New Constraints on Preferred Frame Effects from Binary Pulsars
  Preferred frame effects (PFEs) are predicted by a number of alternative gravity theories which include vector or additional tensor fields, besides the canonical metric tensor. In the framework of parametrized post-Newtonian (PPN) formalism, we investigate PFEs in the orbital dynamics of binary pulsars, characterized by the two strong-field PPN parameters, \alpha_1 and \alpha_2. In the limit of a small orbital eccentricity, \alpha_1 and \alpha_2 contributions decouple. By utilizing recent radio timing results and optical observations of PSRs J1012+5307 and J1738+0333, we obtained the best limits of \alpha_1 and \alpha_2 in the strong-field regime. The constraint on \alpha_1 also surpasses its counterpart in the weak-field regime. 
Lijing Shao, Norbert Wex, Michael Kramer
gr-qc astro-ph.HE