Freeze-In Dark Matter within the Seesaw mechanism

We show that the minimal Type-I Seesaw mechanism can successfully account for the observed dark matter abundance in the form of a keV sterile neutrino. This population can be produced by the decay of the heavier neutral leptons, with masses above the Higgs mass scale, while they are in thermal equilibrium in the early Universe (freeze-in). Moreover, the implementation of the relevant phenomenological constraints (relic abundance, indirect detection and structure formation) on this model automatically selects a region of the parameter space featuring an approximate lepton number symmetry.Comment: 10 pages, 2 figures. Comments are welcome. v2: included decay channel in Z, extended discussion on Higgs vev evolution impact, added reference

Testability of leptogenesis with three RH-neutrinos below the electroweak scale

The Standard Model extended with right-handed neutrinos whose masses are below the electroweak scale provides a simultaneous solution for the origin of neutrino masses and of the baryon asymmetry of the Universe, that can be tested in current experiments. If three right-handed neutrinos participate to the processes, their parameter space of solutions extends to very large mixing angles, saturating the current experimental constraints. Solutions with right-handed neutrino masses at the GeV scale can be probed in the decay of $B$ mesons at the LHC. For this channel the collision of isotopes of intermediate mass such as Ar provides a better sensitivity per unit of running time compared to collisions with protons.Comment: 6 pages, 2 figures. To appear in the proceedings of the Rencontres de Moriond EW 2019, 16-23 March 2019 in La Thuile, Ital

Implication of Sterile Fermions in Particle Physics and Cosmology

The neutrino mass generation mechanism, the nature of dark matter and the origin of the baryon asymmetry of the Universe are three compelling questions that cannot be accounted for in the Standard Model of particle physics. In this thesis we focus on all these issues by providing a possible solution in terms of a minimal extension of the Standard Model, consisting in the addition of a set of sterile fermions to the field content of the theory. Sterile fermions are gauge singlet fields, that can interact via mixing with the active neutrinos. We focus on the Inverse Seesaw mechanism, which is characterised by a low (TeV or lower) new physics scale and that can be tested in current and future experimental facilities. We present the model building analysis that points towards the minimal realisations of the mechanism, and the phenomenological study in order to accommodate light neutrino masses and to impose all the relevant experimental constraints in the model, as well as the expected experimental signatures. We show the viability of the sterile neutrino hypothesis as dark matter component, together with the characteristic features of this scenario in the minimal Inverse Seesaw mechanism. The possibility of successfully accounting for the baryon asymmetry in a testable realisation of the leptogenesis mechanism is also addressed. On the other hand it is important to look for manifestations of sterile fermions in laboratory experiments. We address this point by making predictions for the expected rates of rare lepton number violating decays of vector bosons, that can be mediated by sterile fermions, as well as by studying the impact of sterile fermions on global fit of electroweak precision data

Solar γ\gamma-rays as a Complementary Probe of Dark Matter

We show that observations of solar $\gamma$-rays offer a novel probe of dark matter in scenarios where interactions with the visible sector proceed via a long-lived mediator. As a proof of principle, we demonstrate that there exists a class of models which yield solar $\gamma$-ray fluxes observable with the next generation of $\gamma$-ray telescopes, while being allowed by a variety of current experimental constraints. The parameter space allowed by big bang nucleosynthesis and beam dump experiments naturally leads to mediator lifetimes sufficient to produce observable solar $\gamma$-ray signals. The model allows for solar $\gamma$-ray fluxes up to orders of magnitude larger compared to dwarf spheroidal galaxies, without reaching equilibrium between dark matter annihilation and capture rate. Our results suggest that solar $\gamma$-ray observations are complementary, and in some cases superior, to existing and future dark matter detection efforts.Comment: 15 pages + references, 7 figures, v3: Fermi-LAT and HERD sensitivity corrected, minor presentational improvements, matches journal versio

Probing Dark Matter Long-lived Mediators with Solar γ\gamma rays

We show that solar $\gamma$-ray observations can provide a complementary probe of Dark Matter in scenarios where the interactions with the Standard Model proceed via long-lived mediators. For illustration we consider a simplified model which provides solar $\gamma$-ray fluxes observable with the next generation $\gamma$-ray telescopes, while complying with the existing experimental constraints. Our results suggest that solar $\gamma$-ray fluxes can be orders of magnitude larger than the ones from the Galactic center, while being subject to low backgrounds.Comment: 4 pages, 2 figures. To appear in the proceedings of The European Physical Society Conference on High Energy Physics, 5-12 July 2017 in Venice, Ital

Looking for the minimal inverse seesaw realisation

In this work we consider a simple extension of the Standard Model involving additional fermionic singlets and assume an underlying inverse seesaw mechanism (with one or more right-handed neutrinos and one or more sterile fermions) for neutrino mass generation. Under the assumption that both sterile states and right-handed neutrinos are present, our goal is to determine which is the minimal inverse seesaw realisation that accounts for neutrino data while at the same time complying with all experimental requirements (electroweak precision tests and laboratory constraints). This study aims at identifying the minimal inverse seesaw realisation for the 3-flavour and for the 3 +~more-mixing schemes, the latter giving an explanation for the reactor anomalies and/or providing a possible candidate for the dark matter of the Universe. Based on a perturbative approach, our generic study shows that in the class of inverse seesaw models giving rise to a 3-flavour flavour mixing scheme, only two mass scales are relevant (the light neutrino mass scale, $m_\nu$ and the mass of the right-handed neutrinos, $M_R$) while in the case of a 3 + 1-mixing scheme, an additional mass scale ($\mu$ $\in[m_\nu,M_R]$) is required. For each of the two obtained inverse seesaw frameworks, we conduct a thorough numerical analysis, providing predictions for the hierarchy of the light neutrino spectrum and for the effective mass in neutrinoless double beta decay.Comment: 29 pages, 14 figures. In V2, one paragraph, one figure, 3 references and few minor comments added. Title slightly change