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<B>High Energy-Astrophysics</B><br><I>Equivalence Principle and Cosmic Acceleration</I>

Monday, April 6, 2009
12:00 AM
335 West Hall

Speaker: Lam Hui, Columbia University

Current ideas on modifying general relativity to explain the observed cosmic acceleration all require introducing new gravitational degrees of freedom, most commonly a light scalar field. Such a scalar field, while active on large scales to somehow drive acceleration, must be screened on small scales to match solar system and terrestrial experiments. These generalized scalar-tensor theories encompass both f(R) and extra-dimensional models such as DGP, where the graviton effectively has a resonance width. I will show how such generalized scalar-tensor theories generically lead to violations of the equivalence principle, and for certain screening mechanisms, the violations are order *unity* - such theories are nonetheless consistent with existing constraints, but lend themselves to interesting new astronomical tests. The most promising objects to study are galaxies in cosmic voids.