  We report on ab-initio NCSM calculations of the A=4 mirror Lambda hypernuclei
Lambda-4H and Lambda-4He, using the Bonn-Juelich LO chiral EFT YN potentials
plus a CSB Lambda0--Sigma0 mixing vertex. In addition to reproducing rather
well the 0+ (g.s.) and 1+ (exc.) binding energies, these four-body calculations
demonstrate for the first time that the observed CSB splitting of mirror
levels, reaching hundreds of keV for 0+ (g.s.), can be reproduced using
realistic theoretical interaction models, although with a non-negligible
momentum cutoff dependence. Our results are discussed in relation to recent
measurements of the Lambda-4H (0+ g.s.) binding energy [MAMI A1 Collaboration,
Phys. Rev. Lett. 114, 232501 (2015)] and the Lambda-4He (1+ exc.) excitation
energy [J-PARC E13 Collaboration, Phys. Rev. Lett. 115, 222501 (2015)].
