Carmelita Carbone

Effects of massive neutrinos on the large-scale structure of the Universe

Cosmological neutrinos strongly affect the evolution of the largest structures in the Universe, i.e. galaxies and galaxy clusters. We use large box-size ful l hydrodynamic simulations to investigate the non-linear effects that massive neutrinos ha ve on the spatial properties of cold dark matter (CDM) haloes. We quantify the difference with respect to the concordance ΛCDM model of the halo mass function and of the halo two-point correlation function. We model the redshift-space distortions and compute the errors on the li near distortion parameter β introduced if cosmological neutrinos are assumed to be massless. We find that, if not taken correctly into account and depending on the total neutrino mass Mν, these effects could lead to a potentially fake signature of modified gravity. Future nea rly all-sky spectroscopic galaxy surveys will be able to constrain the neutrino mass if Mν & 0.6 eV, using β measurements alone and independently of the value of the matter power spectrum normalisation σ8. In combination with other cosmological probes, this will strengt hen neutrino mass constraints and help breaking parameter degeneracies.

Designing a space-based galaxy redshift survey to probe dark energy

A space-based galaxy redshift survey would have enormous power in constraining dark energy and testing general relativity, provided that its parameters are suitably optimized. We study viable space-based galaxy redshift surveys, exploring the dependence of the Dark Energy Task Force (DETF) figure-of-merit (FoM) on redshift accuracy, redshift range, survey area, target selection and forecast method. Fitting formulae are provided for convenience. We also consider the dependence on the information used: the full galaxy power spectrum P(k), P(k) marginalized over its shape, or just the Baryon Acoustic Oscillations (BAO). We find that the inclusion of growth rate information (extracted using redshift space distortion and galaxy clustering amplitude measurements) leads to a factor of ∼3 improvement in the FoM, assuming general relativity is not modified. This inclusion partially compensates for the loss of information when only the BAO are used to give geometrical constraints, rather than using the full P(k) as a standard ruler. We find that a space-based galaxy redshift survey covering ∼20 000 deg2 over 0.5≲z≲2 with σz/(1 +z) ≤ 0.001 exploits a redshift range that is only easily accessible from space, extends to sufficiently low redshifts to allow both a vast 3D map of the universe using a single tracer population, and overlaps with ground-based surveys to enable robust modelling of systematic effects. We argue that these parameters are close to their optimal values given current instrumental and practical constraints.

Cosmological parameters degeneracies and non-Gaussian halo bias

We study the impact of the cosmological parameters uncertainties on the measurements of primordial non-Gaussianity through the large-scale non-Gaussian halo bias effect. While this is not expected to be an issue for the standard ΛCDM model, it may not be the case for more general models that modify the large-scale shape of the power spectrum. We consider the so-called local non-Gaussianity model, parametrized by the fNL non-Gaussianity parameter which is zero for a Gaussian case, and make forecasts on fNL from planned surveys, alone and combined with a Planck CMB prior. In particular, we consider EUCLID- and LSST-like surveys and forecast the correlations among fNL and the running of the spectral index αs, the dark energy equation of state w, the effective sound speed of dark energy perturbations c2s, the total mass of massive neutrinos Mν = ∑mν, and the number of extra relativistic degrees of freedom Nνrel. Neglecting CMB information on fNL and scales k > 0.03h/Mpc, we find that, if Nνrel is assumed to be known, the uncertainty on cosmological parameters increases the error on fNL by 10 to 30% depending on the survey. Thus the fNL constraint is remarkable robust to cosmological model uncertainties. On the other hand, if Nνrel is simultaneously constrained from the data, the fNL error increases by ~ 80%. Finally, future surveys which provide a large sample of galaxies or galaxy clusters over a volume comparable to the Hubble volume can measure primordial non-Gaussianity of the local form with a marginalized 1-σ error of the order ΔfNL ~ 2−5, after combination with CMB priors for the remaining cosmological parameters. These results are competitive with CMB bispectrum constraints achievable with an ideal CMB experiment.

The clustering of galaxies and galaxy clusters: constraints on primordial non-Gaussianity from future wide-field surveys

We investigate the constraints on primordial non-Gaussianity with varied bispectrum shapes that can be derived from the power spectrum of galaxies and clusters of galaxies detected in future wide field optical/near-infrared surveys. Having in mind the proposed ESA space mission Euclid as a specific example, we combine the spatial distribution of spectroscopically selected galaxies with that of weak lensing selected cluste rs. We use the physically motivated halo model in order to represent the correlation function of arbitrary tracers of the Large Scale Structure in the Universe. As naively expected, we find that g alaxies are much more effective in jointly constrain the level of primordial non-Gaussiani ty fNL and the amplitude of the matter power spectrumσ8 than clusters of galaxies, due to the much lower abundance of the latter that is not adequately compensated by the larger effe ct on the power spectrum. Nevertheless, combination of the galaxy power spectrum with the cluster-galaxy cross spectrum can decrease the error on the determination of fNL by up to a factor of∼ 2. This decrement is particularly evident for the less studied non-Gaussian bispec trum shapes, the so-called enfolded and the orthogonal ones. Setting constraints on these models can shed new light on various aspects of the physics of the early Universe, and it is hence o f extreme importance. By combining the power spectra of clusters and galaxies with the cl uster-galaxy cross spectrum we

Full-sky maps for gravitational lensing of the cosmic microwave background

We use the large cosmological Millennium Simulation (MS) to construct the first all-sky maps of the lensing potential and the deflection angle, aiming at gravitational lensing of the CMB, with the goal of properly including small-scale non-linearities and non-Gaussianity. Exploiting the Born approximation, we implement a map-making procedure based on direct ray-tracing through the gravitational potential of the MS. We stack the simulation box in redshift shells up to

DEMNUni: the clustering of large-scale structures in the presence of massive neutrinos

z\sim 11

Probing deviations from general relativity with the Euclid spectroscopic survey

, producing continuous all-sky maps with arcminute angular resolution. A randomization scheme avoids repetition of structures along the line of sight and structures larger than the MS box size are added to supply the missing contribution of large-scale (LS) structures to the lensing signal. The angular power spectra of the projected lensing potential and the deflection-angle modulus agree quite well with semi-analytic estimates on scales down to a few arcminutes, while we find a slight excess of power on small scales, which we interpret as being due to non-linear clustering in the MS. Our map-making procedure, combined with the LS adding technique, is ideally suited for studying lensing of CMB anisotropies, for analyzing cross-correlations with foreground structures, or other secondary CMB anisotropies such as the Rees-Sciama effect.

Lensed CMB temperature and polarization maps from the Millennium Simulation

We analyse the clustering features of Large Scale Structures (LSS) in the presence of massive neutrinos, employing a set of large-volume, high-resolution cosmological N-body simulations, where neutrinos are treated as separate collisionless particles. The volume of 8 h-3 Gpc3, combined with a resolution of about 8?1010h-1M? for the cold dark matter (CDM) component, represents a significant improvement over previous N-body simulations in massive neutrino cosmologies. In this work we focus, in the first place, on the analysis of nonlinear effects in CDM and neutrinos perturbations contributing to the total matter power spectrum. We show that most of the nonlinear evolution is generated exclusively by the CDM component. We therefore compare mildly nonlinear predictions from Eulerian Perturbation Theory (PT), and fully nonlinear prescriptions (HALOFIT) with the measurements obtained from the simulations. We find that accounting only for the nonlinear evolution of the CDM power spectrum allows to recover the total matter power spectrum with the same accuracy as the massless case. Indeed, we show that, the most recent version of the (HALOFIT) formula calibrated on ?CDM simulations can be applied directly to the linear CDM power spectrum without requiring additional fitting parameters in the massive case. As a second step, we study the abundance and clustering properties of CDM halos, confirming that, in massive neutrino cosmologies, the proper definition of the halo bias should be made with respect to the cold rather than the total matter distribution, as recently shown in the literature. Here we extend these results to the redshift space, finding that, when accounting for massive neutrinos, an improper definition of the linear bias can lead to a systematic error of about 1-2?% in the determination of the linear growth rate from anisotropic clustering. This result is quite important if we consider that future spectroscopic galaxy surveys, as e.g. Euclid, are expected to measure the linear growth-rate with statistical errors less than about 3?% at z1.

Unified treatment of cosmological perturbations from superhorizon to small scales

We discuss the ability of the planned Euclid mission to detect deviations from General Relativity using its extensive redshift survey of more than 50 Mi llion galaxies. Constraints on the gravity theory are placed measuring the growth rate of struc ture within 14 redshift bins betweenz = 0.7 andz = 2. The growth rate is measured from redshift-space distortio ns, i.e. the anisotropy of the clustering pattern induced by coherent pe culiar motions. This is performed in the overall context of the Euclid spectroscopic survey, w hich will simultaneously measure the expansion history of the universe, using the power spect rum and its baryonic features as a standard ruler, accounting for the relative degeneracies of expansion and growth parameters. The resulting expected errors on the growth rate in the different redshift bins, expressed through the quantity fσ8, range between 1.3% and 4.4%. We discuss the optimisation of the survey configuration and investigate the important depende nce on the growth parameterisation and the assumed cosmological model. We show how a specifi c parameterisation could actually drive the design towards artificially restricted r egions of the parameter space. Finally, in the framework of the popular “γ parameterisation”, we show that the Euclid spectroscopic survey alone will already be able to provide substantial evidence (in Bayesian terms) if the growth index differs from the GR value γ = 0.55 by at least � 0.13. This will combine with the comparable inference power provided by the Euclid weak lensing survey, resulting in Euclid’s unique ability to provide a decisive test of modi fied gravity.

Initial Conditions for Accurate N-Body Simulations of Massive Neutrino Cosmologies

We have constructed the first all-sky cosmic microwave background (CMB) temperature and polarization lensed maps based on a high-resolution cosmological N-body simulation, the Millennium Simulation (MS). We have exploited the lensing potential map obtained using a previously developed map-making procedure which integrates along the line-of-sight the MS dark matter distribution by stacking and randomizing the simulation boxes up to z = 127, and which semi-analytically supplies the large-scale power in the angular lensing potential that is not correctly sampled by the N-body simulation. The lensed sky has been obtained by properly modifying the latest version of the LensPix code to account for the MS structures. We have also produced all-sky lensed maps of the so-called ψ E and ψ B potentials, which are directly related to the electric and magnetic types of polarization. The angular power spectra of the simulated lensed temperature and polarization maps agree well with semi-analytic estimates up to l ≤ 2500, while on smaller scales we find a slight excess of power which we interpret as being due to non-linear clustering in the MS. We also observe how non-linear lensing power in the polarized CMB is transferred to large angular scales by suitably misaligned modes in the CMB and the lensing potential. This work is relevant in view of the future CMB probes, as a way to analyse the lensed sky and disentangle the contribution from primordial gravitational waves.