Relic Neutrino Clustering and Implications for Their Detection

Abstract

We study the gravitational clustering of big bang relic neutrinos onto existing cold dark matter and baryonic structures within the flat ΛCDM model. We then discuss the implications of clustering for scattering-based relic neutrino detection methods, ranging from flux detection via Cavendish-type torsion balances, to target detection using accelerator beams and cosmic rays. ⋆ Talk given by YYYW at DARK2004, College Station TX, USA. Based on [1].

Probing neutrino dark energy with extremely high energy cosmic neutrinos

“…On the other hand, as a direct consequence, the neutrino energy densities ρ ν i (m ν i , A) can stabilize the acceleron by contributing to its effective potential V eff (A, ρ ν i ), which represents the total energy density of the coupled system. Moreover, cosmic expansion manifests itself in the dilution of the neutrino energy densities ρ ν i (z) ∼ (1 + z) 3 . Therefore, it crucially affects the effective acceleron potential V eff (A, ρ ν i (m ν i , z)) by introducing a dependence on cosmic time, here parametrized in terms of the cosmic redshift z.…”

“…Taking now the expansion of the universe into account, the dilution of the neutrino energy densities ρ ν i (z) ∼ (1 + z) 3 introduces a time dependence (here parametrized in terms of the cosmic redshift z) into the effective acceleron potential V eff . Consequently, in the adiabatic limit 2 , the equilibrium value A of the acceleron has to vary with time in order to instantaneously minimize its effective potential V eff (A).…”

“…Neutrinos, being the particles with the weakest known interactions, therefore are assumed to have already decoupled when the universe was just ≈ 1 s old, thereby guaranteeing a substantial relic neutrino abundance today with average number density n ν 0,i = n ν0,i = 56 cm −3 per neutrino species i = 1, 2, 3. Yet, in turn, the weakness of the neutrino interactions so far has spoilt all attempts to probe this 1.95 K cosmic neutrino background (CνB), which is the analog of the 2.73 K cosmic microwave background (CMB) of photons, in a laboratory setting [1][2][3][4]. However, other cosmological measurements, such as the light element abundance, large scale structure (LSS) and the CMB anisotropies are sensitive to the presence of the CνB and therefore have provided us at least with indirect evidence for its existence (see e.g.…”

“…Therefore, it would not seem to be surprising if neutrinos, whose interactions and properties we know comparably little about, were sensitive to further forces mediated by dark particles. Moreover, the scale relevant for neutrino mass squared differences as determined from neutrino oscillation experiments, δm ν 2 ∼ (10 −2 eV) 2 , is of the order of the tiny scale associated with the dark energy, (2 × 10 −3 eV) 4 .…”

Massive Neutrinos: Phenomenological and Cosmological Consequences

“…Let us stress here that we will not consider the possible clustering of neutrinos around massive objects, for simplicity. For more information, see the work from A. Ringwald and Y. Y. Y. Wong[161] and the more recent work from P. F. de Salas et. al [162]…”