We discuss first results for the computation of short distance contributions
to semileptonic form factors for the rare B decays B→K∗ℓ+ℓ−
and Bs→ϕℓ+ℓ−. Our simulations are based on RBC/UKQCD's
Nf=2+1 ensembles with domain wall light quarks and the Iwasaki gauge action.
For the valence b-quark we chose the relativistic heavy quark action.Comment: 7 pages, 1 table, 3 figures, presented at the 33rd International
Symposium on Lattice Field Theory (Lattice2015), July 14-18, 2015, Kobe,
Japa