UC Irvine

We supplement the minimal supersymmetric standard model (MSSM) with vectorlike copies of standard model particles. Such fourth generation particles can raise the Higgs boson mass to the observed value without requiring very heavy superpartners, improving naturalness and the prospects for discovering supersymmetry at the LHC. Here we show that these new particles are also motivated cosmologically: in the MSSM, pure bino dark matter typically overcloses the Universe, but fourth generation particles open up new annihilation channels, allowing binos to have the correct thermal relic density without resonances or coannihilation. We show that this can be done in a sizable region of parameter space while preserving gauge coupling unification and satisfying constraints from collider, Higgs, precision electroweak, and flavor physics.