Freeze-in gravitational waves and dark matter in warm inflation

Abstract

Recent study [1] has suggested that warm inflation may be realized with a minimal extension of the Standard Model by a single scalar inflaton field with an axion-like coupling to gluons. Motivated by this framework, we investigate the gravitational wave spectrum and graviton-portal dark matter production through the freeze-in process generated during warm inflation scenarios. We perform a comparative analysis for different dissipation terms, focusing on their distinct gravitational wave signatures in the high-frequency regime. Our findings reveal qualitative and quantitative differences in the spectral behavior, offering a preliminary pathway for exploring inflationary and dark matter models through high-frequency gravitational wave signals.

Figures (6)

• Figure 1: The comoving GW energy density $e^{4N}\rho_{\rm GW}$ and its production rate $I_{\rm GW}$ in WI with dissipation term $\Upsilon\propto T^3$ and $\Upsilon\propto T$, respectively. All curves are normalized to their respective maximum values. The blue line corresponds to $Q_{\mathrm{ini}}=0.01$ and the red line corresponds to $Q_{\mathrm{ini}}=1$. The black dashed line indicates the end of inflation ($\epsilon_{H}=1$), while the red and blue dashed lines correspond to the onset of radiation domination ($\epsilon_{H}=2$), respectively. Note that the reheating process is more efficient for $\Upsilon\propto T^3$ than for $\Upsilon\propto T$.
• Figure 2: The freeze-in GW spectrum of WI in the high frequency regime for different $Q_{\rm ini}$ and different dissipation terms. The dashed lines correspond to the freeze-in GW spectrum in CI produced during the radiation-dominated epoch with the same reheating temperature. The quartic coupling $\lambda$ is chosen to satisfy the CMB constraints. The upper panel and lower panel shows the GW spectrum for $Q_{\rm ini} = 0.01$ and $Q_{\rm ini} = 1$, respectively. Note the nearly identical spectral shapes and approximately equal peak frequencies, along with an enhanced peak amplitude compared to the CI case.
• Figure 3: The evolution of the Hubble parameter $H$, the plasma temperature $T$, the parameter $Q$, the radiation density parameter $\Omega_r$ and the DM yield $Y_\chi$.
• Figure 4: The correlation between DM mass and the peak amplitude of GW spectra for different $Q_{\rm ini}$ and dissipation terms. The colored bar represents the peak amplitude of GW spectra fixing the observed DM relic density. In the upper panel where $\Upsilon \propto T$, we found that in the case of $Q_{\mathrm{ini}} = 1$, the DM mass does not satisfy the condition $m_\chi \ll T$ for $\lambda < 2.6\times 10^{-16}$.
• Figure 5: The correlation between DM mass and the peak amplitude of GW spectra for different $Q_{\rm ini}$ and dissipation terms, with $\Omega_{\rm peak}h^2$ on the y-axis, $m_\chi$ on the x-axis, and $\lambda$ color-coded.