Some Cosmological Implications of Hidden Sectors

Abstract

We discuss some cosmological implications of extensions of the Standard Model with hidden sector scalars coupled to the Higgs boson. We put special emphasis on the conformal case, in which the electroweak symmetry is broken radiatively with a Higgs mass above the experimental limit. Our refined analysis of the electroweak phase transition in this kind of models strengthens the prediction of a strongly first-order phase transition as required by electroweak baryogenesis. We further study gravitational wave production and the possibility of low-scale inflation as well as a viable dark matter candidate.

Figures (7)

• Figure 1: The parameters $\alpha$ and $\beta$ characterizing the electroweak phase transition as functions of $\zeta$ for several Higgs masses. A universal coupling $\zeta$ and $N_S=12$ scalar fields have been used. The crosses mark the conformal case.
• Figure 2: Same as in Fig. \ref{['fig_PTab']} but for the critical temperature for vacuum degeneracy, $T_c$ (upper curve), and the temperature at the end of the phase transition, $T_f$ (lower curve).
• Figure 3: Same as in Fig. \ref{['fig_PTab']} for the ratio $\phi/T$ at the critical temperature $T_c$ (lower curve) and at the end of the phase transition, when the temperature is $T_f$ (upper curve).
• Figure 4: The deviation of the cubic Higgs coupling from its value in the Standard Model (solid lines). The shaded region corresponds to a strong first-order phase transition: the dotted lines are labeled by the corresponding value of $\phi/T_f$.
• Figure 5: Tunneling actions, $S_3/T$ and $S_4$, as a function of temperature for $M_H=125$ GeV and two different values of the coupling $\zeta$ as indicated. The curves for $S_4$ are stopped when the four-dimensional bounce ceases to be reliable.