Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMIn dark matter (DM) models, the production of a γ line (or of a ‘‘box-shaped’’ γ-ray spectrum) from DM annihilation proceeds in general from a loop diagram involving a heavy charged particle. If the charged particle in the loop carries also a color charge, this leads inevitably to DM annihilation to gluons, with a naturally larger rate. We consider a scenario in which DM candidates annihilate dominantly into gluon pairs, and determine (as far as possible, model-independent) constraints from a variety of observables: (a) the dark matter relic density, (b) the production of antiprotons, (c) DM direct detection and (d) gluon-gluon fusion processes at LHC. Among other things, we show that this scenario together with the recent claim for a possible γ line from the Galactic center in the Fermi-LAT data, leads to a relic abundance of DM that may be naturally close to the cosmological observationsOne of us (M. T.) acknowledges stimulating discussions with Y. Mambrini and U. Ellwanger, and the LPT-Orsay for hospitality. T.H. thanks the Departamento de Física Teórica (UAM-Madrid) and the IFT-Madrid for hospitality and the Comunidad de Madrid (Proyecto HEPHACOS S2009/ESP-1473). This work is supported by the FNRS, the IISN and an ULB-AR

We show that there exists only a quite limited number of higher dimensional operators which can naturally lead to a slow decay of dark matter particles into monochromatic photons. As each of these operators inevitably induces decays into particles other than photons, we show that the γ-lines it induces are always accompanied by a continuum flux of cosmic rays. Hence constraints on cosmic-ray fluxes imply constraints on the intensity of γ-lines and vice versa. A comparison with up to date observational bounds shows the possibilities to observe or exclude cosmic rays associated to γ-line emission, so that one could better determine the properties of the DM particle, possibly discriminating between some of the operators.

In the energy range from few TeV to 25 TeV, upper bounds on the dark matter decay rate into high energy monochromatic neutrinos have recently become comparable to those on monochromatic gamma-ray lines. This implies clear possibilities of a future double "smoking-gun" evidence for the dark matter particle, from the observation of both a gamma and a neutrino line at the same energy. In particular, we show that a scenario where both lines are induced from the same dark matter particle decay leads to correlations that can already be tested. We study this "double monochromatic" scenario by considering the complete list of lowest dimensional effective operators that could induce such a decay. Furthermore, we argue that, on top of lines from decays into twobody final states, three-body final states can also be highly relevant. In addition to producing a distinct hard photon spectrum, three-body final states also produce a line-like feature in the neutrino spectrum that can be searched for by neutrino telescopes. * Electronic address: celaisat@ulb.ac.be;

If a γ-ray line is observed in the near future, it will be important to determine what kind of dark matter (DM) particle could be at its origin. We investigate the possibility that the γ-ray line would be induced by a slow DM particle decay associated to the fact that the DM particle would not be absolutely neutral. A "millicharge" for the DM particle can be induced in various ways, in particular from a kinetic mixing interaction or through the Stueckelberg mechanism. We show that such a scenario could lead in specific cases to an observable γ-ray line. This possibility can be considered in a systematic modelindependent way, by writing down the corresponding effective theory. This allows for a multi-channel analysis, giving in particular upper bounds on the intensity of the associated γ-ray line from cosmic rays emission. Our analysis includes the possibility that in the twobody decay the photon is accompanied with a neutrino. We show that, given the stringent constraints which hold on the millicharge of the neutrinos, this is not an option, except if the DM particle mass lies in the very light KeV-MeV range, allowing for a possibility of explanation of the recently claimed, yet to be confirmed, ∼ 3.5 KeV X-ray line.