NONMINIMAL GRAVITATIONAL COUPLING OF SCALAR BOUND-STATES

We use the large-N approximation to investigate the nonminimal gravitational coupling xiRphi2 of the scalar bound state in the O(N)-symmetric vector model with a phi4 interaction. If the elementary scalar field is minimally coupled to gravity, xi is found to assume values in the interval [- 1,0] only. For the conformally invariant coupling of the elementary boson, the bound state is always minimally coupled (xi=0). The induced xi term is also calculated for spontaneous and explicit symmetry breaking from O(N) to O(N - 1) when the resulting Goldstone bosons can form bound states. The nonminimal gravitational coupling of scalars has important applications in inflationary cosmology.