Browsing by Author "Ballardini, Mario"
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Item Constraining the neutrino mass using a multitracer combination of two galaxy surveys and cosmic microwave background lensing(Oxford University Press, 2022) Ballardini, Mario; Maartens, RoyMeasuring the total neutrino mass is one of the most exciting opportunities available with next-generation cosmological data sets. We study the possibility of detecting the total neutrino mass using large-scale clustering in 21 cm intensity mapping and photometric galaxy surveys, together with cosmic microwave background (CMB) information. We include the scale-dependent halo bias contribution due to the presence of massive neutrinos, and use a multitracer analysis in order to reduce cosmic variance. The multitracer combination of an SKAO-MID 21 cm intensity map with stage 4 CMB dramatically shrinks the uncertainty on total neutrino mass to σ(Mν ) 45 meV, using only linear clustering information (kmax = 0.1 h Mpc−1 ) and without a prior on optical depth. When we add to the multitracer the clustering information expected from Legacy Survey of Space and Time, the forecast is σ(Mν ) 12 meV.Item Cosmological constraints on post-Newtonian parameters in effectively massless scalar-tensor theories of gravity(2019) Rossi, Massimo; Ballardini, Mario; Braglia, MatteoWe study the cosmological constraints on the variation of Newton’s constant and on post-Newtonian parameters for simple models of the scalar-tensor theory of gravity beyond the extended Jordan-BransDicke theory. We restrict ourselves to an effectively massless scalar field with a potential V ∝ F2, where FðσÞ ¼ N2 pl þ ξσ2 is the coupling to the Ricci scalar considered. We derive the theoretical predictions for cosmic microwave background anisotropies and matter power spectra by requiring that the effective gravitational strength at present is compatible with the one measured in a Cavendish-like experiment and by assuming an adiabatic initial condition for scalar fluctuations. When comparing these models with Planck 2015 and a compilation of baryonic acoustic oscillations data, all these models accommodate a marginalized value for H0 higher than in ΛCDM. We find no evidence for a statistically significant deviation from Einstein’s general relativity. We find ξ < 0.064 (jξj < 0.011) at 95% CL for ξ > 0 (for ξ < 0, ξ ≠ −1=6). In terms of post-Newtonian parameters, we find 0.995 < γPN < 1 and 0.99987 < βPN < 1 (0.997 < γPN < 1 and 1 < βPN < 1.000011) for ξ > 0 (for ξ < 0). For the particular case of the conformal coupling, i.e., ξ ¼ −1=6, we find constraints on the post-Newtonian parameters of similar precision to those within the Solar System.Item Energy-momentum tensor and helicity for gauge fields coupled to a pseudoscalar inflaton(University of the Western Cape, 2019) Ballardini, MarioWe study the energy-momentum tensor and helicity of gauge fields coupled through $g \phi F \tilde{F}/4$ to a pseudo-scalar field $\phi$ driving inflation. Under the assumption of a constant time derivative of the background inflaton, we compute analitically divergent and finite terms of the energy density and helicity of gauge fields for any value of the coupling $g$. We introduce a suitable adiabatic expansion for mode functions of physical states of the gauge fields which correctly reproduces ultraviolet divergences in average quantities and identify corresponding counterterms. Our calculations shed light on the accuracy and the range of validity of approximated analytic estimates of the energy density and helicity terms previously existed in the literature in the strongly coupled regime only, i.e. for $g \dot \phi/(2H) \gg 1$. We discuss the implications of our analytic calculations for the backreaction of quantum fluctuations onto the inflaton evolution.Item Larger value for H0 by an evolving gravitational constant(American Physical Society, 2020) Ballardini, Mario; Braglia, Matteo; Emond, William T.We provide further evidence that a massless cosmological scalar field with a nonminimal coupling to the Ricci curvature of the type M 2 pl ( 1 + ξ σ n / M n pl ) alleviates the existing tension between local measurements of the Hubble constant and its inference from cosmic microwave background anisotropies and baryonic acoustic oscillations data in the 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 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 the 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 .Item Measuring lensing ratios with future cosmological surveys(American Physical Society, 2020) Ballardini, Mario; Bermejo-Climent, Jos´e Ramón; Finelli, FabioThe 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 light cone. We then show how the cosmological information in this estimator is affected by the Limber approximation and by the inclusion of the redshift space distortions (RSD) and lensing magnification contributions to the galaxy number counts.Item New constraints on primordial features from the galaxy two-point correlation function(Physical Review, 2023) Moscardini, Lauro; Ballardini, Mario; Marulli, FedericoFeatures in the primordial power spectrum represent the imprinted signal in the density perturbations of the physics and evolution of the early Universe. A measurement of such signals will represents the need to go beyond the minimal assumption made for the initial conditions of the cosmological perturbations. For the first time, we study different templates with undamped oscillations or a bump from the two-point correlation function measured from BOSS DR12 galaxies constraining the amplitude of the features to be at most a few percent. Constraints are competitive to the ones obtained with Planck DR3.Item Non-linear damping of superimposed primordial oscillations on the matter power spectrum in galaxy surveys(IOP Publishing Ltd, 2020) Ballardini, Mario; Murgia, Riccardo; Baldi, MarcoGalaxy 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 darkmatter-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 . 0.6 h/Mpc at 0 ≤ z ≤ 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.Item On the primordial origin of the smoothing excess in the Planck temperature power spectrum in light of LSS data(IOP Publishing, 2022) Ballardini, Mario; Finelli, FabioThe Planck DR3 measurements of the temperature and polarization anisotropies power spectra of the cosmic microwave background (CMB) show an excess of smoothing of the acoustic peaks with respect to ΛCDM, often quantified by a phenomenological parameter A L. A specific feature superimposed to the primordial power spectrum has been suggested as a physical solution for this smoothing excess. Here, we investigate the impact of this specific localized oscillation with a frequency linear in the wavenumber, designed to mimic the smoothing of CMB temperature spectrum corresponding to A L ≃ 1.1-1.2 on the matter power spectrum.Item Probing primordial features with the primary CMB(Elsevier, 2019) Ballardini, MarioWe 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 ℓ ∼ 2 and at ℓ ∼ 22. We show that if the features comes from the primordial power spectrum we should be find consistent constraints of these features model from the CMB temperature angular power spectrum removing or not the late ISW signal. Moreover, this method shows also some improvement on 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 ℓ ∼ 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.Item Probing the primordial Universe using the SKA in combination with other cosmological surveys(University of the Western Cape, 2019) Matthewson, William; Maartens, Roy; Ballardini, MarioNext-generation surveys of the large-scale structure of the Universe will be of great importance in allowing us to extract invaluable information about the nature of the Universe and the physical laws that govern it, at a higher precision than previously possible. In particular, they will allow us to more closely study primordial non-Gaussianity, a feature which leaves an imprint on the power spectrum of galaxies on the ultra-large scales and which acts as a powerful probe of the physics of the early Universe. To investigate the extent to which upcoming surveys will be able to improve our knowledge of primordial non-Gaussianity, we perform a forecast to predict the observational constraints on local-type primordial non-Gaussianity, as well as an extension that includes a scale dependence. We study the constraining power of a multi-tracer approach, where information from different surveys is combined to help suppress cosmic variance and break parameter degeneracies. More specifically, we consider the combination of a 21cm intensity mapping survey with each of two different photometric galaxy surveys, and also examine the effect of including CMB lensing as an additional probe. The forecast constraint from a combination of SKA1, a Euclid-like (LSST-like) survey and a CMB Stage 4 lensing experiment is (fNL) ' 0:9 (1:4) which displays a factor of 2 improvement over the case without CMB lensing, indicating that the surveys considered are indeed complementary. The constraints on the running index of the scale-dependent model are forecast as (nNL) ' 0:12 (0:22) from the same combination of surveys.Item Scalar-tensor theories of gravity, neutrino physics, and the H0 tension(IOP Publishing, 2020) Ballardini, Mario; Braglia, Matteo; Finelli, FabioWe 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) = N2 pl + ξσ2 . 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 × 10−4 for Npl = 0 (induced gravity or equivalently extended Jordan-Brans-Dicke) and (Npl √ 8πG) − 1 < 1.8 × 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 ΛCDM model, all these dynamical models accommodate a higher value for H0 and therefore alleviate the tension between Planck/BAO and distance-ladder measurement from SNe Ia data from 4.4σ at best to 2.7-3.2σ with CMB alone and 3.5-3.6σ including BAO data.