Stochastic gravitational-wave background from axion-monodromy oscillons in string theory during preheating

Axion monodromy is a generic phenomenon in string compactifications. We investigate the production of gravitational-wave background from axion monodromy inflation during preheating. By performing lattice simulations using pseudospectral methods, we find that significant single-peak stochastic gravitational-wave backgrounds are generated during preheating for asymptotic linear $|\varphi |$ and ${\varphi }^{2/3}$ potentials in axion monodromy inflation and cuspy potentials. This may allow us to explore string compactifications through gravitational waves.

Figure 1

Asymptotic linear potential in axion monodromy (blue) and cuspy linear potential (orange).

Figure 2

Present gravitational-wave spectra for string axion monodromy with asymptotic linear potential for $m=1.14\times {10}^{-19}{M}_{\mathrm{pl}}$ and $M=0.01M_{\mathrm{pl}}$ (blue solid curve), and cuspy potential with potential $V\sim |\varphi |$ for ${\lambda }_1=1.3\times {10}^{-40}$. The orange dotted curve is calculated by LATTICEEASY given in [12], and the orange solid curve is calculated by PSpectRe.

Figure 3

Asymptotic ${\varphi }^{2/3}$ potential in axion monodromy (blue) and cuspy ${\varphi }^{2/3}$ potential (orange).

Figure 4

Present gravitational-wave spectra for string axion monodromy with asymptotic ${\varphi }^{2/3}$ potential for $\lambda =3.54\times {10}^{-42}$ and ${\psi }_c=0.01M_{\mathrm{pl}}$ (blue solid curve), and cuspy potential with potential $V\sim {\varphi }^{2/3}$ for ${\lambda }_2=1.0\times {10}^{-40}$ (orange solid curve).