6th Week Paper List

Constraints on Dark Matter from Colliders

Jessica Goodman, Masahiro Ibe, Arvind Rajaraman, William Shepherd, Tim M.P. Tait, Hai-Bo Yu

We show that colliders can impose strong constraints on models of dark matter, in particular when the dark matter is light. We analyze models where the dark matter is a fermion or scalar interacting with quarks and/or gluons through an effective theory containing higher dimensional operators which represent heavier states that have been integrated out of the effective field theory. We determine bounds from existing Tevatron searches for monojets as well as expected LHC reaches for a discovery. We find that colliders can provide information which is complementary or in some cases even superior to experiments searching for direct detection of dark matter through its scattering with nuclei. In particular, both the Tevatron and the LHC can outperform spin dependent searches by an order of magnitude or better over much of parameter space, and if the dark matter couples mainly to gluons, the LHC can place bounds superior to any spin independent search.

Links : https://journals.aps.org/prd/abstract/10.1103/PhysRevD.82.116010

Gamma Rays From Dark Matter Subhalos Revisited: Refining the Predictions and Constraints

Dan Hooper, Samuel J. Witte

Utilizing data from the ELVIS and Via Lactea-II simulations, we characterize the local dark matter subhalo population, and use this information to refine the predictions for the gamma-ray fluxes arising from annihilating dark matter in this class of objects. We find that the shapes of nearby subhalos are significantly altered by tidal effects, and are generally not well described by NFW density profiles, instead prefering power-law profiles with an exponential cutoff. From the subhalo candidates detected by the Fermi Gamma-Ray Space Telescope, we place limits on the dark matter annihilation cross section that are only modestly weaker than those based on observations of dwarf galaxies. We also calculate the fraction of observable subhalos that are predicted to be spatially extended at a level potentially discernible to Fermi.

Links : https://arxiv.org/abs/1610.07587

An alternative Explanation for the Fermi GeV Gamma-Ray Excess

Wim de Boer (1), Iris Gebauer (1), Alexander Neumann (1), Peter L. Biermann (1 and 2) ((1) Karlsruhe Institute of Technology, Karlsruhe, Germany, (2) MPI for Radioastronomy, Bonn, Germany)

The "GeV-excess" of the diffuse gamma-rays in the halo is studied with a template fit based on energy spectra for each possible process of gamma-ray emission. Such a fit allows to determine the background and signal simultaneously, so the Galactic Disk can be included in the analysis. We find evidence that the "excess", characterised by a gamma-ray spectrum peaking at 2 GeV, is much stronger in Molecular Clouds in the disk than the "GeV-excess" observed up to now in the halo. The possible reason why the emissivity of Molecular Clouds peaks at 2 GeV are the energy losses and magnetic cutoffs inside MCs, thus depleting the low energy part of the CR spectra and shifting the maximum of the gamma-ray spectra to higher energies. This peaking of the emissivity in Molecular Clouds at 2 GeV was clearly observed from the spectrum of the Central Molecular Zone, which dominates the emission in the inner few degrees of the Galactic Centre.

Although the spectrum of the Central Molecular Zone peaks at 2 GeV, it cannot be responsible for the "GeV-excess" observed in the halo, since the latitude extension of the Zone is below |b|<0.5∘. However, lines-of-sight into the halo cross Molecular Clouds in the disk, so the emissivity of clouds in the disk will be observed in the halo as an apparent "GeV-excess". The fact, that this "GeV-excess" has the same morphology in the disk {\it and} in the halo as the column density of Molecular Clouds, as traced by the CO map from the Planck satellite resembling an NFW-like latitude profile, and the fact the MCs have an emissivity peaking at 2 GeV shows that the "GeV-excess" originates from Molecular Clouds in the disk, not from a process surrounding the Galactic Centre

Links : https://arxiv.org/abs/1610.08926

Dark Matter interpretation of low energy IceCube MESE excess

M. Chianese, G. Miele, S. Morisi

The 2-years MESE IceCube events show a slightly excess in the energy range 10-100 TeV with a maximum local statistical significance of 2.3σ, once a hard astrophysical power-law is assumed. A spectral index smaller than 2.2 is indeed suggested by multi-messenger studies related to p-p sources and by the recent IceCube analysis regarding 6-years up-going muon neutrinos. In the present paper, we propose a two-components scenario where the extraterrestrial neutrinos are explained in terms of an astrophysical power-law and a Dark Matter signal. We consider both decaying and annihilating Dark Matter candidates with different final states (quarks and leptons) and different halo density profiles. We perform a likelihood-ratio analysis that provides a statistical significance up to 3.9σ for a Dark Matter interpretation of the IceCube low energy excess

Links : https://arxiv.org/abs/1610.04612

The effect of dark matter velocity profile on directional detection of dark matter

Ranjan Laha

Directional detection is an important way to detect dark matter. An input to these experiments is the dark matter velocity distribution. Recent hydrodynamical simulations have shown that the dark matter velocity distribution differs substantially from the Standard Halo Model. We study the impact of some of these updated velocity distribution in dark matter directional detection experiments. We calculate the ratio of events required to confirm the forward-backward asymmetry and the existence of the ring of maximum recoil rate using different dark matter velocity distributions for 19F and Xe targets. We show that with the use of updated dark matter velocity profiles, the forward-backward asymmetry and the ring of maximum recoil rate can be confirmed using a factor of ∼2 -- 3 less events when compared to that using the Standard Halo Model

Links : https://arxiv.org/abs/1610.08632