Light by Light Scattering as a New Probe for Axions
  We study the impact of virtual axions on the polarization of photons inside a
cavity during the interaction of high-power laser pulses. A novel detection
scheme for measuring the axion-induced ellipticity signal during the
Light-by-Light (LBL) scattering process is investigated. We show that a
momentum exchange between photons in a probe laser beam and a high-intensity
target beam may lead to a resonance at the physical mass of the axion.
Consequently, the resonant enhancement of vacuum birefringence gives rise to a
large ellipticity signal. This signal enhancement can be applied in order to
discriminate between the axion contribution to LBL scattering and the standard
model contribution due to electron-positron pairs. The sensitivity of the
scheme is studied for experimentally feasible probe light sources and ultrahigh
intensity laser backgrounds. It is shown that this technique has the potential
to probe the QCD axion in the mass range $10^{-2} \textrm{eV} \lesssim m_{a}
\lesssim 1 \textrm{eV}$. In this region the axion induced signal surpasses the
standard model background.
