Heavy Seesaw Neutrinos as Long-Lived Particles : A Theoretical Perspective

Sammanfattning

The Standard Model of particle physics is a widely accepted theory that describes all known interaction and particles. Despite its success, it has several flaws, including hierarchy problem, strong CP problem, and neutrino mass generation. In particular, the Standard Model does not account for neutrino masses and predicts massless neutrinos despite experimental evidence for neutrinos being massive. The most popular mechanism for generating neutrino masses is Type-I seesaw, which introduces a massive right-handed neutrino. The mechanism arises in many beyond the Standard Model theories. In this project two models are considered - Left-Right-Symmetric Model and U(1)B-L gauge extension of the Standard Model, both of which predict massive neutrinos. Parameter space scans were performed in order to find regions where heavy neutrino are both long-lived and are produced with large cross-section. Long-lived heavy neutrino would produce a displaced vertex thus reducing the Standard Model background. Experimental constraints were taken into account during the scans.For the Left-Right-Symmetric Model, different heavy neutrino production channels were considered, with production via W' boson found to yield the largest cross section. The possibility of heavy neutrino production via SM W boson was also explored.For the U(1)B-L gauge extension interference effects between Z and Z' bosons were taken into account. A few benchmark points were selected for each model, which can be used for future phenomenological studies.