Adding a scalar triplet to the Standard Model is one of the simplest ways of giving mass to neutrinos, providing at the same time a mechanism to stabilize the theory's vacuum. In this paper, we revisit these aspects of the type-II seesaw model pointing out that the boundedfrom-below conditions for the scalar potential in use in the literature are not correct. We discuss some scenarios where the correction can be significant and sketch the typical scalar boson profile expected by consistency.

We provide a generic framework to obtain stable dark matter along with naturally small Dirac neutrino masses generated at the loop level. This is achieved through the spontaneous breaking of the global U (1)B−L symmetry already present in Standard Model. The U (1)B−L symmetry is broken down to a residual even Zn; n ≥ 4 subgroup. The residual Zn symmetry simultaneously guarantees dark matter stability and protects the Dirac nature of neutrinos. The U (1)B−L symmetry in our setup is anomaly free and can also be gauged in a straightforward way. Finally, we present an explicit example using our framework to show the idea in action.

We present a simple U(1)B 3 −3Lµ gauge Standard Model extension that can easily account for the anomalies in R(K) and R(K * ) reported by LHCb. The model is economical in its setup and particle content. Among the Standard Model fermions, only the third generation quark family and the second generation leptons transform non-trivially under the new U(1)B 3 −3Lµ symmetry. This leads to lepton non-universality and flavor changing neutral currents involving the second and third quark families. We discuss the relevant experimental constraints and some implications.These observations are also in tune with the so called P 5 anomaly observed in the angular variable P 5 of B → K * µ + µ − decays [3][4][5][6]. In addition to these, LHCb has also observed other several other anomalies all involving b → s * cesar.bonilla@tum.de †

No abstract

We propose a "scotogenic" mechanism relating small neutrino mass and cosmological dark matter. Neutrinos are Dirac fermions with masses arising only in two-loop order through the sector responsible for dark matter. Two triality symmetries ensure both dark matter stability and strict lepton number conservation at higher orders. A global spontaneously broken U(1) symmetry leads to a physical Diracon that induces invisible Higgs decays which add up to the Higgs to dark matter mode. This enhances sensitivities to spin-independent WIMP dark matter search below m h /2.

We propose a simple model for Dirac neutrinos where the smallness of neutrino mass follows from a parameter κ whose absence enhances the symmetry of the theory. Symmetry breaking is performed in a two-doublet Higgs sector supplemented by a gauge singlet scalar, realizing an accidental global U(1) symmetry. Its spontaneous breaking at the few TeV scale leads to a physical Nambu-Goldstone boson -the Diracon, denoted D -which is restricted by astrophysics and induces invisible Higgs decays such as h → DD. The scheme provides a rich, yet very simple scenario for symmetry breaking studies at colliders such as the LHC.

We present a model where Majorana neutrino mass terms are forbidden by the flavor symmetry group ∆(27). Neutrinos are Dirac fermions and their masses arise in the same way as those of the charged fermions, due to very small Yukawa couplings. The model fits current neutrino oscillation data and correlates the octant of the atmospheric angle θ 23 with the magnitude of the lightest neutrino mass, with maximal mixing excluded for any neutrino mass hierarchy.

The discovery of the Higgs boson suggests that also neutrinos get their mass from spontaneous symmetry breaking. In the simplest ungauged lepton number scheme, the Standard Model (SM) Higgs has now two other partners: a massive CP-even, as well as the massless Nambu-Goldstone boson, called majoron. For weak-scale breaking of lepton number the invisible decays of the CP- even Higgs bosons to the majoron lead to potentially copious sources of events with large missing energy. Using LHC results we study how the constraints on invisible decays of the Higgs boson restrict the relevant parameters, substantially extending those previously derived from LEP and shedding light on spontaneous lepton number violation.Comment: 12 pages, 8 figures; new section added, to appear in PR