Relativistic SU(3) chiral baryon-baryon Lagrangian up to order ^q2

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.