Synopsis: New forces in the dark sector

Interactions between dark matter particles may explain unusual matter-antimatter production rates in the universe.
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Recent experiments, including PAMELA, ATIC, WMAP, and EGRET, have revealed unusually high electron-positron production in the cosmos, more so than can be explained by mechanisms such as supernova explosions or cosmic-ray collisions. This discrepancy is leading some researchers to speculate that dark matter may play a part. Now, Nima Arkani-Hamed at the Institute for Advanced Study in Princeton, Douglas P. Finkbeiner and Tracy R. Slatyer at Harvard University, and Neal Weiner at New York University discuss in Physical Review D how these unusual observations can be consistent with a new kind of force between dark matter particles.

Cosmological theories and the observed dynamics of galaxies require dark matter, and particles called WIMPs (weakly interacting massive particles) are currently favored. One explanation for some of the excess particle-antiparticle amounts seen by satellites may be that dark matter particles are interacting with, and annihilating, each other. Such interactions, however, have to meet several criteria: cross sections for annihilation into leptons (like electrons and positrons) have to be large, yet cross sections for hadron production (e.g., protons, neutrons, pions) must be low. This means that data from PAMELA and others are difficult to explain with a simple picture of thermal WIMP interactions.

Arkani-Hamed et al. propose a new force between dark matter particles that is mediated by a force-carrying boson they call ϕ. Depending on its mass, ϕ can induce increased annihilation rates because the particle collisions can no longer be understood in a simple plane-wave approximation. If the mass of ϕ is on the order of few GeV, then significant increases or decreases in annihilation rates can occur. Although speculative, and one of several models vying to explain the data, the paper lays out ways to test the proposal against future observations. – David Voss


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