Electroweak Phase Transition in the munuSSM

TL;DR

This work studies electroweak baryogenesis in the mu nu SSM, an MSSM-like model with three singlet right-handed neutrinos that induce a TeV-scale seesaw, preventing standard thermal leptogenesis. The authors compute the finite-temperature effective potential $V_{ ext{eff}}^T$ including one-loop corrections and daisy resummation, identifying strongly first-order phase transition regions and novel paths involving rotations in the singlet space. They classify phase-transition trajectories into two primarily viable scenarios, IIIa (two-step with singlet-space rotation) and IIIb (one-step origin-to-EW-broken vacuum), while addressing domain-wall concerns with weak $\ ext{Z}_3$ breaking and maintaining consistency with TeV-scale phenomenology. The results demonstrate a feasible EWBG mechanism in the mu nu SSM, with distinctive collider-accessible spectra and potential gravitational-wave signals.

Abstract

An extension of the MSSM called the munuSSM does not allow a conventional thermal leptogenesis scenario because of the low scale seesaw that it utilizes. Hence, we investigate the possibility of electroweak baryogenesis. Specifically, we identify a parameter region for which the electroweak phase transition is sufficiently strongly first order to realize electroweak baryogenesis. In addition to transitions that are similar to those in the NMSSM, we find a novel class of phase transitions in which there is a rotation in the singlet vector space.

Figures (6)

• Figure 1: A schematic plot of the finite temperature effective potential at the critical temperature of Eq. (\ref{['eq:criticaltemp1']}). The vertical line represents $\phi=0$ and helps to visualize the effect of $\phi\rightarrow-\phi$ symmetry breaking effect of the cubic term which is responsible for the bump at $\phi>0$ for $\{E>0,F_{\mathrm{na}}=0\}$ in Eq. (\ref{['eq:finite T effective potential raw']}).
• Figure 2: On the left, the $\mu \nu$SSM sphaleron solution versus the dimensionless radial coordinate with $h_1$ and $h_2$ (solid line), $h_3$ (dashed line), $h_4$ (dotted line), and $f$ (dashed-dotted line). The solution $h_{\tilde{\nu}^c}$ for the singlet sneutrinos does not satisfy the same boundary condition at $\xi \to 0$ as the $\mathrm{SU}\bigl(2\bigr)_L$ charged scalars. Hence, the solution of minimum energy is the one in which $h_{\tilde{\nu}^c} \approx 1$ for all $\xi$. On the right, the sphaleron energy density, $\mathrm{Eq.}\;(\ref{['eq:SphaleronAction']})$, with gauge kinetic terms (dashed line), scalar kinetic terms (dotted line), scalar potential terms (dashed-dotted line), and the total energy density (solid line). This plot illustrates that the sphaleron action is dominated by the kinetic terms and that the contribution from the scalar potential is negligible.
• Figure 3: The tree level potential plotted over a slice of the $\tilde{\nu}^c_i$ field space with $H_1^0 = H_2^0 = 0$ on the left and $H_1^0 / v_1 = H_2^0 /v_2 = 1$ on the right. The labeled points are defined in the text, and a stationary point of the potential can be found at or near each of the labeled points. The potential grows farther from the central region. In the EW-preserving subspace, the three minima are degenerate, but the Higgs VEV selects out $\vec{y}_{000}$ as the global minimum.
• Figure 4: Same as Fig. \ref{['fig:FieldSpaceTree']} but the contours represent values of the one-loop effective potential at zero temperature. The degeneracy is broken even in the EW-preserving subspace and induces $V_1^0 \left( \vec{x}_{012} \right) < V_1^0 \left( \vec{x}_{001} \right) < V_1^0 \left( \vec{x}_{000} \right)$ .
• Figure 5: A slice of the $\mu \nu$SSM parameter space. Region I suffers from tachyons in the EWSB vacuum. In region II the EWSB vacuum is metastable and we exclude these points. In region III we calculate the electroweak phase transition and find that the path through field space can be classified into one of four types, shown on the right.