Adam, ChristophRomanczukiewicz, T.Wereszczynski, Andrzej2020-04-082020-04-082019Adam, C., Romanczukiewicz, T. & Wereszczynski, A. The ϕ4 model with the BPS preserving defect. J. High Energ. Phys. 2019, 131 (2019). https://doi.org/10.1007/JHEP03(2019)131http://hdl.handle.net/10347/21270The phi(4) model is coupled to an impurity in a way that preserves one-half of the BPS property. This means that the antikink-impurity bound state is still a BPS solution, i.e., a zero-pressure solution saturating the topological energy bound. The kink-impurity bound state, on the other hand, does not saturate the bound, in general. We found that, although the impurity breaks translational invariance, it is, in some sense, restored in the BPS sector where the energy of the antikink-impurity solution does not depend on their mutual distance. This is re ected in the existence of a generalised translational symmetry and a zero mode. We also investigate scattering processes. In particular, we compare the antikinkimpurity interaction close to the BPS regime, which presents a rather smooth, elastic like nature, with other scattering processes. However, even in this case, after exciting a su - ciently large linear mode on the incoming antikink, we can depart from the close-to-BPS regime. This results, for example, in a backward scattering.eng© 2019 The Authors. Open Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are creditedhttps://creativecommons.org/licenses/by/4.0/Field theories in lower dimensionsSolitons monopoles and instantonsIntegrable field theoriesSpace-time symmetriesjournal article10.1007/JHEP03(2019)1311029-8479open access