New limits on the violation of the Strong Equivalence Principle in strong field regimes

The Strong Equivalence Principle (SEP) demands, besides the validity of the Einstein Equivalence Principle, that all self-gravitating bodies feel the same acceleration in an external gravitational field. It has been found that metric theories of gravity other that than general relativity typically predict a violation of the SEP. In case of the Earth-Moon system (weak field system) this violation is called the Nordtvedt effect. It has been shown by Damour and Schäfer, that small-eccentricity long-orbital-period binary pulsars with a white dwarf companion provide excellent conditions to test the SEP in strong field regimes. Based on newly discovered binary pulsars this paper investigates a possible violation of the SEP in strong field regimes. New limits with an improved confidence level are presented. The results of this paper lead to constrains on the combination $ε/2-ζ$ of the only two (post)$^2$-Newtonian parameters $ε$ and $ζ$ that arise from the (post)$^2$-Newtonian approximation of the tensor-multi-scalar theory of Damour and Esposito-Far{è}se.