We investigate the simplest models where baryon and lepton numbers are defined as local symmetries spontaneously broken at the low scale and discuss the implications for cosmology. We define the simplest anomaly-free theory for spontaneous baryon and lepton number symmetry breaking which predicts the existence of lepto-baryons. In this context, we study the new sphaleron condition on the chemical potentials and show the relation between the present baryon asymmetry and the B − L asymmetry generated in the early universe. The properties of the cold dark matter candidate for which stability is a natural consequence from symmetry breaking are briefly discussed.

There exists a class of ultralight Dark Matter (DM) models which could form a Bose-Einstein condensate (BEC) in the early universe and behave as a single coherent wave instead of individual particles in galaxies. We show that a generic BEC-DM halo intervening along the line of sight of a gravitational wave (GW) signal could induce an observable change in the speed of GWs, with the effective refractive index depending only on the mass and self-interaction of the constituent DM particles and the GW frequency. Hence, we propose to use the deviation in the speed of GWs as a new probe of the BEC-DM parameter space. With a multi-messenger approach to GW astronomy and/or with extended sensitivity to lower GW frequencies, the entire BEC-DM parameter space can be effectively probed by our new method in the near future.

We conduct a systematic search for neutrino mass models which only radiatively produce the dimension-5 Weinberg operator. We thereby do not allow for additional symmetries beyond the Standard Model gauge symmetry and we restrict ourselves to minimal models. We also include stable fractionally charged and coloured particles in our search. Additionally, we proof that there is a unique model with three new fermionic representations where no new scalars are required to generate neutrino masses at loop level. This model further has a potential dark matter candidate and introduces a general mechanism for loop-suppression of the neutrino mass via a fermionic ladder.

We explore the dark matter and collider phenomenology of the minimal gauged U(1) B model, consisting of a leptophobic ZB gauge boson, and an accompanying Higgs SB. By requirement of anomaly cancellation, the fermion sector naturally contains a dark matter candidate-a Majorana isosinglet χ stabilized by an inherent Z2 symmetry. The absence of evidence for Z prime dijet resonances at the LHC suggests that the scale of symmetry breaking is ΛB 500 GeV. Saturation of dark matter abundance together with limits on the direct detection cross section (dominated by Higgs exchange) constrains the Higgs mixing angle to |θ| 0.22. For small mixing angles of |θ| 10 −3 , the O(10%) branching fractions of the fermion loop-mediated SB → γγ, Zγ, ZZ modes may provide clues about the fermion content of the model at the LHC.