Pulsar Constraints on Screened Modified Gravity

We calculate the rate of energy loss from compact astrophysical objects due to a scalar field in screened modified gravity models of the chameleon, dilaton and symmetron types. The cosmological evolution of the field results in a time-variation of the scalar charge of screened objects implying the emission of scalar radiation. Focusing on binary objects, this leads to an additional decay in the orbital period complementing that due to the emission of gravitational waves. Using the Hulse-Taylor binary pulsar, the double pulsar PSR J0737-3039 and the pulsar-white dwarf system PSR J1738+033, we find a new observational bound on the time variation of the scalar charge of the earth in the Milky Way. We then translate this into a new bound on the range of the scalar interaction in the Milky Way. Ultimately, we find that pulsar tests are not competitive with current observational constraints.