On the massless treelevel Smatrix in 2d sigma models
Abstract
Motivated by the search for new integrable string models, we study the properties of massless treelevel Smatrices for 2d [ image ]models expanded near the trivial vacuum. We find that, in contrast to the standard massive case, there is no apparent link between massless Smatrices and integrability: in wellknown integrable models the treelevel massless Smatrix fails to factorize and exhibits particle production. Such treelevel particle production is found in several classically integrable models: the principal chiral model, its classically equivalent 'pseudodual' model, its nonabelian dual model and also the [ image ] coset model. The connection to integrability may, in principle, be restored if one expands near a nontrivial vacuum with massive excitations. We discuss IR ambiguities in 2d massless treelevel amplitudes and their resolution using either a small mass parameter or the [ image ]regularization. In general, these ambiguities can lead to anomalies in the equivalence of the Smatrix under field redefinitions, and may be linked to the observed particle production in integrable models. We also comment on the transformation of massless Smatrices under [ image ]model Tduality, comparing the standard and the 'doubled' formulations (with Tduality covariance built into the latter).
 Publication:

Journal of Physics A Mathematical General
 Pub Date:
 April 2019
 DOI:
 10.1088/17518121/ab0b79
 arXiv:
 arXiv:1812.02549
 Bibcode:
 2019JPhA...52n4005H
 Keywords:

 string sigma models;
 integrability;
 massless Smatrix;
 High Energy Physics  Theory
 EPrint:
 30 pages