  We study a Y junction of spin-1/2 Heisenberg chains with an interaction that
breaks both time-reversal and chain exchange symmetries, but not their product
nor SU(2) symmetry. The boundary phase diagram features a stable disconnected
fixed point at weak coupling and a stable three-channel Kondo fixed point at
strong coupling, separated by an unstable chiral fixed point at intermediate
coupling. Using non-abelian bosonization and boundary conformal field theory,
together with density matrix renormalization group and quantum Monte Carlo
simulations, we characterize the signatures of these low-energy fixed points.
In particular, we address the boundary entropy, the spin conductance and the
temperature dependence of the scalar spin chirality and the magnetic
susceptibility at the boundary.
