gravitationally coupled sectors with large anisotropies. These anisotropies are damped via gravitational interactions with the baryon-photon fluid, which is heated up in the process. The injected heat causes measurable distortions of the cosmic microwave background spectrum. We give analytic estimates for the size of the distortions and outline how to calculate them from first principles. These methods are applied to anisotropies in the form of a domain wall/cosmic string network or caused by a first order phase transition or scalar field dynamics. We find that this method can potentially probe large regions of previously unconstrained parameter space and is very much complementary to up-coming searches of gravitational waves caused by such dark sectors.

Constraining First-Order Phase Transitions with Curvature Perturbations.

The randomness of the quantum tunneling process induces superhorizon curvature perturbations during cosmological first-order phase transitions. We for the first time utilize curvature perturbations to constrain the phase transition parameters, and find that the observations of the cosmic microwave background spectrum distortion and the ultracompact minihalo abundance can give strict constraints on the phase transitions below 100GeV, especially for the low-scale phase transitions and some electroweak phase transitions. The current constraints on the phase transition parameters are largely extended by the results of this work, therefore provide an novel approach to probe related new physics.

Level correlations of CMB temperature angular power spectrum

If the principle of statistical isotropy is valid, then the angular power spectrum (APS) of cosmic microwave background (CMB) radiation is uncorrelated between different multipoles. We propose a novel technique to analyse any possible correlations of the foreground-cleaned CMB temperature APS measures (\(C_{\ell }\) and \({\mathcal {D}}_\ell =({\ell (\ell +1)})/({2\pi })C_\ell \)). This is motivated by the behaviour of level spacings between random matrix eigenvalues. This method helps to distinguish uncorrelated statistically isotropic CMB APS from correlated APS, where the latter can arise due to breakdown of isotropy or presence of some residual systematics in the foreground cleaned CMB maps. Spacings of statistically isotropic CMB \(C_\ell \)’s and \({\mathcal {D}}_\ell \)’s are seen to closely obey Poisson statistics and introduction of correlations, changes the distribution to appropriate Wigner–Dyson statistics. For foreground-cleaned CMB, we employ the average spacing of consecutive multipole APS for multipoles \(\in [2,31]\). This estimator is sensitive to departures from the null hypothesis of zero correlations between the APS measures of statistically isotropic CMB. We study full sky WMAP 9-year ILC and 2018 Planck foreground-cleaned maps (Commander, NILC and SMICA). Sans parity distinctions, average spacings are in good agreement with theoretical expectation. With parity distinctions, even multipoles indicate unusually low average spacings for both \(C_\ell \)’s (at \(\ge \)98.86% C.L.) and \({\mathcal {D}}_\ell \)’s (at \({\ge }\)95.07% C.L.). We use an inpainting method based on constrained Gaussian realisations and show that for the Planck U73 and WMAP KQ75 masks, all the foreground-cleaned inpainted CMB maps robustly confirm the existence of such unusually low average spacings of even multipole APS. In addition, this signal is independent of the non-Gaussian cold spot.

Is there a Radio Excess from the Decoupling of Pre-recombination Bremsstrahlung?

Recently it has been suggested that thermal bremsstrahlung emission, when it decouples prior to recombination, creates an excess over the Planck cosmic microwave background spectrum at sub-GHz frequencies. Remarkable by itself, this would also explain a long-standing unexplained deficit in the predictions of the extragalactic radio background. In this brief note, I reiterate that no such non-thermal component can arise by itself when matter and radiation remain kinetically coupled.

Primordial non-gaussianities of inflationary step-like models

We use Minkowski Functionals (MF) to explore the possible presence of non-Gaussian signatures in the recently released cosmic microwave background (CMB) Planck maps. In particular, we investigate MF outcomes for two sets of simulated CMB maps: one seeded by the ΛCDM concordance model, another seeded by the ‘best-fit’ CMB angular power spectrum. By ‘best-fit’ we mean a simulated CMB spectrum seeded by an inflationary model that well reproduce the observed low-ℓ features of the CMB temperature power spectrum. In this way, we obtain the spurious signal introduced by the power spectra with different shapes, signal to be taken into account in the corresponding MF analyses. Interestingly, we investigate the response of the four MF (i.e., Area, Perimeter, Genus, Nclusters ) for several sets of simulated maps. Our analyses confirm that, as already reported in the literature, the Perimeter exhibits the best performance. Moreover, our results show that the Perimeter obtained from the Planck maps (2015) is better fitted by the simulated CMB maps seeded by the angular power spectrum with low-ℓ features with respect to the curves obtained from the CMB maps seeded by the ΛCDM model.