Interference effects in BSM processes

Many models beyond the SM predict new particles and the possibility for (approximate) degeneracies. In case of nearby resonances, interference effects between several unstable BSM particles may be relevant. However, the interference term is neglected by the standard narrow-width approximation (NWA).We have developed an extension of the usual NWA which allows for a consistent treatment of the interference term between nearly mass-degenerate states, including higher-order corrections. Phenomenological consequences of interference effects between neutral MSSM Higgs bosons will be presented. The two heavier states are quasi degenerate in a wide part of the parameter space. Therefore, especially in the MSSM with CP-violating complex phases, interference effects can have a significant impact on the interpretation of searches for additional Higgs bosons