Even highly improved variants of lattice QCD with staggered fermions show
significant violations of taste symmetry at currently accessible lattice
spacings. In addition, the "rooting trick" is used in order to simulate with
the correct number of light sea quarks, and this makes the lattice theory
nonlocal, even though there is good reason to believe that the continuum limit
is in the correct universality class. In order to understand scaling
violations, it is thus necessary to extend the construction of the Symanzik
effective theory to include rooted staggered fermions. We show how this can be
done, starting from a generalization of the renormalization-group approach to
rooted staggered fermions recently developed by one of us. We then explain how
the chiral effective theory follows from the Symanzik action, and show that it
leads to "rooted" staggered chiral perturbation theory as the correct chiral
theory for QCD with rooted staggered fermions. We thus establish a direct link
between the renormalization-group based arguments for the correctness of the
continuum limit and the success of rooted staggered chiral perturbation theory
in fitting numerical results obtained with the rooting trick. In order to
develop our argument, we need to assume the existence of a standard
partially-quenched chiral effective theory for any local partially-quenched
theory. Other technical, but standard, assumptions are also required.Comment: Minor changes, few references added; RevTeX, 35 page