Past exam of the mathematics course of the University of Cambridge 2022 iii Paper 307 3 iii Solution 2026-09-28
Only the fields transform under flavor ; their gauge-color index gives copies of its fundamental. With , the ultraviolet 't Hooft anomalies areThe last two expressions simplify torespectively.
Past exam of the mathematics course of the University of Cambridge 2022 iii Paper 307 3 Solution 2026-09-28
A gauge anomaly breaks a redundancy needed to remove unphysical states and makes a quantum gauge theory inconsistent unless it cancels. A chiral anomaly is instead the quantum violation of a classical global axial current; the theory remains consistent, but processes such as and instanton-induced charge violation become possible. A 't Hooft anomaly is an obstruction to gauging a global symmetry. It is compatible with a consistent theory but is invariant under renormalization-group flow, so any infrared phase must reproduce it through massless fields, spontaneous symmetry breaking, or topological degrees of freedom.
Past exam of the mathematics course of the University of Cambridge 2023 iii Paper 307 3 iv Solution 2026-09-28
For , the infrared fields at the origin are the nine mesons and three baryons plus three antibaryons, for fifteen chiral multiplets. Every elementary quark superfield has R-charge , so its fermion has charge . In the ultraviolet there are twelve quark Weyl fermions and three adjoint gauginos. Hence the two anomalies areEach meson or baryon superfield contains two quarks and has R-charge , so each composite fermion has charge . The unconstrained infrared fields therefore giveBoth results agree, establishing the requested 't Hooft anomaly matching. This smooth composite description is the , example of s-confinement.
Past exam of the mathematics course of the University of Cambridge 2023 iii Paper 307 4 Solution 2026-09-28
Two theories are Seiberg duals when they are distinct ultraviolet gauge theories that flow to the same infrared quantum field theory. Their gauge-invariant operator spectra, global symmetries, 't Hooft anomalies and responses to deformations agree, even though one description may be strongly coupled where the other is weakly coupled.
Past exam of the mathematics course of the University of Cambridge 2023 iii Paper 307 4 vii Solution 2026-09-28
Choose the flavor orientation in which each electric is a fundamental of . Its color components then giveIn the magnetic theory, the eight Spin(8) components of transform in the antifundamental and contribute . The singlet transforms in the symmetric representation of , whose cubic anomaly coefficient is , while and are flavor singlets. Thereforewhere was used. The two 't Hooft anomalies match, as required by Seiberg duality.
Past exam of the mathematics course of the University of Cambridge 2024 iii Paper 305 3 Solution Created 2026-09-24 Updated 2026-09-25
A gauge anomaly breaks a redundancy required to remove unphysical polarizations. It violates the Ward identities and makes the quantum gauge theory inconsistent, so all gauge anomalies must cancel. A chiral anomaly, or Adler-Bell-Jackiw anomaly, instead breaks a classically conserved global axial symmetry; it is physically allowed and explains effects such as anomalous pseudoscalar decays and instanton-induced charge violation. A 't Hooft anomaly is an obstruction to gauging a global symmetry. It is invariant under renormalization-group flow, so 't Hooft anomaly matching constrains the infrared theory to reproduce it through massless fields, symmetry breaking, or a topological sector.
Past exam of the mathematics course of the University of Cambridge 2025 iii Paper 305 3 Solution Created 2026-09-24 Updated 2026-09-25
A gauge anomaly makes gauge redundancy inconsistent and must cancel. A chiral anomaly is the quantum nonconservation of a classically conserved axial current and may be a physical effect. A 't Hooft anomaly is an obstruction to gauging a global symmetry; it is preserved by renormalization-group flow and must be reproduced by the infrared theory, through massless degrees of freedom, symmetry breaking, or topological order.
Past exam of the mathematics course of the University of Cambridge 2025 iii Paper 305 3 vii Solution Created 2026-09-24 Updated 2026-09-25
For , the three right-flavour copies of contribute , while contributes , giving . For , these fields contribute . All fifteen components of , , and have charge , soThe ultraviolet formulas at give , , , and respectively. Every 't Hooft anomaly therefore matches.
Past exam of the mathematics course of the University of Cambridge 2026 iii Paper 305 3 iii Solution Created 2026-09-24 Updated 2026-09-25
Use the charges and and the index convention . The gauge-colour copies of the flavour fundamental giveSumming the charge cubed and the charge over all Weyl components givesEach of these four coefficients is an ultraviolet 't Hooft anomaly.
Past exam of the mathematics course of the University of Cambridge 2026 iii Paper 305 3 Solution Created 2026-09-24 Updated 2026-09-25
A gauge anomaly makes the gauge symmetry inconsistent and must cancel. An Adler-Bell-Jackiw anomaly breaks a classical global chiral symmetry quantum mechanically but does not by itself invalidate the gauge theory. A 't Hooft anomaly is an obstruction to gauging a global symmetry; it remains invariant along renormalization-group flow and constrains the infrared spectrum or symmetry-breaking pattern.
Past exam of the mathematics course of the University of Cambridge 2026 iii Paper 307 1 vii Solution Created 2026-09-24 Updated 2026-09-25
The three Weyl components form one fundamental representation of the global , so coupling to background gauge fields reveals a nonzero 't Hooft anomaly. This does not destroy the global symmetry in flat space or make the theory inconsistent; it constrains any infrared description through 't Hooft anomaly matching. If were instead intended as a dynamical gauge symmetry, the same uncancelled gauge anomaly would make the model inconsistent and additional chiral matter would be required. Ordinary quantum corrections cannot generate the forbidden superpotential, and the non-renormalization theorem protects its absence.