Very-High-Frequency Gravitational Waves from Multi-Monodromy Inflation

Abstract

We show that in multi-stage axion monodromy inflation an interruption near the end of the penultimate stage can lead to a spike in the gravitational wave background. These gravitational waves are in the frequency range and with an amplitude accessible to proposed terrestrial detectors such as the Einstein Telescope, Cosmic Explorer, and future Levitated Sensor Detector experiments.

Figures (6)

• Figure 1: Gravitational wave strain as a function of frequency from different sources discussed in the literature, such as cosmic strings, preheating after inflation, the hot thermal post-big bang plasma, etc. The bright red colored spikes near the center of the image are the signals derived in this paper. Clearly, if they were present in our universe they would dominate over other sources.
• Figure 2: Two-field potential $V=V(\phi_1,\phi_2)$ for the model in eq. (2). Here $M_2/M_1 = 0.1$, $p_1 = 2/5$, $p_2 = 1$, $\mu_1 = \mu_2 = {\cal O}(1)\,M_{\mathrm{P}}$. The red curve depicts a typical two-stage inflationary trajectory, where the field $\phi_1$ slow-rolls down the slope first and then oscillates while decaying near the bottom of the valley. Finally, $\phi_2$ starts to move along the valley.
• Figure 3: Abundance of gravitational waves as a function of frequency, setting $N_{CMB}=\Delta N_e = 35$. Dashed grey: the sensitivity of LISA. Dotted blue: the sensitivity of Big Bang Observer (BBO). The example given here uses $M_1^4 = 2 \times 10^{-9} \,M_{\mathrm{P}}^4$, $\mu_1 = M_{\mathrm{P}}$, $p_1 = 0.2$. We scan $f_{\phi_1}$ over the values shown in the legend.
• Figure 4: Abundance of gravitational waves as a function of frequency for different values of $N_{CMB}$, corresponding to the range of frequencies probed by the Levitated Sensor Detector.
• Figure 5: High-resolution plot of the rising edge of the gravitational wave peak as a function of frequency for $N_{CMB}=50$ corresponding to a $\sim 15 \, \textrm{kHz}$ range signal.