Dark Matter Phenomenology of SM and Enlarged Higgs Sectors Extended with Vector Like Leptons

We will investigate the scenario in which the Standard Model (SM) Higgs sector and its 2-doublet extension (called the Two Higgs Doublet Model or 2HDM) are the "portal" for the interactions between the Standard Model and a fermionic Dark Matter (DM) candidate. The latter is the lightest stable neutral particle of a family of vector-like leptons (VLLs). We will provide an extensive overview of this scenario combining the constraints purely coming from DM phenomenology with more general constraints like Electro-weak Precision Tests (EWPT) as well as with collider searches. In the case that the new fermionic sector interacts with the SM Higgs sector, constraints from DM phenomenology force the new states to lie above the TeV scale. This requirement is relaxed in the case of 2HDM. Nevertheless, strong constraints coming from Electroweak Precision Tests (EWPT) and the Renormalization Group Equations (RGEs) limit the impact of VLFs on collider phenomenology.Comment: 32 pages, 12 figure

Minimal Decaying Dark Matter and the LHC

We consider a minimal Dark Matter model with just two additional states, a Dark Matter Majorana fermion and a colored or electroweakly charged scalar, without introducing any symmetry to stabilize the DM state. We identify the parameter region where an indirect DM signal would be within the reach of future observations and the DM relic density generated fits the observations. We find in this way two possible regions in the parameter space, corresponding to a FIMP/SuperWIMP or a WIMP DM. We point out the different collider signals of this scenario and how it will be possible to measure the different couplings in case of a combined detection.Comment: 33 pages, 13 figure

Gravitino Dark Matter and low-scale Baryogenesis

A very simple way to obtain comparable baryon and DM densities in the early Universe is through their contemporary production from the out-of-equilibrium decay of a mother particle, if both populations are suppressed by comparably small numbers, i.e. the CP violation in the decay and the branching fraction respectively. We present a detailed study of this kind of scenario in the context of a R-parity violating realization of the MSSM in which the baryon asymmetry and the gravitino Dark Matter are produced by the decay of a Bino. The implementation of this simple picture in a realistic particle framework results, however, quite involving, due to the non trivial determination of the abundance of the decaying Bino, as well as due to the impact of wash-out processes and of additional sources both for the baryon asymmetry and the DM relic density. In order to achieve a quantitative determination of the baryon and Dark Matter abundances, we have implemented and solved a system of coupled Boltzmann equations for the particle species involved in their generation, including all the relevant processes. In the most simple, but still general, limit, in which the processes determining the abundance and the decay rate of the Bino are mediated by degenerate right-handed squarks, the correct values of the DM and baryon relic densities are achieved for a Bino mass between 50 and 100 TeV, Gluino NLSP mass in the range 15-60 TeV and a gravitino mass between 100 GeV and few TeV. These high masses are unfortunately beyond the kinematical reach of LHC. On the contrary, an antiproton signal from the decays of the gravitino LSP might be within the sensitivity of AMS-02 and gamma-ray telescopes.Comment: 39 pages, 12 figure

Interplay between Generation Mechanisms and Detection of Supersymmetric Dark Matter in the LHC Era

The object of this thesis is the study of several, possibly complementary, aspects of generation mechanism and detection of the two dark matter (DM) candidates provided by the Minimal Supersymmetric extension of the Standard Model (MSSM), i.e. the gravitino and the neutralino. We have first of all focused on the generation mechanism of neutralino dark matter, examining the possible consequences of relaxing some of the hypothesis on which the typically adopted thermal WIMP paradigm relies. We have, indeed, considered non-thermal dark matter production scenarios motivated, in the context of Supersymmetric theories, in supergravity and superstring frameworks. These classes of theories often feature the presence of long-lived states capable of dominating the energy budget of the Universe at early stages before possibly decaying into dark matter particles. Non thermal production have been studied in a systematic way by mean of a numerical code developed for this purpose. In particular the impact in selecting a preferred mass scale for the Dark matter and, consequently, the impact on the interpretation of new physics discovered or excluded at LHC have been discussed. The second aspect of neutralino dark matter generation which has been investigated is the assumption of kinetic equilibrium during the whole phase of dark matter generation and the validity of the factorization usually implemented to rewrite the system of coupled Boltzmann equation for each coannihilating species as a single equation for the sum of all the number densities. To this purpose has been developed and numerically implemented a formalism for the computation of the kinetic decoupling temperature in the case of coannhilating particles. This formalism has been applied to a definite scenario referred as G2-MSSM. The next topic discussed in this thesis, remaining in the context of neutralino DM, is the capability of current and next generation direct detection experiments of probing the MSSM parameter space. Focusing on some definite setups, satisfying the cosmological bounds on the DM relic density and the current particle physics constraints, the possibility for them of producing direct detection signals has been inspected through Montecarlo Simulations. The final purpose of this analysis is to show as indications about the DM properties, as provided by an experimental detection, can influence some features of the underlying Supersymmetric model which can be probed in the next future by LHC. We have finally moved the focus to the other dark matter candidate within the MSSM, i.e. the gravitino. Remarkably it is a viable dark matter candidate also in presence of R-parity violation. Gravitino dark matter have been studied in the context of a class of Supersymmetric models referred as Tree-Level Gauge Mediation (TGM). These models provide rather definite predictions for the mass of the dark matter being it related to the mechanism of mediation of SUSY breaking. In particular has been investigated a realization of TGM predicting a gravitino mass in the range 10-100 GeV. Cosmological bounds have been investigated both in presence and in absence of R-parity. The model results disfavored in case the R-parity holds, being in severe tension with Big Bang Nucleosynthesis; on the contrary is naturally feasible in presence of a small amount of R-parity violation

Accurate estimate of the relic density and the kinetic decoupling in non-thermal dark matter models

Non-thermal dark matter generation is an appealing alternative to the standard paradigm of thermal WIMP dark matter. We reconsider non-thermal production mechanisms in a systematic way, and develop a numerical code for accurate computations of the dark matter relic density. We discuss in particular scenarios with long-lived massive states decaying into dark matter particles, appearing naturally in several beyond the standard model theories, such as supergravity and superstring frameworks. Since non-thermal production favors dark matter candidates with large pair annihilation rates, we analyze the possible connection with the anomalies detected in the lepton cosmic-ray flux by Pamela and Fermi. Concentrating on supersymmetric models, we consider the effect of these non-standard cosmologies in selecting a preferred mass scale for the lightest supersymmetric particle as dark matter candidate, and the consequent impact on the interpretation of new physics discovered or excluded at the LHC. Finally, we examine a rather predictive model, the G2-MSSM, investigating some of the standard assumptions usually implemented in the solution of the Boltzmann equation for the dark matter component, including coannihilations. We question the hypothesis that kinetic equilibrium holds along the whole phase of dark matter generation, and the validity of the factorization usually implemented to rewrite the system of coupled Boltzmann equation for each coannihilating species as a single equation for the sum of all the number densities. As a byproduct we develop here a formalism to compute the kinetic decoupling temperature in case of coannihilating particles, which can be applied also to other particle physics frameworks, and also to standard thermal relics within a standard cosmology

Impact of Dark Matter Direct and Indirect Detection on Simplified Dark Matter Models

We discuss simple extensions of the Standard Model featuring a (fermionic) stable DM candidate interacting with SM fermions through a $Z^{'}$ mediator. These kind of models offer a wide phenomenology but result, at the same time, particularly manageable, given the limited number of free-parameters, and offer a broad LHC phenomenology. We will discuss the impact Direct and Indirect Dark Matter searches, assuming the latter to be thermal WIMPs. We will show in particular that the combinations of the limits on the DM Spin Independent and Spin Dependent scattering cross-section on nuclei already exclude large portions of the parameter space favored by DM relic density, in particular if, in addition, a DM Indirect signal, like the Galactic Center gamma-ray excess is required.Comment: 7 pages, 2 figures. To appear as proceeding of the conference HEP-EPS 2015, Wien (Austria

2HDM portal for Singlet-Doublet Dark Matter

We present an extensive analysis of a model in which the (Majorana) Dark Matter candidate is a mixture between a SU(2) singlet and two SU(2) doublets. This kind of setup takes the name of singlet-doublet model. We will investigate in detail an extension of this model in which the Dark Matter sector interactions with a 2-doublet Higgs sector enforcing the complementarity between Dark Matter phenomenology and searches of extra Higgs bosons.Comment: 24 pages, 8 figure

The Semi-Hooperon: Gamma-ray and anti-proton excesses in the Galactic Center

A puzzling excess in gamma-rays at GeV energies has been observed in the center of our galaxy using Fermi-LAT data. Its origin is still unknown, but it is well fitted by Weakly Interacting Massive Particles (WIMPs) annihilations into quarks with a cross section around $10^{-26}{\rm cm^3 s^{-1}}$ with masses of $20-50$~GeV, scenario which is promptly revisited. An excess favoring similar WIMP properties has also been seen in anti-protons with AMS-02 data potentially coming from the Galactic Center as well. In this work, we explore the possibility of fitting these excesses in terms of semi-annihilating dark matter, dubbed as semi-Hooperon, with the process ${\rm WIMP\, WIMP \rightarrow WIMP\, X}$ being responsible for the gamma-ray excess, where X=h,Z. An interesting feature of semi-annihilations is the change in the relic density prediction compared to the standard case, and the possibility to alleviate stringent limits stemming from direct detection searches. Moreover, we discuss which models might give rise to a successful semi-Hooperon setup in the context of $\mathcal{Z}_3$,$\mathcal{Z}_4$ and extra "dark" gauge symmetries.Comment: 8 pages, 3 figures, version published in Phys. Lett.