Few-Body Syst (2018) 59:61
Status of the (1405)
Received: 27 January 2018 / Accepted: 16 April 2018 / Published online: 27 April 2018
© Springer-Verlag GmbH Austria, part of Springer Nature 2018
Abstract I give an overview of the current status of the lowest s-wave baryon resonance in the strangeness
(S =−1) channel, the Λ(1405). Recent results from Lattice QCD calculations and new high-precision data
from photoproduction experiments are highlighted in this talk. On the theoretical side various directions
have been explored over the last two decades on the basis of coupled-channel chiral unitary models. New
photoproduction data can be used to reduce statistical uncertainty of the predictions of such models. As for
the systematic uncertainties, a recent comparative analysis of modern approaches exhibits many similarities
but also large ambiguities in some of the predicted properties of the antikaon-nucleon scattering amplitudes.
Some possible ways to reduce such a model dependence are discussed at the end of this manuscript.
The history of the Λ(1405) began about 58 years ago when Dalitz and Tuan [1,2] have found that two of
four solutions describing (at that time) all available experimental data, using a dynamical two-channel model,
predict an existence of a resonance below
KN threshold. After the formulation of the Quark Model, many
hadronic excitations could be successfully arranged according to symmetry patterns of this model. However,
as argued in, e.g., Ref.  both Λ(1405) and Λ(1520) appear as nearly mass-degenerate states in such types
of approaches. Therefore, the description of this state requires a full ﬁeld-theoretical approach reﬂecting all
symmetries of QCD. Most recent theoretical developments will be described in Sect. 2 in more detail.
The importance of the antikaon-nucleon scattering and the production mechanism of Λ(1405) are three-
fold. First, on the side of theory the unusual behavior of the
KNscattering amplitude, related to the presence of
the sub-threshold resonance and many open channels makes the investigation of this interaction an important
testing ground of our understanding of SU(3) dynamics. Second, parametrization of the
on the understanding of the
KN sub-channel. Such three-body channels are important in view of upcoming
experiments at DAΦNE , to measure the Kd threshold amplitude, as well as for the search for the K
bound state performed at, e.g., FINUDA . Third: The investigations of Refs. [6,7] have shown that that
the equation of state of neutron stars is sensitive to the antikaon condensate. The propagation of the latter in
nuclear medium is strongly dependent to the properties of the
KN potential. See also a recent comprehensive
review  on the matter of antikaon nuclear physics.
The speaker is deeply grateful to the organizers for the invitation to present his view on this interesting topic, ﬁnancial support
and inspiring conference.
This article belongs to the Topical Collection “NSTAR 2017–The International Workshop on the Physics of Excited Nucleons”.
M. Mai (
Department of Physics, The George Washington University, 725 21st St. NW, Washington, DC 20052, USA