Constraining Neutrino Mass with the Bispectrum

Oct 21, 2019 - 11:00 am to 12:00 pm
ChangHoon Hahn (UC Berkeley)

Massive neutrinos suppress the growth of structure below their free-streaming scale and

leave an imprint on large-scale structure. Measuring this imprint allows us to constrain the

sum of neutrino masses, Mnu, a key parameter in particle physics beyond the Standard Model. 

However, degeneracies among cosmological parameters, especially between Mnu and sigma8, 

limit the constraining power of standard two-point clustering statistics. I will present whether

we can break these degeneracies and constrain Mnu with the next higher-order correlation

function — the bispectrum. I first examine the redshift-space halo bispectrum of 800 N-body 

simulations from the HADES suite and demonstrate that the bispectrum helps break the 

Mnu-sigma8 degeneracy. Then I will present the full information content of the redshift-space 

halo bispectrum down to nonlinear scales using a Fisher matrix forecast of {Om, Ob, h, ns, sigma8, Mnu}  with 22,000 N-body simulations of the Quijote suite. For kmax=0.5 h/Mpc, the bispectrum

provides Om, Ob, h, ns, and sigma8 constraints 1.9, 2.6, 3.1, 3.6, and 2.6 times tighter than the

power spectrum. For Mnu, the bispectrum improves the 1sigma constraint from 0.2968 to 

0.0572 eV — over 5 times tighter than the power spectrum. Lastly, I will present ongoing projects

that are laying down the framework for a full bispectrum analysis of DESI: including a comprehensive

bias model, data compression for the bispectrum, paired-fixed simulations for the bispectrum, and

efficient simulation-based inference methods.