Sachs-Wolfe Research Articles

Asimulation: Domain formation and impact on observables in resolved cosmological simulations of the (a)symmetron

The symmetron is a dark energy and dark matter candidate that forms topological defects in the late-time universe and holds the promise of resolving some of the cosmological tensions. We performed high-resolution simulations of the dynamical and non-linear (a)symmetron using the recently developed relativistic N-body code asevolution. By extensively testing the temporal and spatial convergence of domain decompositioning and domain wall stability, we determined criteria and physical intuition for the convergence. We applied the resolution criteria to run five high-resolution simulations with 12803 grids and a box size of 500 Mpc h−1 of the (a)symmetron. We considered the behaviour of the scalar field and the domain walls in each scenario. We find the effect on the matter power spectra, the HMFs, and observables computed over the past light cone of an observer, such as the integrated Sachs-Wolfe and non-linear Rees-Sciama effect and the lensing, compared to ΛCDM. We show local oscillations of the fifth force strength and the formation of planar structures in the density field. The dynamics of the field was visualised in animations with high resolution in time. The simulation code is made publicly available.

Relativistic and wide-angle corrections to galaxy power spectra

Galaxy surveys contain information on the largest scales via wide-angle and relativistic contributions. By combining two different galaxy populations, we can suppress the strong cosmic variance on ultra-large scales and thus enhance the detectability of the signals.The relativistic Doppler and Sachs-Wolfe effects are of a similar magnitude to the leading wide-angle corrections, so that it is important to treat them together, especially since they can partially cancel. The power spectra depend on the choice of line of sight for each galaxy pair and we present results for a generalline of sight. Then we estimate the detection significance of the auto- and cross-power spectra for a variety of cases. We use two futuristic galaxy samples based on a `beyond-DESI' survey and a SKA Phase 2 survey, covering 15,000 deg2 up to z=1. We find a detection significance for the total relativistic wide-angle effects that ranges from ~ 5σ to >15σ, depending on the line-of-sight configuration.

Induced cosmological anisotropies and CMB anomalies by a non-abelian gauge-gravity interaction

We present a non-abelian cousin of the model presented in Lee et al. (2024) which induces cosmological anisotropies on top of standard FLRW geometry. This is in some sense doing a cosmological mean field approximation, where the mean field cosmological model under consideration would be the standard FLRW, and the induced anisotropies are small perturbative corrections on top of it. Here we mostly focus on the non-abelian SU(2) gauge fields coupled to the gravity to generate the anisotropies, which can be a viable model for the axion-like particle (ALP) dark sector. The induced anisotropies are consequences of the non-trivial back-reaction of the gauge fields on the gravity sector, and by a clever choice of the parametrization, one can generate the Bianchi model we have studied in this note. We also show that the anisotropies influence the Sachs–Wolfe effect and we discuss the implications.

Structure formation in various dynamical dark energy scenarios

This research investigates the impact of the nature of Dark Energy (DE) on structure formation, focusing on the matter power spectrum and the Integrated Sachs–Wolfe effect (ISW). By analyzing the matter power spectrum at redshifts z=0 and z=5, as well as the ISW effect on the scale of ℓ=10−100, the study provides valuable insights into the influence of DE equations of state (EoS) on structure formation. The findings reveal that dynamical DE models exhibit a stronger matter power spectrum compared to constant DE models, with the JBP model demonstrating the highest amplitude and the CPL model the weakest. Additionally, the study delves into the ISW effect, highlighting the time evolution of the ISW source term F(a) and its derivative dF(a)/da, and demonstrating that models with constant DE EoS exhibit a stronger amplitude of F(a) overall, while dynamical models such as CPL exhibit the highest amplitude among the dynamical models, whereas JBP has the lowest. The study also explores the ISW auto-correlation power spectrum and the ISW cross-correlation power spectrum, revealing that dynamical DE models dominate over those with constant DE EoS across various surveys. Moreover, it emphasizes the potential of studying the non-linear matter power spectrum and incorporating datasets from the small scales to further elucidate the dynamical nature of dark energy. This comprehensive analysis underscores the significance of both the matter power spectrum and the ISW signal in discerning the nature of dark energy, paving the way for future research to explore the matter power spectrum at higher redshifts and in the non-linear regime, providing deeper insights into the dynamical nature of dark energy.

Cross Correlation between the Thermal Sunyaev–Zeldovich Effect and the Integrated Sachs–Wolfe Effect

We present a joint cosmological analysis of the power spectra measurement of the Planck Compton parameter and the integrated Sachs–Wolfe (ISW) maps. We detect the statistical correlation between the Planck thermal Sunyaev–Zeldovich (tSZ) map and ISW data with a significance of a 3.6σ confidence level (CL), with the autocorrelation of the Planck tSZ data being measured at a 25σ CL. The joint auto- and cross-power spectra constrain the matter density to be Ωm=0.317−0.031+0.040 , the Hubble constant to be H0=66.5−1.9+2.0kms−1Mpc−1 , and the rms matter density fluctuations to be σ8=0.730−0.037+0.040 at the 68% CL. The derived large-scale structure S 8 parameter is S8≡σ8(Ωm/0.3)0.5=0.755±0.060 . If using only the diagonal blocks of covariance matrices, the Hubble constant becomes H0=69.7−1.5+2.0kms−1Mpc−1 . In addition, we obtain the constraint of the product of the gas bias, gas temperature, and density as bgasTe/(0.1keV)n¯e/1m−3=3.09−0.380+0.320 . We find that this constraint leads to an estimate on the electron temperature today as Te=(2.40−0.300+0.250)×106K , consistent with the expected temperature of the warm–hot intergalactic medium. Our studies show that the ISW–tSZ cross correlation is capable of probing the properties of the large-scale diffuse gas.

The CMB Cold Spot as predicted by foregrounds around nearby galaxies

Context. The non-Gaussian Cold Spot surrounded by its hot ring is one of the most striking features of the cosmic microwave background (CMB) and has generated significant attention in the literature. It has been speculated that either new physics or the Integrated Sachs-Wolfe effect induced by the presence of a cosmic void at relatively high redshift could account for the observations. Aims. Here, we investigate if the newly discovered systematic decrease in the CMB temperature in the neighbourhood of nearby galaxies may create such a strong temperature depression. In particular, we note that the largest galaxy group complex in the local Universe, the Eridanus super-group with its neighbouring groups, is in the Cold Spot area. Our goal is to analyse observational galaxy data to characterise the neighbourhood of the Cold Spot, explore the properties of these galaxies, and thereby make a prediction of the galaxy induced CMB temperature decrement in this region. Methods. We used the Planck SMICA maps, and as foreground tracers, galaxies from the publicly available observational catalogues: 2MRS, 6dF, and HIPASS, which include information on redshifts, positions, magnitudes, and other astrophysical characteristics. We applied previously explored mean temperature profile shapes to model the expected temperature decrement from the galaxies in the Cold Spot area. Results. Even after correcting for the mean low temperature of the Cold Spot region, we find that the temperature decrement around galaxies is significantly stronger than the mean decrement in other parts of the sky. We discuss whether this could be attributed to the fact that the Cold Spot area coincides with one of the regions populated by the most HI deficient galaxies. Modeling the foreground temperature profile that is mainly associated with spiral galaxies in this location, we find a particularly strong temperature decrement due to the presence of the late-type overabundant largest group complex in the nearby universe. A Cold Spot shape that largely overlaps with the CMB Cold Spot is observed. Conclusions. We conclude that the coincidence of the only nearby spiral-rich group complex located in the Cold Spot region, and the success of the modelling performed, adds strong evidence to the existence of a local extragalactic foreground that may account for the observed temperature depression, alleviating the tension with the Gaussian field that is otherwise expected in the CMB.

Novel integrated Sachs-Wolfe effect from early dark energy

Novel integrated Sachs-Wolfe effect from early dark energy

Field-level multiprobe analysis of the CMB, integrated Sachs-Wolfe effect, and the galaxy density maps

Field-level multiprobe analysis of the CMB, integrated Sachs-Wolfe effect, and the galaxy density maps

Gauge fixing in cosmological perturbations of Unimodular Gravity

With focus on the cosmological evolution of linear perturbations of matter and geometry, we calculate the equivalent expressions to that of the Newtonian and Synchronous gauges within the framework of Unimodular Gravity, being these two gauges commonly used and implemented in Boltzmann codes. An important aspect of our analysis is the inclusion of the energy-momentum current violation, as well as its perturbations. Moreover, for the first time we demonstrate that it is possible to fix both gauges consistently, although as it has been already noticed in previous literature, neither of them is recovered in the sense of the dynamics given in General Relativity for matter and metric fluctuations. Specifically, we show that since the unimodular constraint at the level of linear perturbations lead to only one degree of freedom of scalar modes of metric fluctuations, the dynamics in Unimodular Gravity forces to keep the anisotropic stress in the Newtonian gauge, whereas the cold dark matter comoving frame can not be set in the Synchronous gauge. The physical implications on the density contrast of cold dark matter is reviewed, and the Sachs-Wolfe effect is obtained and compared with previous results in the literature of cosmological perturbations in Unimodular Gravity.

Primordial non-Gaussianity f NL and anisotropies in scalar-induced gravitational waves

Primordial non-Gaussianity encodes vital information of the physics of the early universe, particularly during the inflationary epoch. To explore the local-type primordial non-Gaussianity f NL, we study the anisotropies in gravitational wave background induced by the linear cosmological scalar perturbations during radiation domination in the early universe. We provide the first complete analysis to the angular power spectrum of such scalar-induced gravitational waves. The spectrum is expressed in terms of the initial inhomogeneities, the Sachs-Wolfe effect, and their crossing. It is anticipated to have frequency dependence and multipole dependence, i.e., Cℓ (ν) ∝ [ℓ(ℓ+1)]-1 with ν being a frequency and ℓ referring to the ℓ-th spherical harmonic multipole. In particular, the initial inhomogeneites in this background depend on gravitational-wave frequency. These properties are potentially useful for the component separation, foreground removal, and breaking degeneracies in model parameters, making the non-Gaussian parameter f NL measurable. Further, theoretical expectations may be tested by space-borne gravitational-wave detectors in future.

Seven Hints That Early-Time New Physics Alone Is Not Sufficient to Solve the Hubble Tension

The Hubble tension has now grown to a level of significance which can no longer be ignored and calls for a solution which, despite a huge number of attempts, has so far eluded us. Significant efforts in the literature have focused on early-time modifications of ΛCDM, introducing new physics operating prior to recombination and reducing the sound horizon. In this opinion paper I argue that early-time new physics alone will always fall short of fully solving the Hubble tension. I base my arguments on seven independent hints, related to (1) the ages of the oldest astrophysical objects, (2) considerations on the sound horizon-Hubble constant degeneracy directions in cosmological data, (3) the important role of cosmic chronometers, (4) a number of “descending trends” observed in a wide variety of low-redshift datasets, (5) the early integrated Sachs-Wolfe effect as an early-time consistency test of ΛCDM, (6) early-Universe physics insensitive and uncalibrated cosmic standard constraints on the matter density, and finally (7) equality wavenumber-based constraints on the Hubble constant from galaxy power spectrum measurements. I argue that a promising way forward should ultimately involve a combination of early- and late-time (but non-local—in a cosmological sense, i.e., at high redshift) new physics, as well as local (i.e., at z∼0) new physics, and I conclude by providing reflections with regards to potentially interesting models which may also help with the S8 tension.

The CMB cold spot under the lens: ruling out a supervoid interpretation

The Cosmic Microwave Background (CMB) anisotropies are thought to be statistically isotropic and Gaussian. However, several anomalies are observed, including the CMB Cold Spot, an unexpected cold ∼ 10° region with p-value ≲ 0.01 in standard ΛCDM. One of the proposed origins of the Cold Spot is an unusually large void on the line of sight, that would generate a cold region through the combination of integrated Sachs-Wolfe and Rees-Sciama effects. In the past decade extensive searches were conducted in large scale structure surveys, both in optical and infrared, in the same area for z ≲ 1 and did find evidence of large voids, but of depth and size able to account for only a fraction of the anomaly. Here we analyze the lensing signal in the Planck CMB data and rule out the hypothesis that the Cold Spot could be due to a large void located anywhere between us and the surface of last scattering. In particular, computing the evidence ratio we find that a model with a large void is disfavored compared to ΛCDM, with odds 1 : 13 (1 : 20) for SMICA (NILC) maps, compared to the original odds 56 : 1 (21 : 1) using temperature data alone.

Validating dark energy models using the polarized Sunyaev-Zel’dovich effect with large-angle CMB temperature and E -mode polarization anisotropies

The tomography of the polarized Sunyaev-Zeldvich effect due to free electrons of galaxy clusters can be used to constrain the nature of dark energy because CMB quadrupoles at different redshifts as the polarization source are sensitive to the integrated Sachs-Wolfe effect. Here we show that the low multipoles of the temperature and E-mode polarization anisotropies from the all-sky CMB can improve the constraint further through the correlation between them and the CMB quadrupoles viewed from the galaxy clusters. Using a Monte-Carlo simulation, we find that low multipoles of the temperature and E-mode polarization anisotropies potentially improve the constraint on the equation of state of dark energy parameter by $\sim 17$ percent.

CMB constraints on the early Universe independent of late-time cosmology

The CMB is a powerful probe of early-universe physics but is only observed after passing through large-scale structure, which changes the observed spectra in important model-dependent ways. This is of particular concern given recent claims of significant discrepancies with low redshift data sets when a standard $\Lambda$CDM model is assumed. By using empirical measurements of the CMB lensing reconstruction, combined with weak priors on the smoothness of the lensing spectrum, foregrounds, and shape of any additional integrated Sachs-Wolfe effect, we show how the early-universe parameters can be constrained from CMB observations almost independently of the late-time evolution. This provides a way to test new models for early-universe physics, and measure early-universe parameters, independently of late-time cosmology. Using the empirical measurement of lensing keeps the size of the effect of late-time modelling uncertainty under control, leading to only modest increases in error bars of most early-universe parameters compared to assuming a full evolution model. We provide robust constraints on early-$\Lambda$CDM model parameters using the latest Planck PR4 data and show that with future data marginalizing over a single lensing amplitude parameter is sufficient to remove sensitivity to late-time cosmological model only if the spectral shape matches predictions.

Biases to primordial non-Gaussianity measurements from CMB secondary anisotropies

ABSTRACT Our view of the last-scattering surface in the cosmic microwave background (CMB) is obscured by secondary anisotropies, sourced by scattering, extragalactic emission, and gravitational processes between recombination and observation. Whilst it is established that non-Gaussianity from the correlation between the integrated-Sachs–Wolfe (ISW) effect and gravitational lensing can significantly bias primordial non-Gaussianity (PNG) searches, recent work by Hill suggests that other combinations of secondary anisotropies can also produce significant biases. Building on that work, we use the WebSky and Sehgal et al. simulations to perform an extensive examination of possible biases to PNG measurements for the local, equilateral and orthogonal shapes. For a Planck-like CMB experiment, without foreground cleaning, we find significant biases from cosmic infrared background (CIB)-lensing and thermal Sunyaev–Zel’dovich (tSZ)-lensing bispectra for the local and orthogonal templates, and from CIB and tSZ bispectra for the equilateral template. For future experiments, such as the Simons Observatory, biases from correlations between the ISW effect and the tSZ and CIB will also become important. Finally, we investigate the effectiveness of foreground-cleaning techniques to suppress these biases. We find that the majority of these biases are effectively suppressed by the internal-linear combination method with a total bias below the $1\, \sigma$ statistical error for both experiments. However, the small total bias arises from the cancellation of several $1\, \sigma$ biases for Planck-like experiments and $2\, \sigma$ biases for SO-like. As this cancellation is likely sensitive to the modelling, to ensure robustness against these biases, we recommend that explicit removal methods should be used.

Accurate estimation of angular power spectra for maps with correlated masks

The widely used MASTER approach for angular power spectrum estimation was developed as a fast ${C}_{\ensuremath{\ell}}$ estimator on limited regions of the sky. This method expresses the power spectrum of a masked map (``pseudo-${C}_{\ensuremath{\ell}}$'') in terms of the power spectrum of the unmasked map (the true ${C}_{\ensuremath{\ell}}$) and that of the mask or weight map. However, it is often the case that the map and mask are correlated in some way, such as point source masks used in cosmic microwave background (CMB) analyses, which have nonzero correlation with CMB secondary anisotropy fields and other mm-wave sky signals. In such situations, the MASTER approach gives biased results, as it assumes that the unmasked map and mask have zero correlation. While such effects have been discussed before with regard to specific physical models, here we derive a completely general formalism for any case where the map and mask are correlated. We show that our result (``reMASTERed'') reconstructs ensemble-averaged pseudo-${C}_{\ensuremath{\ell}}$ to effectively exact precision, with significant improvements over traditional estimators for cases where the map and mask are correlated. In particular, we obtain an improvement in the mean absolute percent error from 30% with the MASTER result to essentially no error with the reMASTERed result for an integrated Sachs-Wolfe (ISW) field map with a mask built from the thresholded ISW field, and 10% to effectively zero for a Compton-$y$ map combined with an infrared source mask (the latter being directly relevant to actual data analysis). An important consequence of our result is that for maps with correlated masks, it is no longer possible to invert a simple equation to obtain the true ${C}_{\ensuremath{\ell}}$ from the pseudo-${C}_{\ensuremath{\ell}}$. Instead, our result necessitates the use of forward modeling from theory space into the observable domain of the pseudo-${C}_{\ensuremath{\ell}}$. Our code is publicly available in reMASTERed.https://github.com/kmsurrao/reMASTERed.

Constraining dark matter decay with cosmic microwave background and weak-lensing shear observations

From observations at low and high redshifts, it is well known that the bulk of dark matter (DM) has to be stable or at least very long-lived. However, the possibility that a small fraction of DM is unstable or that all DM decays with a half-life time (τ) significantly longer than the age of the Universe is not ruled out. One-body decaying dark matter (DDM) consists of a minimal extension to the ΛCDM model. It causes a modification of the cosmic growth history as well as a suppression of the small-scale clustering signal, providing interesting consequences regarding theS8tension, which is the observed difference in the clustering amplitude between weak-lensing (WL) and cosmic microwave background (CMB) observations. In this paper, we investigate models in which a fraction or all DM decays into radiation, focusing on the long-lived regime, that is,τ ≳ H0−1(H0−1being the Hubble time). We used WL data from the Kilo-Degree Survey (KiDS) and CMB data fromPlanck. First, we confirm that this DDM model cannot alleviate theS8difference. We then show that the most constraining power for DM decay does not come from the nonlinear WL data, but from CMB via the integrated Sachs-Wolfe effect. From the CMB data alone, we obtain constraints ofτ ≥ 288 Gyr if all DM is assumed to be unstable, and we show that a maximum fraction off = 0.07 is allowed to decay assuming the half-life time to be comparable to (or shorter than) one Hubble time. The constraints from the KiDS-1000 WL data are significantly weaker,τ ≥ 60 Gyr andf < 0.34. Combining the CMB and WL data does not yield tighter constraints than the CMB alone, except for short half-life times, for which the maximum allowed fraction becomesf = 0.03. All limits are provided at the 95% confidence level.

Anisotropic gravitational waves induced by hypermagnetic fields during the electroweak phase transition epoch

We study the anisotropies of gravitational waves induced by weak hypermagnetic fields which are randomly distributed and oriented during the electroweak phase transition in the early universe. The theory setup of this study is the standard model plus a real singlet scalar field, which can produce the needed strongly first order electroweak phase transition. Then we investigate how the hypermagnetic fields can convert to magnetic fields and we compute the departure of energy difference between the symmetric phase and the broken phase when the magnetic fields are turned on. It is found that the presence of the hypermagnetic fields can increase the Euclidean action, thus can decrease nucleation temperature, which can lead to a supercool plasma. We point out that the hypermagnetic field can enhance the gravitational wave production from a first order electroweak phase transition and the inhomogeneity of primordial hypermagnetic field can lead to anisotropies of gravitational waves. By examining three well-motivated distribution of hypermagnetic fields, we calculate the corresponding angular power spectra of stochastic gravitational wave background and find they can be significantly larger than the contributions of the Sachs-Wolfe effects and integrated Sachs-Wolfe effects. Our results show that the anisotropies of gravitational wave could provide a novel probe to the primordial hypermagnetic field in the electroweak phase transition epoch.

The integrated Sachs–Wolfe effect in interacting dark matter–dark energy models

Interacting dark matter-dark energy (IDMDE) models can be considered as one of the present challenges that may affect cosmic structures. The main idea of such models is that the mass of dark matter particles is specified by their interactions with a scalar field whose energy density is characterized by dark energy. In this work, we propose to study the integrated Sachs–Wolfe (ISW) effect in IDMDE models. Regarding this, we initially introduce a theoretical framework for IDMDE models. Moreover, we briefly discuss the stability conditions of IDMDE models, and by specifying a simple functional form for the energy density transfer rate, we calculate the perturbation equations. In the following, we specify the amplitude of the matter power spectrum for IDMDE models and compare it with the corresponding result obtained from the ΛCDM model. Furthermore, we calculate the amplitude of the ISW auto-power spectrum as a function of multipole order l for IDMDE models. The results indicate that the amplitude of the ISW auto-power spectrum in IDMDE models behaves like the one for the ΛCDM model for different values of the phantom dark energy equation of state. While the amplitude of the ISW-auto power spectrum for the IDMDE model should be higher than the one for the ΛCDM model in the case of quintessence dark energy equation of state. Also, it turns out that the corresponding results by different values of the coupling parameter demonstrate that ξ is inversely proportional to the amplitude of the ISW-auto power spectrum in IDMDE models. Finally, by employing four different surveys, we calculate the amplitude of the ISW-cross power spectrum as a function of multipole order l for IDMDE models. The results exhibit that the amplitude of the ISW-cross power spectrum in IDMDE models for all values of ωx is higher than that obtained from the ΛCDM model. Also, it turns out that the amplitude of the ISW-cross power spectrum in IDMDE models changes inversely with the value of coupling parameter ξ.

Leveraging cross-correlations and linear covariance-based filtering for line-intensity map reconstructions at linear scales

We explore the possible application of linear covariance-based (LCB) filtering to line-intensity mapping (LIM) signal reconstructions. Originally introduced for reconstruction of the integrated Sachs-Wolfe effect in the cosmic microwave background, the LCB filter is an optimal map estimator that extends the simple Wiener filter by leveraging external correlated data. Given a detectable strong LIM-galaxy or LIM-LIM cross power spectrum, we show recovery of high-redshift, large-scale line-intensity fluctuations---even in the presence of bright interloper emission---in simulations of a futuristic [C ii] LIM survey as well as simulated future iterations of the CO Mapping Array Project. With sufficient galaxy abundances or low LIM survey noise, normalized cross-correlation between the LCB reconstruction and the true signal reaches 70%--90% on large, linear comoving scales corresponding to $k\ensuremath{\sim}0.1\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$. This suggests the possible use of such signal reconstructions in astrophysical or cosmological contexts that require identifying the locations of line emissivity peaks and voids, although clear shortcomings exist on smaller scales. The successful application of the LCB filter in simulated LIM contexts highlights the importance of cross-correlations to studies of the reionizing and reionized high-redshift universe with LIM and other large-scale structure surveys.