Constraint on B-L cosmic string from leptogenesis with degenerate neutrinos

الأصل · EN

In the early Universe, as a consequence of U(1)B₋ₗ gauge symmetry-breaking, the so-called B-L cosmic strings are expected to be produced at the breaking scale ηB₋ₗ according to the Kibble mechanism. The decaying, collapsing closed loops of these strings can release the right-handed neutrinos, whose subsequent decay can contribute to the baryon asymmetry of the Universe (BAU), through the "slow death"(SD) process and/or the "quick death"(QD) process. In this paper, we assume that the decay of the lightest heavy Majorana neutrinos released from the B-L cosmic string loops can produce a baryon asymmetry consistent with the cosmic microwave background (CMB) observations. Considering the fact that both the neutrinoless double beta decay experiment and the cosmological data show a preference for degenerate neutrinos, we give the lower limits for the breaking scale ηB₋ₗ with the neutrino masses 0.06 eV ≤ m=(m₁²+m₂²+m₃²)¹/² ≤ 1.0 eV, where the full possible cases of degenerate neutrinos are included. We obtain ηB₋ₗ 3.3 × 10¹⁵ GeV, 5.3 × 10¹⁵ GeV and 9.5 × 10¹⁵ GeV for m=0.2 eV, 0.4 eV and 1.0 eV respectively in the SD process, and find the B-L cosmic string has a very small contribution to the BAU in the QD process.