Session J05: Baryon and Lepton Number Violation

Recent theoretical advances in electroweak baryogenesis

Explaining the origin of the cosmic baryon asymmetry is a forefront challenge at the interface of nuclear and high energy physics with cosmology. A compelling possibility as that the asymmetry was generated during the era of electroweak symmetry-breaking, the electroweak baryogenesis scenario. I discuss recent theoretical advances in electroweak baryogenesis, including both computations of the asymmetry and delineation of experimental tests of this scenario.   

Neutrinoless double beta decay: present status and future prospects

In 1937 Ettore Majorana realized that the symmetry properties of Dirac’s hole theory allowed the possibility for electrically neutral spin-1/2 fermions to be their own anti-particles. If so, a rare process known as neutrinoless double-beta decay (0$\nu\beta\beta$) could occur and consequently the total number of leptons in the universe would not be a conserved quantity. Eighty years later, 0$\nu\beta\beta$ remains the only practical experimental technique to probe the Majorana nature of neutrinos. Its observation would profoundly impact our understanding of neutrinos while providing a possible explanation of the mystery of the matter-antimatter imbalance in the universe. With the discovery that neutrinos have non-zero masses, a necessary condition for 0$\nu\beta\beta$, experiments are being pursued with vigor and ingenuity by international collaborations around the world. Significant progress has been made, with current sensitivities attaining half-lives of greater than 10$^{26}$ y. Although searching for such a rare process requires reducing backgrounds to unprecedented levels, the prospects are bright for future ton scale experiments that will be capable of discovery measurements covering the entire inverted neutrino ordering region.   

Searches for baryon number violation in proton decays and neutron-antineutron oscillations.

The status of the conservation law for baryon number (B) is of fundamental significance for particle physics and cosmology. Although no laboratory experiment has observed a process which violates baryon number, both the Standard Model and may other theories beyond the Standard Model predict B violation, and Big Bang cosmology plus inflation implies that one should interpret the baryon asymmetry observed today as evidence for B violation in the early universe. In this talk we briefly review the status of present limits on B violating processes from laboratory experiments and discuss the prospects and possibilities for improved searches using large underground detectors and intense free neutron beams.