Metamorphosis versus Decoupling in Nonabelian Gauge Theories at Very   High Energies
  In the present paper we study the limit of zero mass in nonabelian gauge theories both with Higgs mechanism and in the nonlinear realization of the gauge group (Stueckelberg mass). We argue that in the first case the longitudinal modes undergo a metamorphosis process to the Goldstone scalar modes, while in the second we guess a decoupling process associated to a phase transformation. The two scenarios yield strikingly different behaviors at high energy, mainly ascribed to the presence of a massless Higgs doublet among the physical modes in the case of Higgs mechanism (i.e. not only the Higgs boson). The aim of this work is to show that the problem of unitarity at high energy in nonabelian gauge theory with no Higgs boson can open new perspectives in quantum field theory. 
Ruggero Ferrari (CTP-MIT University of Milan, INFN Milan)
hep-ph hep-lat hep-th