Corrections to the adiabatic limit in the flux tube model

Corrections to the adiabatic potential picture of qq systems are estimated using a flux tube model described recently. Mixing of the lowest adiabatic surfaces is small for heavy-quark systems. For light-quark systems the authors suggest a way of redefining the adiabatic surfaces so that mixing effects are small in this case also. Mixing effects are included in estimates of the lowest hybrid masses.