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Published October 15, 2006 | Published
Journal Article Open

Tidal tails test the equivalence principle in the dark-matter sector


Satellite galaxies currently undergoing tidal disruption offer a unique opportunity to constrain an effective violation of the equivalence principle in the dark sector. While dark matter in the standard scenario interacts solely through gravity on large scales, a new long-range force between dark-matter particles may naturally arise in theories in which the dark matter couples to a light scalar field. An inverse-square-law force of this kind would manifest itself as a violation of the equivalence principle in the dynamics of dark matter compared to baryons in the form of gas or stars. In a previous paper, we showed that an attractive force would displace stars outwards from the bottom of the satellite's gravitational potential well, leading to a higher fraction of stars being disrupted from the tidal bulge further from the Galactic center. Since stars disrupted from the far (near) side of the satellite go on to form the trailing (leading) tidal stream, an attractive dark-matter force will produce a relative enhancement of the trailing stream compared to the leading stream. This distinctive signature of a dark-matter force might be detected through detailed observations of the tidal tails of a disrupting satellite, such as those recently performed by the Two-Micron All-Sky Survey (2MASS) and Sloan Digital Sky Survey (SDSS) on the Sagittarius (Sgr) dwarf galaxy. Here we show that this signature is robust to changes in our models for both the satellite and Milky Way, suggesting that we might hope to search for a dark-matter force in the tidal features of other recently discovered satellite galaxies in addition to the Sgr dwarf.

Additional Information

© 2006 The American Physical Society (Received 2 August 2006; revised 21 September 2006; published 27 October 2006) We wish to thank Professors John Dubinski and Larry Widrow for assistance with the use of their code GALACTICS, and CITAzens Pat McDonanld, Neal Dalal, Christoph Pfrommer, and Jonathan Sievers for useful conversations. All computations were performed on CITA's McKenzie cluster [63], which was funded by the Canada Foundation for Innovation and the Ontario Innovation Trust. Kesden acknowledges support from the NASA Graduate Research Program, and the National Sciences and Engineering Research Coucil (NSERC) of Canada. Kamionkowski acknowledges support from the DoE DE-FG03-92-ER40701, NASA NNG05GF69G, and the Gordon and Betty Moore Foundation.

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