ANNIHILATION OF DEFECTS ANNIHILATION OF DEFECTS IN LIQUID CRYSTALS MILAN SVETEC Regional Development Agency MURA Ltd, Lendavska 5a, 9000 Murska Sobota, Slovenia and Laboratory of Physics of Complex Systems, Faculty of Education, University of Maribor, Koroška 160, 2000 Maribor, Slovenia MILAN AMBROŽIČ Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia SAMO KRALJ * Laboratory of Physics of Complex Systems, Faculty of Education, University of Maribor, Koroška 160, 2000 Maribor, Slovenia Abstract. The annihilation of defect is studied theoretically in liquid crystals (LCs). We consider the annihilation of point disclinations in nematic and line edge dislocations in smectic A LC phase, respectively. We stress qualitative similarities in these processes. The whole annihilation regime is taken into account, consisting of the pre-collision, collision and post-collision stage. Keywords: liquid crystals; edge dislocations; point disclinations; annihilation 1. Introduction The physics of topological defects 1 attracts scientists for years. They appear in phases that are reached via a continuous symmetry breaking phase transition. Because this phenomenon is very common in nature, defects are found in many (often completely different) physical systems. Note that the first theory on the origin of topological defects was made in cosmology 2 . Due to their essentially topological basis the physics of defects exhibits many universalities 1,3 . Therefore it is adequate to find a system in which some universal features of defects can be studied relatively easily. For this purpose various liquid crystal (LC) phases 4,5 are very convenient by virtue of their fluidity, softness, optic anisotropy, and diversity of phases and structures. They can exhibit point and line defects in orientational ordering. In addition smectic phases exhibit also line defects in translational ordering. The defects in LCs are also called dislocations and disclinations, referring to the local non- unique description of orientational and translational hydrodynamic ordering fields, * Correspondence to: samo.kralj@uni-mb.si