In massless QCD, a quark condensate breaks to the diagonal vector subgroup. The associated Goldstone modes are the light pseudoscalar mesons.
The pion decay constant normalizes the axial current matrix element and the leading pion nonlinear-sigma-model action. It has mass dimension one in four spacetime dimensions.
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Chiral symmetry breaking is a fundamental concept in particle physics and field theory, particularly in the context of quantum field theories that describe the strong interactions, like Quantum Chromodynamics (QCD). To understand chiral symmetry breaking, it's important to grasp the concepts of chirality and symmetry in particle physics. ### Chirality Chirality refers to the "handedness" of particles, specifically fermions (such as quarks and leptons).