  The beta decay process of the 11Li halo nucleus into 9Li and d is studied in
a three-body model. The 11Li nucleus is described as a 9Li+n+n system in
hyperspherical coordinates on a Lagrange mesh. Various 9Li+d potentials are
compared involving a forbidden state, a physical bound state, and a resonance
near 0.25 MeV in the s-wave. With an added surface absorption, they are
compatible with elastic scattering data. The transition probability per time
unit is quite sensitive to the location of the resonance. For a fixed resonance
location, it does not depend much on the potential choice at variance with the
6He delayed deuteron decay. The calculated transition probability per time unit
is larger than the experimental value but the difference can be explained by a
slightly higher resonance location and/or by absorption from the 9Li+d final
channel.
