Leptogenesis with cosmic strings

A new scenario for baryogenesis is described. The basic idea is that theories beyond the standard model which contain a ${\rm U}(1)_{B-L}$ gauge symmetry, where $B$ and $L$ are respectively baryon and lepton numbers, predict the existence of $B-L$ cosmic strings with right-handed neutrinos trapped as transverse zero modes. Cosmic string loops loose their energy via gravitational radiation and rapidly decay releasing these right-handed neutrinos. These decay into lepton and electroweak Higgs boson producing an initial lepton asymmetry. This lepton asymmetry is then converted into a baryon asymmetry via sphaleron transitions. The minimal extension of the standard model and the minimal grand unified theory for which this scenario works are respectively ${\rm SU}(3)_c \times {\rm SU}(2)_L \times {\rm U}(1)_R \times {\rm U}(1)_{B-L}$ and SO(10).