Search

The kinematic Sunyaev-Zel'dovich (kSZ) effect---the Doppler boosting of Cosmic Microwave Background (CMB) photons scattering off free electrons with nonzero line-of-sight velocity---is an excellent probe of the distribution of baryons in the Universe. In this paper, we measure the kSZ effect due to ionized gas traced by infrared-selected galaxies from the $unWISE$ catalog. We employ the ``projected-field'' kSZ estimator, which does not require spectroscopic galaxy redshifts. To suppress contributions from non-kSZ signals associated with the galaxies (e.g., dust emission and thermal SZ), this estimator requires foreground-cleaned CMB maps, which we obtain from $Planck$ and $WMAP$ data. Using a new ``asymmetric'' estimator that combines different foreground-cleaned CMB maps to maximize the signal-to-noise, we measure the ${\mathrm{kSZ}}^{2}$-galaxy cross-power spectrum for three subsamples of the $unWISE$ galaxy catalog. These subsamples peak at mean redshifts $z\ensuremath{\approx}0.6$, 1.1, and 1.5, have average halo mass $\ensuremath{\sim}1--5\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }\text{ }{h}^{\ensuremath{-}1}{M}_{\ensuremath{\bigodot}}$, and in total contain over 500 million galaxies. After marginalizing over contributions from CMB lensing, we measure the amplitude of the kSZ signal ${A}_{{\mathrm{kSZ}}^{2}}=0.42\ifmmode\pm\else\textpm\fi{}0.31(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.02(\mathrm{sys})$, $5.02\ifmmode\pm\else\textpm\fi{}1.01(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.49(\mathrm{sys})$, and $8.23\ifmmode\pm\else\textpm\fi{}3.23(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.57(\mathrm{sys})$, for the three subsamples, where ${A}_{{\mathrm{kSZ}}^{2}}=1$ corresponds to our fiducial theoretical model. The combined statistical significance of our kSZ detection exceeds $5\ensuremath{\sigma}$. Our theoretical model includes the first calculation of lensing magnification contributions to the ${\mathrm{kSZ}}^{2}$-galaxy cross-power spectrum, which are significant for the $z\ensuremath{\approx}1.1$ and 1.5 subsamples. We discuss possible explanations for the excess kSZ signal associated with the $z\ensuremath{\approx}1.1$ sample, and show that foreground contamination in the CMB maps is very unlikely to be the cause. From our measurements of ${A}_{{\mathrm{kSZ}}^{2}}$, we constrain the product of the baryon fraction ${f}_{b}$ and free electron fraction ${f}_{\mathrm{free}}$ to be $({f}_{b}/0.158)({f}_{\mathrm{free}}/1.0)=0.65\ifmmode\pm\else\textpm\fi{}0.24$, $2.24\ifmmode\pm\else\textpm\fi{}0.25$, and $2.87\ifmmode\pm\else\textpm\fi{}0.57$ at $z\ensuremath{\approx}0.6$, 1.1, and 1.5, respectively, consistent with a large fraction of the cosmic baryon abundance existing in an ionized state at low redshifts.

Measurements of the thermal Sunyaev-Zel'dovich (tSZ) effect have long been recognized as a powerful cosmological probe. Here we assess the importance of relativistic temperature corrections to the tSZ signal on the power spectrum analysis of the Planck Compton-$y$ map, developing a novel formalism to account for the associated effects. The amplitude of the tSZ power spectrum is found to be sensitive to the effective electron temperature, $\bar{T}_e$, of the cluster sample. Omitting the corresponding modifications leads to an underestimation of the $yy$-power spectrum amplitude. Relativistic corrections thus add to the error budget of tSZ power spectrum observables such as $\sigma_8$. This could help alleviate the tension between various cosmological probes, with the correction scaling as $\Delta \sigma_8/\sigma_8 \simeq 0.019\,[k\bar{T}_e\,/\,5\,{\rm keV}]$ for Planck. At the current level of precision, this implies a systematic shift by $\simeq 1\sigma$, which can also be interpreted as an overestimation of the hydrostatic mass bias by $\Delta b \simeq 0.046\,(1-b)\,[k\bar{T}_e\,/\,5\,{\rm keV}]$, bringing it into better agreement with hydrodynamical simulations. It is thus time to consider relativistic temperature corrections in the processing of current and future tSZ data., Comment: 6 pages, 4 figures, minor changes, updated to match version accepted by MNRAS

Delabrouille, J., et al., This paper discusses the science case for a sensitive spectro-polarimetric survey of the microwave sky. Such a survey would provide a tomographic and dynamic census of the three-dimensional distribution of hot gas, velocity flows, early metals, dust, and mass distribution in the entire Hubble volume, exploit CMB temperature and polarisation anisotropies down to fundamental limits, and track energy injection and absorption into the radiation background across cosmic times by measuring spectral distortions of the CMB blackbody emission. In addition to its exceptional capability for cosmology and fundamental physics, such a survey would provide an unprecedented view of microwave emissions at sub-arcminute to few-arcminute angular resolution in hundreds of frequency channels, a data set that would be of immense legacy value for many branches of astrophysics. We propose that this survey be carried out with a large space mission featuring a broad-band polarised imager and a moderate resolution spectro-imager at the focus of a 3.5 m aperture telescope actively cooled to about 8K, complemented with absolutely-calibrated Fourier Transform Spectrometer modules observing at degree-scale angular resolution in the 10–2000 GHz frequency range. We propose two observing modes: a survey mode to map the entire sky as well as a few selected wide fields, and an observatory mode for deeper observations of regions of specific interest., This work has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No 725456, CMBSPEC) as well as the Royal Society (grants UF130435 and RG140523). JARM acknowledges financial support from the Spanish Ministry of Science and Innovation (MICINN) under the project AYA2017-84185-P, and from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement 687312 (RADIOFOREGROUNDS). C.H.-M. acknowledges the support of the Spanish Ministry of Science through project PGC2018-097585-B-C21. Financial support from the ASI/Physics Department of the University of Roma–Tor Vergata agreement n. 2016-24-H.0 for study activities of the Italian cosmology community is acknowledged. JLB is supported by the Allan C. and Dorothy H. Davis Fellowship, and has been supported by the Spanish MINECO under grant BES-2015-071307, co-funded by the ESF during part of the development of this work.

The early dark energy (EDE) scenario aims to increase the value of the Hubble constant ($H_0$) inferred from cosmic microwave background (CMB) data over that found in $\Lambda$CDM, via the introduction of a new form of energy density in the early universe. The EDE component briefly accelerates cosmic expansion just prior to recombination, which reduces the physical size of the sound horizon imprinted in the CMB. Previous work has found that non-zero EDE is not preferred by Planck CMB power spectrum data alone, which yield a 95% confidence level (CL) upper limit $f_{\rm EDE} < 0.087$ on the maximal fractional contribution of the EDE field to the cosmic energy budget. In this paper, we fit the EDE model to CMB data from the Atacama Cosmology Telescope (ACT) Data Release 4. We find that a combination of ACT, large-scale Planck TT (similar to WMAP), Planck CMB lensing, and BAO data prefers the existence of EDE at $>99.7$% CL: $f_{\rm EDE} = 0.091^{+0.020}_{-0.036}$, with $H_0 = 70.9^{+1.0}_{-2.0}$ km/s/Mpc (both 68% CL). From a model-selection standpoint, we find that EDE is favored over $\Lambda$CDM by these data at roughly $3\sigma$ significance. In contrast, a joint analysis of the full Planck and ACT data yields no evidence for EDE, as previously found for Planck alone. We show that the preference for EDE in ACT alone is driven by its TE and EE power spectrum data. The tight constraint on EDE from Planck alone is driven by its high-$\ell$ TT power spectrum data. Understanding whether these differing constraints are physical in nature, due to systematics, or simply a rare statistical fluctuation is of high priority. The best-fit EDE models to ACT and Planck exhibit coherent differences across a wide range of multipoles in TE and EE, indicating that a powerful test of this scenario is anticipated with near-future data from ACT and other ground-based experiments., Comment: v1: 25+20 pages, 6+18 figures, submitted to PRD; v2: 26+20 pages, 7+18 figures, results unchanged, matches PRD accepted version. MCMC chains available at https://lambda.gsfc.nasa.gov/product/act/actpol_mcmc_chains_get.html

A quasi-static approximation (QSA) for modified gravity can be applied in a number of ways. We consider three different analytical formulations based on applying this approximation to: (1) the field equations; (2) the equations for the two metric potentials; (3) the use of the attractor solution derived within the Equation of State (EoS) approach. We assess the veracity of these implementations on the effective gravitational constant ($\mu$) and the slip parameter ($\eta$), within the framework of Horndeski models. In particular, for a set of models we compare cosmological observables, i.e., the matter power spectrum and the CMB temperature and lensing angular power spectra, computed using the QSA, with exact numerical solutions. To do that, we use a newly developed branch of the CLASS code: QSA_class. All three approaches agree exactly on very small scales. Typically, we find that, except for $f(R)$ models where all the three approaches lead to the same result, the quasi-static approximations differ from the numerical calculations on large scales ($k \lesssim 3 - 4 \times 10^{-3}\,h\,{\rm Mpc}^{-1}$). Cosmological observables are reproduced to within 1% up to scales ${\rm K} = k/H_0$ of the order of a few and $\ell>5$ for the approaches based on the field equations and on the EoS, and we also do not find any appreciable difference if we use the scale-dependent expressions for $\mu$ and $\eta$ with respect to the value on small scales, showing that the formalism and the conclusions are reliable and robust, fixing the range of applicability of the formalism. We discuss why the expressions derived from the equations for the potentials have limited applicability. Our results are in agreement with previous analytical estimates and show that the QSA is a reliable tool and can be used for comparison with current and future observations to constrain models beyond $\Lambda$CDM., Comment: The manuscript is divided into two parts: the main paper (37 pages, 3 figures, 1 table) and the Supplementary Materials (24 pages, 1 table). Improved discussion on the validity of the quasi-static approximation. Matches the published version on JCAP

Spectral distortions (SDs) of the cosmic microwave background (CMB) provide a powerful tool for studying particle physics. Here we compute the distortion signals from decaying particles that convert directly into photons at different epochs during cosmic history, focusing on injection energies $E_\mathrm{inj}\lesssim 20\,\mathrm{keV}$. We deliver a comprehensive library of SD solutions that can be used to study a wide range of particle physics scenarios. We use {\tt CosmoTherm} to compute the SD signals, including effects on the ionization history and opacities of the Universe. We also consider the effect of blackbody-induced stimulated decay, which can modify the injection history significantly. Then, we use data from COBE/FIRAS and EDGES to constrain the properties of the decaying particles. We explore scenarios where these provide a dark matter (DM) candidate or constitute only a small fraction of DM. We complement the SD constraints with CMB anisotropy constraints, highlighting new effects from injections at very-low photon energies ($h\nu\lesssim 10^{-4}\,\mathrm{eV}$). Our model-independent constraints exhibit rich structures in the lifetime-energy domain, covering injection energies $E_\mathrm{inj}\simeq 10^{-10}\mathrm{eV}-10\mathrm{keV}$ and lifetimes $\tau_X\simeq 10^5\,\mathrm{s}-10^{33}\mathrm{s}$. We discuss the constraints on axions and axion-like particles that convert directly into two photons, revising existing SD constraints in the literature. Our limits are competitive with other constraints for axion masses $m_a c^2\gtrsim 27\,\mathrm{eV}$ and we find that simple estimates based on the overall energetics are generally inaccurate. Future CMB spectrometers could significantly improve the obtained constraints, thus providing an important complementary probe of early-universe particle physics., Comment: match published version

The Sunyaev-Zeldovich (SZ) effect provides a powerful cosmological probe, which traditionally is approached independently as cluster number count (CNC) or power spectrum (PS) analysis. Here, we devise a new method for analysing the $y$-map by introducing the survey completeness function, conventionally only used in the CNC analysis, in the $yy$-PS modeling. This provides a systematic method, based mainly on SZ observables, for obtaining two complementary $y$-maps, one incorporating detected/resolved clusters and the other relying only on diffuse/unresolved SZ contributions. We use the catalogue of clusters obtained in the \Planck CNC analysis to define the completeness function linking these two $y$-maps. The split depends on the chosen signal-to-noise detection threshold, which we vary in our discussion. We carefully propagate the effect of completeness cuts on the non-Gaussian error contributions in the $yy$-PS analysis, highlighting the benefits of masking massive clusters. Our analysis of the \Planck $yy$-PS for the unresolved component yields a mass bias of $b=0.15\pm0.04$, consistent with the standard value ($b\approx0.2$), in comparison to $b=0.4\pm 0.05$ for the total $yy$-PS. We find indications for this drift being driven by the CIB-tSZ cross correlation, which dominantly originates from clusters in the resolved component of the $y$-map. Another possible explanation is the presence of a mass-dependent bias, which has been theoretically motivated and can be quantified with our novel method. We furthermore find first hints for the presence of the 2-halo terms in the $yy$-PS. Finally, the proposed method provides a new framework for combining the complementary information of the CNC and PS analyses in upcoming SZ surveys., Comment: 19 pages, 22 figures

In this proceeding I summarise the current status of cosmological constraints obtained from current SZ data, focusing on the Planck thermal SZ power spectrum and cluster counts. I discuss the consistency between Planck SZ data and other SZ cluster or galaxy surveys as well as the apparent discrepancy between SZ and CMB for the amplitude of matter clustering σ8. Finally I discuss forecasted constraints on massive neutrinos and the X-ray mass bias in the context of future SZ power spectrum measurements.

We consistently include the effect of massive neutrinos in the thermal Sunyaev Zeldovich (SZ) power spectrum and cluster counts analyses, highlighting subtle dependencies on the total neutrino mass and data combination. In particular, we find that using the transfer functions for cold dark matter (CDM) + baryons in the computation of the halo mass function, instead of the transfer functions including neutrino perturbations, as prescribed in recent work, yields an ≈0.25 per cent downward shift of the σ8 constraint from tSZ power spectrum data, with a fiducial neutrino mass Σmν = 0.06 eV. In ΛCDM, with an X-ray mass bias corresponding to the expected hydrostatic mass bias, i.e. (1 − b) ≃ 0.8, our constraints from Planck SZ data are consistent with the latest results from SPT, DES-Y1, and KiDS+VIKING-450. In νΛCDM, our joint analyses of Planck SZ with Planck 2015 primary CMB yield a small improvement on the total neutrino mass bound compared to the Planck 2015 primary CMB constraint, as well as (1 − b) = 0.64 ± 0.04 (68 per cent CL). For forecasts, we find that competitive neutrino mass measurements using cosmic variance limited SZ power spectrum require masking the heaviest clusters and probing the small-scale SZ power spectrum up to ℓmax ≈ 104. Although this is challenging, we find that SZ power spectrum can realistically be used to tightly constrain intracluster medium properties: we forecast a 2 per cent determination of the X-ray mass bias by combining CMB-S4 and our mock SZ power spectrum with ℓmax = 103.

We use the Equation of State (EoS) approach to study the evolution of the dark sector in Horndeski models, the most general scalar-tensor theories with second order equations of motion. By including the effects of the dark sector into our code EoS\_class, we demonstrate the numerical stability of the formalism and excellent agreement with results from other publicly available codes for a range of parameters describing the evolution of the function characterising the perturbations for Horndeski models, $\alpha_{\rm x}$, with ${\rm x}=\{{\rm K}, {\rm B}, {\rm M}, {\rm T}\}$. After demonstrating that on sub-horizon scales ($k\gtrsim 10^{-3}~{\rm Mpc}^{-1}$ at $z=0$) velocity perturbations in both the matter and the dark sector are typically subdominant with respect to density perturbations in the equation of state for perturbations, we find an attractor solution for the dark sector gauge-invariant density perturbation $\Delta_{\rm ds}$ by neglecting its time derivatives in the equation describing its time evolution, as commonly done in the well-known quasi-static approximation. Using this result, we provide simplified expressions for the equation-of-state functions: the dark sector entropy perturbations $w_{\rm ds}\Gamma_{\rm ds}$ and anisotropic stress $w_{\rm ds}\Pi_{\rm ds}$. From this we derive a growth factor-like equation for both matter and dark sector and are able to capture the relevant physics for several observables with great accuracy. We finally present new analytical expressions for the well-known modified gravity phenomenological functions $\mu$, $\eta$ and $\Sigma$ for a generic Horndeski model as functions of $\alpha_{\rm x}$. We show that on small scales they reproduce expressions presented in previous works, but on large scales, we find differences with respect to other works., Comment: 43 pages, 13 figures. It matches the accepted version on JCAP

We investigate generalized Einstein-Aether theories that are compatible with the Planck Cosmic Microwave Background (CMB) temperature anisotropy, polarisation, and lensing data. For a given dark energy equation of state, $w_{\rm de}$, we formulate a designer approach and we investigate their impact on the CMB temperature anisotropy and matter power spectra. We use the Equation of State approach to parametrize the perturbations and find that this approach is particularly useful in identifying the most suitable and numerically efficient parameters to explore in a Markov chain Monte Carlo (MCMC) analysis. We find the data constrains models with $w_{\rm de} = -1$ to be compatible with $\Lambda$CDM. For $w_{\rm de} \not= -1$ models, which avoid the gravitational waves constraint through the entropy perturbation, we constrain $w_{\rm de}$ to be $w_{\rm de } = -1.06^{+0.08}_{-0.03}$ (CMB) and $w_{\rm de } =-1.04^{+0.05}_{-0.02}$ (CMB+Lensing) at $68\%$C.L., and find that these models can be different from $\Lambda$CDM and still be compatible with the data. We also find that these models can ameliorate some anomalies in $\Lambda$CDM when confronted with data, such as the low-$\ell$ and high-$k$ power in the CMB temperature anisotropy and matter power spectra respectively, but not simultaneously. We also investigate the anomalous lensing amplitude, quantified by $A_{\rm lens}$, and find that that for $w_{\rm de} = -1$ models, $A_{\rm lens} = 1.15^{+0.07}_{-0.08}$ (CMB) and $A_{\rm lens} = 1.12\pm0.05$ (CMB+Lensing) at $68\%$C.L. $\sim$ 2$\sigma$ larger than expected, similar to previous analyses of $\Lambda$CDM., Comment: 20 pages, 9 figures, 4 tables. Public version of the code will be released upon acceptance by PRD

Electron-ion Bremsstrahlung (free-free) emission and absorption occur in many astrophysical plasmas for a wide range of physical conditions. This classical problem has been studied multiple times, and many analytical and numerical approximations exist. However, accurate calculations of the transition from the non-relativistic to the relativistic regime remain sparse. Here we provide a comprehensive study of the free-free Gaunt factors for ions with low charge (Z, 12 pages + 5 pages appendix and references, 17 figures, to be submitted to MNRAS, BRpack will be made available at www.chluba.de/BRpack

We compare Einstein-Boltzmann solvers that include modifications to General Relativity and find that, for a wide range of models and parameters, they agree to a high level of precision. We look at three general purpose codes that primarily model general scalar-tensor theories, three codes that model Jordan-Brans-Dicke (JBD) gravity, a code that models f(R) gravity, a code that models covariant Galileons, a code that models Ho\v{r}ava-Lifschitz gravity and two codes that model non-local models of gravity. Comparing predictions of the angular power spectrum of the cosmic microwave background and the power spectrum of dark matter for a suite of different models, we find agreement at the sub-percent level. This means that this suite of Einstein-Boltzmann solvers is now sufficiently accurate for precision constraints on cosmological and gravitational parameters., Comment: 23 pages; 11 figures. Matches version accepted in PRD

International audience; We constrain the dark energy equation of state parameter, $${w}$$, using the power spectrum of the thermal Sunyaev–Zeldovich (tSZ) effect. We improve upon previous analyses by taking into account the trispectrum in the covariance matrix and marginalizing over the foreground parameters, the correlated noise, the mass bias B in the Planck universal pressure profile, and all the relevant cosmological parameters (i.e. not just Ω_m and σ_8). We find that the amplitude of the tSZ power spectrum at ℓ ≲ 10^3 depends primarily on F ≡ σ_8(Ω_m/B)^0.40h^−0.21, where B is related to more commonly used variable b by B = (1 − b)^−1. We measure this parameter with 2.6 per cent precision, F = 0.460 ± 0.012 (68 per cent CL). By fixing the bias to B = 1.25 and adding the local determination of the Hubble constant H_0 and the amplitude of the primordial power spectrum constrained by the Planck cosmic microwave background (CMB) data, we find $${w}$$ = −1.10 ± 0.12, σ_8 = 0.802 ± 0.037, and Ω_m = 0.265 ± 0.022 (68 per cent CL). Our limit on $${w}$$ is consistent with and is as tight as that from the distance-alone constraint from the CMB and H_0. Finally, by combining the tSZ power spectrum and the CMB data we find, in the Λ cold dark mattermodel, the mass bias of B = 1.71 ± 0.17, i.e. 1 − b = 0.58 ± 0.06 (68 per cent CL).

We extend the phenomenology of loop quantum cosmology (LQC) to second order in perturbations. Our motivation is twofold. On the one hand, since LQC predicts a cosmic bounce that takes place at the Planck scale, the second order contributions could be large enough to jeopardize the validity of the perturbative expansion on which previous results rest. On the other hand, the upper bounds on primordial non-Gaussianity obtained by the Planck Collaboration are expected to play a significant role on explorations of the LQC phenomenology. We find that the bounce in LQC produces an enhancement of non-Gaussianity of several orders of magnitude, on length scales that were larger than the curvature radius at the bounce. Nonetheless, we find that one can still rely on the perturbative expansion to make predictions about primordial perturbations. We discuss the consequences of our results for LQC and its predictions for the cosmic microwave background., Minor updates: current version matches the accepted PRD manuscript

The discovery of apparent cosmological acceleration has spawned a huge number of dark energy and modified gravity theories. The f(R) models of gravity are obtained when one replaces the Ricci scalar in the Einstein-Hilbert action by an arbitrary function of the Ricci scalar. In this work we provide expressions for the equations of state (EoS) for perturbations which completely characterize the linearized perturbations in f(R) gravity, including the scalar, vector, and tensor modes. The EoS formalism is a powerful and elegant parametrization where the modification to General Relativity are treated as a dark-energy-fluid. The perturbed dark-energy-fluid variables such as the anisotropic stress or the entropy perturbation are explicitly given in terms of parameters of the model of interest.

International audience; The prediction of a phase of inflation whose number of e-folds is constrained is an important feature of loop quantum cosmology. This work aims at giving some elementary clarifications on the role of the different hypotheses leading to this conclusion. We show that the duration of inflation does not depend significantly on the modified background dynamics in the quantum regime.

Non-perturbative quantum-gravity effects can change the fate of black holes and make them bounce in a time scale shorter than the Hawking evaporation time. In this article, we show that this hypothesis can account for the GeV excess observed from the galactic center by the Fermi satellite. By carefully taking into account the secondary component due to the decay of unstable hadrons, we show that the model is fully self-consistent. This phenomenon presents a specific redshift-dependance that could allow to distinguish it from other astrophysical phenomena possibly contributing to the GeV excess., 6 pages, 3 figures

We study the equations for the evolution of cosmological perturbations in $f(\mathcal{R})$ and conclude that this modified gravity model can be expressed as a dark energy fluid at background and linearized perturbation order. By eliminating the extra scalar degree of freedom known to be present in such theories, we are able to characterize the evolution of the perturbations in the scalar sector in terms of equations of state for the entropy perturbation and anisotropic stress which are written in terms of the density and velocity perturbations of the dark energy fluid and those in the matter, or the metric perturbations. We also do the same in the much simpler vector and tensor sectors. In order to illustrate the simplicity of this formulation, we numerically evolve perturbations in a small number of cases.

Loop quantum gravity is a mature theory. To proceed to explicit calculations in cosmology, it is necessary to make assumptions and simplifications based on the symmetries of the cosmological setting. Symmetry reduction is especially critical when dealing with cosmological perturbations. The present article reviews several approaches to the problem of building a consistent formalism that describes the dynamics of perturbations on a quantum spacetime and tries to address their respective strengths and weaknesses. We also review the main open issues in loop quantum cosmology., Invited article for an IJMP volume dedicated to loop quantum gravity

It is often argued that inflation erases all the information about what took place before it started. Quantum gravity, relevant in the Planck era, seems therefore mostly impossible to probe with cosmological observations. In general, only very ad hoc scenarios or hyper fine-tuned initial conditions can lead to observationally testable theories. Here we consider a well-defined and well motivated candidate quantum cosmology model that predicts inflation. Using the most recent observational constraints on the cosmic microwave background B modes, we show that the model is excluded for all its parameter space, without any tuning. Some important consequences are drawn for the deformed algebra approach to loop quantum cosmology. We emphasize that neither loop quantum cosmology in general nor loop quantum gravity are disfavored by this study but their falsifiability is established., 5 pages, 2 figure

Quantum gravity may allow black holes to tunnel into white holes. If so, the lifetime of a black hole could be shorter than the one given by Hawking evaporation, solving the information paradox. More interestingly, this could open to a new window for quantum-gravity phenomenology, in connection with the existence of primordial black holes. We discuss in particular the power of the associated explosion and the possibility to observe an astrophysical signal in the radio and in the gamma wavelengths., 6 pages, Proceedings of the 2015 Karl Schwarzschild Meeting on Gravitational Physics

Loop quantum cosmology tries to capture the main ideas of loop quantum gravity and to apply them to the Universe as a whole. Two main approaches within this framework have been considered to date for the study of cosmological perturbations: the dressed metric approach and the deformed algebra approach. They both have advantages and drawbacks. In this article, we accurately compare their predictions. In particular, we compute the associated primordial tensor power spectra. We show -- numerically and analytically -- that the large scale behavior is similar for both approaches and compatible with the usual prediction of general relativity. The small scale behavior is, the other way round, drastically different. Most importantly, we show that in a range of wavenumbers explicitly calculated, both approaches do agree on predictions that, in addition, differ from standard general relativity and do not depend on unknown parameters. These features of the power spectrum at intermediate scales might constitute a universal loop quantum cosmology prediction that can hopefully lead to observational tests and constraints. We also present a complete analytical study of the background evolution for the bouncing universe that can be used for other purposes., 15 pages, 7 figures

In effective models of loop quantum cosmology, the holonomy corrections are associated with deformations of space-time symmetries. The most evident manifestation of the deformations is the emergence of an Euclidean phase accompanying the non-singular bouncing dynamics of the scale factor. In this article, we compute the power spectrum of scalar perturbations generated in this model, with a massive scalar field as the matter content. Instantaneous and adiabatic vacuum-type initial conditions for scalar perturbations are imposed in the contracting phase. The evolution through the Euclidean region is calculated based on the extrapolation of the time direction pointed by the vectors normal to the Cauchy hypersurface in the Lorentzian domains. The obtained power spectrum is characterized by a suppression in the IR regime and oscillations in the intermediate energy range. Furthermore, the speculative extension of the analysis in the UV reveals a specific rise of the power., Comment: 13 pages, 4 figures

Recent data from heavy ion collisions at RHIC show unexpectedly large near-angle correlations that broaden longitudinally with increasing centrality. The amplitude of this ridge-like correlation rises rapidly, reaches a maximum, and then falls in the most central collisions. In this letter we explain how this behavior can be explained as initial-state coordinate-space anisotropies converted into final-state momentum-space correlations. We propose $v_n^2/\epsilon_{n,\mathrm{part}}^{2}$ as a useful way to study length scales and provide a prediction for the ridge in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV., Comment: 1 Figure and text added