Baryogenesis via leptogenesis in presence of cosmic strings Original Research Article

We study the effect on leptogenesis due to image cosmic strings of a image extension of the Standard Model. The disappearance of closed loops of image cosmic strings can produce heavy right handed neutrinos, imageʹs, whose CP-asymmetric decay in out-of-thermal equilibrium condition can give rise to a net lepton (L) asymmetry which is then converted, due to sphaleron transitions, to a baryon (B) asymmetry. This is studied by using the relevant Boltzmann equations and including the effects of both thermal and string generated non-thermal imageʹs. We explore the parameter region spanned by the effective light neutrino mass parameter image, the mass image of the lightest of the heavy right-handed neutrinos (or equivalently the Yukawa coupling image) and the scale of image symmetry breaking, image, and show that there exist ranges of values of these parameters, in particular with image and image, for which the cosmic string generated non-thermal imageʹs can give the dominant contribution to, and indeed produce, the observed baryon asymmetry of the universe when the purely thermal leptogenesis mechanism is not sufficient. We also discuss how, depending on the values of image, image and image, our results lead to upper bounds on image, where δ is the CP-violating phase that determines the CP asymmetry in the decay of the heavy right handed neutrino responsible for generating the L-asymmetry.