Springer : Wash-in leptogenesis after axion inflation

Domcke, Valerie; Schmitz, Kai; Kamada, Kohei; Yamada, Masaki; Mukaida, Kyohei

doi:10.1007/JHEP01(2023)053

Article
Report number	arXiv:2210.06412 ; CERN-TH-2022-162 ; RESCEU-17/22 ; KEK-TH-2455 ; MS-TP-22-37 ; TU-1170
Title	Wash-in leptogenesis after axion inflation
Author(s)	Domcke, Valerie (CERN) ; Kamada, Kohei (Tokyo U., RESCEU) ; Mukaida, Kyohei (KEK, Tsukuba ; Sokendai, Tsukuba) ; Schmitz, Kai (CERN ; Munster U.) ; Yamada, Masaki (Tohoku U. ; Tohoku U., Astron. Inst.)
Publication	2023-01-12
Imprint	2022-10-12
Number of pages	56
Note	56 pages, 4 figures, 2 tables. v2: updated references, factor of 2 corrected in Eq. (3.8), matches version published in JHEP
In:	JHEP 2301 (2023) 053
DOI	10.1007/JHEP01(2023)053
Subject category	astro-ph.CO ; Astrophysics and Astronomy ; hep-ph ; Particle Physics - Phenomenology
Abstract	CP violation and the violation of baryon-minus-lepton number B-L do not necessarily have to occur simultaneously in order to accomplish successful leptogenesis. Instead, it suffices if new CP-violating interactions at high energies result in primordial charge asymmetries, which are then reprocessed into a nonvanishing B-L asymmetry by right-handed neutrinos (RHNs) at lower energies. In this paper, we study this novel mechanism known as "wash-in leptogenesis", utilizing axion inflation as the source of high-scale CP violation. We specifically consider axion inflation coupled to the Standard Model hypercharge sector, which results in the dual production of hypermagnetic helicity and fermionic charge asymmetries. Although the survival of these charges is endangered by sphaleron processes, magnetic diffusion, and the chiral plasma instability, we find a large range of viable scenarios. We consistently account for RHN flavor effects and coherence among the Standard Model lepton flavors across a wide range of RHN masses. We find a lower bound of 10^(5...9) GeV on the mass of the lightest RHN involved in wash-in leptogenesis, depending on the onset of turbulence in the chiral plasma and the Hubble scale of inflation. Our model is representative of a broader class of new leptogenesis scenarios and suggests interesting observational signatures with regard to intergalactic magnetic fields, primordial black holes, and gravitational waves.
Copyright/License	publication: © 2023-2025 The Authors (License: CC-BY-4.0), sponsored by SCOAP³ preprint: (License: CC BY 4.0)

$Estimates of the parameter region where the yield parameter $\chi$ [see Eqs.~\eqref{eq:chi} and \eqref{eq:chisim}] is of the right order of magnitude for successful baryogenesis (see Secs.~\ref{subsec:washin} and \ref{subsec:decay}). The contour lines indicate where in parameter space we expect $\chi = 10^{-7.5}$, while the shaded bands cover the corresponding range from $\chi = 10^{-8}$ to $\chi = 10^{-7}$. Here, larger values of $H_{\rm end}$ correspond to larger values of $\chi$, according to the scaling law $\chi \propto H_{\rm end}^{3/2}$ for fixed $\xi$ [see Eqs.~\eqref{eq:Treh} and \eqref{eq:chisim}]. We compare the equilibrium estimate (blue) and maximal estimate (red) in the magnetic picture~\cite{Domcke:2018eki} to the GEF estimate (black) in the electric picture~\cite{Gorbar:2021zlr} for different values of the damping factor $\Delta$ [see Eq.~\eqref{eq:delta}]. The reheating temperature $T_{\rm rh}$ follows from the Hubble rate $H_{\rm end}$ according to Eq.~\eqref{eq:Treh}.$ $Evolution of the global CS, $B\!+\!L$, $B\!-\!L$, $B$, and $L$ charges in the benchmark scenario discussed in Sec.~\ref{sec:bau} all the way from the end of axion inflation to the EWPT. Panels (a) and (b) describe the initial conditions after axion inflation and the chemical equilibrium shortly before wash-in leptogenesis (see Sec.~\ref{subsec:transport}); panels (c), (d), and (e) illustrate the situation shorty after wash-in leptogenesis, below the equilibration temperature of the electron Yukawa interaction, and at the time of sphaleron freeze-out towards the end of the EWPT (see Sec.~\ref{subsec:washin}). The red bars in panel (e) indicate the outcome of baryogenesis from helicity decay (see Sec.~\ref{subsec:decay}). Every panel contains the bars shown in all previous panels plus new bars that indicate the relevant new contributions to the respective charges. The total charges at the respective stages of the evolution are indicated by the black dots and horizontal black dashed lines.$ $Viable parameter space for successful baryogenesis after primordial hypermagnetogenesis. In each temperature regime, (i) to (v), the vertical bars respectively indicate the required values of the dimensionless helicity density $\chi$ if the BAU receives contributions from wash-in leptogenesis \textit{and} baryogenesis via helicity (green bars) or from wash-in leptogenesis \textit{only} (orange bars). In temperature regime (vi), $T_{\rm sph}\lesssim T \lesssim 10^5\,\textrm{GeV}$, we indicate the $\chi$ value that leads to correct baryon asymmetry if baryogenesis via helicity decay yields the only contribution to the BAU, $\chi \simeq 7.9 \times 10^{-8}$. Smaller $\chi$ values are typically harmless, while larger values will lead to the overproduction of baryon number, barring cancellations with other contributions of different origin. The shaded region in the lower right corner highlights where the chiral plasma instability \textit{would} occur, around $T \sim T_{\rm CPI}$ [see Eq.~\eqref{eq:TCPI}], if it were not already rendered ineffective at higher temperatures by the electron Yukawa interaction. If the initial conditions after the end of hypermagnetogenesis are located in the shaded region in the top left corner, the initial magnetic Reynolds number (either $\textrm{Re}_{\rm mag}^{\rm ini, max}$ or $\textrm{Re}_{\rm mag}^{\rm ini, visc}$) is expected to be smaller than unity [see Eqs.~\eqref{eq:Rm_max} and \eqref{eq:Rm_visc}], which results in magnetic diffusion setting in at temperatures $T \sim T_{\rm diff}$ [see Eq.~\eqref{eq:Tdiff}]. The temperature $T_{\rm diff}$ can be read off from the brown axis in dependence of the initial temperature $T_{\rm rh}$ (or $T_{\rm end}$). The requirement $T_{B-L} > T_{\rm diff}$ can moreover be turned into a lower bound $M_1^{\rm min}$ on the $N_1$ mass. See text for more details.$ Show more plots

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