Where shadows lie: reconstruction of anisotropies in the neutrino sky

Abstract

The Cosmic Neutrino Background (CNB) encodes a wealth of information, but has not yet been observed directly. To determine the prospects of detection and to study its information content, we reconstruct the phase-space distribution of local relic neutrinos from the three-dimensional distribution of matter within 200 h -1 Mpc of the Milky Way. Our analysis relies on constrained realization simulations and forward modelling of the 2M++ galaxy catalogue. We find that the angular distribution of neutrinos is anti-correlated with the projected matter density, due to the capture and deflection of neutrinos by massive structures along the line of sight. Of relevance to tritium capture experiments, we find that the gravitational clustering effect of the large-scale structure on the local number density of neutrinos is more important than that of the Milky Way for neutrino masses less than 0.1 eV. Nevertheless, we predict that the density of relic neutrinos is close to the cosmic average, with a suppression or enhancement over the mean of (-0.3%, +7%, +27%) for masses of (0.01, 0.05, 0.1) eV. This implies no more than a marginal increase in the event rate for tritium capture experiments like PTOLEMY. We also predict that the CNB and CMB rest frames coincide for 0.01 eV neutrinos, but that neutrino velocities are significantly perturbed for masses larger than 0.05 eV. Regardless of mass, we find that the angle between the neutrino dipole and the ecliptic plane is small, implying a near-maximal annual modulation in the bulk velocity. Along with this paper, we publicly release our simulation data, comprising more than 100 simulations for six different neutrino masses.

Local clustering of relic neutrinos: comparison of kinetic field theory and the Vlasov equation

“…In the rest of this section, we give a brief summary of the different techniques that were applied in order to calculate the local density of relic neutrinos (roughly following a chronological order). Note that, except for the full-fledged N -body simulations of [22,27], all methods are based on the N -one-body approximation and this also forms the basis for this JCAP07(2024)050 work. Due to different assumptions concerning the gravitational potential, a direct one-to-one comparison between the results of the works [20][21][22][23][24][25][26][27] is not always possible.…”

“…Note that, except for the full-fledged N -body simulations of [22,27], all methods are based on the N -one-body approximation and this also forms the basis for this JCAP07(2024)050 work. Due to different assumptions concerning the gravitational potential, a direct one-to-one comparison between the results of the works [20][21][22][23][24][25][26][27] is not always possible.…”

“…Extracting the local neutrino density from the N -body simulations in [22] is of course not directly possible since N -body simulations can in general only reproduce local structures in a statistical sense. Very recently, the authors of [27] therefore performed so called constrained simulations in which objects appear at the right positions relative to us.…”

“…Estimating the local overdensity of relic neutrinos is crucial for direct detection experiments since it is proportional to the expected detection rate (for a discussion of current experimental bounds on the overdensity and the sensitivities of future experiments see [15][16][17][18][19]). Therefore, several works have calculated the local relic neutrino density [20][21][22][23][24][25][26][27].…”

Neutrino Portal to Freeze-in Dark Matter

“…We assume a local overdensity around the Earth so that the matter effect is isotropic. Theoretically, while gravitational clustering alone can only give an O(1) enhancement [103][104][105][106][107], possible nonstandard neutrino interactions could in principle give η ≫ 1. For instance, in a model with Yukawa interactions mediated by an ultralight scalar, neutrinos can form stable clusters with η max ∼ 10 7 [108].…”