Reheating the Standard Model from a hidden sector

We consider a scenario where the inflaton decays to a hidden sector thermally decoupled from the visible Standard Model sector. A tiny portal coupling between the hidden and the visible sectors later heats the visible sector so that the Standard Model degrees of freedom come to dominate the energy density of the Universe before big bang nucleosynthesis. We find that this scenario is viable, although obtaining the correct dark matter abundance and retaining successful big bang nucleosynthesis is not obvious. We also show that the isocurvature perturbations constituted by a primordial Higgs condensate are not problematic for the viability of the scenario.

Figure 1

Blue and yellow lines show the evolution of the SM and $Z_2$-symmetric $s$ energy densities, respectively. The dot-dashed line shows when $T_{\mathrm{h}}=2m_{\mathrm{b}}$, the solid line shows when $s$ becomes nonrelativistic, and the dashed line marks the freeze-out of $s$ at $\frac{1}{4!}{n}_{\mathrm{s}}^3⟨v^3{\sigma }_{ssss\to ss}⟩=H$. Here $m_{\mathrm{s}}=0.1\mathrm{GeV}$, ${\lambda }_{\mathrm{hs}}={10}^{-7}$, and ${\lambda }_{\mathrm{s}}=1$.

Figure 2

Relative energy densities as a function of the SM temperature, and scaling of different components as a function of the scale factor for parameter values shown in the upper panel. Blue, yellow, and green lines show the evolution of the SM, $s$, and $\psi$ energy densities, respectively. The solid line shows when $T_{\mathrm{h}}=m_{\mathrm{s}}$, the dashed line marks the DM freeze-out at $n_{\psi }⟨v{\sigma }_{\psi \overline{\psi }\to ss}⟩=3H$, the dot-dashed line marks the $s$ freeze-out at $\frac{1}{3!}{n}_{\mathrm{s}}^2⟨v^2{\sigma }_{sss\to ss}⟩=3H$, and the dotted line shows when ${\mathrm{\Gamma }}_s=3H$.

Figure 3

The light and dark blue regions are ruled out by the overproduction of DM for two different values of $y$ shown in the plot. The purple region is excluded by the BBN constraint, $T_{\mathrm{SM}}<4\mathrm{MeV}$, and the dashed purple lines show where $T_{\mathrm{SM}}=20\mathrm{MeV}$ (thick) and $T_{\mathrm{SM}}=100\mathrm{MeV}$ (thin) at the time the SM sector becomes the dominant energy density component. In the green region ${\mathrm{\Gamma }}_s>3H$ already before the freeze-out of $s$, and there our approximations are not applicable. Left (right) from the vertical yellow dot-dashed line in the lower (upper) panel the $ssss\to ss$ processes determine the $s$ freeze-out instead of $sss\to ss$. Thin contours show ${\log }_{10}A$; see Eq. (21).