Freeze-in and freeze-out production of Higgs portal Majorana fermionic dark matter during and after reheating

TL;DR

This work analyzes Higgs-portal Majorana dark matter production during a non-instantaneous reheating epoch, considering both freeze-in and freeze-out mechanisms and distinguishing pre- and post-EWSB production channels. By modeling reheating with a monomial inflaton potential $V(\phi)\propto \phi^{2n}$ and solving the coupled Boltzmann equations for $\rho_{\phi}$ and $\rho_{R}$, the authors reveal how the inflaton EoS $w_{\phi}$ and the maximum/reheating temperatures shape the DM yield. They map the viable $(m_{χ},\Lambda)$ parameter space under Lyman-$\alpha$, unitarity, and gravitational production constraints, and compare with current and projected direct-detection experiments, finding most of the allowed region lies below experimental reach. The results highlight the significant role of reheating history and EWSB in Higgs-portal DM phenomenology and indicate that substantial experimental advances would be required to probe this scenario.

Abstract

In this paper, we investigate the production of Majorana fermionic dark matter (DM) via the Higgs portal, considering both freeze-in and freeze-out mechanisms during and after the post-inflationary reheating phase. We assume that the Universe is reheated through the decay of the inflaton ($φ$) into a pair of fermions $f$ and $\bar f$ via the interaction $y\,φ\,\bar f\,f$, where $y$ is the dimensionless Yukawa coupling. Our analysis focuses on how the non-standard evolution of the Hubble expansion rate and the thermal bath temperature during reheating influence DM production. Additionally, we examine the impact of electroweak symmetry breaking (EWSB), distinguishing between scenarios where DM freeze-in or freeze-out occurs before or after EWSB. We further explore the viable DM parameter space and its compatibility with current and future detection experiments, including XENONnT, LUX-ZEPLIN (LZ), XLZD, and collider searches. Moreover, we incorporate constraints from the Lyman-$α$ bound to ensure consistency with small-scale structure formation.

Figures (10)

• Figure 1: The evolution of the energy densities of the inflaton (dashed red) and radiation (solid red), along with the bath temperature (solid blue), is shown as a function of normalized scale factor $A(=a/a_{\rm end})$ for $T_{\rm re}=10^9$ GeV (left) and $T_{\rm re}=10$ GeV (right). The top (bottom) panel corresponds to $w_{\rm\phi}=0.0\,(0.5)$, and the vertical black solid lines represent the end of reheating $A_{\rm re}$.
• Figure 2: Feynman diagrams illustrating the dominant DM production channels.
• Figure 3: The evolution of the co-moving number density of DM for freeze-in as a function of the scale factor $A$ (bottom x-axis) and the bath temperature $T$ (top x-axis) for $w_{\rm\phi}=0.0$ (left), $w_{\rm\phi}=0.5$ (right) with $T_{\rm re}=10^{9}$ GeV. Each plot presents three different cases, Left panel: $m_{\rm\chi} (=10^6\,\hbox{GeV})<T_{\rm re}$ (solid line, $\Lambda=8.4\times10^{18}$ GeV), $T_{\rm re}<m_{\rm\chi} (=10^{11}\,\hbox{GeV})<T_{\rm max}$ (dashed line, $\Lambda=3.6\times10^{16}\,\hbox{GeV}$) and $m_{\rm\chi}(=5.0\times10^{12}\,\hbox{GeV})>T_{\rm max}$ (dot-dashed, $\Lambda=2.0\times10^{12}\,\hbox{GeV}$); Right panel: $m_{\rm\chi} (=10^6\,\hbox{GeV})<T_{\rm re}$ (solid line, $\Lambda=7.2\times10^{19}$ GeV), $T_{\rm re}<m_{\rm\chi} (=10^{11}\,\hbox{GeV})<T_{\rm max}$ (dashed line, $\Lambda=2.0\times10^{22}\,\hbox{GeV}$) and $m_{\rm\chi}(=1.5\times10^{15}\,\hbox{GeV})>T_{\rm max}$ (dot-dashed, $\Lambda=7.5\times10^{16}\,\hbox{GeV}$). The vertical red line corresponds to $T\sim T_{\rm fi}$, and the vertical black line corresponds to $T=T_{\rm re}$.
• Figure 4: The behavior of the DM parameter space $(\Lambda, m_{\rm\chi})$ for the freeze-in mechanism in the pre-EWSB scenario, consistent with the observed relic abundance. Here, we consider three different EoS $w_{\rm\phi}=0.0$ (left), $1/3$ (middle), and $0.5$ (right), with a fixed $T_{\rm re}=10^9$ GeV. Different segments of the line correspond to distinct mass regimes: solid ($m_{\rm\chi}<T_{\rm re}$), dashed ($T_{\rm re}<m_{\rm\chi}<T_{\rm max}$), and dot-dashed ($m_{\rm\chi}>T_{\rm max}$). The region above the line corresponds to an underabundant DM scenario, where the predicted relic abundance is below the observed value.
• Figure 5: The evolution of the comoving DM number density for freeze-out as a function of the scale factor $A$ (bottom x-axis) and the bath temperature $T$ (top x-axis) for $w_{\rm\phi}=0.0$ (left), $w_{\rm\phi}=0.5$ (right) with $T_{\rm re}=10^{9}$ GeV. Each plot presents two different cases: freeze-out after reheating $T_{\rm fo}<T_{\rm re}$ (solid line), and freeze-out during reheating $T_{\rm fo}>T_{\rm re}$ (dashed line). In both plots, $\Lambda=10^8$ GeV. The vertical red line corresponds to $T\sim T_{\rm fo}$, and the vertical black line corresponds to $T=T_{\rm re}$.