[Paper Review] Euclid preparation. Sensitivity to neutrino parameters

Euclid Collaboration, M. Archidiacono+247 more|arXiv (Cornell University)|May 9, 2024

Cosmology and Gravitation Theories4 citations

TL;DR

This paper investigates Euclid's sensitivity to neutrino parameters, showing that its weak-lensing and cosmic-shear data—especially when combined with CMB data—will tightly constrain the effective number of relativistic species ($N_{\rm eff}$) and neutrino masses. With Planck + Euclid, the 95% CL upper bound on $\Delta N_{\rm eff}$ reaches $<0.144$, tightening to $<0.063$ with future CMB surveys like LiteBIRD and CMB-S4, offering strong constraints on beyond-Standard-Model particles and potential resolution to the Hubble tension.

ABSTRACT

The Euclid mission of the European Space Agency will deliver weak gravitational lensing and galaxy clustering surveys that can be used to constrain the standard cosmological model and extensions thereof. We present forecasts from the combination of these surveys on the sensitivity to cosmological parameters including the summed neutrino mass $M_ν$ and the effective number of relativistic species $N_{ m eff}$ in the standard $Λ$CDM scenario and in a scenario with dynamical dark energy ($w_0 w_a$CDM). We compare the accuracy of different algorithms predicting the nonlinear matter power spectrum for such models. We then validate several pipelines for Fisher matrix and MCMC forecasts, using different theory codes, algorithms for numerical derivatives, and assumptions concerning the non-linear cut-off scale. The Euclid primary probes alone will reach a sensitivity of $σ(M_ν)=$56meV in the $Λ$CDM+$M_ν$ model, whereas the combination with CMB data from Planck is expected to achieve $σ(M_ν)=$23meV and raise the evidence for a non-zero neutrino mass to at least the $2.6σ$ level. This can be pushed to a $4σ$ detection if future CMB data from LiteBIRD and CMB Stage-IV are included. In combination with Planck, Euclid will also deliver tight constraints on $ΔN_{ m eff}&lt; 0.144$ (95%CL) in the $Λ$CDM+$M_ν$+$N_{ m eff}$ model, or $ΔN_{ m eff}&lt; 0.063$ when future CMB data are included. When floating $(w_0, w_a)$, we find that the sensitivity to $N_{ m eff}$ remains stable, while that to $M_ν$ degrades at most by a factor 2. This work illustrates the complementarity between the Euclid spectroscopic and imaging/photometric surveys and between Euclid and CMB constraints. Euclid will have a great potential for measuring the neutrino mass and excluding well-motivated scenarios with additional relativistic particles.

Motivation & Objective

• To assess Euclid's sensitivity to neutrino parameters, particularly $N_{\rm eff}$ and $\sum m_\nu$, in the context of the $\Lambda$CDM model and its extensions.
• To evaluate how combining Euclid's weak-lensing and cosmic-shear data with CMB data lifts the degeneracy between $N_{\rm eff}$ and $H_0$.
• To determine whether Euclid can provide the first detection of non-zero neutrino mass and constrain the neutrino mass ordering.
• To test the viability of light relics beyond the Standard Model, such as Goldstone bosons or Weyl fermions, via constraints on $N_{\rm eff}$.
• To investigate the potential of Euclid to resolve the Hubble tension by constraining decoupling times of relativistic species.

Proposed method

• The analysis uses Fisher matrix forecasts based on Euclid's primary probes: cosmic shear and weak-lensing power spectra from the DEMNUni simulations.
• The method includes marginalization over dynamical dark energy parameters to assess robustness of constraints.
• It combines Euclid's weak-lensing data with CMB data from Planck, LiteBIRD, and CMB Stage-IV to break the $N_{\rm eff}$–$H_0$ degeneracy.
• The study considers a fiducial model with $N_{\rm eff} = 3.044$ (standard neutrinos only) and computes 95% confidence level upper bounds on $\Delta N_{\rm eff}$.
• The framework assumes a $\Lambda$CDM+$\sum m_\nu$+$N_{\rm eff}$ cosmological model, with constraints derived from likelihood analysis of cosmic shear and power spectrum data.
• Simulations and forecasts are validated using high-performance computing resources, including CINECA and RWTH Aachen University clusters.

Experimental results

Research questions

• RQ1 Can Euclid alone detect a non-zero neutrino mass, and what is the expected sensitivity?
• RQ2 How does combining Euclid with CMB data improve constraints on $N_{\rm eff}$ and reduce the $H_0$–$N_{\rm eff}$ degeneracy?
• RQ3 What is the upper bound on $\Delta N_{\rm eff}$ from Euclid + Planck, and how does it improve with future CMB surveys?
• RQ4 Can Euclid rule out light relics like Goldstone bosons or massless gauge bosons based on $N_{\rm eff}$ constraints?
• RQ5 To what extent can Euclid constrain the decoupling time of relativistic species, even before the QCD transition?

Key findings

• With Planck and Euclid data combined, the 95% confidence level upper bound on $\Delta N_{\rm eff}$ is $<0.144$ in the $\Lambda$CDM+$\sum m_\nu$+$N_{\rm eff}$ model.
• When combined with future CMB data from LiteBIRD and CMB Stage-IV, the bound tightens to $\Delta N_{\rm eff} < 0.063$.
• These constraints remain robust when marginalizing over dynamical dark energy parameters, indicating stability across model extensions.
• Euclid alone can already constrain decoupling times of relativistic species after the QCD transition, and with CMB data, even earlier decoupling times (e.g., before QCD) become measurable.
• The combined data set will have strong potential to rule out many well-motivated models of additional relativistic particles, such as Goldstone bosons or Weyl fermions.
• The results suggest that Euclid will provide the first strong evidence for non-zero neutrino mass and significant hints on the neutrino mass ordering.