An Effective Theory of Dirac Dark Matter

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A stable Dirac fermion with four-fermion interactions to leptons suppressed by a scale {Lambda} {approx} 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 ... continued below

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11 pages

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Harnik, Roni; /Stanford U., Phys. Dept. /SLAC; Kribs, Graham D.; U., /Oregon & , June 11, 2010.

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A stable Dirac fermion with four-fermion interactions to leptons suppressed by a scale {Lambda} {approx} 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.

Physical Description

11 pages

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  • Journal Name: Phys.Rev.D79:095007,2009

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  • Report No.: SLAC-PUB-13482
  • Grant Number: AC02-76SF00515
  • Office of Scientific & Technical Information Report Number: 981683
  • Archival Resource Key: ark:/67531/metadc1013344

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

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  • June 11, 2010

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  • Oct. 14, 2017, 8:36 a.m.

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  • Nov. 2, 2017, 8:11 p.m.

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Harnik, Roni; /Stanford U., Phys. Dept. /SLAC; Kribs, Graham D.; U., /Oregon & ,. An Effective Theory of Dirac Dark Matter, article, June 11, 2010; [California]. (digital.library.unt.edu/ark:/67531/metadc1013344/: accessed November 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.