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28 March, 2012

In High Energy Physics on April 5, 2012 by physthjc

**1) Asymptotic Darkness**

**On Asymptotic Darkness in Horava-Lifshitz GRavity**

*abstract: * Ho\v{r}ava-Lifshitz gravity is shown to exhibit a peculiar behavior, when scattering amplitudes are considered. At low energies it seems to classicalize i.e. the effective size of the interaction grows as a function of the $s$-parameter, with BHs forming part of the spectrum; but when the probing energy is increased such that higher order operators become important, this behavior changes and the classicalon recedes to a new configuration where ordinary quantum regimes take over. Eventually, the theory behaves as a usual field theory that allows probing arbitrarily small distances. In particular, the classical potential created by a point-like source is finite everywhere exhibiting a Vainshtein alike screening behavior. The transition from one behavior to the other is carefully described in a particular case.

**2) Asymmetric Dark Matter**

**Closing in on asymmetric dark matter I: Model independent limits for interaction with quarks **

*abstract: * It is argued that experimental constraints on theories of asymmetric dark matter (ADM) almost certainly require that the DM be part of a richer hidden sector of interacting states of comparable mass or lighter. A general requisite of models of ADM is that the vast majority of the symmetric component of the DM number density must be removed in order to explain the observed relationship $\Omega_B\sim\Omega_{DM}$ via the DM asymmetry. Demanding the efficient annihilation of the symmetric component leads to a tension with experimental limits if the annihilation is directly to Standard Model (SM) degrees of freedom. A comprehensive effective operator analysis of the model independent constraints on ADM from direct detection experiments and LHC monojet searches is presented. Notably, the limits obtained essentially exclude models of ADM with mass 1GeV$\lesssim m_{DM} \lesssim$ 100GeV annihilating to SM quarks via heavy mediator states. This motivates the study of portal interactions between the dark and SM sectors mediated by light states. Resonances and threshold effects involving the new light states are shown to be important for determining the exclusion limits.

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