The suppression of neutralino annihilation into Zh

The indirect detection of neutralino dark matter is most promising through annihilation channels producing a hard energy spectrum for the detected particles, such as neutralino annihilation into Zh. A cancellation however makes this particular annihilation channel generically subdominant in the huge parameter space of supersymmetric models. This cancellation requires non-trivial relations between neutralino mixings and masses, which we derive from gauge independence and unitarity of the MSSM. To show how the cancellation overshoots leaving only a subdominant result, we use a perturbative expansion in powers of the electroweak/supersymmetry breaking ratio m(Z)/m(chi).