[Paper Review] DEMNUni: disentangling dark energy from massive neutrinos with the void size function

G Verza, C. Carbone+2 more|arXiv (Cornell University)|Dec 19, 2022

Cosmology and Gravitation Theories4 citations

TL;DR

This paper demonstrates that the void size function (VSF) in cosmological simulations can effectively disentangle the degeneracy between dynamical dark energy and massive neutrinos. Using the DEMNUni N-body simulations, it shows that the VSF distinguishes all tested combinations of dark energy equations of state and total neutrino masses with sensitivity exceeding Poisson noise, making it a powerful probe for upcoming surveys like Euclid.

ABSTRACT

Cosmic voids, the underdense regions in the Universe, are impacted by dark energy and massive neutrinos. In this work, relying on the DEMNUni suite of cosmological simulations, we explore the void size function in cosmologies with both dynamical dark energy and massive neutrinos. We investigate the impact of different choices of dark matter tracers on the void size function and study its sensitivity to the joint effect of modifying the dark energy equation of state and the sum of neutrino masses. We show that dark energy and massive neutrinos produce separable effects on the void size function. This statistic therefore allows us to distinguish among a wide range of combinations of dark energy equations of state and total neutrino masses, and its exploitation in forthcoming large galaxy surveys will be extremely useful in breaking degeneracies among these cosmological parameters.

Motivation & Objective

• To investigate the sensitivity of the void size function (VSF) to joint variations in dark energy equation of state (EoS) and total neutrino mass.
• To assess whether the VSF can break degeneracies between dynamical dark energy and massive neutrinos that are difficult to distinguish with other probes.
• To evaluate the impact of different dark matter tracers (haloes and CDM particles) on the VSF in cosmological simulations.
• To determine the feasibility of using the VSF as a cosmological probe in upcoming large-scale galaxy surveys such as Euclid.

Proposed method

• Utilized the DEMNUni suite of cosmological N-body simulations with a comoving volume of (2 h⁻¹Gpc)³ and 2048³ dark matter and neutrino particles.
• Simulated 15 cosmological models with varying dark energy EoS (via CPL parameterization) and total neutrino masses (0, 0.16, 0.32 eV).
• Applied a void finder algorithm to identify cosmic voids in the density field traced by haloes and CDM particles across different redshifts.
• Computed the void size function as the number density of voids per logarithmic size bin, comparing results across cosmological models.
• Quantified statistical significance by comparing differences in VSFs to Poisson noise levels.
• Explored robustness by re-running analysis with fixed σ₈ instead of fixed Aₛ, confirming results are insensitive to this choice.

Experimental results

Research questions

• RQ1 Can the void size function distinguish between different dark energy equations of state and total neutrino masses in the presence of degeneracies?
• RQ2 How does the choice of dark matter tracer (e.g., haloes vs. CDM particles) affect the measured void size function?
• RQ3 To what extent does the VSF's sensitivity exceed Poisson noise in distinguishing cosmological models with both dynamical dark energy and massive neutrinos?
• RQ4 Does fixing σ₈ instead of Aₛ alter the VSF's ability to break degeneracies, and how does this affect interpretability?
• RQ5 Can the VSF be used as a standalone or complementary probe to break degeneracies in future galaxy surveys like Euclid?

Key findings

• The void size function shows statistically significant differences between all tested combinations of dark energy EoS and total neutrino masses, with differences exceeding Poisson noise in all cases.
• The VSF remains sensitive to cosmological parameters even when fixing σ₈ instead of Aₛ, and in some cases, sensitivity is enhanced, indicating robustness to prior choices.
• The VSF can distinguish between dynamical dark energy models (with w₀ and wₐ varying) and the cosmological constant, even when these models are degenerate in other probes.
• The DEMNUni simulation volume and resolution closely match those expected from upcoming surveys like Euclid, making the VSF a viable and powerful cosmological probe for future data.
• The VSF's sensitivity to both dark energy and massive neutrinos suggests it can help break existing degeneracies in cosmological parameter estimation.
• The results support the use of the VSF in combination with other void statistics, such as void-galaxy cross-correlation, to further enhance cosmological constraints.