Abstract
Leptogenesis can successfully explain the matter-antimatter asymmetry via out-of-equilibrium decays of heavy Majorana neutrinos in the early Universe. In this article, we focus on nonresonant thermal leptogenesis and the possibility of lowering its scale. In order to do so, we calculate the lepton asymmetry produced from the decays of one and two heavy Majorana neutrinos using three-flavored density matrix equations in an exhaustive exploration of the model parameter space. We find regions of the parameter space where thermal leptogenesis is viable at intermediate scales, $T\ensuremath{\sim}{10}^{6}\text{ }\text{ }\mathrm{GeV}$. However, the viability of thermal leptogenesis at such scales requires a certain degree of cancellation between the tree- and one-loop level contribution to the light neutrino mass matrix, and we quantify such fine-tuning.
Highlights
There is overwhelming experimental evidence for an excess of matter over antimatter in the Universe
The baryon asymmetry may be parametrized by the baryon-to-photon ratio, ηB, which is defined to be ηB
We revisit the question: how low can the scale of thermal leptogenesis go? We focus solely on the possibility that the heavy neutrinos are Majorana in nature and find thermal leptogenesis is possible at intermediate scales without resonant effects
Summary
There is overwhelming experimental evidence for an excess of matter over antimatter in the Universe. This asymmetry remains a fundamental and unresolved mystery whose explanation demands new physics beyond the standard model (SM). The baryon asymmetry may be parametrized by the baryon-to-photon ratio, ηB, which is defined to be ηB ≡ nB − nγ. ; where nB, nBand nγ are the number densities of baryons, antibaryons and photons, respectively. This quantity can be measured using two independent methods that probe the Universe at different stages of its evolution. BBN, [1] and cosmic microwave background radiation, CMB, data [2] give
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