A formalism for treating the scattering of decuplet baryons in chiral effective field theory is developed. The minimal Lagrangian and potentials in leading-order SU(3) chiral effective field theory for the interactions of octet baryons ($B$) and decuplet baryons ($D$) for the transitions $BB\to BB$, $BB\leftrightarrow DB$, $DB\to DB$, $BB\leftrightarrow DD$, $DB\leftrightarrow DD$, and $DD\to DD$ are provided. As an application of the formalism we compare with results from lattice QCD simulations for $\Omega\Omega$ and $N\Omega$ scattering. Implications of our results pertinent to the quest for dibaryons are discussed.

Brueckner theory is used to investigate the properties of hyperons in nuclear matter. The hyperon-nucleon interaction is taken from chiral effective field theory at next-to-leading order with SU(3) symmetric low-energy constants. Furthermore, the underlying nucleon-nucleon interaction is also derived within chiral effective field theory. We present the single-particle potentials of Lambda and Sigma hyperons in symmetric and asymmetric nuclear matter computed with the continuous choice for intermediate spectra. The results are in good agreement with the empirical information. In particular, our calculation gives a repulsive Sigma-nuclear potential and a weak Lambda-nuclear spin-orbit force.

In this proceeding we summarize results for baryonic contact terms derived within SU(3) chiral effective field theory. The four-baryon contact terms, necessary for the description of the hyperon-nucleon interaction, include SU(3) symmetric and explicit chiral symmetry breaking terms. They also include four-baryon contact terms involving pseudoscalar mesons, which become important for three-body forces. Furthermore we derive the leading order six-baryon contact terms in the non-relativistic limit and study their contribution to the $\Lambda NN$ three-body contact interaction. These results could play an important role in studies of hypernuclei or hyperons in nuclear matter.

The existence of baryon-baryon bound states in the strangeness sector is examined in the framework of SU(3) chiral effective field theory. Specifically, the role of SU(3) symmetry breaking contact terms that arise at next-to-leading order in the employed Weinberg power counting scheme is explored. We focus on the 1 S 0 partial wave and on baryon-baryon channels with maximal isospin since in this case there are only two independent SU(3) symmetry breaking contact terms. At the same time, those are the channels where most of the bound states have been predicted in the past. Utilizing pp phase shifts and Σ + p cross section data allows us to pin down one of the SU(3) symmetry breaking contact terms and a clear indication for the decrease of attraction when going from the NN system to strangeness S = −2 is found, which rules out a bound state for ΣΣ with isospin I = 2. Assuming that the trend observed for S = 0 to S = −2 is not reversed when going to ΞΣ and ΞΞ makes also bound states in those systems rather unlikely.

Results for theΛN andΣN interactions obtained at next-to-leading order in chiral e ffective field theory are reported. At the order considered there are contributions from onean d two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives . SU(3) flavor symmetry is imposed for constructing the hyperon-nucleon interaction while the explicit SU(3) symm etry breaking by the physical masses of the pseudoscalar mesons ( π, K, η) is taken into account. An excellent description of the hype ron-nucleon system can be achieved at next-to-leading order. It is on the same level of quality as t he one obtained by the most advanced phenomenological hyperon-nucleon interaction models.

We calculate the one-photon loop radiative corrections to the charged pion-pair production process π − γ → π + π − π −. In the low-energy region this reaction is governed by the chiral pion-pion interaction. The pertinent set of 42 irreducible photon-loop diagrams is calculated by using the package FeynCalc. Electromagnetic counterterms with two independent low-energy constants \(\hat k_1\) and \(\hat k_2\) are included in order to remove the ultraviolet divergences generated by the photon loops. Infrared finiteness of the virtual radiative corrections is achieved by including soft photon radiation below an energy cut-off Λ. The purely electromagnetic interaction of the charged pions mediated by one-photon exchange is also taken into account. The radiative corrections to the total cross section (in the isospin limit) vary between +10% close to threshold and about −1% at a center-of-mass energy of 7m π . The largest contribution comes from the simple one-photon exchange. Radiative corrections to the π + π − and π − π − mass spectra are studied as well. The Coulomb singularity of the final-state interaction produces a kink in the dipion mass spectra. The virtual radiative corrections to elastic π − π − scattering are derived additionally.

We calculate hyperon–nucleon and hyperon–hyperon interactions at next-to-leading order in SU(3) baryon chiral perturbation theory extending earlier work by the Bonn–Juelich group. The constructed potentials in momentum space include all one- and two-meson exchange terms generated by the SU(3) chiral Lagrangian. Effects from intermediate decuplet baryons are considered as well. These chiral baryon–baryon potentials, together with appropriate contact terms, provide a new basis for systematic studies of hyperon–nucleon scattering and light hypernuclei.

We construct the most general chiral effective Lagrangian for baryon–baryon contact interactions in flavor SU(3) up to order O(q2) using a covariant power counting. A subset of these contact terms contributes to the baryon–baryon potential in chiral effective field theory. The Lorentz invariant effective Lagrangian is constructed to fulfill the invariance under charge conjugation, parity transformation, Hermitian conjugation and the local chiral symmetry group SU(3)L×SU(3)R. Goldstone bosons and external fields are included as well, thus providing additional four-baryon contact vertices involving e.g. pseudoscalar mesons and/or photons. In order to eliminate the linearly dependent terms, we use the Fierz identities, the equations of motion, and a Cayley–Hamilton relation for SU(3). As an application the baryon–baryon scattering contact potentials in low partial waves are considered.