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.
