Extra dimensions, orthopositronium decay, and stellar cooling

In extensions of the Randall-Sundrum II model, the photon can be localized on the brane by gravity only. An intriguing prediction of these models is the possibility of e+e- annihilation into states living in extra dimensions. The search for this effect has motivated the present round of precision orthopositronium decay experiments. It turns out that in this framework a photon in plasma should also be subject to a similar kind of invisible decay. This has important astrophysical consequences, namely, it changes the plasmon decay rate in globular cluster stars and the core-collapse supernova cooling rate. The resulting bounds on the model parameter exceed the possible reach of orthopositronium experiments by many orders of magnitude.