LAUSR

Mikhail A. Ivanov, Jürgen G. Körner, Valery E. Lyubovitskij, 4, 5, 6, 7 and Zhomart Tyulemissov 8, 9 Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna, Russia PRISMA Cluster of Excellence, Institut für Physik, Johannes Gutenberg-Universität, D-55099 Mainz, Germany Institut für Theoretische Physik, Universität Tübingen, Kepler Center for Astro and Particle Physics, Auf der Morgenstelle 14, D-72076 Tübingen, Germany Departamento de F́ısica y Centro Cient́ıfico Tecnológico de Valparáıso-CCTVal, Universidad Técnica Federico Santa Maŕıa, Casilla 110-V, Valparáıso, Chile Millennium Institute for Subatomic Physics at the High-Energy Frontier (SAPHIR) of ANID, Fernández Concha 700, Santiago, Chile Department of Physics, Tomsk State University, 634050 Tomsk, Russia Tomsk Polytechnic University, 634050 Tomsk, Russia 8 The Institute of Nuclear Physics, Ministry of Energy of the Republic of Kazakhstan, 050032 Almaty, Kazakhstan 9 Al-Farabi Kazakh National University, 050040 Almaty, Kazakhstan We systematically study two-body nonleptonic decays of light lambda hyperon Λ → pπ(nπ) with account for both shortand long-distance effects. The short-distance effects are induced by five topologies of external and internal weak W exchange, while long-distance effects are saturated by an inclusion of the so-called pole diagrams with intermediate 1 2 + and 1 2 − baryon resonances. The contributions from 1 2 + resonances are calculated straightforwardly by account for nucleon and Σ baryons whereas the contributions from 1 2 − resonances are calculated by using the well-known soft-pion theorem in the current-algebra approach. It allows one to express the parity-violating Swave amplitude in terms of parity-conserving matrix elements. From our previous analysis of heavy baryons we know that short-distance effects induced by internal topologies are not suppressed in comparison with external W -exchange diagram and must be included for description of data. Here, in the case of Λ decays we found that the contribution of external and internal W -exchange diagrams is sizably suppressed, e.g., by one order of magnitude in comparison with data, which are known with quite good accuracy. Pole diagrams play the major role to get consistency with experiment.