Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Lie-algebraic classification of effective theories with enhanced soft
  limits   A great deal of effort has recently been invested in developing methods of
calculating scattering amplitudes that bypass the traditional construction
based on Lagrangians and Feynman rules. Motivated by this progress, we
investigate the long-wavelength behavior of scattering amplitudes of massless
scalar particles: Nambu-Goldstone (NG) bosons. The low-energy dynamics of NG
bosons is governed by the underlying spontaneously broken symmetry, which
likewise allows one to bypass the Lagrangian and connect the scaling of the
scattering amplitudes directly to the Lie algebra of the symmetry generators.
We focus on theories with enhanced soft limits, where the scattering amplitudes
scale with a higher power of momentum than expected based on the mere existence
of Adler's zero. Our approach is complementary to that developed recently by
Cheung et al., and in the first step we reproduce their result. That is, as far
as Lorentz-invariant theories with a single physical NG boson are concerned, we
find no other nontrivial theories featuring enhanced soft limits beyond the
already well-known ones: the Galileon and the Dirac-Born-Infeld (DBI) scalar.
Next, we show that in a certain sense, these theories do not admit a nontrivial
generalization to non-Abelian internal symmetries. Namely, for compact internal
symmetry groups, all NG bosons featuring enhanced soft limits necessarily
belong to the center of the group. For noncompact symmetry groups such as the
ISO($n$) group featured by some multi-Galileon theories, these NG bosons then
necessarily belong to an Abelian normal subgroup. The Lie-algebraic consistency
constraints admit two infinite classes of solutions, generalizing the known
multi-Galileon and multi-flavor DBI theories.

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The categories of this paper are: cmp-lg
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The categories of this paper are: math
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: physics
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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: cs
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The categories of this paper are: bayes-an
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-ex
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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: quant-ph