New mass bound on fermionic dark matter from a combined analysis of classical dSphs

Abstract

Dwarf spheroidal galaxies (dSphs) are the most compact dark matter-dominated objects observed so far. The Pauli exclusion principle limits the number of fermionic dark matter particles that can compose a dSph halo. This results in a well-known lower bound on their particle mass. So far, such bounds were obtained from the analysis of individual dSphs. In this paper, we model dark matter halo density profiles via the semi-analytical approach and analyse the data from eight 'classical' dSphs assuming the same mass of dark matter fermion in each object. First, we find out that modelling of Carina dSph results in a much worse fitting quality compared to the other seven objects. From the combined analysis of the kinematic data of the remaining seven 'classical' dSphs, we obtain a new 2σ lower bound of m 190 eV on the dark matter fermion mass. In addition, by combining a sub-sample of four dSphs -Draco, Fornax, Leo I and Sculptor -we conclude that 220 eV fermionic dark matter appears to be preferred over the standard CDM at about 2σ level. However, this result becomes insignificant if all seven objects are included in the analysis. Future improvement of the obtained bound requires more detailed data, both from 'classical' and ultra-faint dSphs.

Degenerate fermion dark matter from a broken U(1)B−L gauge symmetry

“…Another interesting possibility of DM resulting in a cored halo profile in a low mass galaxy is the fermion DM in the quantum degenerate limit. Along the similar line, the hypothesis of the fermion DM as the self-gravitating (quasi) degenerate gas was invoked in [28][29][30][31][32] to explain the kinematics of dwarf spheroidal galaxies (dSphs). The fitting procedures for the kinematic data (stellar velocity dispersion and halo radius of dSphs) yielded a sub-keV mass regime as the possible fermion DM mass (see also Refs.…”

“…Intriguingly, for y à ¼ y Ã;max , the criterion 0.3 Mpc ≲ λ FS ≲ 0.5 Mpc gives the mass constraint 0.25 keV ≲ m DM ≲ 0.37 keV, which lies in the range of the degenerate fermion DM mass accounting for the cored DM profiles of dSphs in Refs. [28][29][30][31]. Another choice of y à < y Ã;max will make 0.3 Mpc ≲ λ FS ≲ 0.5 Mpc correspond to a larger m DM range.…”

“…However, indeed there exist some uncertainties in the velocity anisotropy parameter used for the fitting of the stellar velocity dispersion, the lower bound of the Fornax dSphs halo radius, and the baryon's effect on the DM halo profile. Also, still for some dSphs other than Fornax, the best fitting for the stellar velocity dispersion is done by m DM as large as 550-650 eV [30]. Here, without performing a detailed fitting analysis to infer the degenerate fermion DM mass, we take a conservative attitude to understand 100 eV ≲ m DM ≲ 1 keV as the interesting range relating to the degenerate fermion DM solution to the core-cusp problem.…”

Absorption of fermionic dark matter by nuclear targets

“…For example, CνB detection experiments must resolve β − energies at the possible scale of SM neutrinos' masses, m ν ∼ 0.1 eV, thus requiring a target with a low Q value: tritium. By contrast, the fermionic dark matter we consider is heavier: m χ 190 eV [101,102], so this target selection criterion is irrelevant. This motivates us to consider different β − decaying isotopes more generally than the present proposals.…”

“…2.2. It is interesting that with less than 1 kg yr of tritium, a future experiment could start probing the lightest possible fermionic dark matter [101,102] with these charged current interactions. This provides further motivation to pursue proposals such as PTOLEMY.…”