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Exploring soft constraints on effective actions
We study effective actions for simultaneous breaking of space-time and
internal symmetries. Novel features arise due to the mixing of Goldstone modes
under the broken symmetries which, in contrast to the usual Adler's zero, leads
to non-vanishing soft limits. Such scenarios are common for spontaneously
broken SCFT's. We explicitly test these soft theorems for sYM
in the Coulomb branch both perturbatively and non-perturbatively. We explore
the soft constraints systematically utilizing recursion relations. In the pure
dilaton sector of a general CFT, we show that all amplitudes up to order are completely determined in terms of the -point
amplitudes at order with . Terms with at most one derivative
acting on each dilaton insertion are completely fixed and coincide with those
appearing in the conformal DBI, i.e. DBI in AdS. With maximal supersymmetry,
the effective actions are further constrained, leading to new
non-renormalization theorems. In particular, the effective action is fixed up
to eight derivatives in terms of just one unknown four-point coefficient and
one more coefficient for ten-derivative terms. Finally, we also study the
interplay between scale and conformal invariance in this context.Comment: 20+4 pages, 1 figure; v2: references added, typos corrected; v3:
typos corrected, JHEP versio
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