Symmetry restoration in gauge boson wave packet collisions in Yang-Mills-Higgs theory.

The idea of the restoration of spontaneously broken gauge symmetries under extreme conditions (high temperature, high fermion densities, strong external gauge elds) was intensely studied in the 1970's and is well known [1,2] (for review see [3,4]). Under these conditions spontaneously broken gauge theories undergo various phase transitions resulting, in most cases, in the restoration of the originally broken symmetries. The consequences of such restoration| masslessness of the gauge bosons and fermions, long range character of the interactions, etc.|are very important for the properties of the very early Universe. These properties may also play a signi cant role in the context of neutron stars and in the multiparticle production at high-energy interactions. It has long been realized [1,2] that the Lagrangian of the Standard Model with a non-zero vacuum expectation value for the scalar eld is a covariant generalization of the Ginzburg-Landau equation which describes a wide variety of \ordered" systems (ferromagnets, super uids, superconductors, crystals, etc.) and their phase transitions. From this point of view very di erent systems have common general properties due to their di erently revealed broken symmetries. Using the analogy with superconductivity, where a strong external electromagnetic current (magnetic eld) destroys superconductivity resulting in the transition to the normal state, an intense current of weakly interacting particles (e.g. of W -bosons) can restore the gauge symmetry and cause the transition to a new phase with massless gauge quanta [2,5]. The present paper is devoted to the study of the restoration of the spontaneously broken gauge symmetry in the collisions of intense, energetic W -boson wave packets. The paper is organized as follows. Section II describes the symmetry restoration at zero temperature in the SU(2) Higgs model. In Section III this phenomenon is compared with the well-known results of symmetry restoration at high temperature. Section IV is devoted to the stability problem of the one-loop radiatively corrected e ective potential with the external gauge eld in the light of the existence of the heavy t-quark. In Section V we present lattice calculations of gauge boson wave packet collisions in which the restoration of the SU(2) gauge symmetry is manifested. Section VI contains short concluding remarks.