Resonances in coupled-channel scattering from lattice QCD

Understanding the excited spectrum of hadrons from first principles remains a challenging prospect. The majority of excited hadrons are seen as resonances in the scattering of lighter stable hadrons like pions and kaons. Many resonances decay into multiple final states necessitating coupled-channel analyses, and recently it has become possible to obtain coupled-channel scattering amplitudes from lattice QCD. I will describe the methods used in these calculations, to first compute large spectra, that are then used to constrain scattering t-matrices, from which the complex resonance poles can be extracted. Several recent applications of these methods will be described, including the first extraction of a strongly-coupled scattering amplitude from QCD where an a0 resonance was found in coupled-channel pi-eta K-Kbar scattering.