Molecular Chemistry for Dark Matter

Abstract

Molecular cooling is essential for studying the formation of sub-structure of dissipative dark-matter halos that may host compact objects such as black holes. Here, we analyze the reaction rates relevant for the formation, dissociation, and transition of hydrogenic molecules while allowing for different values of the physical parameters: the coupling constant, the proton mass, and the electron mass. For all cases, we re-scale the reaction rates for the standard molecular hydrogen, so our results are valid as long as the dark matter is weakly coupled and one of the fermions is much heavier than the other. These results will allow a robust numerical treatment of cosmic structure, in particular for mini-halos for which molecular cooling is important, in a dissipative dark matter scenario.

Molecular Chemistry for Dark Matter. II. Recombination, Molecule Formation, and Halo Mass Function in Atomic Dark Matter

“…These reactions also require the addition of terms that we collectively denote by D d x dz p D to Equation (1) to account for the effect of the molecular reactions on the free proton fraction. The reaction rates, c Hi , appearing below are summarized in Table 1 (i is the reaction number in the table), and are obtained by rescaling Standard Model rates according to the procedure described in Section 2.2 and in Ryan et al (2021a). The number density of neutral dark atoms is…”

“…For the reactions involved in the formation of molecular states we adopt the rescaling procedure described in detail in Ryan et al (2021a). The reaction rates in Table 1 are fits to either theoretical calculations or experimental data.…”

“…One might worry that other reactions deemed unimportant in the Standard Model by Galli & Palla (1998) could also contribute for nonstandard parameters. This issue is discussed in more detail in Ryan et al (2021a). Briefly, the volumetric rates c Hi of the unimportant reactions may be low either due to a strong parametric suppression of the rate coefficient c Hi or due to the small relative abundance of the reactants.…”

“…This paper is the second in a series of three. In Paper I, Ryan et al (2021a), we defined a rescaling procedure to compute the molecular chemistry for atomic dark matter from known Standard Model results. Paper III, Ryan et al (2021b), describes DARKKROME, a modification of the chemistry package KROME (Grassi et al 2014) to include the chemistry of atomic dark matter.…”

Scattering searches for dark matter in subhalos: neutron stars, cosmic rays, and old rocks

“…( 9) for T cold T hot ), and on the right by a black-dashed contour of t meet = t cool (1000 K) = 1.2 × 10 7 yr, and would be excluded if an NS at r = r is measured to be below On the other hand, if DM has substantial selfinteractions then PSR J2144-3933 already places a strong bound on subhalo DM. In this case we consider fluid accretion of the DM onto NSs, especially relevant for theories of dissipative and strongly self-interacting DM [94][95][96][97][98], for which DM will have a sizable sound speed (much like the interstellar medium), especially if collected into dense subhalos. The effective DM collection radius of the NS will now be enhanced by another factor of v esc / v rel (i.e.…”