  We present results for Higgs boson pair production with variations of the
trilinear Higgs boson self-coupling at next-to-leading order (NLO) in QCD
including the full top quark mass dependence. Differential results at 14 TeV
are presented, and we discuss the implications of anomalous trilinear couplings
as well as differences between the PYTHIA 8.2 and HERWIG 7.1 parton showers in
combination with POWHEG. The implementation of the NLO QCD calculation with
variable Higgs boson self-coupling is made publicly available in the
POWHEG-BOX-V2 Monte Carlo framework. A simple method for using the new
implementation to study also variations of the top quark Yukawa coupling is
described.
