Assuming that the lightest neutral component in an SU (2) L gauge multiplet is the main ingredient of dark matter in the universe, we calculate the elastic scattering cross section of the dark matter with nucleon, which is an important quantity for the direct detection experiments. When the dark matter is a real scalar or a Majorana fermion which has only electroweak gauge interactions, the scattering with quarks and gluon are induced through one-and two-loop quantum processes, respectively, and both of them give rise to comparable contributions to the elastic scattering cross section. We evaluate all of the contributions at the leading order and find that there is an accidental cancellation among them. As a result, the spin-independent cross section is found to be O(10 −(46−48) ) cm 2 , which is far below the current experimental bounds.

We consider supersymmetric models with right-handed neutrinos where neutrino masses are purely Dirac-type. In this model, right-handed sneutrino can be the lightest supersymmetric particle and can be a viable candidate of cold dark matter of the universe. Right-handed sneutrinos are never thermalized in the early universe because of weakness of Yukawa interaction, but are effectively produced by decays of various superparticles. We show that the present mass density of righthanded sneutrino can be consistent with the observed dark matter density.PACS numbers: 14.60. Pq, 12.60.Jv 98.80.Cq, 95.35.+d In recent years, various experiments have confirmed the phenomenon of neutrino oscillation. (See, for example, [1,2,3,4,5].) Those results strongly suggest very small but non-vanishing neutrino masses. This fact raises serious problems because the non-vanishing neutrino mass is not allowed in the standard model of particle physics and also because suggested values of neutrino masses are extremely small. The easiest way of generating neutrino masses is to introduce right-handed neutrinos; with this extension, Yukawa couplings of neutrinos may exist. Consequently, neutrinos can acquire masses after electroweak symmetry breaking.Even with right-handed neutrinos, there are two different classes of scenarios for generating neutrino masses. Probably, more popular one is with Majorana masses for right-handed neutrinos, i.e., so-called "seesaw" scenario [6]. In this scenario, smallness of the neutrino masses is explained by the Majorana masses of right-handed neutrinos which are much larger than the electroweak scale.Small neutrino masses can be, however, realized without seesaw mechanism. With vanishing Majorana masses of the right handed neutrinos, which may be the consequence of exact lepton-number symmetry, neutrino masses become Dirac-type. As we will see, in this case, Yukawa coupling constants for neutrinos are, roughly speaking, O(10 −13 ) or smaller to make the neutrino masses to be consistent with the results of neutrinooscillation experiments. One might think that such small Yukawa coupling constants are unnatural. It is, however, natural in 't Hooft's sense [7] since some symmetry (i.e., chiral symmetry in neutrino sector) is restored in the limit of vanishing neutrino Yukawa coupling constants. In this model, however, right-handed neutrinos are mostly irrelevant for collider experiments and cosmology since their interaction is extremely weak.In supersymmetric models, which is strongly motivated as a solution to various problems in the standard model of particle physics, like hierarchy and naturalness problems, situation changes. In particular, superpartners of righthanded neutrinos may play an important role in cosmology. When small neutrino masses are purely Dirac-type, masses of right-handed sneutrinos are dominantly from effects of supersymmetry (SUSY) breaking. Then, one should note that the lightest superparticle (LSP) may be the (lightest) right-handed neutrinoν R . Importantly, since the LSPν R becomes s...

In this article we have calculated the spin-independent cross section of nucleondark matter scattering process at loop level, which is relevant to dark matter direct detection. Paying particular attention to the scattering of gluon with dark matter, which contributes as leading order in the perturbation, we have systematically evaluated loop diagrams with tracking the characteristic loop momentum which dominates in the loops. Here loop diagrams whose typical loop momentum scales are the masses of quarks and other heavier particles are separately presented. Then, we have properly taken into account each contribution to give the cross section. We assume that the dark matter is pure bino or wino in the supersymmetric models. The application to other models is straightforward.

If dark matter is unstable and the mass is within GeV-TeV regime, its decays produce high-energy photons that give contribution to the extragalactic gamma-ray background (EGRB). We constrain dark matter decay by analyzing the 50-month EGRB data measured with Fermi satellite, for different decay channels motivated with several supersymmetric scenarios featuring R-parity violation. We adopt the latest astrophysical models for various source classes such as active galactic nuclei and star-forming galaxies, and take associated uncertainties properly into account. The lower limits for the lifetime are very stringent for a wide range of dark matter mass, excluding the lifetime shorter than 10 28 s for mass between a few hundred GeV and ∼1 TeV, e.g., for bb decay channel. Furthermore, most dark matter models that explain the anomalous positron excess are also excluded. These constraints are robust, being little dependent on astrophysical uncertainties, unlike other probes such as Galactic positrons or anti-protons.

Abstract:We complete the calculation of the wino-nucleon scattering cross section up to the next-to-leading order in α s . We assume that the other sparticles are decoupled and wino interacts with the Standard Model particles via the weak interaction. As a result, the uncertainties coming from the perturbative QCD are significantly reduced to be smaller than those from the nucleon matrix elements. The resultant scattering cross section is found to be larger than the leading-order one by about 70%, which is well above the neutrino background. In the limit of large wino mass the spin-independent scattering cross section with proton turns out σ −0.4 × 10 −47 cm 2 (errors come from perturbative calculation and input parameters, respectively). The computation for a generic SU(2) L multiplet dark matter is also presented.