Microwave Background Research Articles

Quantum Entanglement Asymmetry and the Cosmic Matter–Antimatter Imbalance: A Theoretical and Observational Analysis

We propose a distinct mechanism to explain the matter–antimatter imbalance observed in the universe, rooted in quantum entanglement asymmetry (QEA). Our concept of QEA differs from its usage in the recent literature, where it typically measures how much symmetry is broken within a subsystem of a larger quantum system. Here, we define QEA as an intrinsic asymmetry in the entanglement properties of particle–antiparticle pairs in the early universe, leading to a preferential survival of matter over antimatter. We develop a theoretical framework incorporating QEA into the standard cosmological model, providing clear justification for the asymmetry in entangled states and corresponding modifications to the Hamiltonian. Numerical simulations using lattice Quantum Chromodynamics (QCD) demonstrate that QEA can produce a net baryon asymmetry consistent with observations. We also predict specific signatures in Cosmic Microwave Background (CMB) anisotropies and large-scale structure formation, offering potential avenues for empirical verification. This work aims to deepen the understanding of cosmological asymmetries and highlight the significance of quantum entanglement in the universe’s evolution.

5σ tension between Planck cosmic microwave background and eBOSS Lyman-alpha forest and constraints on physics beyond ΛCDM

We find that combined cosmic microwave background, baryon acoustic oscillations, and supernovae data analyzed under Λ cold dark matter (ΛCDM) are in 4.9σ tension with the extended Baryon Oscillation Spectroscopic Survey (eBOSS) Lyα forest in inference of the linear matter power spectrum at wave number ∼1hMpc−1 and redshift = 3. Model extensions can alleviate this tension: running in the tilt of the primordial power spectrum (αs∼−0.01); a fraction ∼(1−5)% of ultralight axion dark matter (DM) with particle mass ∼10−25 eV or warm DM with mass ∼10 eV. The new Dark Energy Spectroscopic Instrument survey, coupled with high-accuracy modeling, will help distinguish the source of this discrepancy. Published by the American Physical Society 2025

Forecasts of effects of beam systematics and deprojection on the third-generation ground-based cosmic microwave background experiment

Forecasts of effects of beam systematics and deprojection on the third-generation ground-based cosmic microwave background experiment

Variation of the low-mass end of the stellar initial mass function with redshift and metallicity

Abstract We report the stellar mass functions obtained from 20 radiation hydrodynamical simulations of star cluster formation in 500 M⊙ molecular clouds with metallicities of 3, 1, 1/10 and 1/100 of the solar value, with the clouds subjected to levels of the cosmic microwave background radiation that are appropriate for star formation at redshifts z = 0, 3, 5, 7, and 10. The calculations include a thermochemical model of the diffuse interstellar medium and treat dust and gas temperatures separately. We find that the stellar mass distributions obtained become increasingly bottom light as the redshift and/or metallicity are increased. Mass functions that are similar to a typical Galactic initial mass function are obtained for present-day star formation (z = 0) independent of metallicity, and also for the lowest-metallicity (1/100 solar) at all redshifts up to z = 10, but for higher metallicities there is a larger deficit of brown dwarfs and low-mass stars as the metallicity and redshift are increased. These effects are a result of metal-rich gas being unable to cool to as lower temperatures at higher redshift due to the warmer cosmic microwave background radiation. Based on the numerical results we provide a parameterisation that may be used to vary the stellar initial mass function with redshift and metallicity; this could be used in simulations of galaxy formation. For example, a bottom-light mass function reduces the mass-to-light ratio compared to a typical Galactic stellar initial mass function, which may reduce the estimated masses of high-redshift galaxies.

Dark matter-radiation scattering enhances CMB phase shift through dark matter-loading

A phase shift in the acoustic oscillations of cosmic microwave background (CMB) spectra is a characteristic signature for the presence of non-photon radiation propagating differently from photons, even when the radiation couples to the Standard Model particles solely gravitationally. It is well-established that compared to the presence of free-streaming radiation, CMB spectra shift to higher ℓ-modes in the presence of self-interacting non-photon radiation such as neutrinos and dark radiation. In this study, we further demonstrate that the scattering of non-photon radiation with dark matter can further amplify this phase shift. We show that when the energy density of the interacting radiation surpasses that of interacting dark matter around matter-radiation equality, the phase shift enhancement is proportional to the interacting dark matter abundance and remains insensitive to the radiation energy density. Given the presence of dark matter-radiation interaction, this additional phase shift emerges as a generic signature of models featuring an interacting dark sector or neutrino-dark matter scattering. Using neutrino-dark matter scattering as an example, we numerically calculate the amplified phase shift and offer an analytical interpretation of the result by modeling photon and neutrino perturbations with coupled harmonic oscillators. This framework also explains the phase shift contrast between self-interacting and free-streaming neutrinos. Fitting models with neutrino-dark matter or dark radiation-dark matter interactions to CMB and large-scale structure data, we validate the presence of the enhanced phase shift, affirmed by the linear dependence observed between the preferred regions of the sound horizon angle θ s and interacting dark matter abundance. An increased θ s and a suppressed matter power spectrum is therefore a generic feature of models containing dark matter scattering with abundant dark radiation.

Constraining primordial non-Gaussianity with Density-Split Clustering

Obtaining tight constraints on primordial non-Gaussianity (PNG) is a key step in discriminating between different models for cosmic inflation. The constraining power from large-scale structure (LSS) measurements is expected to overtake that from cosmic microwave background (CMB) anisotropies with the next generation of galaxy surveys including the Dark Energy Spectroscopic Instrument (DESI) and Euclid. We consider whether Density-Split Clustering (DSC) can help improve PNG constraints from these surveys for local, equilateral and orthogonal types. DSC separates a surveyed volume into regions based on local density and measures the clustering statistics within each environment. Using the Quijote simulations and the Fisher information formalism, we compare PNG constraints from the standard halo power spectrum, DSC power spectra and joint halo/DSC power spectra. We find that the joint halo/DSC power spectra outperform the halo power spectrum by factors of ∼ 1.4, 8.8, and 3.6 for local, equilateral and orthogonal PNG, respectively. This is driven by the higher-order information that DSC captures on small scales. We find that applying DSC to a halo field does not allow sample variance cancellation on large scales by providing multiple tracers of the same volume with different local PNG responses. Additionally, we introduce a Fourier space analysis for DSC and study the impact of several modifications to the pipeline, such as varying the smoothing radius and the number of density environments and replacing random query positions with lattice points.

Chasing cosmic inflation: constraints for inflationary models and reheating insights

We investigate the impact of different choice of prior's range for the reheating epoch on cosmic inflation parameter inferencein light of cosmic microwave background (CMB) anisotropy measurements from the Planck 2018 legacy releasein combination with BICEP/Keck Array 2018 data and additional late-time cosmological observations such as uncalibratedType Ia supernovae from the Pantheon catalogue, baryon acoustic oscillations and redshift space distortionsfrom SDSS/BOSS/eBOSS.Here, we explore in particular the implications for the combination of reheating and inflationary-model parameter spaceconsidering R+R 2 inflation and a broad class of α-attractor and D-brane models.Propagating the uncertainties due to an unknown reheating phase, these inflationary models completely cover the n s-r parameter space allowed by Planck and BICEP/Keck dataand represent good targets for future CMB and large-scale structure experiments.We perform a Bayesian model comparison of inflationary models, taking into account the reheating uncertaintiesassuming a conservative but accurate modelling of inflationary predictions.R+R 2 inflation, T-model α-attractor inflation for n=1, E-model α-attractor inflation for n=1/2,and KKLT inflation for p=5 are the better performing models, with none being preferred at a statistically significant level.

Euclid preparation

The Euclid mission of the European Space Agency will provide weak gravitational lensing and galaxy clustering surveys that can be used to constrain the standard cosmological model and its extensions, with an opportunity to test the properties of dark matter beyond the minimal cold dark matter paradigm. We present forecasts from the combination of the Euclid weak lensing and photometric galaxy clustering data on the parameters describing four interesting and representative non-minimal dark matter models: a mixture of cold and warm dark matter relics; unstable dark matter decaying either into massless or massive relics; and dark matter undergoing feeble interactions with relativistic relics. We modelled these scenarios at the level of the non-linear matter power spectrum using emulators trained on dedicated N-body simulations. We used a mock Euclid likelihood and Monte Carlo Markov chains to fit mock data and infer error bars on dark matter parameters marginalised over other parameters. We find that the Euclid photometric probe (alone or in combination with cosmic microwave background data from the Planck satellite) will be sensitive to the effect of each of the four dark matter models considered here. The improvement will be particularly spectacular for decaying and interacting dark matter models. With Euclid, the bounds on some dark matter parameters can improve by up to two orders of magnitude compared to current limits. We discuss the dependence of predicted uncertainties on different assumptions: the inclusion of photometric galaxy clustering data, the minimum angular scale taken into account, and modelling of baryonic feedback effects. We conclude that the Euclid mission will be able to measure quantities related to the dark sector of particle physics with unprecedented sensitivity. This will provide important information for model building in high-energy physics. Any hint of a deviation from the minimal cold dark matter paradigm would have profound implications for cosmology and particle physics.

New shape for cross-bispectra in Chern-Simons gravity

Chern-Simons gravity is known to suffer from graviton ghost production during inflation, which suppresses the parity-violating power spectrum at scales relevant to cosmic microwave background observations. In this work, we show that allowing the initial conditions of inflation to deviate from the standard Bunch-Davies state can enhance parity-violating non-Gaussianity in the scalar-tensor cross-bispectra. Our results reveal a significant additional contribution to the cross-bispectra in the flattened configuration, offering a new avenue to constrain parity-violating gravity.

Prospects for cosmological research with the FAST array: 21-cm intensity mapping survey observation strategies

Precise cosmological measurements are essential for understanding the evolution of the universe and the nature of dark energy. The Five-hundred-meter Aperture Spherical Telescope (FAST), the most sensitive single-dish radio telescope, has the potential to provide the precise cosmological measurements through neutral hydrogen 21 cm intensity mapping sky survey. This paper primarily explores the potential of technological upgrades for FAST in cosmology. The most crucial upgrade begins with equipping FAST with a wide-band receiver (0 < z < 2.5). This upgrade can enable FAST to achieve higher precision in cosmological parameter estimation than the Square Kilometre Array Phase 1 Mid-Frequency Array. On this basis, expanding to a FAST array (FASTA) consisting of six identical FASTs would offer significant improvements in precision compared to FAST. Additionally, compared with the current results from the data combination of cosmic microwave background, baryon acoustic oscillations (optical galaxy surveys), and type Ia supernovae, FASTA can provide comparable constraints. Specifically, for the dark-energy equation-of-state parameters, FASTA can achieve σ(w 0) = 0.09 and σ(wa ) = 0.33.

Enhancing primordial B-mode detection: comprehensive delensing pipelines for improved sensitivity to r

Recognizing the impact of contamination from weak gravitational lensing B-modes induced by Large Scale Structure, we examine delensing methods to enhance sensitivity to the tensor-to-scalar ratio r in primordial B-mode detection experiments. This study presents a realistic pipeline to improve r constraints using foreground-cleaned maps with negligible residuals. The pipeline, based on simulations, is adaptable for future experiments. We focus on two delensing approaches: (1) subtracting the gradient-order lensing B-mode template, computed by convolving the E-mode with the lensing potential, from the observed B-mode signal; and (2) remapping observations using the estimated inverse deflection angle. For parameter constraints, we employ three models to reduce r uncertainty and bias, finding consistent uncertainties across models, though biases vary due to the multipole-dependence of the delensing fraction. We demonstrated this pipeline using simulated observation maps from future CMB polarization experiments, which included current representative ground-based small aperture telescopes (sub-1m), next-generation ground-based large aperture telescopes (6m), and highly competitive future space-based medium aperture missions (3m). Results show a delensing efficiency of 40% with the small-aperture telescope alone, increasing to 65% when combined with the large-aperture telescope, and 80% with the satellite mission. These lead to reductions in r uncertainty by 46% for ground-based and 63% for space missions. The most promising method adds the lensing template B-mode as an additional frequency channel, minimizing bias on r.

CMB Polarization as a Probe for Inflationary Cosmology

This paper discusses some information about the cosmic microwave background radiation (CMB)’s polarization and the study of the early state of the universe. The early state of the universe. The heat emitted after the Big Bang is called the CMB, and the CMB polarization carries important information about the shape and structure of the early universe and is an important means to study the state of the early universe. This paper first introduces the background knowledge of CMB, and then discusses the theoretical framework of inflation theory, including some important concepts and different models of inflation theory, specific CMB polarization modes, and some specific techniques for analyzing CMB polarization data. Next, the paper discusses the observational evidence for the CMB, including important experiments such as WMAP, Planck, and BICEP, and their support for inflation theory. The paper also introduces the data analysis method of CMB polarization.

Back to the phase space: Thermal axion dark radiation via couplings to standard model fermions

We investigate the cosmological consequences of axion interactions with standard model fermions accurately and precisely. Our analysis is entirely based on a phase space framework that allows us to keep track of the axion distribution in momentum space across the entire expansion history. First, we consider flavor-diagonal couplings to charged leptons and quantify the expected amount of dark radiation as a function of the coupling strength. Leptophilic axions are immune from complications due to strong interactions and our predictions do not suffer from theoretical uncertainties. We then focus on flavor-diagonal interactions with the three heavier quarks whose masses are all above the scale where strong interactions become nonperturbative. The top quark case is rather safe because its mass is orders of magnitude above the confinement scale, and the consequent predictions are solid. The bottom and charm masses are in more dangerous territory because they are very close to the QCD crossover. We present a comprehensive discussion of theoretical uncertainties due to both the choice of the scale where we stop the Boltzmann evolution and the running of QCD parameters. Finally, we compute the predicted amount of dark radiation expressed as an effective number of additional neutrino species. We compare our predictions with the ones obtained via standard approximate procedures, and we find that adopting a rigorous phase space framework alters the prediction by an amount larger than the sensitivity of future cosmic microwave background observatories. Published by the American Physical Society 2024

Cosmic multipoles in galaxy surveys – I. How inferences depend on source counts and masks

ABSTRACT We present a new approach to constructing and fitting dipoles and higher-order multipoles in synthetic galaxy samples over the sky. Within our Bayesian paradigm, we illustrate that this technique is robust to masked skies, allowing us to make credible inferences about the relative contributions of each multipole. We also show that dipoles can be recovered in surveys with small footprints, determining the requisite source counts required for concrete estimation of the dipole parameters. This work is motivated by recent probes of the cosmic dipole in galaxy catalogues. Namely, the kinematic dipole of the cosmic microwave background, as arising from the motion of our heliocentric frame at $\approx 370\ \text{km}\, \text{s}^{-1}$, implies that an analogous dipole should be observed in the number counts of galaxies in flux-density-limited samples. Recent studies have reported a dipole aligning with the kinematic dipole but with an anomalously large amplitude. Accordingly, our new technique will be important as forthcoming galaxy surveys are made available and for revisiting previous data.

Constraining dark energy with the integrated Sachs-Wolfe effect

We use the integrated Sachs-Wolfe (ISW) effect, by now detectable at ∼5σ within the context of Λ cold dark matter (ΛCDM) cosmologies, to place strong constraints on dynamical dark energy theories. Working within an effective field theory (EFT) framework for dark energy we find that including ISW constraints from galaxy–cosmic microwave background (CMB) cross-correlations significantly strengthens existing large-scale structure constraints, yielding bounds consistent with ΛCDM and approximately reducing the viable parameter space by ∼70%. This is a direct consequence of O(1) changes induced in these cross-correlations by otherwise viable dark energy models, which we discuss in detail. We compute constraints by adapting the ΛCDM ISW likelihood from Stölzner [] for dynamical dark energy models using galaxy data from 2 MASS, wide-field infrared survey explorer (WISE) × SuperCOSMOS, Sloan Digital Sky Survey Data Release 12, the catalog of photometric quasars and NRAO Very Large Array Sky Survey, CMB data from Planck 18, and baryon acoustic oscillation and redshift space distortion large-scale structure measurements from BOSS and 6dF. We show constraints both in terms of EFT-inspired αi and phenomenological μ/Σ parametrizations. Furthermore we discuss the approximations involved and related aspects of bias modeling in detail and highlight what these constraints imply for the underlying dark energy theories. Published by the American Physical Society 2024

QCD axion: Some like it hot

We compare the quantum chromodynamics (QCD) axion phase-space distribution from unitarized next-to-leading order chiral perturbation theory with the one extracted from pion-scattering data. We derive a robust bound by confronting momentum-dependent Boltzmann equations against up-to-date observations of the cosmic microwave background, of the baryonic acoustic oscillations and of primordial abundances. These datasets imply ma≤0.16 eV for the 95% credible interval, i.e., ∼30% stronger bound than what previously found. We present forecasts using dedicated likelihoods for future cosmological surveys and the sphaleron rate from unquenched lattice QCD. Published by the American Physical Society 2024

Lepton Asymmetries in Cosmology

The cosmological lepton asymmetry, i.e., an excess of leptons over antileptons, is still only loosely constrained, and might be much larger than its tiny baryonic counterpart. If this is the case, charge neutrality requires the lepton asymmetries to be confined in the neutrino sector. We recall the observational effects of neutrino asymmetries on the abundance of light elements produced during Big Bang Nucleosynthesis and on the pattern of cosmic microwave background anisotropies. We point to the necessity of solving the neutrino transport equations, taking into account the effect of flavour oscillation, to derive general and robust constraints on lepton asymmetries. We review the current bounds and briefly discuss prospects for next-generation CMB experiments.

Cogenesis of baryon and dark matter with PBHs and the QCD axion

With entropy injection, an early matter-dominated epoch (EMD) impels the axion decay constant fa toward larger values to produce correct axion dark matter (DM) abundance, thereby unfolding the low-mass axion (ma≲10−5 eV) parameter space to be searched for in axion experiments. We implement this proposition in a scenario where fa and the leptogenesis scale in a seesaw mechanism are equivalent. We show that if, instead, the EMD is provided by evaporating ultralight primordial black holes (PBHs), the scenario becomes strikingly testable with gravitational wave (GW) background alongside the axion searches. In particular, while being consistent with correct axion DM abundance, the scale fa≳1012 GeV, corresponding to the unflavored regime of leptogenesis with hierarchical right-handed neutrinos, can be probed with GW and axion experiments, which is otherwise not testable at neutrino or collider experiments. Additionally, axions produced from PBH evaporation can give rise to dark radiation within reach of future cosmic microwave background experiments. Published by the American Physical Society 2024

Reconciling S8: insights from interacting dark sectors

ABSTRACT We do a careful investigation of the prospects of dark energy (DE) interacting with cold dark matter in alleviating the $S_8$ clustering tension. To this end, we consider various well-known parametrizations of the DE equation of state (EoS) and consider perturbations in both the dark sectors, along with an interaction term. Moreover, we perform a separate study for the phantom and non-phantom regimes. Using cosmic microwave background (CMB), baryon acoustic oscillations, and Type Ia supernovae data sets, constraints on the model parameters for each case have been obtained and a generic reduction in the $H_0 \!\!-\!\! \sigma _{8,0}$ correlation has been observed, both for constant and dynamical DE EoS. This reduction, coupled with a significant negative correlation between the interaction term and $\sigma _{8,0}$, contributes to easing the clustering tension by lowering $\sigma _{8,0}$ to somewhere in between the early CMB and late-time clustering measurements for the phantom regime, for almost all the models under consideration. Additionally, this is achieved without exacerbating the Hubble tension. In this regard, the interacting Chevallier–Polarski–Linder and Jassal–Bagla–Padmanabhan models perform the best in relaxing the $S_8$ tension to $&amp;lt;\!\! 1\sigma$. However, for the non-phantom regime the $\sigma _{8,0}$ tension tends to have worsened, which reassures the merits of phantom DE from latest data. We further investigate the role of redshift space distortion data sets and find an overall reduction in tension, with a $\sigma _{8,0}$ value relatively closer to the CMB value. We finally check whether further extensions of this scenario, such as the inclusion of the sound speed of DE and warm dark matter interacting with DE, can have some effects.

Fast Solution of Sylvester‐Structured Systems for Spatial Source Separation of the Cosmic Microwave Background

ABSTRACTImplementation of many statistical methods for large, multivariate data sets requires one to solve a linear system that, depending on the method, is of the dimension of the number of observations or each individual data vector. This is often the limiting factor in scaling the method with data size and complexity. In this paper, we illustrate the use of Krylov subspace methods to address this issue in a statistical solution to a source separation problem in cosmology where the data size is prohibitively large for direct solution of the required system. Two distinct approaches, adapted from techniques in the literature, are described: one that uses the method of conjugate gradients directly to the Kronecker‐structured problem and another that reformulates the system as a Sylvester matrix equation. We show that both approaches produce an accurate solution within an acceptable computation time and with practical memory requirements for the data size that is currently available.