Instanton Effects in Euclidean vacuum, Real Time Production, and in the Light-front Wave Functions

Nontrivial topological structures of non-Abelian gauge fields were discovered in the 1970’s. Instanton solutions, describing vacuum tunneling through topological barriers, have fermionic zero modes which are at the origin of (cid:48) t Hooft effective Lagrangian. In the 1980’s instanton ensembles have been used to explain chiral symmetry breaking. In the 1990’s a large set of numerical simulations were performed deriving Euclidean correlation functions. The special role of scalar diquarks in nucleons, and color superconductivity in dense quark matter have been elucidated. In these lectures, we discuss further developments of physics related to gauge topology. We show that the instanton-antiinstanton “streamline” configurations describe “sphaleron transitions” in high energy collisions, which result in production of hadronic clusters with nontrivial topologi-cal/chiral charges. (They are not yet observed, but discussions of dedicated experiments at LHC and RHIC are ongoing.) Another new direction is instanton effects in hadronic spectroscopy, both in the rest frame and on the light front. We will discuss their role in central and spin-dependent potentials, formfactors and antiquark nuclear “sea”. Finally, we summarize the advances in the semiclassical theory of deconfinement, and chiral phase transitions at finite temperature, in QCD and in some of its “deformed” versions. Confinement remains one the most interesting and challenging nonperturbative phenomenon in non-Abelian gauge theories. Recent semiclassical (for SU(2)) and lattice (for QCD) studies have suggested that confinement arises from interactions of statistical ensembles of instanton-dyons with the Polyakov loop. In this work, we extend studies of semiclassical ensemble of dyons to the SU (3) Yang-Mills theory. We find that such interactions do generate the expected first-order deconfinement phase transition. The properties of the ensemble, including correlations and topological susceptibility, are studied over a range of temperatures above and below T c . Additionally, the dyon ensemble is studied in the Yang-Mills theory containing an extra trace-deformation term. It is shown that such a term can cause the theory to remain confined and even retain the same topological observables at high temperatures.