Light dark matter anomalies after LUX

Abstract

The landscape of dark matter direct detection has been profoundly altered by the slew of recent experiments. While some have claimed signals consistent with dark matter, others have seen few, if any, events consistent with dark matter. The results of the putative detections are often incompatible with each other in the context of naive spin-independent scattering, as well as with the null results. In particular, in light of the conflicts between the DM interpretation of the three events recently reported by the CDMS-Si experiment and the first results of the LUX experiment, there is a strong need to revisit the assumptions that go into the DM interpretations of both signals and limits. We attempt to reexamine a number of particle physics, astrophysics and experimental uncertainties. Specifically, we examine exothermic scattering, isospin-dependent couplings, modified halo models through astrophysics independent techniques, and variations in the assumptions about the scintillation light in liquid Xenon. We find that only a highly tuned isospin-dependent scenario remains as a viable explanation of the claimed detections, unless the scintillation properties of LXe are dramatically different from the assumptions used by the LUX experiment.

Dark matter interpretation of the Fermi -LAT observation toward the Galactic Center

“…For the vector models, which contribute to the spin-independent cross section σ SI , we follow the usual convention mapping onto this quantity defined at zero relative velocity. For pseudo-scalar interactions, we compute the integrated cross section for DM scattering with a nucleon by integrating over the recoil energy of the nucleus and the velocity of the DM, which we assume follows a Maxwellian distribution, using techniques developed in [74][75][76][77], (specifically using the code presented in Ref. [76]).…”

Isospin-violating dark matter with colored mediators

“…As LUX experiment [11] currently imposes the most stringent bound on DM, one necessarily considers DM that has negligible interaction with the Xenon nucleus. Recent studies after the LUX result [17][18][19]27] have shown that the isospin-violating DM is still compatible with one of positive signals, those of the CDMS-II Si experiment.…”

“…alternatives (e.g., modified halo models) or varying assumptions about the Xenon scintillation efficiencies [17][18][19]. A scenario that still remains viable in reconciling some of these results is the isospin-violating DM [20][21][22][23][24][25][26].…”

Effective field theory treatment of the neutrino background in direct dark matter detection experiments

“…Different WIMP-nucleus scattering models will correspond to different nuclear responses, which often include a sum of responses contributing, and can also lead to interference terms between the responses [7,27,28]. A study of a variety of spin-1/2 dark matter UV complete models whose responses are described by these non-standard responses was given in [10], and a general survey of simplified models of spin-0, spin-1/2, and spin-1 dark matter models was carried out in [29]. There exist additional nuclear responses beyond these five, but are typically not considered due to P and CP properties of the nuclear ground state and an assumption of CP conservation of the interaction.…”

“…Additional nuclear responses were identified that augment the standard SI and SD responses. Though these operators induce nuclear recoil energy spectra that differ from the traditional SI/SD models [9], the upper limits on the WIMP-nucleon cross section are not strongly affected, except for experiments with relatively high recoil energy thresholds, greater than tens of keV [10].…”