Searching for axion resonances in vacuum birefringence with three-beam collisions

We consider birefringent (i.e., polarization changing) scattering of x-ray photons at the superposition of two optical laser beams of ultrahigh intensity and study the resonant contributions of axions or axionlike particles, which could also be short lived. Applying the specifications of the Helmholtz International Beamline for Extreme Fields (HIBEF), we find that this setup can be more sensitive than previous light-by-light scattering (birefringence) or light-shining-through-wall experiments in a certain domain of parameter space. By changing the pump and probe laser orientations and frequencies, one can even scan different axion masses, i.e., chart the axion propagator.

Figure 1

Axion $s$-channel contribution to light-by-light scattering. The initial and final x-ray photons with momenta $k_{\mathrm{in}}$ and $k_{\mathrm{out}}$ interact with the fields of the two optical lasers $k_{\mathrm{L}1}$, $k_{\mathrm{L}2}$ via the internal axion propagator (dashed line).

Figure 2

Sketch of the experimental setup.

Figure 3

Accessible parameter space based on $N_{\text{signal}}\ge 1$ from Eq. (6) in terms of axion mass $m_{\varphi }$ and coupling $g_{\varphi }$. The optical laser orientations relative to the XFEL (at $\vartheta =0$) are $\vartheta =8\pi /9$ (blue solid curve), $\vartheta =3\pi /4$ (red dashed curve), and $\vartheta =\pi /2$ (purple dot-dashed curve). The green shaded region in the top left corner denotes the parameter region probed by PVLAS (birefringence [80]). The limits obtained by NOMAD (light-shining-through-wall [49]) are given by the black dashed curve.

Figure 4

Signal strength $N_{\text{signal}}$ from (6) for $\vartheta =8\pi /9$, plotted as a function of $m_{\varphi }$ at fixed coupling $g_{\varphi }={10}^{-3}{\mathrm{GeV}}^{-1}$. The solid blue curve represents the axion $s$-channel contribution alone while the black dot-dashed curve incorporates the combined effect of axion $s$ and $t$ channels as well as the QED contribution (red dashed horizontal line).