From direct detection to relic abundance: the case of proton-philic spin-dependent inelastic Dark Matter

초록

We discuss strategies to make inferences on the thermal relic abundance of a Weakly Interacting Massive Particle (WIMP) when the same effective dimension-six operator that explains an experimental excess in direct detection is assumed to drive decoupling at freeze-out, and apply them to the explicit scenario of WIMP inelastic up-scattering with spin-dependent couplings to protons (proton-philic Spin-dependent Inelastic Dark Matter, pSIDM), a phenomenological set-up containing two Dark Matter (DM) particles. 1 and. 2 with masses m(x). = m(x1) and m(x2) = m(x)+ delta that we have shown in a previous paper to explain the DAMA effect in compliance with the constraints from other detectors. We also update experimental constraints on pSIDM, extend the analysis to the most general spin-dependent momentum-dependent interactions allowed by non-relativistic Effective Field Theory (EFT), and consider for the WIMP velocity distribution in our Galaxy f(v) both a halo-independent approach and a standard Maxwellian. Under these conditions we find that the DAMA effect can be explained in terms of the particle. 1 in compliance with all the other constraints for all the analyzed EFT couplings and also for a Maxwellian f(v). As far as the relic abundance is concerned, we show that the problem of calculating it by using direct detection data to fix the model parameters is affected by a strong sensitivity on f(v) and by the degeneracy between the WIMP local density.. and the WIMP-nucleon scattering cross section, since.. must be rescaled with respect to the observed DM density in the neighborhood of the Sun when the calculated relic density Omega is smaller than the observed one Omega(0). As a consequence, a DM direct detection experiment is not directly sensitive to the physical cut-off scale of the EFT, but on some dimensional combination that does not depend on the actual value of Omega. However, such degeneracy can be used to develop a consistency test on the possibility that the WIMP is a thermal relic in the first place. When we apply it to the pSIDM scenario we find that only a WIMP with the standard spin-dependent interaction O = (X) over bar (1)gamma(mu)gamma X-5(2)(q) over tilde gamma(mu)gamma(5)q + h.c. with quarks can be a thermal relic for, approximately, 10GeV <= m(x). <= 16GeV, 17 keV <= delta <= 28 keV, and a large uncertainty on Omega, 6 x 10(-7) Omega(0) 0 <= Omega <= Omega(0) In order for the scenario to work the WIMP galactic velocity distribution must depart from a Maxwellian. Moreover, all theX(2) states must have already decayed today, and this requires some additional mechanism besides that provided by the O operator.

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