One possibility that I'm entertaining is that cold fusion is a photoelectric effect, operating at X-ray or gamma energies. There are some interesting correlations in this connection. The basic idea is that the cathode has cavities in which photons resonate, in turn triggering an unknown process. There are cavities and structures on cathodes on the order of hundreds of nanometers that have been observed using scanning electron microscopes.
An interesting review paper in Nature titled "Optical microcavities" (2003) discusses a number of developments in exploring optical microcavities. A typical cavity is several micrometers across. These microcavities have a parameter Q, which is a measure of the resonance quality. The higher the Q, the less likely photons are to dissipate. A high Q permits strong coupling to take place. Strong coupling implies a coupling constant g that is around or larger than 1. When it occurs, you can get a phenomenon in which an atom in an exited state emits a photon which transfers to a "cavity mode" and then eventually is reabsorbed by the atom many times, an effect called the Rabi cycle. With a g << 1, there will be weak coupling, which will lead to the photon being dissipated too quickly to see such an effect. Some of the experiments exhibit a Q ~ 13,000, which is very high. Also, systems in which strong coupling takes place must be modeled using non-perturbative methods. One possible implication is that such systems are less well-understood by physicists, who are unable to rely on perturbation theory, a basic tool in quantum mechanics.
Is it even possible for a gamma or an X-ray to resonate in a cavity on the scale of hundreds of nanometers? If not, what are the wavelengths associated with the cavity modes for cavities on this scale?