Search

Observation of lepton number violation would represent a groundbreaking discovery with profound consequences for fundamental physics and as such, it has motivated an extensive experimental program searching for neutrinoless double beta decay. However, the violation of lepton number can be also tested by a variety of other observables. We focus on the possibilities of probing this fundamental symmetry within the framework of the Standard Model Effective Field Theory (SMEFT) beyond the minimal dimension-5. Specifically, we study the bounds on ∆L = 2 dimension-7 effective operators beyond the electron flavor imposed by all relevant low-energy observables and confront them with derived high-energy collider limits. We also discuss how the synergy of the analyzed multi-frontier observables can play a crucial role in distinguishing among different dimension-7 SMEFT operators. [ABSTRACT FROM AUTHOR]

We discuss sensitivities to lepton flavor violating (and conserving) interactions at future muon colliders, especially at μ+μ+ colliders. Compared with the searches for rare decays of μ and τ, we find that the TeV-scale future colliders have better sensitivities depending on the pattern of hierarchy in the flavor mixings. As an example, we study the case with the type-II seesaw model, where the flavor mixing parameters have direct relation to the neutrino mass matrix. At a μ+μ+ collider, the number of events of the μ+μ+ → μ+τ+ process can be larger than O 100 with the center of mass energy s = 2 TeV, and with an integrated luminosity L = 1 ab−1, while satisfying bounds from rare decays of μ and τ. We discuss impacts of the overall mass scale of neutrinos as well as CP violating phases to the number of expected events. [ABSTRACT FROM AUTHOR]

In the near future, the Deep Underground Neutrino Experiment and the European Spallation Source aim to reach unprecedented sensitivity in the search for neutron-antineutron (n- n ¯ ) oscillations, whose observation would directly imply |∆B| = 2 violation and hence might hint towards a close link to the mechanism behind the observed baryon asymmetry of the Universe. In this work, we explore the consequences of such a discovery for baryogenesis first within a model-independent effective field theory approach. We then refine our analysis by including a source of CP violation and different hierarchies between the scales of new physics using a simplified model. We analyse the implication for baryogenesis in different scenarios and confront our results with complementary experimental constraints from dinucleon decay, LHC, and meson oscillations. We find that for a small mass hierarchy between the new degrees of freedom, an observable rate for n- n ¯ oscillation would imply that the washout processes are too strong to generate any sizeable baryon asymmetry, even if the CP violation is maximal. On the other hand, for a large hierarchy between the new degrees of freedom, our analysis shows that successful baryogenesis can occur over a large part of the parameter space, opening the window to be probed by current and future colliders and upcoming n- n ¯ oscillation searches. [ABSTRACT FROM AUTHOR]

We investigate the possibility to probe lepton number violating (LNV) operators in the rare kaon decay K → πνν. Performing the analysis in the Standard Model effective field theory with only light active Majorana neutrinos, we determine the current limits on the corresponding LNV physics scale from the past E949 experiment at BNL as well as the currently operating experiments NA62 at CERN and KOTO at J-PARC. We focus on the specific signature of scalar currents in K → πνν arising from the LNV nature of the operators and study the effect on the experimental sensitivity, stressing the need for dedicated searches for beyond the SM currents. We find that the rare kaon decays probe high operator scales ΛLNV≈ 15 to 20 TeV in different quark and neutrino flavours compared to neutrinoless double beta decay. Furthermore, we comment that the observation of LNV in kaon decays can put high-scale leptogenesis under tension. Finally, we discuss the connection with small radiatively generated neutrino masses and show how the severe constraints therefrom can be evaded in a minimal ultraviolet-complete scenario featuring leptoquarks. [ABSTRACT FROM AUTHOR]

We study the photophobic ALP model in high-mass regions under LHC Run-II. Since the ALP is predominantly coupled with electroweak gauge bosons such as ZZ, WW, and Zγ, and less with di-photon, the model may be probed via multi-boson final-state processes. We find that on-shell ALP productions with Zγ final states currently provide the best sensitivities for ma > 40 GeV. [ABSTRACT FROM AUTHOR]