We study the direct detection prospects for a representative set of simplified models of sub-GeV dark matter (DM), accounting for existing terrestrial, astrophysical and cosmological constraints. We focus on dark matter lighter than an MeV, where these constraints are most stringent, and find three scenarios with accessible direct detection cross sections: (i) DM interacting via an ultralight kinetically mixed dark photon, (ii) a DM subcomponent interacting with nucleons or electrons through a light scalar or vector mediator, and (iii) DM coupled with nucleons via a mediator heavier than ∼ 100 keV. A Vacuum stability for scalar χ model 35 B Self-interaction cross sections 36 C Thermalization of the mediator 37 D In-medium couplings of light vectors 38 References 39

International audienceThis document outlines a set of simplified models for dark matter and its interactions with Standard Model particles. It is intended to summarize the main characteristics that these simplified models have when applied to dark matter searches at the LHC, and to provide a number of useful expressions for reference. The list of models includes both s-channel and t-channel scenarios. For s-channel, spin-0 and spin-1 mediation is discussed, and also realizations where the Higgs particle provides a portal between the dark and visible sectors. The guiding principles underpinning the proposed simplified models are spelled out, and some suggestions for implementation are presented

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High-precision measurements of the temperature and polarization anisotropies of the cosmic microwave background radiation have been employed to set robust constraints on dark matter annihilation during recombination. In this work we improve and generalize these constraints to apply to energy deposition during the recombination era with arbitrary redshift dependence. Our approach also provides more rigorous and model-independent bounds on dark matter annihilation and decay scenarios. We employ principal component analysis to identify a basis of weighting functions for the energy deposition. The coefficients of these weighting functions parameterize any energy deposition model and can be constrained directly by experiment. For generic energy deposition histories that are currently allowed by WMAP 7 data, up to 3 principal component coefficients are measurable by Planck and up to 5 coefficients are measurable by an ideal cosmic variance limited experiment. For WIMP dark matter, our analysis demonstrates that the effect on the CMB is described well by a single (normalization) parameter and a "universal" redshift dependence for the energy deposition history. We give WMAP 7 constraints on both generic energy deposition histories and the universal WIMP case.PACS numbers: 95.35.+d,98.80.Es

We show that ultra-peripheral heavy-ion collisions at the LHC can be used to search for axionlike particles with mass below 100 GeV. The Z 4 enhanced photon-photon luminosity from the ions provides a large exclusive production rate, with a signature of a resonant pair of back-to-back photons and no other activity in the detector. In addition, we present both new and updated limits from recasting multi-photon searches at LEP II and the LHC, which are more stringent than those currently in the literature for the mass range 100 MeV to 100 GeV.