HKLL bulk reconstruction for small ∆

We discuss the extension of the HKLL (Hamilton, Kabat, Lifschytz, and Lowe) bulk reconstruction for non-interacting scalar fields corresponding to conformal weights ∆ smaller than the original condition ∆ > d − 1. We give explicit formulas for the cases d − 2 < ∆ ≤ d − 1 and ∆ = d − s with integer s. In the latter case we show that smearing CFT fields over a region of the boundary consisting of points light-like separated from the bulk point is sufficient for bulk reconstruction, whereas in general smearing over all light-like and space-like separated points is required

A two-dimensional integrable axionic sigma-model and T-duality

An $S$-matrix is proposed for the two dimensional O(3) $\sigma$-model with a dynamical $\theta$-term (axion model). Exploiting an Abelian T-duality transformation connecting the axion model to an integrable SU(2)$\times$U(1) symmetric principal $\sigma$-model, strong evidence is presented for the correctness of the proposed $S$-matrix by comparing the perturbatively calculated free energies with the ones based on the Thermodynamical Bethe Ansatz. This T-duality transformation also leads to a new Lax-pair for both models. The quantum non-integrability of the O(3) $\sigma$-model with a {\sl constant} $\theta$-term, in contradistinction to the axion model, is illustrated by calculating the $2\to3$ particle production amplitude to lowest order in $\theta$.Comment: 11 pages, LaTe