New universality class of chiral symmetry breaking in the strongly coupledU(1) chi U phi model

We describe a 4D U(1) lattice gauge theory with charged scalar phi and ferm ion chi matter fields (chi U phi model). At sufficiently strong gauge coupl ing, the chiral symmetry is broken and the mass of the unconfined composite fermion F = <(chi)over bar>phi is generated dynamically by gauge interacti on. The scalar supresses this symmetry breaking and induces a line of secon d order transitions with scaling properties similar to the Nambu-Jona-Lasin io model. However, in the vicinity of a particular, tricritical point the s caling properties are different. Here we study the effective Yukawa couplin g between the massive fermion and the Goldstone boson. The perturbative tri viality bound of Yukawa models is nearly saturated. The theory is similar t o strongly coupled Yukawa models except the occurrence of an additional sta te - a gauge ball of mass m(S) similar or equal to 1/2m(F). This, and non-c lassical values of tricritical exponents suggest that at the tricritical po int the chi U phi model constitutes a new universality class. Nevertheless, it might be a microscopic model for the Higgs-Yukawa mechanism of symmetry breaking.