“…Moreover, the use of standard adaptive mesh refinement techniques based on a posteriori error estimators is marred by the pollution effect [5,27]. Recently, Discontinuous Galerkin (DG) methods [14,24,34] have been increasingly applied to wave propagation problems in general [13] and the Helmholtz equation in particular [2,3,18,19,20,21] including hybridized DG approximations [23]. An a posteriori error analysis of DG methods for standard second order elliptic boundary value problems has been performed in [1,8,10,26,31,35], and a convergence analysis has been 1 provided in [9,25,32].…”