arXiv subjects

Mario Ballardini

Publications and source records attributed to Mario Ballardini.

At least 37 records · Page 2Linked to original sources

arXiv2021

Cosmological parameter forecasts by a joint 2D tomographic approach to CMB and galaxy clustering

The cross-correlation between the cosmic microwave background (CMB) fields and matter tracers carries important cosmological information. In this paper, we forecast by a signal-to-noise ratio analysis the information contained in the cross-correlation of the CMB anisotropy fields with source counts for future cosmological observations and its impact on cosmological parameters uncertainties, using a joint tomographic analysis. We include temperature, polarization and lensing for the CMB fields and galaxy number counts for the matter tracers. By restricting ourselves to quasi-linear scales, we forecast by a Fisher matrix formalism the relative importance of the cross-correlation of source counts with the CMB in the constraints on the parameters for several cosmological models. We obtain that the CMB-number counts cross-correlation can improve the dark energy Figure of Merit (FoM) at most up to a factor $\sim 2$ for LiteBIRD+CMB-S4 $\times$ SKA1 compared to the uncorrelated combination of both probes and will enable the Euclid-like photometric survey to reach the highest FoM among those considered here. We also forecast how CMB-galaxy clustering cross-correlation could increase the FoM of the neutrino sector, also enabling a statistically significant ($\gtrsim$ 3$σ$ for LiteBIRD+CMB-S4 $\times$ SPHEREx) detection of the minimal neutrino mass allowed in a normal hierarchy by using quasi-linear scales only. Analogously, we find that the uncertainty in the local primordial non-Gaussianity could be as low as $σ(f_{\rm NL}) \sim 1.5-2$ by using two-point statistics only with the combination of CMB and radio surveys such as EMU and SKA1. Our results highlight the additional constraining power of the cross-correlation between CMB and galaxy clustering from future surveys which is mainly based on quasi-linear scales and therefore sufficiently robust to non-linear effects.

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arXiv2021

Early modified gravity in light of the $H_0$ tension and LSS data

We present a model of Early Modified Gravity (EMG) consisting in a scalar field $σ$ with a non-minimal coupling to the Ricci curvature of the type $M^2_{\rm pl}+ξσ^2$ plus a cosmological constant and a small effective mass and demonstrate its ability to alleviate the $H_0$ tension while providing a good fit to Cosmic Microwave Background (CMB) anisotropies and Baryon Acoustic Oscillations (BAO) data. In this model the scalar field, frozen deep in the radiation era, grows around the redshift of matter-radiation equality because of the coupling to non-relativistic matter. The small effective mass, which we consider here as induced by a quartic potential, then damps the scalar field into coherent oscillations around its minimum at $σ=0$, leading to a weaker gravitational strength at early times and naturally recovering the consistency with laboratory and Solar System tests of gravity. We analyze the capability of EMG with positive $ξ$ to fit current cosmological observations and compare our results to the case without an effective mass and to the popular early dark energy models with $ξ=0$. We show that EMG with a quartic coupling of the order of $λ\sim\mathcal{O}({\rm eV}^4/M_{\rm pl}^4)$ can substantially alleviate the $H_0$ tension also when the full shape of the matter power spectrum is included in the fit in addition to CMB and Supernovae (SN) data.

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arXiv2020

Scalar-tensor theories of gravity, neutrino physics, and the $H_0$ tension

We use $Planck$ 2018 data to constrain the simplest models of scalar-tensor theories characterized by a coupling to the Ricci scalar of the type $F(σ) R$ with $F(σ) = N_{pl}^2 + ξσ^2$. We update our results with previous $Planck$ and BAO data releases obtaining the tightest constraints to date on the coupling parameters, that is $ξ< 5.5 \times 10^{-4}$ for $N_{pl}=0$ (induced gravity or equivalently extended Jordan-Brans-Dicke) and $(N_{pl} \sqrt{8 πG})-1 < 1.8 \times 10^{-5}$ for $ξ= -1/6$ (conformal coupling), both at 95% CL. Because of a modified expansion history after radiation-matter equality compared to the $Λ$CDM model, all these dynamical models accommodate a higher value for $H_0$ and therefore alleviate the tension between $Planck$/BAO and distance-ladder measurement from SNe Ia data from $4.4σ$ at best to $2.3σ$. We show that all these results are robust to changes in the neutrino physics. In comparison to the $Λ$CDM model, partial degeneracies between neutrino physics and the coupling to the Ricci scalar allow for smaller values $N_{\rm eff} \sim 2.8$, $1σ$ lower compared to the standard $N_{\rm eff} = 3.046$, and relax the upper limit on the neutrino mass up to 40%.

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arXiv2020

Cosmology Intertwined III: $f σ_8$ and $S_8$

The standard $Λ$ Cold Dark Matter cosmological model provides a wonderful fit to current cosmological data, but a few tensions and anomalies became statistically significant with the latest data analyses. While these anomalies could be due to the presence of systematic errors in the experiments, they could also indicate the need for new physics beyond the standard model. In this Letter of Interest we focus on the tension of the Planck data with weak lensing measurements and redshift surveys, about the value of the matter energy density $Ω_m$, and the amplitude or rate of the growth of structure ($σ_8,fσ_8$). We list a few interesting models for solving this tension, and we discuss the importance of trying to fit with a single model a full array of data and not just one parameter at a time.

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arXiv2020

Cosmology Intertwined II: The Hubble Constant Tension

The current cosmological probes have provided a fantastic confirmation of the standard $Λ$ Cold Dark Matter cosmological model, that has been constrained with unprecedented accuracy. However, with the increase of the experimental sensitivity a few statistically significant tensions between different independent cosmological datasets emerged. While these tensions can be in portion the result of systematic errors, the persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the need for new physics. In this Letter of Interest we will focus on the $4.4σ$ tension between the Planck estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we will list a few interesting new physics models that could solve this tension and discuss how the next decade experiments will be crucial.

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arXiv2020

Cosmology Intertwined I: Perspectives for the Next Decade

The standard $Λ$ Cold Dark Matter cosmological model provides an amazing description of a wide range of astrophysical and astronomical data. However, there are a few big open questions, that make the standard model look like a first-order approximation to a more realistic scenario that still needs to be fully understood. In this Letter of Interest we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances present between the different cosmological probes, as the Hubble constant $H_0$ value, the $σ_8 - S_8$ tension, and the anomalies present in the Planck results. Finally, we will give an overview of upgraded experiments and next-generation space-missions and facilities on Earth, that will be of crucial importance to address all these questions.

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arXiv2020

Cosmology Intertwined IV: The Age of the Universe and its Curvature

A precise measurement of the curvature of the Universe is of primeval importance for cosmology since it could not only confirm the paradigm of primordial inflation but also help in discriminating between different early Universe scenarios. The recent observations, while broadly consistent with a spatially flat standard $Λ$ Cold Dark Matter ($Λ$CDM) model, are showing tensions that still allow (and, in some cases, even suggest) a few percent deviations from a flat universe. In particular, the Planck Cosmic Microwave Background power spectra, assuming the nominal likelihood, prefer a closed universe at more than 99\% confidence level. While new physics could be in action, this anomaly may be the result of an unresolved systematic error or just a statistical fluctuation. However, since a positive curvature allows a larger age of the Universe, an accurate determination of the age of the oldest objects provides a smoking gun in confirming or falsifying the current flat $Λ$CDM model.

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arXiv2020

A larger value for $H_0$ by an evolving gravitational constant

We provide further evidence that a massless cosmological scalar field with a non-minimal coupling to the Ricci curvature of the type $M^2_{\rm pl}(1+ξσ^n/M_{\rm pl}^n) $ alleviates the existing tension between local measurements of the Hubble constant and its inference from CMB anisotropies and baryonic acoustic oscillations data in presence of a cosmological constant. In these models, the expansion history is modified compared to $Λ$CDM at early time, mimicking a change in the effective number of relativistic species, and gravity weakens after matter-radiation equality. Compared to $Λ$CDM, a quadratic ($n=2$) coupling increases the Hubble constant when {\em Planck} 2018 (alone or in combination with BAO and SH0ES) measurements data are used in the analysis. Negative values of the coupling, for which the scalar field decreases, seem favored and consistency with Solar System can be naturally achieved for a large portion of the parameter space without the need of any screening mechanism. We show that our results are robust to the choice of $n$, also presenting the analysis for $n=4$.

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arXiv2020

Measuring lensing ratios with future cosmological surveys

The ratio between the CMB lensing/galaxy counts and the galaxy shear/galaxy counts cross-correlations combines the information from different cosmological probes to infer cosmographic measurements that are less dependent on astrophysical uncertainties and can constrain the geometry of the Universe. We discuss the future perspectives for the measurement of this lensing ratio as previously introduced, i.e. with the use of the Limber and flat-sky approximations and neglecting all the effects on the galaxy survey from observing on the past lightcone. We then show how the cosmological information in this estimator is affected by the Limber approximation and by the inclusion of the redshift space distorsions (RSD) and magnification lensing contributions to the galaxy number counts. We find that the magnification lensing contribution induces a multipole dependence of the lensing ratio that we show to be detectable at a statistical significant level combining post-$Planck$ CMB surveys and a Euclid-like experiment. We propose an improved estimator which takes into account this angular scale dependence. Using this extended formalism, we present forecasts for upcoming and future cosmological surveys and we show at which extent the lensing ratio information can improve the CMB constraints on cosmological parameters. We get that for extended cosmological models where the neutrino mass, the spatial curvature and the dark energy equation of state are allowed to vary, the constraints from $Planck$ on these parameters and on $H_0$ can be reduced by $\sim 40\%$ with the inclusion of a single lensing ratio and by $\sim 60-70\%$ adding the joint measurement of 9 lensing ratios with a Euclid-like survey. We also find that neglegcting the contribution from magnification lensing can induce a bias on the derived cosmological parameters in a combined analysis.

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arXiv2020

Non-linear damping of superimposed primordial oscillations on the matter power spectrum in galaxy surveys

Galaxy surveys are an important probe for superimposed oscillations on the primordial power spectrum of curvature perturbations, which are predicted in several theoretical models of inflation and its alternatives. In order to exploit the full cosmological information in galaxy surveys it is necessary to study the matter power spectrum to fully non-linear scales. We therefore study the non-linear clustering in models with superimposed linear and logarithmic oscillations to the primordial power spectrum by running high-resolution dark-matter-only N-body simulations. We fit a Gaussian envelope for the non-linear damping of superimposed oscillations in the matter power spectrum to the results of the N-body simulations for $k \lesssim 0.6\ h/$Mpc at $0 \leq z \leq 5$ with an accuracy below the percent. We finally use this fitting formula to forecast the capabilities of future galaxy surveys, such as Euclid and Subaru, to probe primordial oscillation down to non-linear scales alone and in combination with the information contained in CMB anisotropies.

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arXiv2019

ATLAS Probe: Breakthrough Science of Galaxy Evolution, Cosmology, Milky Way, and the Solar System

ATLAS (Astrophysics Telescope for Large Area Spectroscopy) is a concept for a NASA probe-class space mission. It is the spectroscopic follow-up mission to WFIRST, boosting its scientific return by obtaining deep NIR & MIR slit spectroscopy for most of the galaxies imaged by the WFIRST High Latitude Survey at z>0.5. ATLAS will measure accurate and precise redshifts for ~200M galaxies out to z=7 and beyond, and deliver spectra that enable a wide range of diagnostic studies of the physical properties of galaxies over most of cosmic history. ATLAS and WFIRST together will produce a definitive 3D map of the Universe over 2000 sq deg. ATLAS Science Goals are: (1) Discover how galaxies have evolved in the cosmic web of dark matter from cosmic dawn through the peak era of galaxy assembly. (2) Discover the nature of cosmic acceleration. (3) Probe the Milky Way's dust-enshrouded regions, reaching the far side of our Galaxy. (4) Discover the bulk compositional building blocks of planetesimals formed in the outer Solar System. These flow down to the ATLAS Scientific Objectives: (1A) Trace the relation between galaxies and dark matter with less than 10% shot noise on relevant scales at 1<z<7. (1B) Probe the physics of galaxy evolution at 1<z<7. (2) Obtain definitive measurements of dark energy and tests of General Relativity. (3) Measure the 3D structure and stellar content of the inner Milky Way to a distance of 25 kpc. (4) Detect and quantify the composition of 3,000 planetesimals in the outer Solar System. ATLAS is a 1.5m telescope with a FoV of 0.4 sq deg, and uses Digital Micro-mirror Devices (DMDs) as slit selectors. It has a spectroscopic resolution of R = 1000, and a wavelength range of 1-4 microns. ATLAS has an unprecedented spectroscopic capability based on DMDs, with a spectroscopic multiplex factor ~6,000. ATLAS is designed to fit within the NASA probe-class space mission cost envelope.

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arXiv2019

Constraining primordial non-Gaussianity using two galaxy surveys and CMB lensing

Next-generation galaxy surveys will be able to measure perturbations on scales beyond the equality scale. On these ultra-large scales, primordial non-Gaussianity leaves signatures that can shed light on the mechanism by which perturbations in the early Universe are generated. We perform a forecast analysis for constraining local type non-Gaussianity and its two-parameter extension with a simple scale-dependence. We combine different clustering measurements from future galaxy surveys -- a 21cm intensity mapping survey and two photometric galaxy surveys -- via the multi-tracer approach. Furthermore we then include CMB lensing from a CMB Stage 4 experiment in the multi-tracer, which can improve the constraints on bias parameters. We forecast $σ(f_{\rm NL}) \simeq 0.9$ (1.4) by combining SKA1, a Euclid-like (LSST-like) survey, and CMB-S4 lensing. With CMB lensing, the precision on $f_{\rm NL}$ improves by up to a factor of 2, showing that a joint analysis is important. In the case with running of $f_{\rm NL}$, our results show that the combination of upcoming cosmological surveys could achieve $σ(n_{\rm NL}) \simeq 0.12$ (0.22) on the running index.

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arXiv2019

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 $γ_{\rm PN}$ comparable to those from the Solar System.

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arXiv2019

Primordial Non-Gaussianity

Our current understanding of the Universe is established through the pristine measurements of structure in the cosmic microwave background (CMB) and the distribution and shapes of galaxies tracing the large scale structure (LSS) of the Universe. One key ingredient that underlies cosmological observables is that the field that sources the observed structure is assumed to be initially Gaussian with high precision. Nevertheless, a minimal deviation from Gaussianityis perhaps the most robust theoretical prediction of models that explain the observed Universe; itis necessarily present even in the simplest scenarios. In addition, most inflationary models produce far higher levels of non-Gaussianity. Since non-Gaussianity directly probes the dynamics in the early Universe, a detection would present a monumental discovery in cosmology, providing clues about physics at energy scales as high as the GUT scale.

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arXiv2019

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.

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arXiv2019

Measuring ISW with next-generation radio surveys

The late-time integrated Sachs-Wolfe (ISW) signal in the CMB temperature anisotropies is an important probe of dark energy when it can be detected by cross-correlation with large-scale structure surveys. Because of their huge sky area, surveys in the radio are well-suited to ISW detection. We show that 21cm intensity mapping and radio continuum surveys with the SKA in Phase~1 promise a $\sim5σ$ detection if we use tomography, with a similar forecast for the precursor EMU survey. In SKA Phase~2, the 21cm galaxy redshift survey and the continuum survey could deliver a $\sim6σ$ detection. Our analysis of the radio surveys aims for theoretical accuracy on large scales. Firstly, we include all the effects on the radio surveys from observing on the past lightcone: redshift-space distortions and lensing magnification can have a significant impact on the ISW signal to noise ratio, while Doppler and other relativistic distortions are not significant. Secondly, we use the full information in the observable galaxy angular power spectra $C_\ell(z,z')$, by avoiding the Limber approximation and by including all cross-correlations between redshift bins in the covariance. Without these cross-bin correlations, the ISW signal to noise ratio is biased.

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arXiv2019

ATLAS Probe: Breakthrough Science of Galaxy Evolution, Cosmology, Milky Way, and the Solar System

ATLAS (Astrophysics Telescope for Large Area Spectroscopy) Probe is a concept for a NASA probe-class space mission. It is the follow-up space mission to WFIRST, boosting its scientific return by obtaining deep IR slit spectroscopy for 70% of all galaxies imaged by a 2000 sq deg WFIRST High Latitude Survey at z>0.5. ATLAS will measure accurate and precise redshifts for 200M galaxies out to z < 7, and deliver spectra that enable a wide range of diagnostic studies of the physical properties of galaxies over most of cosmic history. ATLAS Probe science spans four broad categories: (1) Revolutionizing galaxy evolution studies by tracing the relation between galaxies and dark matter from galaxy groups to cosmic voids and filaments, from the epoch of reionization through the peak era of galaxy assembly; (2) Opening a new window into the dark Universe by weighing the dark matter filaments using 3D weak lensing with spectroscopic redshifts, and obtaining definitive measurements of dark energy and modification of General Relativity using galaxy clustering; (3) Probing the Milky Way's dust-enshrouded regions, reaching the far side of our Galaxy; and (4) Exploring the formation history of the outer Solar System by characterizing Kuiper Belt Objects. ATLAS Probe is a 1.5m telescope with a field of view of 0.4 sq deg, and uses Digital Micro-mirror Devices (DMDs) as slit selectors. It has a spectroscopic resolution of R = 1000 over 1-4 microns, and a spectroscopic multiplex factor >5,000. ATLAS is designed to fit within the NASA probe-class space mission cost envelope; it has a single instrument, a telescope aperture that allows for a lighter launch vehicle, and mature technology. ATLAS Probe will lead to transformative science over the entire range of astrophysics: from galaxy evolution to the dark Universe, from Solar System objects to the dusty regions of the Milky Way.

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arXiv2018

On the ISW-cluster cross-correlation in future surveys

We investigate the cosmological information contained in the cross-correlation between the Integrated Sachs-Wolfe (ISW) of the Cosmic Microwave Background (CMB) anisotropy pattern and galaxy clusters from future wide surveys. Future surveys will provide cluster catalogues with a number of objects comparable with galaxy catalogues currently used for the detection of the ISW signal by cross-correlation with the CMB anisotropy pattern. By computing the angular power spectra of clusters and the corresponding cross-correlation with CMB, we perform a signal-to-noise ratio (SNR) analysis for the ISW detection as expected from the eROSITA and the Euclid space missions. We discuss the dependence of the SNR of the ISW-cluster cross-correlation on the specifications of the catalogues and on the reference cosmology. We forecast that the SNRs for ISW-cluster cross-correlation are alightly smaller compared to those which can be obtained from future galaxy surveys but the signal is expected to be detected at high significance, i.e. more than $> 3\,σ$. We also forecast the joint constraints on parameters of model extensions of the concordance $Λ$CDM cosmology by combining CMB and the ISW-cluster cross-correlation.

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