Constraining dark matter-neutrino interactions using the CMB and large-scale structure

Abstract

We present a new study on the elastic scattering cross section of dark matter (DM) and neutrinos using the latest cosmological data from Planck and large-scale structure experiments. We find that the strongest constraints are set by the Lyman-α forest, giving σ DM−ν 10 −33 (m DM /GeV) cm 2 if the cross section is constant and a present-day value of σ DM−ν 10 −45 (m DM /GeV) cm 2 if it scales as the temperature squared. These are the most robust limits on DM-neutrino interactions to date, demonstrating that one can use the distribution of matter in the Universe to probe dark ("invisible") interactions. Additionally, we show that scenarios involving thermal MeV DM and a constant elastic scattering cross section naturally predict (i) a cut-off in the matter power spectrum at the Lyman-α scale, (ii) N eff ∼ 3.5 ± 0.4, (iii) H 0 ∼ 71 ± 3 km s −1 Mpc −1 and (iv) the possible generation of neutrino masses.

Analysis of the Angular Dependence of Time Delay in Gravitational Lensing

“…This remarkable fact justifies our claim: our time delay Equation (18), which is equivalent to (1) once the smoothness condition is imposed, is the generalization at the arbitrary angles of the standard expression (4), and, differently from (4), it has been obtained in one shot only without having to consider two distinct steps (geometrical and Shapiro).…”

“…The exact expression for the time delay (1), using (18), is then given by the sum of the three terms ∆τ i (22), (26) and (27). We stress that the two expressions for time delay ∆t (1) and ∆t old (4) are expressed by means of the same parameters: no new degrees of freedom have been introduced.…”

“…This is a remarkable result, because it proves that Equation (1) is the generalization of the standard one to the arbitrary angles. To get this result, the crucial step is that the formula ∆t, written in the form (18), is expressed in terms of the same degrees of freedom appearing in the standard Equation (4).…”

“…Now we are able to expand in the small angles limit the time delay Equation (1) term by term, according to (18). For what concerns ∆τ 1 (22), we have…”

“…For instance, it has been showed on general basis that dynamical dark energy [15,16] or a specific quintessence model [17] can solve the tension. Other possibilities have also been considered, such as dark matter-neutrinos interactions [18,19].…”