Chiral gauge theory

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In quantum field theory, a chiral gauge theory is a quantum field theory with charged chiral (i.e. Weyl) fermions. For instance, the Standard Model is a chiral gauge theory. For topological reasons, chiral charged fermions cannot be given a mass without breaking the gauge symmetry, which will lead to inconsistencies unlike a global symmetry. It is notoriously difficult to construct a chiral gauge theory from a theory which does not already contain chiral fields at the fundamental level^{[citation needed]}. A consistent chiral gauge theory must have no gauge anomaly (or global anomaly). Almost by necessity, regulators will have to break the gauge symmetry. This is responsible for gauge anomalies in the first place.