a coupling to the Higgs. We show that current phenomenological bounds preclude this possibility. 

There are two potential options. The first is decoupling the Zino by making it heavy while tuning the photino mass to be ∼ µ . This implies taking the limit where M$_{1}$ and M$_{2}$ are large while the combination M$_{1}$c 2 w + M$_{2}$s 2 w stays small, which requires sgn( M$_{1}$ ) ̸ = sgn( M$_{2}$ ). Then the Zino-photino mixing will go like ( M$_{1}$ − M$_{2}$ ) /m$_{˜}$ $_{Z}$> O (1). Note that we are free to take M$_{1}$ < m$_{Z}$ to suppress this mixing, but due to the LEP bound on the chargino mass, M$_{2}$ > m$_{Z}$ . The second option is to try to eliminate the photino-Zino mixing by taking M$_{1}$ = M$_{2}$ . Then the Zino and photino have the same mass and the Higgsino will mix with both, resulting in a DM state which is an equal admixture of all 4 gauge eigenstates. Therefore, a neutralino cannot be a mixture of only photino and Higgsino. 

[1] E. Komatsu et al. (WMAP), Astrophys. J. Suppl. 180 , 330 (2009), 0803.0547. 

[2] O. Adriani et al. (PAMELA), Nature 458 , 607 (2009), 0810.4995. 

[3] A. A. Abdo et al. (The Fermi LAT), Phys. Rev. Lett. 102 , 181101 (2009), 0905.0025. 

[4] R. Bernabei et al. (DAMA), Phys. Lett. B480 , 23 (2000). 

[5] R. Bernabei et al. (DAMA), Eur. Phys. J. C56 , 333 (2008), 0804.2741. 

[6] B. W. Lee and S. Weinberg, Phys. Rev. Lett. 39 , 165 (1977). 

[7] G. Servant and T. M. P. Tait, New J. Phys. 4 , 99 (2002), hep-ph/0209262. 

[8] S. P. Martin (1997), hep-ph/9709356. 

[9] N. Arkani-Hamed, A. Delgado, and G. F. Giudice, Nucl. Phys. B741 , 108 (2006), hep- ph/0601041. 

[10] T. Moroi and L. Randall, Nucl. Phys. B570 , 455 (2000), hep-ph/9906527. 

[11] R. Catena and P. Ullio (2009), 0907.0018. 

[12] P. Salucci, F. Nesti, G. Gentile, and C. F. Martins (2010), 1003.3101. 

[13] R. J. Gaitskell, Ann. Rev. Nucl. Part. Sci. 54 , 315 (2004). 

[14] G. Jungman, M. Kamionkowski, and K. Griest, Phys. Rept. 267 , 195 (1996), hep-ph/9506380. 

[15] V. Barger, W.-Y. Keung, and G. Shaughnessy, Phys. Rev. D78 , 056007 (2008), 0806.1962. 

[16] G. Belanger, E. Nezri, and A. Pukhov, Phys. Rev. D79 , 015008 (2009), 0810.1362. 

