Leptogenesis During an Era of Early SU(2) Confinement

TL;DR

The paper investigates leptogenesis in a cosmology where SU(2)_L undergoes an early confinement, leaving a single non-anomalous global charge $r=-2Y+B-L$ and a rich composite spectrum from which a baryon asymmetry can emerge. Heavy Majorana neutrinos introduce $r$-violation and, crucially, CP violation arising from a strong-phase in the EFT coupling, enabling an $r$-asymmetry to be generated during the decay of a heavy composite scalar $\Phi$ into $N$ and composite states $\Psi$, with the asymmetry then mapping to a $B-L$ asymmetry after deconfinement. The evolution is governed by Boltzmann equations, with a CP asymmetry parameter $\epsilon$ arising from loop corrections and a washout strength $K_1$, and the final BAU is given by $Y_{\Delta B}(\infty) = -\frac{28}{79} Y_{\Delta r}$. The analysis shows that the observed baryon asymmetry can be reproduced for Lambda_W in the range $10^{11}$–$10^{14}$ GeV and Yukawa couplings $|Y|^2 \sim 10^{-2}$–1, with $M_R \sim 10^{10}$–$10^{14}$ GeV, illustrating how nonstandard cosmological histories can broaden viable leptogenesis parameter space and reducing the reliance on CP violation in low-energy neutrino decays.

Abstract

We explore leptogenesis during a cosmological epoch during which the electroweak $SU(2)_L$ force is confined. During weak confinement, there is only one conserved non-anomalous global charge, $r$, which is a linear combination of lepton-number, baryon-number, and hypercharge. The inclusion of heavy Majorana neutrinos leads to an $r$-charge and $CP$-violating interaction, allowing for the generation of an $r$-charge asymmetry, which translates into a baryon asymmetry post $SU(2)_L$ deconfinement. Determining the resulting baryon asymmetry as a function of the model parameters, we find that the predicted baryon-asymmetry can match observations for a wide swath of parameter space. While leptogenesis under the assumption of a standard cosmology relies on the complex phase of the neutrino Yukawa couplings, the asymmetry generated in this novel background cosmology primarily depends on a strong phase from $SU(2)_L$ confinement and favors negligible $CP$-violation in the right-handed neutrino decays.

Figures (6)

• Figure 1: Schematic representation showing the underlying neutrino $N$-$\ell$-$\varphi$ Yukawa interaction dressed by a bystander $\mathop{\mathrm{SU}}\nolimits(2)_L$ Higgs doublet during weak confinement, resulting in a $N$-$\Psi$-$\Phi$ interaction.
• Figure 2: Washout strength $K_1$ in the plane of the Yukawa coupling $\sum |Y_{\alpha\beta}|^2$ and confinement scale $\Lambda_W$, for two values of $m_\Psi / m_\Phi$ and $\theta$, as indicated. Regions above the dotted line, $K_1 = 1$, are in the weak washout regime.
• Figure 3: Feynman diagrams for the decay $\Phi \rightarrow \Psi N$, including the tree level diagram (a), higher order corrections induced by the Yukawa interactions [(b) and (c)], and from the $\Phi$-$\Psi$-$\Psi$ vertex (d).
• Figure 4: Feynman diagram indicating schematically how $\Psi$ decays into 3 singlets, $\xi$. The $\otimes$ symbol denotes an insertion of the mixing of a $\Psi$ into a $\xi$.
• Figure 5: The ratio of the decay width $\Gamma(\Psi\rightarrow\xi\xi\xi)$