Gravitational Wave Production and Baryogenesis in a Simple Left-Right model

Abstract

The left-right model with the simplest Higgs structure has a $SU(2)_L$ doublet $H_L$, a $SU(2)_R$ doublet $H_R$, and a singlet $\sigma$ that couples to the doublets as $\sigma(|H_L|^2-|H_R|^2)$. The left-right symmetry has $H_L\leftrightarrow H_R$ and $\sigma\leftrightarrow-\sigma$. We study gravitational wave production and baryogenesis in the electroweak phase transitions in the model. For two benchmark points, $\sigma$ first gets a vev, followed by $H_R$ and then $H_L$. An interesting feature is that the vev of $H_L$ is initially much higher than its zero temperature value, leading to a more strongly first-order transition and higher frequency gravitational waves. An unusual benchmark point has the $\sigma$ vev at zero when the electroweak symmetry breaks. This results in both $H_L$ and $H_R$ vevs being equal and in the multi-TeV range. At a lower temperature, the $\sigma$ vev turns on, breaking the left-right symmetry and $H_L$ drops to its standard model value. Since the electroweak symmetry is broken at the multi-TeV scale, the frequency of gravitational waves will be much higher than usual. Baryogenesis is also discussed.