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An Effective Theory of Dirac Dark Matter | | Roni Harnik
; Graham D. Kribs
; | | Date: |
31 Oct 2008 | | Abstract: | A stable Dirac fermion with four-fermion interactions to leptons suppressed
by a scale Lambda ~ 1 TeV is shown to provide a viable candidate for dark
matter. The thermal relic abundance matches cosmology, while nuclear recoil
direct detection bounds are automatically avoided in the absence of (large)
couplings to quarks. The annihilation cross section in the early Universe is
the same as the annihilation in our galactic neighborhood. This allows Dirac
fermion dark matter to naturally explain the positron ratio excess observed by
PAMELA with a minimal boost factor, given present astrophysical uncertainties.
We use the Galprop program for propagation of signal and background; we discuss
in detail the uncertainties resulting from the propagation parameters and, more
importantly, the injected spectra. Fermi/GLAST has an opportunity to see a
feature in the gamma-ray spectrum at the mass of the Dirac fermion. The excess
observed by ATIC/PPB-BETS may also be explained with Dirac dark matter that is
heavy. A supersymmetric model with a Dirac bino provides a viable UV model of
the effective theory. The dominance of the leptonic operators, and thus the
observation of an excess in positrons and not in anti-protons, is naturally
explained by the large hypercharge and low mass of sleptons as compared with
squarks. Minimizing the boost factor implies the right-handed selectron is the
lightest slepton, which is characteristic of our model. Selectrons (or
sleptons) with mass less than a few hundred GeV are an inescapable consequence
awaiting discovery at the LHC. | | Source: | arXiv, 0810.5557 | | Services: | Forum | Review | PDF | Favorites | |
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