Fermion Zero Modes and Cosmological Constant

A general condition for the existence of fermion zero modes is derived for the M-5-brane, the M-2-brane and the D=4, N=2 Majumdar-Papapetrou 0-brane. The fermion zero modes of these p-branes do not exist if the supersymmetry spinor generator goes to a constant at the horizon and they exist only if it vanishes there. In particular it is shown that the fermion zero mode of the M-2-brane in D=11 can be forbidden from existence if Rarita-Schwinger gamma tracelessness condition is imposed on the gravitino field. Non-existence of fermion zero mode is interpreted, in analogy to the three dimensional example of Becker et.al., as a world with zero cosmological constant without supersymmetric excited states. Also derived are the spin of the M-5-brane and its 3-form electric and magnetic dipole moments.