Abstract
We construct, in the SU(2) Yang-Mills-Higgs theory of the electroweak interactions, a non-contractible loop of four-dimensional configurations. From this we argue that there may exist a new constrained instanton I ★ with action ∼ 16 π 2/ g 2 and zero topological charge. We also discuss the spectral flow of the Dirac operator along the loop and expect I ★ to have fermion zero-modes. As a possible application for I ★ we consider the total ( B + L)-violating cross section, evaluated semiclassically from the imaginary part of the forward elastic scattering amplitude. We find a threshold-like behaviour for non-perturbative effects at a parton center-of-mass energy close to the sphaleron energy E S ∼ 10 TeV.
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