Long-Range Forces in Heterogeneous Fluid Membranes

We find a new long-range interaction between foreign inclusions (e.g. mobile proteins) in a fluid membrane which is mediated by the membrane itself. The interaction falls off as 1/R4, can be attractive or repulsive depending on the temperature and the elastic properties of the inclusion and the membrane, and for large distances is large compared with electrostatic, van der Waals, and other lipid-mediated forces.