  Using lattice simulations, we study the extent of the conformal window for an
SU(3) gauge theory with N_f Dirac fermions in the fundamental representation.
We extend our recently reported work, describing the general framework and the
lattice simulations in more detail. We find that the theory is conformal in the
infrared for N_f = 12, governed by an infrared fixed point, whereas the N_f = 8
theory exhibits confinement and chiral symmetry breaking. We therefore conclude
that the low end of the conformal window N_f^c lies in the range 8 <= N_f^c <=
12. We discuss open questions and the potential relevance of the present work
to physics beyond the standard model.
