A tighter constraint on post-Newtonian gravity using millisecond pulsars

Some theories of gravity predict the existence of preferred-frame effects and violations of conservation of energy and momentum. General relativity predicts no such effects. In the parameterized post-Newtonian (PPN) formalism, the parameter alpha(3) = 0 if these effects do not exist. The period derivatives (P over dot) of millisecond pulsars are used to more tightly constrain these effects by showing that \alpha(3)\ < 5 x 10(-16).