Past exam of the mathematics course of the University of Cambridge 2009 iii Paper 42 3 Solution Created 2026-10-03 Updated 2026-10-14
Use left Grassmann derivatives and define the supersymmetric covariant derivatives . Multiplication in the indicated order gives exactly the printed differential operator:Thus the equation is in two-dimensional N=(1,1) superspace.
Under a Lorentz boost, take and . The derivatives have boost weights , and have weights . Consequently has weight zero, and is a Lorentz scalar. Both and the ordinary function are scalar superfields, so the equation is Lorentz invariant.
For supersymmetry, and anticommutation of distinct odd coordinates giveMoving either supercharge through the two odd derivatives introduces two minus signs, hence . If , with odd constant parameters, the chain rule for an even scalar superfield givesTherefore a solution is mapped to a solution, proving supersymmetry invariance.
To compute the supersymmetric Liouville equation, order the odd coordinates as and anticommute the fermionic component fields with both coordinates. In particular, . Direct application of the operator givesLet . Only the two products of its degree-one terms survive in ; for example, . Hence and . The exponential function expands exactly asEquating the constant terms fixes the auxiliary field, . The linear and quadratic terms then give the requested component field equations of motion:The signs here follow from the printed operator, the printed component expansion, and left Grassmann derivatives; no convention change has been made in eliminating the auxiliary field.