Vacuum stability with spontaneous violation of lepton number

The vacuum of the Standard Model is known to be unstable for the measured values of the top and Higgs masses. Here we show how vacuum stability can be achieved naturally if lepton number is violated spontaneously at the TeV scale. More precise Higgs measurements in the next LHC run should provide a crucial test of our symmetry breaking scenario. In addition, these schemes typically lead to enhanced rates for processes involving lepton flavour violation .Comment: 9 pages, 4+2 figures; some references added, some textual modifications: 2 figures added, appendices added. Results unchanged. Matches published versio

Flavour-symmetric type-II Dirac neutrino seesaw mechanism

We propose a Standard Model extension with underlying A4 flavour symmetry where small Dirac neutrino masses arise from a Type-II seesaw mechanism. The model predicts the "golden" flavour-dependent bottom-tau mass relation, requires an inverted neutrino mass ordering and non-maximal atmospheric mixing angle. Using the latest neutrino oscillation global fit we derive restrictions on the oscillation parameters, such as a correlation between Dirac CP phase and the lightest neutrino mass.Comment: 10 pages, 4 figure

Higgs decay into two photons from a 3HDM with flavor symmetry

In this short letter we show that the excess of events in the decay of Higgs to two photons reported by ATLAS and CMS can be easily accommodated in a flavor renormalizable three Higgs doublet model (3HDM). The model is consistent with all fermion masses, mixing angles, and flavor changing neutral current constraints.Comment: 4 pages, 3 figures, version to be published in PL

Implications of helminth immunomodulation on COVID-19 co-infections

Coronavirus disease 2019 (COVID-19) and helminths infections can be in a synergistic epidemic in developing and suburban areas of industrialized countries. The coinfected hosts will derive a parasite-specific Th2 innate and adaptive immune response with CD4+ T cells, eosinophils, interleukin-4, interleukin-5, and interleukin-10. In the early stages of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection, virus-specific Th1 cytotoxic CD8+ T cell, interleukin-6, interferon-γ, and interleukin-27 by lung are keys in controlling viral replication in the lung epithelial cells and limiting the pathology to other organs, like the intestine. CD4+ and CD8+ T cells are associated with protective immunity against and during COVID-19. However, viral evasion mechanisms occur. Interference of the interferon-γ secretion, like in helminths immunomodulation, can contribute to COVID-19 severity. Immunomodulation can result in mild, moderate, or severe COVID-19 depending on which helminth is coinfecting by regulating or avoiding host cytokine and pro-inflammatory response, decreasing viral load, and affecting vaccine-induced antibody response. We discuss the implications of immunomodulation on COVID-19 caused by helminth co-infection and for public health in the context of COVID-19 vaccine use in helminth endemic zones

Neutrino parameters in the Planck-scale lepton number breaking scenario with extended scalar sectors

Two-loop effects on the right-handed neutrino masses can have an impact on the low-energy phenomenology, especially when the right-handed neutrino mass spectrum is very hierarchical at the cut-off scale. In this case, the physical masses of the lighter right-handed neutrinos can be dominated by quantum effects induced by the heavier ones. Further, if the heaviest right-handed neutrino mass is at around the Planck scale, two-loop effects on the right-handed neutrino masses generate, through the seesaw mechanism, an active neutrino mass which is in the ballpark of the experimental values. In this paper we investigate extensions of the Planck-scale lepton number breaking scenario by additional Higgs doublets (inert or not). We find that under reasonable assumptions these models lead simultaneously to an overall neutrino mass scale and to a neutrino mass hierarchy in qualitative agreement with observations.Comment: 18 pages, 6 figures; v2 matches published versio