The large charge symmetry breaking (CSB) implied by the Λ binding
energy difference ΔBΛ4​(0g.s.+​)≡BΛ​(Λ4​He)−BΛ​(Λ4​H) = 0.35±0.06 MeV
of the A=4 mirror hypernuclei ground states, determined from emulsion
studies, has defied theoretical attempts to reproduce it in terms of CSB in
hyperon masses and in hyperon-nucleon interactions, including one pion exchange
arising from Λ−Σ0 mixing. Using a schematic strong-interaction
ΛN↔ΣN coupling model developed by Akaishi and
collaborators for s-shell Λ hypernuclei, we revisit the evaluation of
CSB in the A=4Λ hypernuclei and extend it to p-shell mirror
Λ hypernuclei. The model yields values of ΔBΛ4​(0g.s.+​)∼0.25 MeV. Smaller size and mostly negative p-shell
binding energy differences are calculated for the A=7−10 mirror hypernuclei,
in rough agreement with the few available data. CSB is found to reduce by
almost 30 keV the 110 keV  Λ10​B g.s. doublet splitting
anticipated from the hyperon-nucleon strong-interaction spin dependence,
thereby explaining the persistent experimental failure to observe the 2exc−​→1g.s.−​γ-ray transition.Comment: a few clarifying statements added to v2; matches published PLB
version plus a note added after publication on p.1