Monopole radiation in modified gravity

Modifications to General Relativity typically introduce a scalar degree of freedom. Experimental constraints require that the "fifth" force produced by this field must be screened in high density environments. An important consequence of the screening mechanism is that the scalar charge of a spherically symmetric expanding or pulsating object, such as a supernova or variable star, is not conserved and monopole radiation can be emitted thereby. We calculate the energy loss rate due to scalar monopole radiation in supernovae and variable stars for a generalized model of f(R) gravity in which the matter coupling strength beta is allowed to be much larger than unity. For models which become screened at the gravitational potential of our galaxy, monopole radiation constraints require beta < 100.