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| Main Authors: | , , |
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| Format: | Preprint |
| Published: |
2024
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2409.08828 |
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Table of Contents:
- In a canonical type-I seesaw scenario, the Standard Model is extended with three singlet right-handed neutrinos (RHNs) $N_i, i=1,2,3$ with masses $M_i, i=1,2,3$ to simultaneously explain sub-eV masses of light neutrinos and baryon asymmetry of the Universe at high scales. In this paper, we show that a relatively low-scale thermal leptogenesis accompanied by gravitational wave signatures is possible when the type-I seesaw is extended with a singlet fermion ($S$) and a singlet scalar ($ρ$), where $S$ and $ρ$ are odd under a discrete $Z_2$ symmetry. We also add a vectorlike fermion doublet $Ψ$ and impose a $Z^\prime_2$ symmetry under which both $N_1$ and $Ψ$ are odd while all other particles are even. This gives rise to a singlet-doublet Majorana fermion dark matter in our setup. At a high scale, the $Z_2$ symmetry is broken spontaneously by the vacuum expectation value of $ρ$ and leads to (i) mixing between RHNs ($N_2, N_3$) and $S$, and (ii) formation of Domain walls (DWs). In the former case, the final lepton asymmetry is generated by the out-of-equilibrium decay of $S$, which dominantly mixes with $N_2$. We show that the scale of thermal leptogenesis can be lowered to $M_S \sim 2 \times 10^6$ GeV, which is \textit{3} orders of magnitude lower than the thermal leptogenesis in canonical type-I seesaw. In the latter case, the disappearance of the DWs gives observable gravitational wave signatures, which can be probed at LISA, DECIGO, ${\rm μARES}$ etc.