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2 years ago by up to six orders of magnitude below the Fermi constant . The above argument fails, and the bounds on the X-Nucleon cross-sections for the lighter DM candidates can be evaded, as we explain in the following if the mediator V of the X-q interaction is light. Specifically if V is lighter than the nucleon or the CDM particle X -or more generally than the invariant mass MXX¯ of the pairs in the above LHC signal events-we can no longer approximate the V exchange in the pair production process by a local four Fermi interaction . The X-Nuclear elastic scattering in the direct search experiments generate very small momentum transfers: q = mX.βX ∼ 1003 .mX=MeV for mX ∼GeV. (βX ∼ 1003 is the typical virial velocity of the DM in the galactic halo). The scattering cross-section ∼ g 2 g 02 [m2 X + q 2 ] ]2 ∼ g 2 g 02mX X 4 is therefore enhanced relative to the X¯ X production cross-section ∼ g 02 g 2m(X¯ X) )4 with g, g the coupling of the mediator V to X¯ X and ¯q q q) by factors of ∼ 104 4 108 for mX = 1/2 GeV and invariant mass mX¯X ∼ 5 5 50 GeV. The non-observation at LHC of missing DM pairs cannot then constrain elastic cross-section in direct searches. A natural candidate for the light mediator V is the dark photon which kinetically mixes with our photon and is relatively light (MV ≤ GeV), and which has featured in [3] as well as in a class of CDM models in ref. [22] . To avoid as yet a far larger missing energy signal due to escaping dark photons the latter should decay in the detector into e +e e or µ +µ or pions and we should verify that those final states cannot be picked up at LHC and/or fixed target experiment as in Jeff lab [21]. Additional constraints that any DM scenario should satisfy, stems from the negative results of indirect searches for DM via γ rays from XX¯ annihilations in over-dense regions and the galactic center in particular. The latter are readily satisfied here for two independent reasons. First for a predominantly asymmetric DM with only a tiny fraction of un-annihilated X¯ anti-particles remaining no further annihilations can happen. Second the total energy in X¯ X annihilations of only ∼ GeV implies that even the (rare!) two body annihilations X¯ X → 2 photons yield 0.5 GeV photons. The cosmic rays producing π 0 s in the atmosphere generate a very large γ background in which even the sharp 0.5 Gev line will be drowned. Withnthe LHC bounds inoperative, we can allow significant ∼ 10030 cm2 X-N cross-sections. A strict mirror model analogy suggests low energy XX cross-sections as high as 100 24 cm ∼ σ(N, N) barely consistent with bounds suggested by observing some
Even at this maximal rate if a solar type star were to accrete in Hubble time a solar mass of dark matter, we need that the DM density in its neighborhood will be 109 times larger than the local halo density of 0.4 GeV cmm 3 . In general CDM starts clustering before baryons and our star may naturally be situated in a dark matter minihalo. If this dark mini-halo formed at redshift z its density can be enhanced in comparison with the cosmological DM density of KeV/cm3 by (6z) 3 ∼ 2 × 108 for z ∼ 100. The CMB spectrum and simulations [20], certainly exclude forming mini-halos of solar mass at larger redshifts. Even then this achieves at most a 103 enhancement relative to the local halo density. It seems that only if DM was dissipative it could have clustered more effectively reaching the 109 enhancement required. In passing, we note that the total DM accretion is not enhanced for bigger, more massive red/blue giant stars . The surface density M/R2 of the such giant stars is smaller making it difficult to accrete the minimal amount of X particles required in order to initiate the non-linear regime and hence reach the unitarity limit . Furthermore the lifetime of these stars scales like MM 3 making them live considerably shorter than solar systems. Also for more compact objects such as white dwarfs /neutron stars the enhanced focusing is offset by the far smaller areas. Turning to collider constraints on dark matter (DM) properties in our model, the Atlas and CMS detectors at the LHC accelerator operate at unexplored energies and unprecedented rates. Their implications for DM properties stem from the fact that the detectors, triggered by large transverse momenta are ideal for detecting missing (transverse) energy. This underlies the remarkable, extensive SUSY searches at LHC as pair production of SUSY particles yields, often via spectacular decay chains, stable neutral lightest susy partner (LSP) s which escape the detector leaving an extra signature of missing transverse momentum. The failure to find any evidence for dark matter this way implies that dark matter of mass less than 100 GeV and O(weak) X-Nucleon scattering cross-section are excluded , if the production of XX¯ pairs from a quark-anti-quark in proton-proton collision at LHC and the X-quark or the X-N scattering in direct underground DM searches proceed via a mediator heavier than both the ordinary and dark nucleon. The detailed analysis in [2] improves the rather weak bounds on WIMP nucleon elastic cross-sections obtained by direct underground searches for m(X) ≤ GeV,