Testing Seesaw and Leptogenesis via Gravitational Waves: Majorana versus Dirac

Abstract

We investigate the B-L gauge extension of the Standard Model that the Dirac seesaw mechanism with thermal Leptogenesis can be tested using the stochastic gravitational background (SGWB) emanating from a network of cosmic strings when B-L symmetry is broken. With right-handed neutrino mass lighter than the typical scale of grand unification, the B-L symmetry protecting the right-handed neutrinos leads to constraints on the Yukawa couplings for both Dirac and Majorana scenarios. Estimating the predicted gravitational wave background we find that future space-borne missions could probe the range concerning thermal Dirac Leptogenesis. In a comparative analysis between such probes of gravitational wave sourced from cosmic strings in Dirac and Majorana Leptogenesis in the B-L extension, based on the energy scales of the Leptogenesis, for instance, GW detectors will be able to probe the scale of Dirac Leptogenesis upto $ 10^{9}$ GeV, while for Majorana Leptogenesis it would be upto $ 10^{12}$ GeV.

Figures (9)

• Figure 1: The variation of mass scales with respect to $\langle\varphi\rangle$ in the plane of ratios $M_{\zeta_1}/M_{\zeta_3}$(dashed) and $M_{\zeta_1}/M_{\zeta_4}(dotted)$.
• Figure 2: The vertex and self-energy loop diagrams of $\zeta$ decay: $\zeta_i \rightarrow \nu_{R, \alpha} \nu_{R, \beta}$.
• Figure 3: The dependence of CP-asymmetry with respect to $\langle \varphi \rangle$. The parameter choice are: $M_{c}=1\times 10^{15}$ GeV, $\mu= 6.3\times 10^{14}$ GeV, $M_{c}'=1.26\times 10^{15}$ GeV, $\mu'=7.94\times 10^{14}$ GeV, and $\text{Tr}[\lambda^{\dagger}\lambda] = 10^{-4}$.
• Figure 4: The abundances of $Y_{\zeta_1}$ (blue) and $Y_{B}$ (green). We consider $M_{c}=8\times 10^{13}$ GeV, $\mu= 10^{13}$ GeV, $M_{c}'=10^{14}$ GeV, $\mu'=10^{13}$ GeV, $\langle \varphi \rangle=10^{12}$ GeV, and $\text{Tr}[\lambda^{\dagger}\lambda] = 7.2 \times 10^{-4}$. The horizontal dashed line correspond to the observed baryon asymmetry of the Universe.
• Figure 5: Variation of the SGWB spectra from local cosmic strings with respect to the vacuum expectation value (VEV) $\langle \varphi \rangle = \eta$.