Bounds on light, weakly interacting particles from observational lifetimes of helium-burning stars

The lifetimes of low-mass population I helium-burning stars as derived from the number of ``clump'' giants in the open cluster M67 and in the old galactic disk population agree very well with calculations. This provides an observational basis for previous speculative bounds on axions, Majorons, supersymmetric particles, and exotic scalar and vector bosons. We find a slightly improved bound on the neutrino magnetic dipole moment of μ_ν3×{}10^-11{{μ}}B$. The possibility of detecting axionlike particles in the laboratory is severely constrained.