A dark matter quest through decaying axinos and vector-like portals

Abstract

To date there is no definite particle physics interpretation of dark matter. At the same time, LHC searches at √s = 14 TeV yielded no signals of physics beyond the Standard Model. Minimal models of new physics that predict extra states at the TeV scale are thus in some tension with the experimental data and some well-studied dark matter candidates face very stringent bounds. In the first and main part of this work, we discuss extended supersymmetric models that also address the strong CP-problem of the Standard Model. This has a well-motivated solution in axion models, which include a new neutral pseudoscalar, the axion, and an extra broken U(1)_PQ global symmetry group. Both the axion and the axino, its supersymmetric partner, are valid dark matter candidates. We examine the case of a light axino dark matter that decays radiatively emitting a photon and producing the 3.5 keV X-ray line reported in 2014. Such a possibility is disfavored in most of the parameter space for several scenarios. We then construct an original R-parity violating supersymmetric model with a Dine-Fischler-Srednicki-Zhitnitsky axion and study in detail the one-loop decay of the light axino into photon plus neutrino. We examine cosmological constraints as well as those coming from X-ray signals, obtaining bounds on the R-parityviolating couplings and on fa, the scale of the breaking of U(1)_PQ. <br /> For the last project presented in this thesis, we consider the simplified model approach to describe dark matter phenomenology. Among simplified models with t-channel mediator, the vector-like portal has the interesting feature that the bremsstrahlung cross section can lift the chiral suppression of the two-body annihilation process and drive the relic density. Furthermore virtual internal bremsstrahlung produces a pronounced peak in the gamma-ray spectrum. We extend the existent analyses to the case of massive quark final states. We present a detailed calculation of the radiative corrections and discuss the effective approach for high mediator masses. Through approximated expressions for the differential and total cross section of the three-body process, we implement the VIB effects into software tools that simulate the hadronization process. Here this effects was not otherwise included for massive quark final states. Our result for the full inclusive cross section is part of a larger study that constraints the parameter space for this model through several complementary searches.