Power Spectrum Of Temperature Anisotropies Research Articles

Understanding large scale CMB anomalies with the generalized nonminimal derivative coupling during inflation

We study the observational implications of a class of inflationary models wherein the inflaton is coupled to the Einstein tensor through a generalized nonminimal derivative coupling (GNMDC). In particular, we explore whether these models can generate suitable features in the primordial spectrum of curvature perturbations as a possible explanation for the large-scale anomalies associated with the angular power spectrum of CMB temperature anisotropies. We derive model-independent constraints on the GNMDC function for such a scenario, considering both the scalar and tensor perturbations. We modify cosmomc to accommodate our GNMDC framework and investigate different classes of inflationary models using a fully consistent numerical approach. We find that the hilltop-quartic model with a specific choice of the GNMDC function provides a considerable improvement over the best-fit reference $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model with a nearly scale-invariant power spectrum. While the large-scale structure observations should be able to provide independent constraints, future CMB experiments, such as CMB-S4 and CMB-Bharat, are expected to constrain further the parameter space of such beyond canonical single-field inflationary models.

The galaxy power spectrum take on spatial curvature and cosmic concordance

The concordance of the Λ CDM cosmological model in light of current observations has been the subject of an intense debate in recent months. The 2018 Planck Cosmic Microwave Background (CMB) temperature anisotropy power spectrum measurements appear at face value to favour a spatially closed Universe with curvature parameter Ω K < 0 . This preference disappears if Baryon Acoustic Oscillation (BAO) measurements are combined with Planck data to break the geometrical degeneracy, although the reliability of this combination has been questioned due to the strong tension present between the two datasets when assuming a curved Universe. Here, we approach this issue from yet another point of view, using measurements of the full-shape (FS) galaxy power spectrum, P ( k ) , from the Baryon Oscillation Spectroscopic Survey DR12 CMASS sample. By combining Planck data with FS measurements, we break the geometrical degeneracy and find Ω K = 0 . 0023 ± 0 . 0028 . This constrains the Universe to be spatially flat to sub-percent precision, in excellent agreement with results obtained using BAO measurements. However, as with BAO, the overall increase in the best-fit χ 2 suggests a similar level of tension between Planck and P ( k ) under the assumption of a curved Universe. While the debate on spatial curvature and the concordance between cosmological datasets remains open, our results provide new perspectives on the issue, highlighting the crucial role of FS measurements in the era of precision cosmology.

Do we have any hope of detecting scattering between dark energy and baryons through cosmology?

ABSTRACT We consider the possibility that dark energy and baryons might scatter off each other. The type of interaction we consider leads to a pure momentum exchange, and does not affect the background evolution of the expansion history. We parametrize this interaction in an effective way at the level of Boltzmann equations. We compute the effect of dark energy-baryon scattering on cosmological observables, focusing on the cosmic microwave background (CMB) temperature anisotropy power spectrum and the matter power spectrum. Surprisingly, we find that even huge dark energy-baryon cross-sections $\sigma _{xb} \sim {\cal O}({\rm b})$, which are generically excluded by non-cosmological probes such as collider searches or precision gravity tests, only leave an insignificant imprint on the observables considered. In the case of the CMB temperature power spectrum, the only imprint consists in a sub-per cent enhancement or depletion of power (depending whether or not the dark energy equation of state lies above or below −1) at very low multipoles, which is thus swamped by cosmic variance. These effects are explained in terms of differences in how gravitational potentials decay in the presence of a dark energy-baryon scattering, which ultimately lead to an increase or decrease in the late-time integrated Sachs–Wolfe power. Even smaller related effects are imprinted on the matter power spectrum. The imprints on the CMB are not expected to be degenerate with the effects due to altering the dark energy sound speed. We conclude that, while strongly appealing, the prospects for a direct detection of dark energy through cosmology do not seem feasible when considering realistic dark energy-baryon cross-sections. As a caveat, our results hold to linear order in perturbation theory.

Connecting early and late epochs by f(z)CDM cosmography

The cosmographic approach is gaining considerable interest as a model-independent technique able to describe the late expansion of the universe. Indeed, given only the observational assumption of the cosmological principle, it allows to study the today observed accelerated evolution of the Hubble flow without assuming specific cosmological models. In general, cosmography is used to reconstruct the Hubble parameter as a function of the redshift, assuming an arbitrary fiducial value for the current matter density, Ωm, and analysing low redshift cosmological data. Here we propose a different strategy, linking together the parametric cosmographic behavior of the late universe expansion with the small scale universe. In this way, we do not need to assume any “a priori” values for the cosmological parameters, since these are constrained at early epochs using both the Cosmic Microwave Background Radiation (CMBR) and Baryonic Acoustic Oscillation (BAO) data. In other words, we want to develop a cosmographic approach without assuming any background model but considering a f(z)CDM model where the function f(z) is given by a suitable combination of polynomials capable of tracking the cosmic luminosity distance, replacing the cosmological constant Λ. In order to test this strategy, we describe the late expansion of the universe using the Pad'e polynomials. Specifically, we adopt a P(2,2) series, that is a promising rational series which guarantees a good convergence also at high redshift. This approach is discussed in the light of the recent H(z) values indicators, combined with Supernovae Pantheon sample, galaxy clustering and early universe data, as CMBR and BAO. We found an interesting dependence of the current matter density value with cosmographic parameters, proving the inaccuracy of setting the value of Ωm in cosmographic analyses. Furthermore, a non-negligible effect of the cosmographic parameters on the CMBR temperature anisotropy power spectrum is shown, and constraints by selected joint datasets are reported. Finally, we found that the cosmographic series, truncated at third order, shows a better χ2 best fit value then the vanilla ΛCDM model. This can be interpreted as the requirement that higher order corrections have to be considered to correctly describe low redshift data and remove the degeneration of the models.

Cosmological constraints from galaxy clustering in the presence of massive neutrinos

The clustering ratio is defined as the ratio between the correlation function and the variance of the smoothed overdensity field. In LCDM cosmologies not accounting for massive neutrinos, it has already been proved to be independent from bias and redshift space distortions on a range of linear scales. It therefore allows for a direct comparison of measurements (from galaxies in redshift space) to predictions (for matter in real space). In this paper we first extend the applicability of such properties of the clustering ratio to cosmologies that include massive neutrinos, by performing tests against simulated data. We then investigate the constraining power of the clustering ratio when cosmological parameters such as the total neutrino mass and the equation of state of dark energy are left free. We analyse the joint posterior distribution of the parameters that must satisfy, at the same time, the measurements of the galaxy clustering ratio in the SDSS DR12, and the angular power spectrum of temperature and polarization anisotropies of the CMB measured by the Planck satellite. We find the clustering ratio to be very sensitive to the CDM density parameter, but not very much so to the total neutrino mass. Lastly, we forecast the constraining power the clustering ratio will achieve with forthcoming surveys, predicting the amplitude of its errors in a Euclid-like galaxy survey. In this case, we find it is expected to improve the constraint at 95% level on the CDM density by 40% and on the total neutrino mass by 14%.

Cross‐tests of cosmic microwave background features in the primordial spectra

The recent Planck data on the power spectrum of temperature anisotropies of the cosmic microwave background marginally support deviations from the $\Lambda$CDM model at several multipoles. With a view towards current and forthcoming observational surveys, we trace these features to other observables like the scalar bispectrum and the tensor power spectrum. A possible detection of such bumps in these channels would increase their statistical significance shedding light on the ultra violet mechanisms responsible for their appearance in the data.

Direct search for features in the primordial bispectrum

We study features in the bispectrum of the primordial curvature perturbation correlated with the reconstructed primordial power spectrum from the observed cosmic microwave background temperature data. We first show how the bispectrum can be completely specified in terms of the power spectrum and its first two derivatives, valid for any configuration of interest. Then using a model-independent reconstruction of the primordial power spectrum from the Planck angular power spectrum of temperature anisotropies, we compute the bispectrum in different triangular configurations. We find that in the squeezed limit at k ~ 0.06/Mpc and k ~ 0.014/Mpc there are marginal 2sigma deviations from the standard featureless bispectrum, which meanwhile is consistent with the reconstructed bispectrum in the equilateral configuration.

Quasi-matter bounce and inflation in the light of the CSL model

The Continuous Spontaneous Localization (CSL) model has been proposed as a possible solution to the quantum measurement problem by modifying the Schr\"{o}dinger equation. In this work, we apply the CSL model to two cosmological models of the early Universe: the matter bounce scenario and slow roll inflation. In particular, we focus on the generation of the classical primordial inhomogeneities and anisotropies that arise from the dynamical evolution, provided by the CSL mechanism, of the quantum state associated to the quantum fields. In each case, we obtained a prediction for the shape and the parameters characterizing the primordial spectra (scalar and tensor), i.e. the amplitude, the spectral index and the tensor-to-scalar ratio. We found that there exist CSL parameter values, allowed by other non-cosmological experiments, for which our predictions for the angular power spectrum of the CMB temperature anisotropy are consistent with the best fit canonical model to the latest data released by the Planck Collaboration.

Mixed inflaton and spectator field models: CMB constraints and μ distortion

We discuss mixed inflaton and spectator field models where both the fields are responsible for the observed density fluctuations. We combine the angular power spectrum of the CMB temperature anisotropy from the Planck 2013 result and other ground-based CMB observations in order to constrain both the general mixed model as well as some specific representative scenarios. Based on the Markov Chain Monte Carlo method, in addition to constraints on model parameters, we obtain the predictive posterior distributions of the CMB spectral μ distortion for those models. We demonstrate that the standard single-field inflaton model typically predicts μ ∼ 10−8 with a relatively narrow distribution, whereas for the mixed models, the distribution turns out to be much broader, and μ could be larger by almost an order of magnitude. Hence future experiments of μ distortion could provide a tool for the critical testing of the mixed source models of the primordial perturbation.

QUANTIFYING DISCORDANCE IN THE 2015 PLANCK CMB SPECTRUM

ABSTRACT We examine the internal consistency of the Planck 2015 cosmic microwave background (CMB) temperature anisotropy power spectrum. We show that tension exists between cosmological constant cold dark matter ( &Lambda; CDM ?> ) model parameters inferred from multipoles &ell; &lt; 1000 ?> (roughly those accessible to Wilkinson Microwave Anisotropy Probe), and from &ell; &ge; 1000 ?> , particularly the CDM density, &OHgr; c h 2 ?> , which is discrepant at 2.5 &sgr; ?> for a Planck -motivated prior on the optical depth, &tau; = 0.07 &PlusMinus; 0.02 ?> . We find some parameter tensions to be larger than previously reported because of inaccuracy in the code used by the Planck Collaboration to generate model spectra. The Planck &ell; &ge; 1000 ?> constraints are also in tension with low-redshift data sets, including Planck ’s own measurement of the CMB lensing power spectrum ( 2.4 &sgr; ?> ), and the most precise baryon acoustic oscillation scale determination ( 2.5 &sgr; ?> ). The Hubble constant predicted by Planck from &ell; &ge; 1000 ?> , H 0 = 64.1 &PlusMinus; 1.7 ?> km s &minus; 1 ?> Mpc−1, disagrees with the most precise local distance ladder measurement of 73.0 &PlusMinus; 2.4 ?> km s &minus; 1 ?> Mpc−1 at the 3.0 &sgr; ?> level, while the Planck value from &ell; &lt; 1000 ?> , 69.7 &PlusMinus; 1.7 ?> km s &minus; 1 ?> Mpc−1, is consistent within 1 &sgr; ?> . A discrepancy between the Planck and South Pole Telescope high-multipole CMB spectra disfavors interpreting these tensions as evidence for new physics. We conclude that the parameters from the Planck high-multipole spectrum probably differ from the underlying values due to either an unlikely statistical fluctuation or unaccounted-for systematics persisting in the Planck data.

Wiggly whipped inflation

Motivated by BICEP2 results on the CMB polarization B-mode which imply primordial gravitational waves are produced when the Universe has the expansion rate of about H ≈ 1014 GeV, and by deviations from a smooth power-law behavior for multipoles ℓ <50 in the CMB temperature anisotropy power spectrum found in the WMAP and Planck experiments, we have expanded our class of large field inflationary models that fit both the BICEP2 and Planck CMB observations consistently. These best-fitted large field models are found to have a transition from a faster roll to the slow roll V(ϕ)=m2 ϕ2/2 inflation at a field value around 14.6 MPl and thus a potential energy of V(ϕ) ∼ (1016 GeV)4. In general this transition with sharp features in the inflaton potential produces not only suppression of scalars relative to tensor modes at small k but also introduces wiggles in the primordial perturbation spectrum. These wiggles are shown to be useful to explain some localized features in the CMB angular power spectrum and can also have other observational consequences. Thus, primordial GW can be used now to make a tomography of inflation determining its fine structure. The resulting Wiggly Whipped Inflation scenario is described in details and the anticipated perturbation power spectra, CMB power spectra, non-Gaussianity and other observational consequences are calculated and compared to existing and forthcoming observations.

Scalar-tensor correlations and large-scale power suppression

Recent measurements from the BICEP2 cosmic microwave background polarization experiment indicate the presence of primordial gravitational waves with surprisingly large amplitude. If these results are confirmed, they point to a discrepancy with temperature anisotropy power spectrum measurements and suggest that extensions to the standard cosmological model may be required to resolve the discrepancy. One intriguing extension is an anticorrelation between tensors and scalars to naturally suppress the temperature power. Here I examine this possibility and show that such a suppression is not possible in the presence of a general form of anticorrelation.

Secondary CMB anisotropies from bulk motions in the presence of stochastic magnetic fields

Bulk motions of electrons along the line of sight induce secondary temperature fluctuations in the post-decoupling, reionized universe. In the presence of a magnetic field not only the scalar mode but also the vector mode act as a source for the bulk motion. The resulting angular power spectrum of temperature anisotropies of the cosmic microwave background is calculated assuming a simple model of reionization.Contributions from the standard adiabatic, curvature mode and a non helical magnetic field are included. The contribution due to magnetic fields with field strengths of order nG and negative magnetic spectral indices becomes important for multipoles larger than $\ell \sim 10^4$.

Multifield inflation after Planck: Isocurvature modes from nonminimal couplings

Recent measurements by the {\it Planck} experiment of the power spectrum of temperature anisotropies in the cosmic microwave background radiation (CMB) reveal a deficit of power in low multipoles compared to the predictions from best-fit $\Lambda$CDM cosmology. The low-$\ell$ anomaly may be explained by the presence of primordial isocurvature perturbations in addition to the usual adiabatic spectrum, and hence may provide the first robust evidence that early-universe inflation involved more than one scalar field. In this paper we explore the production of isocurvature perturbations in nonminimally coupled two-field inflation. We find that this class of models readily produces enough power in the isocurvature modes to account for the \emph{Planck} low-$\ell$ anomaly, while also providing excellent agreement with the other {\it Planck} results.

Constraints on the Sunyaev–Zel'dovich signal from the warm–hot intergalactic medium from WMAP and SPT data

The fraction of ionized gas in the Warm Hot Intergalactic Medium induces temperature anisotropies on the Cosmic Microwave Background similar to those of clusters of galaxies. The Sunyaev-Zel'dovich anisotropies due to these low density, weakly non-linear, baryon filaments can not be distinguished from that of clusters using frequency information, but they can be separated since their angular scales are very different. To determine the relative contribution of the WHIM SZ signal to the radiation power spectrum of temperature anisotropies, we explore the parameter space of the concordance LCDM model using Monte Carlo Markov Chains and the Wilkinson Microwave Anisotropy Probe 7yr and South Pole Telescope data. We find marginal evidence of a contribution by diffuse gas, with amplitudes of A_WHIM=10-20 muK^2, but the results are also compatible with a null contribution from the WHIM, allowing to set an upper limit of A_WHIM < 43 muK^2 (95.4% C.L.). The signal produced by galaxy clusters remains at A_CL=4.5 muK^2, a value similar to what is obtained when no WHIM is included. From the measured WHIM amplitude we constrain the temperature-density phase diagram of the diffuse gas, and find it to be compatible with numerical simulations. The corresponding baryon fraction in the WHIM varies from 0.43 to 0.47, depending on model parameters. Planck data could set tighter constraints on the temperature-density relation.

Exploring the origin of the fine structures in the CMB temperature angular power spectrum

The angular power spectrum of the cosmic microwave background (CMB) temperature anisotropies is a good probe to look into the primordial density fluctuations at large scales in the universe. Here we re-examine the angular power spectrum of the Wilkinson Microwave Anisotropy Probe data, paying particular attention to the fine structures (oscillations) at $\ell=100 \sim 150$ reported by several authors. Using Monte-Carlo simulations, we confirm that the gap from the simple power law spectrum is a rare event, about 2.5--3$\sigma$, if these fine structures are generated by experimental noise and the cosmic variance. Next, in order to investigate the origin of the structures, we examine frequency and direction dependencies of the fine structures by dividing the observed QUV frequency maps into four sky regions. We find that the structures around $\ell \sim 120$ do not have significant dependences either on frequencies or directions. For the structure around $\ell \sim 140$, however, we find that the characteristic signature found in the all sky power spectrum is attributed to the anomaly only in the South East region.

Resonant signatures of heavy scalar fields in the cosmic microwave background

We investigate the possibility that a heavy scalar field, whose mass exceeds the Hubble scale during inflation, could leave non-negligible signatures in the Cosmic Microwave Background (CMB) temperature anisotropy power spectrum through the parametric resonance between its background oscillations and the inflaton fluctuations. By assuming the heavy scalar field couples with the inflaton derivatively, we show that the resonance can be efficient without spoiling the slow-roll inflation. The primordial power spectrum modulated by the resonance has a sharp peak at a specific scale and could be an origin of the anomalies observed in the angular power spectrum of the CMB. In some values of parameters, the modulated spectrum can fit the observed data better than the simple power-law power spectrum, though the resultant improvement of the fit is not large enough and hence other observations such as non-Gaussianity are necessary to confirm that the CMB anomalies are originated from the resonant effect of the heavy scalar field. The resonant signatures can provide an opportunity to observe heavy degrees of freedom during inflation and improve our understanding of physics behind inflation.

Gauging the contribution of X-ray sources to reionization through the kinetic Sunyaev-Zel'dovich effect

Measurements of the kinetic Sunyaev-Zel'dovich (kSZ) effect from instruments such as the South Pole Telescope (SPT) and the Atacama Cosmology Telescope (ACT) will soon put improved constraints on reionization. Popular models assume that UV photons alone are responsible for reionization of the intergalactic medium. We explore the effects of a significant contribution of X-rays to reionization on the kSZ signal. Because X-rays have a large mean free path through the neutral intergalactic medium, they introduce partial ionization in between the sharp-edged bubbles created by UV photons. This smooth ionization component changes the power spectrum of the cosmic microwave background (CMB) temperature anisotropies. We quantify this effect by running semi-numerical simulations of reionization. We test a number of different models of reionization without X-rays that have varying physical parameters, but which are constrained to have similar total optical depths to electron scattering. These are then compared to models with varying levels of contribution to reionization from X-rays. We find that models with more than a 10% contribution from X-rays produce a significantly lower power spectrum of temperature anisotropies than all the UV-only models tested. The expected sensitivity of SPT and ACT may be insufficient to distinguish between our models, however, a non-detection of the kSZ signal from the epoch of reionization could result from the contribution of X-rays. It will be important for future missions with improved sensitivity to consider the impact of X-ray sources on reionization.

Application of XFaster power spectrum and likelihood estimator to Planck

We develop the XFASTER cosmic microwave background (CMB) temperature and polarization anisotropy power spectrum and likelihood technique for the Planck CMB satellite mission. We give an overview of this estimator and its current implementation, and present the results of applying this algorithm to simulated Planck data. We show that it can accurately extract the power spectrum of Planck data for the high-l multipoles range. We compare the XFASTER approximation for the likelihood to other high-l likelihood approximations such as Gaussian and Offset Lognormal and a low-l pixel-based likelihood. We showthat theXFASTER likelihood is not only accurate at high l, but also performs well at moderately low multipoles. We also present results for cosmological parameter Markov chain Monte Carlo estimation with the XFASTER likelihood. As long as the low-l polarization and temperature power are properly accounted for, e.g. by adding an adequate low-l likelihood ingredient, the input parameters are recovered to a high level of accuracy.

The Effect of Varying Sound Velocity on Primordial Curvature Perturbations

We study the effects of sudden change in the sound velocity on primordial curvature perturbation spectrum in inflationary cosmology, assuming that the background evolution satisfies the slow-roll condition throughout. It is found that the power spectrum acquires oscillating features which are determined by the ratio of the sound speed before and after the transition and the wavenumeber which crosses the sound horizon at the transition, and their analytic expression is given. In some values of those parameters, the oscillating primordial power spectrum can better fit the observed Cosmic Microwave Background temperature anisotropy power spectrum than the simple power-law power spectrum, although introduction of such a new degree of freedom is not justified in the context of Akaike's Information Criterion.