Search

Motivated by the growing evidence for the possible lepton flavor universality violation after the first results from Fermilab's muon $g\ensuremath{-}2$ measurement, we revisit one of the most widely studied anomaly free extensions of the standard model namely, gauged ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ model, to find a common explanation for muon $g\ensuremath{-}2$ as well as baryon asymmetry of the universe via leptogenesis. The minimal setup allows TeV scale resonant leptogenesis satisfying light neutrino data while the existence of light ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ gauge boson affects the scale of leptogenesis as the right handed neutrinos are charged under it. For ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ gauge boson mass at GeV scale or above, the muon $g\ensuremath{-}2$ favored parameter space is already ruled out by other experimental data while bringing down its mass to sub-GeV regime leads to vanishing lepton asymmetry due to highly restrictive structures of lepton mass matrices at the scale of leptogenesis. Extending the minimal model with two additional Higgs doublets can lead to a scenario consistent with successful resonant leptogenesis and muon $g\ensuremath{-}2$ while satisfying all relevant experimental data.

We study a possibility of a strong first-order phase transition taking place below the electroweak scale in the context of a $U(1{)}_{D}$ gauge extension of the standard model. As pointed out recently by the NANOGrav Collaboration, gravitational waves from such a phase transition with appropriate strength and nucleation temperature can explain their 12.5 yr data. We first find the parameter space of this minimal model consistent with NANOGrav findings by considering only a complex singlet scalar and $U(1{)}_{D}$ vector boson. The existence of a singlet fermion charged under $U(1{)}_{D}$ can give rise to dark matter in this model, preferably of nonthermal type, while incorporating additional fields can also generate light neutrino masses through typical low-scale seesaw mechanisms like a radiative or inverse seesaw.

In the light of the recent result from KamLAND-Zen (KLZ) and GERDA Phase-II, we update the bounds on the effective mass and the new physics parameters, relevant for neutrinoless double beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$). In addition to the light Majorana neutrino exchange, we analyze beyond standard model contributions that arise in left-right symmetry and R-parity violating supersymmetry. The improved limit from KLZ constrains the effective mass of light neutrino exchange down to sub-eV mass regime 0.06 eV. Using the correlation between the $^{136}\mathrm{Xe}$ and $^{76}\mathrm{Ge}$ half-lives, we show that the KLZ limit individually rules out the positive claim of observation of $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ for all nuclear matrix element compilation. For the left-right symmetry and R-parity violating supersymmetry, the KLZ bound implies a factor of 2 improvement of the effective mass and the new physics parameters. The future ton scale experiments such as, nEXO will further constrain these models, in particular, will rule out standard as well as Type-II dominating LRSM inverted hierarchy scenario.