Right-handed neutrinos (RHNs) provide a natural portal to a dark sector accommodating dark matter (DM). In this work, we consider that the dark sector is connected to the standard model only via RHNs and ask how DM can be produced from RHNs. Our framework concentrates on a rather simple and generic interaction that couples RHNs to a pair of dark particles. Depending on whether RHNs are light or heavy in comparison to the dark sector and also on whether one or both of them are in the freeze-in/out regime, there are many distinct scenarios resulting in rather different results. We conduct a comprehensive and systematic study of all possible scenarios in this paper. For illustration, we apply our generic results to the type-I seesaw model with the dark sector extension, addressing whether and when DM in this model can be in the freeze-in or freeze-out regime. Some observational consequences in this framework are also discussed.

/pdf/dark-matter-produced-from-right-handed-neutrinos-cvu6830s.pdf

Dark matter produced from right-handed neutrinos

The observed dark matter relic abundance may be explained by different mechanisms, such as thermal freeze-out/freeze-in, with one or more symmetric/asymmetric components. In this work we investigate the role played by asymmetries in determining the yield and nature of dark matter in non-minimal scenarios with more than one dark matter particle. In particular, we show that the energy density of a particle may come from an asymmetry, even if the particle is asymptotically symmetric by nature. To illustrate the different effects of asymmetries, we adopt a model with two dark matter components. We embed it in a multi-component cogenesis scenario that is also able to reproduce neutrino masses and the baryon asymmetry. In some cases, the model predicts an interesting monochromatic neutrino line that may be searched for at neutrino telescopes. 

/pdf/asymmetries-in-extended-dark-sectors-a-cogenesis-scenario-1ei62pcg.pdf

Asymmetries in extended dark sectors: a cogenesis scenario

Abstract In this paper, we propose the sterile neutrino portal dark matter in $$\nu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ν</mml:mi> </mml:math> THDM. This model can naturally generate tiny neutrino mass with the neutrinophilic scalar doublet $$\Phi _{\nu }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>Φ</mml:mi> <mml:mi>ν</mml:mi> </mml:msub> </mml:math> and sterile neutrinos N around TeV scale. Charged under a $$Z_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>Z</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> symmetry, one Dirac fermion singlet $$\chi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>χ</mml:mi> </mml:math> and one scalar singlet $$\phi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ϕ</mml:mi> </mml:math> are further introduced in the dark sector. The sterile neutrinos N are the mediators between the DM and SM. Depending on the coupling strength, the DM can be either WIMP or FIMP. For the WIMP scenario, pair annihilation of DM into NN is the key channel to satisfy various bounds, which could be tested at indirect detection experiments. For the FIMP scenario, besides the direct production of DM from freeze-in mechanism, contributions from late decay of NLOP is also important. When sterile neutrinos are heavier than the dark sector, NLOP is long-lived due to tiny mixing angle between sterile and light neutrinos. Constrains from free-streaming length, CMB, BBN and neutrino experiments are considered. 

/pdf/sterile-neutrino-portal-dark-matter-in-nu-thdm-3g7ktn5v.pdf

Sterile neutrino portal dark matter in $$\nu $$THDM

In this paper we explore interactions between neutrinos and Dark Matter. In particular, we study how the propagation of astrophysical neutrinos can be modified by computing the most general potential generated by the galactic DM background. We use on-shell techniques to compute this potential in a completely model independent way and obtain an expression valid for any Dark Matter mass and spin. Afterwards, we use this expression to analyse under what circumstances such potential can be important at the phenomenological level, and we find that under some assumptions only ultra light scalar Dark Matter could be of any relevance to oscillation experiments. 

/pdf/characterising-dark-matter-induced-neutrino-potentials-16t4yxeo.pdf

Characterising dark matter-induced neutrino potentials

The continued non-observation of events emanating from dark matter (DM) annihilations in various direct and indirect detection experiments calls into question the mechanism for determining the relic density of a weakly interacting massive particle. However, if the relic density is determined primarily by a semi-annihilation process, as opposed to the usual annihilation, this tension can be ameliorated. Here, we investigate a Z3 symmetric effective field theory incorporating a fermionic dark matter that semi-annihilates to right-handed neutrinos (RHN). The dynamics of the RHN and the impact of its late decays are also scrutinised while obtaining the correct DM relic. Finally, indirect detection bounds on the semi-annihilation cross-sections are drawn from the gamma-ray observations in the direction of Dwarf Spheroidal Galaxies (Fermi-LAT), and including the projections obtained for the H.E.S.S. and the CTA detectors. 

/pdf/semiannihilation-of-fermionic-dark-matter-3b4qkxcn.pdf

Semiannihilation of fermionic dark matter

A bstract Stringent constraints on the interactions of dark matter with the Standard Model suggest that dark matter does not take part in gauge interactions. In this regard, the possibility of communicating between the visible and dark sectors via gauge singlets seems rather natural. We consider a framework where the dark matter talks to the Standard Model through its coupling to sterile neutrinos, which generate active neutrino masses. We focus on the case of Majorana dark matter, with its relic abundance set by thermal freeze-out through annihilations into sterile neutrinos. We use an effective field theory approach to study the possible sterile neutrino portals to dark matter. We find that both lepton-number-conserving and lepton-number-violating operators are possible, yielding an interesting connection with the Dirac/Majorana character of active neutrinos. In a second step, we open the different operators and outline the possible renormalisable models. We analyse the phenomenology of the most promising ones, including a particular case in which the Majorana mass of the sterile neutrinos is generated radiatively. 

/pdf/sterile-neutrino-portals-to-majorana-dark-matter-effective-239dwmh9.pdf

Sadia Idrees

Papers

Sterile neutrino portals to Majorana dark matter: effective operators and UV completions