Gauge Singlet Vector-like Fermion Dark Matter, LHC Di-photon Rate and
  Unitarity Constraints

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Abstract

We consider a gauge-singlet vector-like fermion dark matter model that also contains a gauge-singlet scalar and an SU(2) singlet vector-like quark. The dark matter has a tree-level coupling with the gauge-singlet scalar but communicates with the standard model via loop-level scalar-gluon-gluon and scalar-photon-photon effective couplings induced by the vector-like quark. The main focus of the paper is to study the implications of such effective couplings. We also include the Higgs-portal coupling of the dark matter due to scalar-Higgs mixing. In the model parameter space, we present the dark matter relic-density, the dark-matter-nucleon direct-detection scattering cross-section, the large hadron Collider diphoton resonance signal rate, and the theoretical upper-bounds on the fermion-scalar couplings from perturbative unitarity.

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Big-Bang Nucleosynthesis

Subir Sarkar, Brian Fields, Paolo Molaro (2015)

A critical review is given of the current status of cosmological nucleosynthesis. In the framework of the Standard Model with 3 types of relativistic neutrinos, the baryon-to-photon ratio, \(\eta\), corresponding to the inferred primordial abundances of deuterium and helium-4 is consistent with the independent determination of \(\eta\) from observations of anisotropies in the cosmic microwave background. However the primordial abundance of lithium-7 inferred from observations is significantly below its expected value. Taking systematic uncertainties in the abundance estimates into account, there is overall concordance in the range \(\eta = (5.7-6.7)\times 10^{-10}\) at 95% CL (corresponding to a cosmological baryon density \(\Omega_B h^2 = 0.021 - 0.025\)). The D and He-4 abundances, when combined with the CMB determination of \(\eta\), provide the bound \(N_\nu=3.28 \pm 0.28\) on the effective number of neutrino species. Other constraints on new physics are discussed briefly.

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Particle Dark Matter: Evidence, Candidates and Constraints

Joseph Silk, Dan Hooper, Gianfranco Bertone (2004)

In this review article, we discuss the current status of particle dark matter, including experimental evidence and theoretical motivations. We discuss a wide array of candidates for particle dark matter, but focus on neutralinos in models of supersymmetry and Kaluza-Klein dark matter in models of universal extra dimensions. We devote much of our attention to direct and indirect detection techniques, the constraints placed by these experiments and the reach of future experimental efforts.