Impact of

Interference and mixing effects between neutral Higgs bosons in the MSSM with complex parameters are shown to have a significant impact on the interpretation of LHC searches for additional Higgs bosons. Complex MSSM parameters introduce mixing between the $$\mathcal {CP}$$-even and $$\mathcal {CP}$$-odd Higgs states h, H, A into the mass eigenstates $$h_1, h_2, h_3$$ and generate $$\mathcal {CP}$$-violating interference terms. Both effects are enhanced in the case of almost degenerate states. Employing as an example an extension of a frequently used benchmark scenario by a non-zero phase $$\phi _{A_t}$$, the interference contributions are obtained for the production of neutral Higgs bosons in gluon-fusion and in association with b-quarks followed by the decay into a pair of $$\tau $$-leptons. While the resonant mixing increases the individual cross sections for the two heavy Higgs bosons $$h_2$$ and $$h_3$$, strongly destructive interference effects between the contributions involving $$h_2$$ and $$h_3$$ leave a considerable parameter region unexcluded that would appear to be ruled out if the interference effects were neglected