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 the 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 $m_{Z}/m_{\chi}$. 
Benjamin Labonne, Emmanuel Nezri, Jean Orloff