In quest of a relativistic constituent quark model- some constructive remarks

The set-up of a relativistic constituent quark model in four dimensions is one of the outstanding problems in particle physics. For the time being this involves a great deal of model building which, very probably, will not change in the near future. In this paper the authors offer some general remarks which might help putting such models into shape. Most of the earlier attempts are found controversial. In particular, a conventional quark constituent interpretation could not be recovered. (Auth.)