title: New Fermionic Soft Theorems for Supergravity Amplitudes.
abstract: Soft limits of a massless S matrix are known to reflect the symmetries of the theory. In particular, for theories with Goldstone bosons, the double-soft limit of scalars reveals the coset structure of the vacuum manifold. In this Letter, we propose that such universal double-soft behavior is not only true for scalars, but also for spin-1/2 particles in four dimensions and fermions in three dimensions. We first consider the Akulov-Volkov theory and demonstrate that the double-soft limit of Goldstinos yields the supersymmetry algebra. More surprisingly, we also find that amplitudes in 4≤N≤8 supergravity theories in four dimensions as well as N=16 supergravity in three dimensions behave universally in the double-soft-fermion limit, analogous to the scalar ones. The validity of the new soft theorems at loop level is also studied. The results for supergravity are beyond what is implied by supersymmetry Ward identities and may impose nontrivial constraints on the possible counterterms for supergravity theories.
authors.affiliation: Department of Physics and Astronomy, National Taiwan University, Taipei 10617, Taiwan, Republic of China.
authors.forename: Wei-Ming
authors.initials: WM
authors.lastname: Chen
authors.affiliation: Department of Physics and Astronomy, National Taiwan University, Taipei 10617, Taiwan, Republic of China.|School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540, USA.
authors.forename: Yu-Tin
authors.initials: YT
authors.lastname: Huang
authors.affiliation: Dipartimento di Fisica, Università di Roma "Tor Vergata" and INFN Sezione di Roma "Tor Vergata," Via della Ricerca Scientifica, 00133 Roma, Italy.
authors.forename: Congkao
authors.initials: C
authors.lastname: Wen