Lattice calculations allow us to probe the low-lying, non-perturbative spectrum of QCD
using first principles numerical calculations. Here we present the low-lying spectrum
in the scalar sector with vacuum quantum numbers, including in fully dynamical QCD for
the first time the mixing between glueball, q-qbar, and meson-meson states.
As lattice calculations are necessarily restricted to finite-volume, we want to connect
the spectrum of QCD in a cubic volume to infinite-volume resonance parameters.
For this, we apply Lüscher's formalism for relating stationary state energies in
finite-volume to the infinite-volume scattering matrix to elastic K-pi scattering, where
the partial wave mixing induced by the finite-volume is included for $\ell < 3$.