Journal
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
Volume 52, Issue 14, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1751-8121/ab0b79
Keywords
string sigma models; integrability; massless S-matrix
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Funding
- European Research Council under the FP7 [615203]
- EPSRC [EP/N509486/1]
- STFC [ST/P000762/1]
- STFC [ST/P000762/1] Funding Source: UKRI
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Motivated by the search for new integrable string models, we study the properties of massless tree-level S-matrices for 2d sigma-models expanded near the trivial vacuum. We find that, in contrast to the standard massive case, there is no apparent link between massless S-matrices and integrability: in well-known integrable models the tree-level massless S-matrix fails to factorize and exhibits particle production. Such tree-level particle production is found in several classically integrable models: the principal chiral model, its classically equivalent 'pseudo-dual' model, its non-abelian dual model and also the SO(N + 1)/SO(N) coset model. The connection to integrability may, in principle, be restored if one expands near a non-trivial vacuum with massive excitations. We discuss IR ambiguities in 2d massless tree-level amplitudes and their resolution using either a small mass parameter or the i epsilon-regularization. In general, these ambiguities can lead to anomalies in the equivalence of the S-matrix under field redefinitions, and may be linked to the observed particle production in integrable models. We also comment on the transformation of massless S-matrices under sigma-model T-duality, comparing the standard and the 'doubled' formulations (with T-duality covariance built into the latter).
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