DM Interpretation Research Articles

Consistency test of the AMS-02 antiproton excess with direct detection data based on the effective field theory approach

The potential antiproton excess in the AMS-02 data is of much interest and can probably come from dark matter annihilations. Based on the effective field theory approach, in this work we investigate the compatibility of the DM interpretation of the AMS-02 antiproton excess and the null results from direct detection experiments, LUX, PandaX-II, and XENON1T. We focus on dimension-five and -six operators with fermion DM . Only one of dimension-five and one of dimension-six operators can successfully account for the antiproton excess, while the rest either are excluded by direct detection or require very small cut-off scales which invalidate the effective field theory approach.

Dark matter constraints from dwarf galaxies: a data-driven analysis

Dwarf galaxies represent a powerful probe of annihilating dark matter particle models, with gamma-ray data setting some of the best bounds available. A major issue in improving over existing constraints consists in the limited knowledge of the astrophysical background (mostly diffuse photons, but also unresolved sources). Perhaps more worrisome, several approaches in the literature suffer of the difficulty of assessing the systematic error due to background mis-modelling. Here we propose a data-driven method to estimate the background at the dwarf position and its uncertainty, relying on an appropriate use of the whole-sky data, via an optimisation procedure of the interpolation weights. While this article is mostly methodologically oriented, we also report the bounds based on latest Fermi-LAT data and updated information for J-factors for both isolated and stacked dwarfs. Our results are very competitive with the Fermi-LAT ones, while being derived with a more general and flexible method. We discuss the impact of profiling over the J-factor as well as over the background probability distribution function, with the latter resulting for instance crucial in drawing conclusions of compatibility with DM interpretations of the so-called Galactic Centre Excess.

OLD NEUTRON STARS AS PROBES OF ISOSPIN-VIOLATING DARK MATTER

Isospin-violating dark matter (IVDM), which couples differently with protons and neutrons, provides a promising mechanism to ameliorate the tension among recent direct detection experiments. Assuming DM is non-interacting bosonic asymmetric IVDM, we investigate how the existence of old neutron stars limits the DM-proton scattering cross-section $\sigma_{\rm p}$, especially the effects of the isospin violating DM-nucleon interactions and the symmetry energy in the equation of state of isospin asymmetric nuclear matter. Our calculations are completely based on general relativity and especially the structure of neutron stars is obtained by solving the Tolman-Oppenheimer-Volkoff equations with nuclear matter equation of state constrained by terrestrial experiments. We find that, by considering the more realistic neutron star model rather than a simple uniform neutron sphere as usual, the $\sigma_{\rm p}$ bounds from old neutron stars can be varied by more than an order of magnitude depending on the specific values of the DM neutron-to-proton coupling ratio $f_{\rm n}/f_{\rm p}$, and they can be further varied by more than a factor of two depending on the density dependence of the symmetry energy. In particular, we demonstrate that the observed nearby isolated old neutron star PSR B1257+12 can set a very strong limit on $\sigma_{\rm p}$ for low-mass DM particles ($ \le 20 \, {\rm GeV}$) that reaches a sensitivity beyond the current best limits from direct detection experiments and disfavors the DM interpretation of previously-reported positive experimental results, including the IVDM.

Dark matter in light of the LUX results

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 or neutrino recoil? Interpretation of recent experimental results

The elastic nuclear recoil signal, being under intense scrutiny by multiple underground experiments, can be interpreted either as coming from the interaction of nuclei with WIMP dark matter or from the scattering of new species of MeV-energy neutrinos. The most promising model for the latter case is a neutrino $\nu_b$ that interacts with baryon number, and with a flux sourced by the oscillations of regular solar $^8$B neutrinos. We re-analyze this model in light of the latest experimental results. In contrast to the light-DM interpretation of various tentative positive signals (anomalies) that is now seriously challenged by the negative results of the LUX experiment, the neutrino interpretation remains a viable explanation to most of the anomalies. Considering future prospects, we show that the superCDMS experiment alone, when equipped with Ge and Si detectors, will be able to detect $\nu_b$ and discriminate the model from a light DM interpretation. In addition, we also provide the forecast for the new CRESST-II run that now operates with new detectors and diminished backgrounds.

Up-shot of inelastic down-scattering at CDMS-Si

We study dark matter that inelastically scatters and de-excites in direct detection experiments, as an interpretation of the CDMS-Si events in light of the recent LUX data. The constraints from LUX and XENON10 require the mass-splitting between the DM excited and de-excited states to be $|\delta| \gtrsim 50$ keV. At the same time, the CDMS-Si data itself do not allow for a consistent DM interpretation for mass splittings larger than $|\delta| \sim $200 keV. We find that a low threshold analysis will be needed to rule out this interpretation of the CDMS-Si events. In a simple model with a kinetically mixed dark photon, we show that the CDMS-Si rate and the thermal relic abundance can both be accommodated.

Dark Matter interpretations of the [formula omitted] excesses after FERMI

The cosmic-ray excess observed by PAMELA in the positron fraction and by FERMI and HESS in e − + e + can be interpreted in terms of DM annihilations or decays into leptonic final states. Final states into τ's or 4 μ give the best-fit to the excess. However, in the annihilation scenario, they are incompatible with photon and neutrino constraints, unless DM has a quasi-constant density profile. Final states involving e's are less constrained but poorly fit the excess, unless hidden sector radiation makes their energy spectrum smoother, allowing a fit to all the data with a combination of leptonic modes. In general, DM lighter than about a TeV cannot fit the excesses, so PAMELA should find a greater positron fraction at higher energies. The DM interpretation can be tested by FERMI γ observations above 10 GeV: if the e ± excess is everywhere in the DM halo, Inverse Compton scattering on ambient light produces a well-predicted γ excess that FERMI should soon detect.