Conjecture on hidden superconformal symmetry of N=4 supergravity

We argue that the observed UV finiteness of the 3-loop extended supergravities may be a manifestation of a hidden local superconformal symmetry of supergravity. We focus on the SU(2,24) dimensionless superconformal model. In the Poincaré gauge where the compensators are fixed to φ2=6MP2 this model becomes a pure classical N=4 Einstein supergravity. We argue that in N=4 the higher-derivative superconformal invariants like φ-4W2W ̄2 and the consistent local anomaly δ(lnâ¡ φW2) are not available. This conjecture on hidden local N=4 superconformal symmetry of Poincaré supergravity may be supported by subsequent loop computations. © 2013 American Physical Society.14 p A discussion of half-maximal D=6 superconformal models is addedstatus: publishe