K+K+ scattering length from lattice QCD

The K+K+ scattering length is calculated in fully-dynamical lattice QCD with domain-wall valence quarks on the MILC asqtad-improved gauge configurations with rooted-staggered sea quarks. Three-flavor mixed-action chiral perturbation theory at next-to-leading order, which includes the leading effects of the finite lattice spacing, is used to extrapolate the results of the lattice calculation to the physical value of m(K)(+)/f(K)(+). We find m(K)(+)a(K)(+)K(+)=-0.352 +/- 0.016, where the statistical and systematic errors have been combined in quadrature.