Pseudo-Dirac bino dark matter

While the bino-dominated lightest neutralino of the minimal supersymmetric standard model (MSSM) is an interesting and widely studied candidate of dark matter, the p-wave suppression of its annihilation cross section requires fine-tuning of the MSSM spectra to be consistent with Wilkinson Microwave Anisotropy Probe (WMAP) observations. We propose a pseudo-Dirac bino that arises in theories with D-type supersymmetry breaking as an intriguing alternative candidate of dark matter. The pseudo-Dirac nature of the bino gives a natural mechanism of enhanced coannihilation because these two states are degenerate in the absence of electroweak symmetry breaking. In addition, the lightest state can be consistent with limits of direct-detection experiments because of the lack of vector interactions, as with the case of the MSSM bino.