DEMNUni: massive neutrinos and the bispectrum of large scale structures

Abstract

The main effect of massive neutrinos on the large-scale structure consists in a few percent suppression of matter perturbations on all scales below their free-streaming scale. Such effect is of particular importance as it allows to constraint the value of the sum of neutrino masses from measurements of the galaxy power spectrum. In this work, we present the first measurements of the next higher-order correlation function, the bispectrum, from N-body simulations that include massive neutrinos as particles. This is the simplest statistics characterising the non-Gaussian properties of the matter and dark matter halos distributions. We investigate, in the first place, the suppression due to massive neutrinos on the matter bispectrum, comparing our measurements with the simplest perturbation theory predictions, finding the approximation of neutrinos contributing at quadratic order in perturbation theory to provide a good fit to the measurements in the simulations. On the other hand, as expected, a linear approximation for neutrino perturbations would lead to O(f ν ) errors on the total matter bispectrum at large scales. We then attempt an extension of previous results on the universality of linear halo bias in neutrino cosmologies, to non-linear and non-local corrections finding consistent results with the power spectrum analysis.

Tree-level bispectrum in the effective field theory of large-scale structure extended to massive neutrinos

“…Their analysis of the shape dependence of the tree-level bispectrum yields, in agreement with our result, that the neutrino contribution to the total matter bispectrum is the same in the equilateral and flat configurations. However, the difference between our results is much larger for the squeezed configuration as they observe a steep enhanced suppression, which is not observed by [66] and us, which will be discussed in more depth in Sec. 5.…”

Status of Neutrino Properties and Future Prospects—Cosmological and Astrophysical Constraints

“…The level of complexity of Nbody simulations has been increasing over the years, so that the physical processes included in the simulations and the final results are much closer to the observations than they used to be at the beginning. Recent examples are given by the MassiveNuS [69] suite, based on the Gadget-2 code [70] modified to include the effects of massive neutrinos, the DEMNUni suite [71][72][73], the TianNu simulation [74][75][76], the BAHAMAS project [77], the gevolution simulations [78], and the nuCONCEPT simulations [79] (see also [80] for a method combining the particle and fluid descriptions) 7 . Nevertheless, the uncertainties related to the non-linear evolution of cosmological structures are still higher than those affecting the linear theory, therefore reducing the constraining power coming from the inclusion of those scales in cosmological analysis.…”

The two-loop bispectrum of large-scale structure

“…The kernel F2 (k 2 , k 3 ) can be written as a linear combination of the basis shape functions (35). As usual, the EFT enjoys the same symmetry as the underlying theory, and therefore momentum conservation requires that also F2 (k, p) becomes zero for k +p → 0.…”

“…The most important property for our purposes is that the E 1 , E 2 , E 3 , Γ shapes form a basis of shape functions. Indeed, one realizes that it is related to the shape functions b (1) − b (5) introduced in ( 35) by a basis transformation, when eliminating one of the five shapes in (35) by assuming the constraint (36) from momentum conservation holds. Concretely, we have…”

“…Beyond the power spectrum, the bispectrum provides complementary information and is instrumental in disentangling bias from the impact of fundamental parameters [31][32][33][34][35][36][37][38][39][40][41]. Within an EFT framework the matter bispectrum has been studied in [42,43].…”