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Abstract: Observations of galaxies suggest a one-to-one analytic relation between theinferred gravity of dark matter at any radius and the enclosed baryonic mass, arelation summarized by Milgrom-s law of modified Newtonian dynamics MOND.However, present-day covariant versions of MOND usually require some additionalfields contributing to the geometry, as well as an additional hot dark mattercomponent to explain cluster dynamics and cosmology. Here, we envisage aslightly more mundane explanation, suggesting that dark matter does exist butis the source of MOND-like phenomenology in galaxies. We assume a canonicalaction for dark matter, but also add an interaction term between baryonicmatter, gravity, and dark matter, such that standard matter effectively obeysthe MOND field equation in galaxies. We show that even the simplest realizationof the framework leads to a model which reproduces some phenomenologicalpredictions of cold dark matter CDM and MOND at those scales where these aremost successful. We also devise a more general form of the interaction term,introducing the medium density as a new order parameter. This allows for newphysical effects which should be amenable to observational tests in the nearfuture. Hence, this very general framework, which can be furthermore related toa generalized scalar-tensor theory, opens the way to a possible unification ofthe successes of CDM and MOND at different scales.

Autor: Jean-Philippe Bruneton, Stefano Liberati, Lorenzo Sindoni, Benoit Famaey


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