CMB Anisotropy Research Articles

Cosmology with recombination spectrum

Precision measurement of the cosmological recombination spectrum can provide an entire new window to look at the early universe. We aim to quantify the information hidden in the cosmological recombination spectrum and for this purpose we have developed a new code following the algorithm proposed in [1,2]. Our code is closely based on the COSMOSPEC [3] code. We find, using Fisher information matrix and assuming that the foregrounds can be subtracted by using higher or lower frequency channels and spatial information, that going beyond the detection will need an experiment with sensitivity 25× better compared to the proposed experiment PIXIE. Such an experiment will be able to measure the cosmological parameters with a precision that is competitive with the CMB anisotropy experiments. The best constrainted parameter is baryon energy density, Ωb, which can be nailed down with incredible precision in principle. We also show that the shape of the hydrogen lines is connected to the speed of the hydrogen recombination, with the peaks of the recombination lines coinciding with the peak of the recombination rate. In general, the shape of the lines encodes information about the rate of recombination as a function of redshift.

CMB anisotropy and BBN constraints on pre-recombination decay of dark matter to visible particles

Injection of high energy electromagnetic particles around the recombination epoch can modify the standard recombination history and therefore the CMB anisotropy power spectrum. Previous studies have put strong constraints on the amount of electromagnetic energy injection around the recombination era (redshifts z≲ 4500). However, energy injected in the form of energetic (> keV) visible standard model particles is not deposited instantaneously. The considerable delay between the time of energy injection and the time when all energy is deposited to background baryonic gas and CMB photons, together with the extraordinary precision with which the CMB anisotropies have been measured, means that CMB anisotropies are sensitive to energy that was injected much before the epoch of recombination. We show that the CMB anisotropy power spectrum is sensitive to energy injection even at z = 10000, giving stronger constraints compared to big bang nucleosynthesis and CMB spectral distortions. We derive, using Planck CMB data, the constraints on long-lived unstable particles decaying at redshifts z≲ 10000 (lifetime τX≳ 1011s) by explicitly evolving the electromagnetic cascades in the expanding Universe, thus extending previous constraints to lower particle lifetimes. We also revisit the BBN constraints and show that the delayed injection of energy is important for BBN constraints. We find that the constraints can be weaker by a factor of few to almost an order of magnitude, depending on the energy, when we relax the quasi-static or on-the-spot assumptions.

CMB sky for an off-center observer in a local void. Part I. Framework for forecasts

The Universe is not perfectly homogeneous, the large scale structure forms overdense regions and voids. In this paper, we consider the possibility that we occupy a special position in our Universe, close to the center of a local underdense region that we model as an LTB void embedded in a homogeneous and isotropic Universe. The CMB sky measured by an off-center observer in this void is not statistically isotropic. In addition to the non-stochastic CMB anisotropies due to the geometry of the model, we also observe a lensing-like distortion of the CMB anisotropies. In this article, we propose a framework to forecast the precision with which we can measure the amplitude of the lensing-like deformation of the CMB temperature anisotropies. For illustrative purposes, we apply this method to a couple of large-scale void models differing over the matter density profile and we show that the CMB temperature data from the Planck satellite is potentially capable to detect the effect for the large voids chosen here. A companion paper will be dedicated to a systematic exploration of different realistic void models.

Resonant assisted annihilation

Assisted annihilation is a novel mechanism to generate viable sub-GeV thermal dark matter, where a pair of stable dark matter annihilates with an assister to Standard Model states. Typically such 3 → 2 annihilation topologies are flux suppressed compared to 2 → 2 processes. In this paper, we explore the possibility of a resonant 3 → 2 assisted annihilation dominantly driving the freeze-out of dark matter. We demonstrate that in a simple multipartite scalar extension of the Standard Model this can be realized in certain regions of parameter space to provide viable dark matter relic density, in agreement with observation. We demonstrate that for photophilic assisters parts of the parameter space are already constrained by indirect detection experiments and the measurements of CMB anisotropies while substantial regions remain beyond the present limit.

Searching cosmic strings network in the CMB

The CMB stochastic field provides us with a unique opportunity to search for the predicted imprints of various cosmological theories. In this work, we explore the detectability of the cosmic string (CS) network traces in the pixel-space through its gravitational impact on the CMB anisotropies, i.e. the Gott–Kaiser–Stebbins effect. First, in a classical approach, we use a series of multi-scale edge-detection algorithms followed by certain critical and excursion sets measures on the CMB simulated data (with different levels of contributions from the CSs). With this pipeline the minimum value of detectable CS’s tension for noiseless maps with a resolution of [Formula: see text] is found to be [Formula: see text]. Calling for the help the power of the machine learning algorithms with our proposed feature vectors, decreases the above lower bound to [Formula: see text]. The methods developed and used in this work are quite general and applicable to a wide variety of pattern search problems in the various stochastic fields ranging from cosmological random fields to other natural and artificial complex systems.

Dark matter component decaying after recombination: constraints from diffuse gamma-ray and neutrino flux measurements

We consider scenario of the dark matter consisting of two fractions, stable part being dominant and a smaller unstable fraction, which has decayed after the recombination epoch. It has been suggested in ref. [1] that the above scenario may alleviate tension between high-redshift (CMB anisotropy) and low-redshift (cepheid variables and SNe Ia, cluster counts) cosmological measurements. We derive constraints on the heavy relics branching to qq̄, e+e−, μ+μ−, τ+τ−, νeν̄e, νμν̄μ, W+W− and γγ in the above scenario by comparison of the secondary γ and ν fluxes produced by the process with recent diffuse γ and ν flux measurements and show that the model is excluded for DM masses larger than 600 GeV if there is no decay of DM to invisible radiation.

Secondary CMB anisotropies from magnetized haloes

Magnetized plasmas within haloes of galaxies leave their footprint on the polarized anisotropies of the cosmic microwave background. The two dominant effects of astrophysical haloes are Faraday rotation, which generates rotation of the plane of linear polarization, and Faraday conversion, which induces a leakage from linear polarization to circular polarization. We revisit these sources of secondary anisotropies by computing the angular power spectra of the Faraday rotation angle and the Faraday conversion rate by the large-scale structures. To this end, we use the halo model and we pay special attention to the impact of magnetic field projections. Assuming magnetic fields of haloes to be uncorrelated, we found a vanishing two-halo term, and angular power spectra peaking at multipoles ℓ ∼ 104. The Faraday rotation angle is dominated by the contribution of thermal electrons. For the Faraday conversion rate, we found that both thermal electrons and relativistic, non-thermal electrons contribute equally in the most optimistic case for the density and Lorentz factor of relativistic electrons, while in more pessimistic cases the thermal electrons give the dominant contribution. Assuming the magnetic field to be independent of the halo mass, the angular power spectra for both effects roughly scale with the amplitude of matter perturbations as ∼σ38, and with a very mild dependence with the density of cold dark matter. Introducing a dependence of the magnetic field strength with the halo mass leads to an increase of the scaling at large angular scales (above a degree) with the amplitude of matter fluctuations up to ∼σ9.58 for Faraday rotation and ∼σ158 for Faraday conversion for a magnetic field strength scaling linearly with the halo mass. Introducing higher values of the magnetic field for galaxies, as compared to clusters, instead leads to a decrease of such a scaling at arcminute scales down to ∼σ0.98 for Faraday rotation.

Inflationary tensor fossils deformed by solid matter-scalar field interaction

We study effect of superhorizon tensor perturbations on scalar perturbations, so called effect of clustering fossils, in cosmological model in which inflation is driven by both solid matter and scalar field. The effect deforms primordial scalar power spectrum causing asymmetry in it, which leaves imprint on CMB anisotropies and the cosmic structure. Parameter space of this combined model allows for enhancement of logarithmic scale dependence of this deformation, as opposed to simpler models in which such scale dependence is suppressed by slow-roll parameters.

Baryon acoustic oscillations at z = 2.34 from the correlations of Lyα absorption in eBOSS DR14

We measure the imprint of primordial baryon acoustic oscillations (BAOs) in the correlation function of Lyα absorption in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) and the extended BOSS (eBOSS) in Data Release 14 (DR14) of the Sloan Digital Sky Survey (SDSS)-IV. In addition to 179 965 spectra with absorption in the Lyman-α (Lyα) region, we use Lyα absorption in the Lyman-β region of 56 154 spectra for the first time. We measure the Hubble distance, DH, and the comoving angular diameter distance, DM, relative to the sound horizon at the drag epoch rd at an effective redshift z = 2.34. Using a physical model of the correlation function outside the BAO peak, we find DH(2.34)/rd = 8.86 ± 0.29 and DM(2.34)/rd = 37.41 ± 1.86, within 1σ from the flat-ΛCDM model consistent with CMB anisotropy measurements. With the addition of polynomial “broadband” terms, the results remain within one standard deviation of the CMB-inspired model. Combined with the quasar-Lyα cross-correlation measurement presented in a companion paper, the BAO measurements at z = 2.35 are within 1.7σ of the predictions of this model.

Polarisation as a tracer of CMB anomalies: Planck results and future forecasts

The lack of power anomaly is an intriguing feature at the largest angular scales of the CMB anisotropy temperature pattern, whose statistical significance is not strong enough to claim any new physics beyond the standard cosmological model. We revisit the former statement by also considering polarisation data. We propose a new one-dimensional estimator which takes jointly into account the information contained in the TT, TE and EE CMB spectra. By employing this estimator on Planck 2015 low-$\ell$ data, we find that a random $\Lambda$CDM realisation is statistically accepted at the level of $3.68 \%$. Even though Planck polarisation contributes a mere $4 \%$ to the total information budget, its use pushes the lower-tail-probability down from the $7.22 \%$ obtained with only temperature data. Forecasts of future CMB polarised measurements, as e.g. the LiteBIRD satellite, can increase the polarisation contribution up to $6$ times with respect to Planck at low-$\ell$. We argue that the large-scale E-mode polarisation may play an important role in analysing CMB temperature anomalies with future mission.

Accelerated expansion of the universe and chasing photons from the CMB to study the late time integrated Sachs-Wolfe effect over different redshift ranges

In this study, we are going to discuss the accelerated expansion of the universe and how this accelerated expansion affects the paths of photons from cosmic microwave background radiation (CMB). Then we will see how wide-field galaxy surveys along with cosmic CMB anisotropy maps can help us in studying dark energy. The cross-correlation of galaxy over/under-density maps with CMB anisotropy maps help us in measuring one of the most useful signatures of dark energy i.e. Integrated Sachs-Wolfe (ISW) effect. ISW effect explains the blue-shifting and red-shifting of CMB photons when they reach to us after passing through large scale structures and super-voids respectively. We will look into the theoretical foundations behind ISW effect and discuss how modern all sky galaxy surveys like EMU-ASKAP will be useful in studying the effect.

Testing extended Jordan-Brans-Dicke theories with future cosmological observations

The extended Jordan-Brans-Dicke (eJBD) theory of gravity is constrained by a host of astrophysical and cosmological observations spanning a wide range of scales. The current cosmological constraints on the first post-Newtonian parameter in these simplest eJBD models in which the recent acceleration of the Universe is connected with the variation of the effective gravitational strength are consistent, but approximately two order of magnitude larger than the time-delay test within the Solar System. We forecast the capabilities of future galaxy surveys in combination with current and future CMB anisotropies measurements to further constrain the simplest dark energy models within eJBD theory of gravity. By considering two cases of a monomial potential (a quartic potential or a cosmological constant), we show how Euclid-like galaxy clustering and weak lensing data in combination with BOSS and future CMB observations have the potential to reach constraints on the first post-Newtonian parameter γPN comparable to those from the Solar System.

Cosmic Inflation, Quantum Information and the Pioneering Role of John S Bell in Cosmology

According to the theory of cosmic inflation, the large scale structures observed in our Universe (galaxies, clusters of galaxies, Cosmic Background Microwave—CMB—anisotropy…) are of quantum mechanical origin. They are nothing but vacuum fluctuations, stretched to cosmological scales by the cosmic expansion and amplified by gravitational instability. At the end of inflation, these perturbations are placed in a two-mode squeezed state with the strongest squeezing ever produced in Nature (much larger than anything that can be made in the laboratory on Earth). This article studies whether astrophysical observations could unambiguously reveal this quantum origin by borrowing ideas from quantum information theory. It is argued that some of the tools needed to carry out this task have been discussed long ago by J. Bell in a, so far, largely unrecognized contribution. A detailled study of his paper and of the criticisms that have been put forward against his work is presented. Although J. Bell could not have realized it when he wrote his letter since the quantum state of cosmological perturbations was not yet fully characterized at that time, it is also shown that Cosmology and cosmic inflation represent the most interesting frameworks to apply the concepts he investigated. This confirms that cosmic inflation is not only a successful paradigm to understand the early Universe. It is also the only situation in Physics where one crucially needs General Relativity and Quantum Mechanics to derive the predictions of a theory and, where, at the same time, we have high-accuracy data to test these predictions, making inflation a playground of utmost importance to discuss foundational issues in Quantum Mechanics.

Nonlocal entanglement and directional correlations of primordial perturbations on the inflationary horizon

Models are developed to estimate properties of relic cosmic perturbations with "spooky" nonlocal correlations on the inflationary horizon, analogous to those previously posited for information on black hole event horizons. Scalar curvature perturbations are estimated to emerge with a dimensionless power spectral density $\Delta_S^2\approx H t_P$, the product of inflationary expansion rate $H$ with Planck time $t_P$, larger than standard inflaton fluctuations. Current measurements of the spectrum are used to derive constraints on parameters of the effective potential in a slow-roll background. It is shown that spooky nonlocality can create statistically homogeneous and isotropic primordial curvature perturbations that are initially directionally antisymmetric. New statistical estimators are developed to study unique signatures in CMB anisotropy and large scale galaxy surveys.

Improved CMB anisotropy constraints on primordial magnetic fields from the post-recombination ionization history

We investigate the impact of a stochastic background of Primordial Magnetic Fields (PMF) generated before recombination on the ionization history of the Universe and on the Cosmic Microwave Background radiation (CMB). Pre-recombination PMFs are dissipated during recombination and reionization via decaying MHD turbulence and ambipolar diffusion. This modifies the local matter and electron temperatures and thus affects the ionization history and Thomson visibility function. We use this effect to constrain PMFs described by a spectrum of power-law type, extending our previous study (based on a scale-invariant spectrum) to arbitrary spectral index. We derive upper bounds on the integrated amplitude of PMFs due to the separate effect of ambipolar diffusion and MHD decaying turbulence and their combination. We show that ambipolar diffusion is relevant for $n_{\rm B}>0$ whereas for $n_{\rm B}<0$ MHD turbulence is more important. The bound marginalized over the spectral index on the integrated amplitude of PMFs with a sharp cut-off is $\sqrt{\langle B^2 \rangle}<0.83$ nG. We discuss the quantitative relevance of the assumptions on the damping mechanism and the comparison with previous bounds.

Primordial circular polarization in the cosmic microwave background

Circular (“V-mode”) polarization is expected to be vanishing in the CMB, since it is not produced in Thomson scattering. However, considering that the conventional CMB anisotropies are generated via an early universe mechanism such as inflation or a bouncing scenario, it is possible that circular polarization could be primordially produced and survive to the surface of last scattering. We study this in detail, and find a large class of inflationary models that produce a nearly scale invariant spectrum of scalar V-mode anisotropies. We study the inflationary production and subsequent evolution via the Boltzmann hierarchy, and show that V-mode polarization present in the CMB is suppressed by a factor of at least 101013 relative to the primordial V, consistent with expectation of negligible V-mode polarization from inflation. We consider alternative possibilities for sourcing V primordially, such as the V-mode polarization induced by circularly polarized primordial gravitational waves, or producing V after inflation, via new interactions at recombination.

Systematic effects and self-consistency in the primordial helium abundance determination

Observations of light element abundances (4He, D, 7Li) provide a powerful and independent test of the Standard Model of Big Bang Nucleosynthesis. The 4He abundance is measured most accurately among the light elements. This value is determined from observations of spectral lines from small-scale extragalactic sources (HII regions) in the optical and near infrared ranges. The intensity of the forbidden lines like [OIII] and [SII] allows to obtain the physical characteristics of the source, such as temperature and metallicity. Intensities of the 4He lines are used to determine the abundance of this element in the object. However, there are various systematic effects that should be taken in account for precise definition of this physical quantity. These include (1) interstellar reddening, (2) emissivities of 4He in different wavelengths, (3) underlying absorption for H and He lines, (4) temperature and (5) ionization structure HII regions, (6) collisional and fluorescent excitation of H and He lines. Incorrect accounting of these effects can lead to overestimation or underestimation of the primordial helium abundance Yp by several percent.At the moment, there are two independent groups of researchers dealing with this problem. The results for the calculation using the same data sample for these groups are as follows: Yp = 0.2551 ± 0.0022 (Izotov, Thuan, Guseva, 2014) and Yp = 0.2449 ± 0.0040 (Aver, Olive, Skillman, 2015). The last result is consistent with the result Yp = 0.2467 ± 0.0006 based on the study of the CMB anisotropy on (P.A.R. Ade et al., 2015). However, the values of Yp obtained by these groups do not coincide even within the margin of error, and at the moment there is no clear answer to the question of which of these two groups got correct result. In the paper, differences in the methods of processing data and obtaining the quantity of the primordial helium abundance are investigated, in particular, how the groups take into account the named systemic effects. An error analysis and comparative tests are performed.

Probing primordial features with the primary CMB

CMB photons travel from the last scattering surface, when the primary CMB has been generated, along the surface of the light cone to us. During their travel, they are affected by many secondary effects such as the integrated Sachs-Wolfe effect and CMB lensing. These CMB secondary effects modify the CMB primary power spectrum adding degeneracies and decreasing the sensibility to primordial parameters. The possibility to reconstruct the primary CMB anisotropies will allow us to have a more direct observable to test the physics of the early universe. We propose to study the imprint of features in the primordial power spectrum with the primary CMB after the subtraction of the reconstructed ISW signal from the observed CMB temperature angular power spectrum. We consider the application to features models able to fit two of the large scales anomalies observed in the CMB temperature angular power spectrum: the deficit of power at $\ell \sim 2$ and at $\ell \sim 22$. This method allows to improve significantly the constraints on the features parameters up to $16\%$ for models predicting a suppression of power of the quadrupole and up to $27\%$ for models with features at $\ell \sim 22$, assuming instrumental sensitivity similar to the $Planck$ satellite (depending on the goodness of the ISW reconstruction). Furthermore, it gives the opportunity to understand if these anomalies are attributed to early- or late-time physics.

Measurements of the Matter Density Perturbation Amplitude from Cosmological Data

We compare various physically different measurements of linear matter density perturbation amplitude, $sigma_8$, which are obtained from the observations of CMB anisotropy, galaxy cluster mass function, weak gravitation lensing, matter power spectrum and redshift space distortions. We show that $\sigma_8$ measurement from CMB gravitational lensing signal based on Planck CMB temperature anisotropy data at high multipoles, $\ell>1000$, contradict to all other measurements obtained both from remaining Planck CMB anisotropy data and from other cosmological data, at about $3.7\sigma$ significance level. Therefore, these data currently should not be combined with other data to constrain cosmological parameters. With the exception of Planck CMB temperature anisotropy data at high multipoles, all other measurements are in good agreement between each other and give the following measurements of linear density perturbation amplitude: $\sigma_8=0.792\pm0.006$, mean density of the Universe: $\Omega_m=0.287\pm0.007$, and Hubble constant: $H_0 = 69.4\pm 0.6$~km~s$^{-1}$~Mpc$^{-1}$. Taking in account the data on baryon acoustic oscillations and (or) direct measurements of the Hubble constant, one can obtain different constraints on sum of neutrino mass and number of relativistic species.

Galaxy kinematics and mass calibration in massive SZE-selected galaxy clusters toz = 1.3

The galaxy phase-space distribution in galaxy clusters provides insights into the formation and evolution of cluster galaxies, and it can also be used to measure cluster mass profiles. We present a dynamical study based on $\sim$3000 passive, non-emission line cluster galaxies drawn from 110 galaxy clusters. The galaxy clusters were selected using the Sunyaev-Zel'dovich effect (SZE) in the 2500~deg$^2$ SPT-SZ survey and cover the redshift range $0.2 < z < 1.3$. We model the clusters using the Jeans equation, while adopting NFW mass profiles and a broad range of velocity dispersion anisotropy profiles. The data prefer velocity dispersion anisotropy profiles that are approximately isotropic near the center and increasingly radial toward the cluster virial radius, and this is true for all redshifts and masses we study. The pseudo-phase-space density profile of the passive galaxies is consistent with expectations for dark matter particles and subhalos from cosmological $N$-body simulations. The dynamical mass constraints are in good agreement with external mass estimates of the SPT cluster sample from either weak lensing, velocity dispersions, or X-ray $Y_X$ measurements. However, the dynamical masses are lower (at the 2.2$\sigma$ level) when compared to the mass calibration favored when fitting the SPT cluster data to a $\Lambda$CDM model with external cosmological priors, including CMB anisotropy data from Planck. The discrepancy grows with redshift, where in the highest redshift bin the ratio of dynamical to SPT+Planck masses is $\eta=0.63^{+0.13}_{-0.08}\pm0.06$ (statistical and systematic), corresponding to a $2.6\sigma$ discrepancy.