Alpenglow - A Signature for Chameleons in Axion-Like Particle Search Experiments

Abstract

We point out that chameleon field theories might reveal themselves as an 'afterglow' effect in axion-like particle search experiments due to chameleon-photon conversion in a magnetic field. We estimate the parameter space which is accessible by currently available technology and find that afterglow experiments could constrain this parameter space in a way complementary to gravitational and Casimir force experiments.In addition, one could reach photon-chameleon couplings which are beyond the sensitivity of common laser polarization experiments. We also sketch the idea of a Fabry-Perot cavity with chameleons which could increase the experimental sensitivity significantly.

Figures (4)

• Figure 1: Illustration of an afterglow experiment to search for chameleon particles. (a) Filling the vacuum tube by means of a laser beam with chameleons via photon-chameleon conversion in a magnetic field. (b) An isotropic chameleon gas forms. (c) Afterglow from chameleon-photon conversion in a magnetic field.
• Figure 2: Combined constraints on $n=1$ chameleon theories in terms of the potential parameters $\Lambda$, in units of the energy scale $\rho_\Lambda^{1/4}\simeq 0.002\ {\rm eV} \simeq (0.1\ {\rm mm})^{-1}$ corresponding to the energy density of dark energy, versus the inverse coupling scale $1/M$, in units of $M_{\rm Pl}\simeq 1.2\cdot 10^{19}$ GeV. Current constraints (blue solid line; from Ref. Mota:2006fz) arise from searches for violations of the weak equivalence principle (WEP), from searches for deviations from the $1/r^2$ law of the gravitational force (Irvine and Eöt-Wash), and from bounds on the strength of any fifth force from measurements of the Casimir force. Future space-based tests will improve the current limits to the one shown as a light-blue dotted dashed line. A search for an afterglow due to chameleon-photon reconversion at ALPS phase zero will be sensitive to the region indicated by the red solid line, corresponding to a loading and measurement time of $\Delta t = t = 100$ s. The red dotted line corresponds to the academic case $\Delta t = 1$ y and $t=1$ h.
• Figure 3: Coherent evolution of the chameleon amplitude with number of cycles $N$. For illustration, we took $M=100$ GeV, $m=10\,\mu$eV, $\ell=10$ m, $B=5$ T and $\omega=1$ eV. The upper panel shows the case $\delta_1+\delta_2=0$ and a rapid oscillation. For the lower panel we chose $\delta=0$, such that the chameleon amplitudes add up resonantly. In this case the asymptotic amplitude is $|\phi_\infty|\sim1/P_{\gamma\to\phi}$. Also shown is the envelope $|\phi_\infty|^2\cdot(1\pm e^{-t\Gamma_\text{load}})^2$ as a dotted line. After $N=100$ cycles the laser is switched off (marked as a dashed line) and the chameleon amplitude decays exponentially. Note that we use different ordinates in both panels.
• Figure 4: Coherent evolution of the photon amplitude with number of cycles $N$ for the benchmark points of Fig. (\ref{['fig:chameleonamp']}). We show the intensity of the right-moving (left-moving) photons transmitted at $z=\ell$ ($z=0$) from the cavity as a thick green (thin red) line. In the resonant case (lower panel) the cavity acts as a mirror: The amplitude of right-moving photons is suppressed, whereas the left-moving photons reach the laser intensity. Again, after $N=100$ cycles the laser is switched off and photons are emitted with exponentially decaying intensities to both sides. In the resonant case the intensity of the beam reaches the laser intensity.