Neutrino zeromodes on electroweak strings in light of topological insulators

Speaker: Dr. Yu Hamada (DESY)
Abstract: It is known that SU(2)xU(1) electroweak theory gives a non-trivial soliton solution called Z-string. Because it is an unstable solution in the SM, it is considered that it does not play any role in cosmology and phenomenology. On the other hand, since it couples to SM fermions inevitably, fermion zeromodes appear on the string as zero-energy solutions of Dirac equations. In this talk, we examine zeromodes coming from neutrino fields on the Z-string and their effect on the stability of the string in the SM and its extensions. We propose using topological invariants constructed from the momentum (and real) space topology of Green's functions, often used for investigating edge modes in condensed matter physics. We analyze the SM and then examine type-I and type-II seesaw models as well as their hybrid. Based on this analysis, we also comment on proposals in the literature to stabilize the Z-string.