Emergent fermions modify symmetries in 2+1d

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• Matthew Yu (University of Oxford)
• Monday 06 October 2025, 10:00-11:30
• Seminar Room 2, Newton Institute.

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BID - Quantum field theory with boundaries, impurities, and defects

The finite symmetries of a fermionic QFT in 2+1d is given by a fusion 2-category. I will explain how the symmetry can be modified when one allows for stacking with TQF Ts of the form Spin(n)_1, and then condensing, to be an equivalence relation for QFTs. Such an equivalence relation enables a finite set of inequivalent modifications to the original fusion 2-categorical symmetry. This shows that the question of what is the categorical symmetry for a QFT is one that depends on an equivalence condition. I will relate the order of the symmetry modifications to the image of a map between groups of minimal nondegenerate extensions, and to the tangential structure set by the initial categorical symmetry on the background manifold for the QFT .

This talk is part of the Isaac Newton Institute Seminar Series series.

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