Abstract
Many GUT models conserve the difference between the baryon and lepton number, $B-L$. These models can create baryon and lepton asymmetries from heavy Higgs or gauge boson decays with $B+L \neq 0$ but with $B-L=0$. Since the sphaleron processes violate $B+L$, such GUT-generated asymmetries will finally be washed out completely, making GUT baryogenesis scenarios incapable of reproducing the observed baryon asymmetry of the Universe. In this work, we revisit the idea to revive GUT baryogenesis, proposed by Fukugita and Yanagida, where right-handed neutrinos erase the lepton asymmetry before the sphaleron processes can significantly wash out the original $B+L$ asymmetry, and in this way one can prevent a total washout of the initial baryon asymmetry. By solving the Boltzmann equations numerically for baryon and lepton asymmetries in a simplified 1+1 flavor scenario, we can confirm the results of the original work. We further generalize the analysis to a more realistic scenario of three active and two right-handed neutrinos to highlight flavor effects of the right-handed neutrinos. Large regions in the parameter space of the Yukawa coupling and the right-handed neutrino mass featuring successful baryogenesis are identified.
Highlights
The unaccounted baryon asymmetry in the Universe is one of the reasons why the Standard Model (SM) is imperfect and challenges physicists to come up with new ideas of asymmetry generation mechanisms
The =L washout processes can convert an initial B þ L asymmetry originating from grand unified theory (GUT) baryogenesis into a final B − L asymmetry being immune against the action of the sphaleron processes
To evade complications from finite-temperature corrections, we confine ourselves to cases where the GUT B þ L injection scale is lower than MN
Summary
The unaccounted baryon asymmetry in the Universe is one of the reasons why the Standard Model (SM) is imperfect and challenges physicists to come up with new ideas of asymmetry generation mechanisms. Due to the Majorana mass term MN which violates the lepton number, the right-handed neutrinos can mediate L washout processes such as ll ↔ HÃHÃ; lH ↔ l HÃ; ð2Þ which destroy the initial lepton number asymmetry from GUT baryogenesis, while leaving the baryon number intact, resulting in a nonvanishing B − L asymmetry which cannot be washed out by sphaleron effects. N-mediated washout processes generate a nonvanishing B − L asymmetry from the initial condition of a vanishing B − L but finite B þ L asymmetry, making a part of the baryon asymmetry immune against the action of the sphalerons As a result, both the final B and L asymmetries can become nonzero. We start with the case of one lepton generation and one right-handed neutrino, and generalize this scenario to the realistic case of three generations plus two right-handed neutrinos
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