Past exam of the mathematics course of the University of Cambridge 2023 iii Paper 307 4 ii Solution 2026-09-28
Past exam of the mathematics course of the University of Cambridge 2023 iii Paper 307 4 iv Solution 2026-09-28
In the proposed Spin(8) theory, the gaugino contributes to the mixed gauge-R anomaly. The fields have superfield R-charge one, so their fermions contribute zero. The spinor has fermion R-charge and index one, giving . The singlets and do not enter the gauge anomaly. Henceand the proposed R-symmetry survives quantization.
Spurion selection rule for perturbative non-renormalization Created 2026-10-06 Updated 2026-10-07
In the local Wilsonian effective action, retain the elementary chiral superfields and a nonzero infrared cutoff. Promote each coefficient in to a chiral spurion. Holomorphy excludes . Assigning and forces a regular perturbative term of R-charge two to be linear in these spurions. Ordinary flavor charges constrain its field monomial. The perturbative gauge-coupling independence of the Wilsonian superpotential removes gauge-dependent coefficients. With the gauge coupling zero, a single holomorphic vertex cannot close a loop through free - propagators; extra vertices would violate the spurion degree or holomorphy. Its coefficient is therefore the tree coefficient. Gauge anomalies of the formal R-symmetry are tracked by a transforming holomorphic gauge coupling. Keeping the infrared cutoff matters: singular one-particle-irreducible terms and elimination of entire massive fields are different operations.
The background-field holomorphy method is discussed in Seiberg's non-renormalization paper.
Let generate a holomorphic gauge transformation, with and moment map . Substitution of the Kähler covariant derivative of a superpotential gives the displayed identity. Consequently, a finite point with and all also has . Pure D-term breaking with vanishing chiral auxiliary fields can therefore evade this argument only where or outside its hypotheses. In conventional two-derivative matter-coupled supergravity, a constant Fayet–Iliopoulos term gauges an R-symmetry and constrains the transformation of ; a neutral superpotential and an independently assigned nonzero constant shift are not generally consistent. The gauge-covariance restriction is derived in Van Proeyen's discussion of Fayet–Iliopoulos terms and R-symmetry.
Wess–Zumino spurion charge assignment 2026-10-07
For quadratic and cubic interactions, assigning the couplings chiral spurion transformations makes each monomial formally covariant. The ordinary leaves neutral, while the R-symmetry gives it charge one and the superpotential charge two. The neutral ratio and the covariant factor give the symmetry-allowed holomorphic form . Perturbative regularity and tree matching are additionally needed for superpotential non-renormalization; symmetry alone leaves an arbitrary function. Fixed numerical couplings need not enjoy these formal symmetries as actual field symmetries.