Dark matter and dark radiation
We explore the feasibility and astrophysical consequences of a new long-range U(1) gauge field ("dark electromagnetism") that couples only to dark matter, not to the standard model. The dark matter consists of an equal number of positive and negative charges under the new force, but annihilations are suppressed if the dark-matter mass is sufficiently high and the dark fine-structure constant α^ is sufficiently small. The correct relic abundance can be obtained if the dark matter also couples to the conventional weak interactions, and we verify that this is consistent with particle-physics constraints. The primary limit on alpha^ comes from the demand that the dark matter be effectively collisionless in galactic dynamics, which implies α^<~10^-3 for TeV-scale dark matter. These values are easily compatible with constraints from structure formation and primordial nucleosynthesis. We raise the prospect of interesting new plasma effects in dark-matter dynamics, which remain to be explored.
Additional Information© 2009 The American Physical Society. Received 16 December 2008; published 23 January 2009. We are very grateful to Sonny Mantry for collaboration in the early stages of this work, and to Jonathan Feng, George Field, Josh Frieman, Manoj Kaplinghat, Keith Lee, Arvind Rajaraman, and Mark Wise for helpful comments. This work was supported by Department of Energy Project No. DE-FG03-92-ER40701 and the Gordon and Betty Moore Foundation.
Published - ACKprd09.pdf