Heavy quark contributions to deep inelastic scattering

We show that in an asymptotically free gauge theory, the contribution of heavy quarks to deep inelastic structure functions can be computed in terms of the contributions of light quarks. In the standard model with four quark multiplets and an SU(3) gauge group, we estimate that for 10 GeV² < Q² < 40 GeV² the charmed quark contribution to structure functions will be several percent for x < 0.2 and tenths of a percent for x < 0.2. Our main theoretical tool is an expansion, analogous to the usual operator product expansion, of an operator constructed from heavy quark fields as a sum of light quark and gluon operators with c-number coefficients. This expansion is valied order by order in perturbation theory.