ar X iv : h ep - t h / 95 10 06 2 v 1 1 0 O ct 1 99 5 Strong Coupling Hadron Masses in 1 / d Expansion

Motivated by the weak-strong coupling expansion [1], we calculate the spectrum of hadrons using a systematic 1/d (d-dimensionality of spacetime) in addition to a strong coupling expansion in β. The 1/d expansion is pushed to the next to leading order in (1/d) for mesons and next to next to leading order for baryons. We do the calculation using Wilson fermions with arbitrary r and show that doublers decouple from the spectrum only when r is close to the Wilson's value r = 1. For these r the spectrum is much closer to the lattice results and the phenomenological values than those obtained by using either the (nonsystematic) " randomwalk " approximation or the hopping parameter expansion. In particular, the value of the nucleon to ρ-meson mass ratio is lowered to 3 log d−1/4 2arccosh2 + O(1/d) ≈ 1.48. The result holds even for β as large as 5, where the weak-strong coupling expansion is applicable and therefore these results are expected to be reasonable. It is commonly believed that for low energy physical quantities in QCD, such as hadron masses, there is no small expansion parameter, and the theory is " strongly coupled ". The theory only has an asymptotic weak coupling expansion successfully describes high energy quantities but breaks down at low energies. Recently one of us proposed a scheme combining weak and strong coupling expansion in a " double expansion scheme " [1]. The high 1