MHz Gravitational Waves from Short-term Anisotropic Inflation

Understand

We reveal the universality of short-term anisotropic inflation.

• As a demonstration, we study inflation with an exponential type gauge kinetic function which is ubiquitous in models obtained by dimensional reduction from higher dimensional fundamental theory.
• It turns out that an anisotropic inflation universally takes place in the later stage of conventional inflation.
• Remarkably, we find that primordial gravitational waves with a peak amplitude around $10^{-26}$ ~ $10^{-27}$ are copiously produced in high-frequency bands 10MHz~100MHz.