We perform a comprehensive study of cosmological constraints on non-standard neutrino self-interactions using cosmic microwave background (CMB) and baryon acoustic oscillation data. We consider different scenarios for neutrino self-interactions disti
nguished by the fraction of neutrino states allowed to participate in self-interactions and how the relativistic energy density, N$_{textrm{eff}}$, is allowed to vary. Specifically, we study cases in which: all neutrino states self-interact and N$_{textrm{eff}}$ varies; two species free-stream, which we show alleviates tension with laboratory constraints, while the energy in the additional interacting states varies; and a variable fraction of neutrinos self-interact with either the total N$_{textrm{eff}}$ fixed to the Standard Model value or allowed to vary. In no case do we find compelling evidence for new neutrino interactions or non-standard values of N$_{textrm{eff}}$. In several cases we find additional modes with neutrino decoupling occurring at lower redshifts $z_{textrm{dec}} sim 10^{3-4}$. We do a careful analysis to examine whether new neutrino self-interactions solve or alleviate the so-called $H_0$ tension and find that, when all Planck 2018 CMB temperature and polarization data is included, none of these examples ease the tension more than allowing a variable N$_{textrm{eff}}$ comprised of free-streaming particles. Although we focus on neutrino interactions, these constraints are applicable to any light relic particle.
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 us
ing 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 a $approx$ 0.25% downward shift of the $sigma_8$ constraint from tSZ power spectrum data, with a fiducial neutrino mass $Sigma m_ u=0.06$ eV. In $Lambda$CDM, with an X-ray mass bias corresponding to the expected hydrostatic mass bias, i.e., $(1-b)simeq0.8$, our constraints from Planck SZ data are consistent with the latest results from SPT, DES-Y1 and KiDS+VIKING-450. In $ uLambda$CDM, 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 $(1-b)=0.64pm0.04$~(68%~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 $ell_mathrm{max}approx10^4$. Although this is challenging, we find that SZ power spectrum can realistically be used to tightly constrain intra-cluster medium properties: we forecast a 2% determination of the X-ray mass bias by combining CMB-S4 and our mock SZ power spectrum with $ell_mathrm{max}=10^3$.
We forecast the sensitivity of thirty-five different combinations of future Cosmic Microwave Background and Large Scale Structure data sets to cosmological parameters and to the total neutrino mass. We work under conservative assumptions accounting f
or uncertainties in the modelling of systematics. In particular, for galaxy redshift surveys, we remove the information coming from non-linear scales. We use Bayesian parameter extraction from mock likelihoods to avoid Fisher matrix uncertainties. Our grid of results allows for a direct comparison between the sensitivity of different data sets. We find that future surveys will measure the neutrino mass with high significance and will not be substantially affected by potential parameter degeneracies between neutrino masses, the density of relativistic relics, and a possible time-varying equation of state of Dark Energy.
In cosmologies with massive neutrinos, the galaxy bias defined with respect to the total matter field (cold dark matter, baryons, and non-relativistic neutrinos) depends on the sum of the neutrino masses $M_{ u}$, and becomes scale-dependent even on
large scales. This effect has been usually neglected given the sensitivity of current surveys, but becomes a severe systematic for future surveys aiming to provide the first detection of non-zero $M_{ u}$. The effect can be corrected for by defining the bias with respect to the density field of cold dark matter and baryons instead of the total matter field. In this work, we provide a simple prescription for correctly mitigating the neutrino-induced scale-dependent bias effect in a practical way. We clarify a number of subtleties regarding how to properly implement this correction in the presence of redshift-space distortions and non-linear evolution of perturbations. We perform a MCMC analysis on simulated galaxy clustering data that match the expected sensitivity of the textit{Euclid} survey. We find that the neutrino-induced scale-dependent bias can lead to important shifts in both the inferred mean value of $M_{ u}$, as well as its uncertainty. We show how these shifts propagate to other cosmological parameters correlated with $M_{ u}$, such as the cold dark matter physical density $Omega_{cdm} h^2$ and the scalar spectral index $n_s$. In conclusion, we find that correctly accounting for the neutrino-induced scale-dependent bias will be of crucial importance for future galaxy clustering analyses. We encourage the cosmology community to correctly account for this effect using the simple prescription we present in our work. The tools necessary to easily correct for the neutrino-induced scale-dependent bias will be made publicly available in an upcoming release of the Boltzmann solver texttt{CLASS}.
Theoretical uncertainties on non-linear scales are among the main obstacles to exploit the sensitivity of forthcoming galaxy and hydrogen surveys like Euclid or the Square Kilometre Array (SKA). Here, we devise a new method to model the theoretical e
rror that goes beyond the usual cut-off on small scales. The advantage of this more efficient implementation of the non-linear uncertainties is tested through a Markov-Chain-Monte-Carlo (MCMC) forecast of the sensitivity of Euclid and SKA to the parameters of the standard $Lambda$CDM model, including massive neutrinos with total mass $M_ u$, and to 3 extended scenarios, including 1) additional relativistic degrees of freedom ($Lambda$CDM + $M_ u$ + $N_mathrm{eff}$), 2) a deviation from the cosmological constant ($Lambda$CDM + $M_ u$ + $w_0$), and 3) a time-varying dark energy equation of state parameter ($Lambda$CDM + $M_ u$ + $left(w_0,w_a right)$). We compare the sensitivity of 14 different combinations of cosmological probes and experimental configurations. For Euclid combined with Planck, assuming a plain cosmological constant, our method gives robust predictions for a high sensitivity to the primordial spectral index $n_{rm s}$ ($sigma(n_s)=0.00085$), the Hubble constant $H_0$ ($sigma(H_0)=0.141 , {rm km/s/Mpc}$), the total neutrino mass $M_ u$ ($sigma(M_ u)=0.020 , {rm eV}$). Assuming dynamical dark energy we get $sigma(M_ u)=0.030 , {rm eV}$ for the mass and $(sigma(w_0), sigma(w_a)) = (0.0214, 0.071)$ for the equation of state parameters. The predicted sensitivity to $M_ u$ is mostly stable against the extensions of the cosmological model considered here. Interestingly, a significant improvement of the constraints on the extended model parameters is also obtained when combining Euclid with a low redshift HI intensity mapping survey by SKA1, demonstrating the importance of the synergy of Euclid and SKA.
The interplay between cosmology and earth based experiments is crucial in order to pin down neutrino physics. Indeed cosmology can provide very tight, yet model dependent, constraints on some neutrino properties. Here we focus on the neutrino mass su
m, reviewing the up to date current bounds and showing the results of our forecast of the sensitivity of future experiments. Finally, we discuss the case for sterile neutrinos, explaining how non standard sterile neutrino self-interactions can reconcile the oscillation anomalies with cosmology.
We forecast the main cosmological parameter constraints achievable with the CORE space mission which is dedicated to mapping the polarisation of the Cosmic Microwave Background (CMB). CORE was recently submitted in response to ESAs fifth call for med
ium-sized mission proposals (M5). Here we report the results from our pre-submission study of the impact of various instrumental options, in particular the telescope size and sensitivity level, and review the great, transformative potential of the mission as proposed. Specifically, we assess the impact on a broad range of fundamental parameters of our Universe as a function of the expected CMB characteristics, with other papers in the series focusing on controlling astrophysical and instrumental residual systematics. In this paper, we assume that only a few central CORE frequency channels are usable for our purpose, all others being devoted to the cleaning of astrophysical contaminants. On the theoretical side, we assume LCDM as our general framework and quantify the improvement provided by CORE over the current constraints from the Planck 2015 release. We also study the joint sensitivity of CORE and of future Baryon Acoustic Oscillation and Large Scale Structure experiments like DESI and Euclid. Specific constraints on the physics of inflation are presented in another paper of the series. In addition to the six parameters of the base LCDM, which describe the matter content of a spatially flat universe with adiabatic and scalar primordial fluctuations from inflation, we derive the precision achievable on parameters like those describing curvature, neutrino physics, extra light relics, primordial helium abundance, dark matter annihilation, recombination physics, variation of fundamental constants, dark energy, modified gravity, reionization and cosmic birefringence. (ABRIDGED)
