Gravitational radiation from compact binary systems in screened modified gravity

Screened modified gravity (SMG) is a kind of scalar-tensor theory with screening mechanisms, which can suppress the fifth force in dense regions and allow theories to evade the solar system and laboratory tests. In this paper, we investigate how the screening mechanisms in SMG affect the gravitational radiation damping effects, calculate in detail the rate of the energy loss due to the emission of tensor and scalar gravitational radiations, and derive their contributions to the change in the orbital period of the binary system. We find that the scalar radiation depends on the screened parameters and the propagation speed of scalar waves, and the scalar dipole radiation dominates the orbital decay of the binary system. For strongly self-gravitating bodies, all effects of scalar sector are strongly suppressed by the screening mechanisms in SMG. By comparing our results to observations of binary system PSR $\mathrm{J}1738+0333$, we place the stringent constraints on the screening mechanisms in SMG. As an application of these results, we focus on three specific models of SMG (chameleon, symmetron, and dilaton), and derive the constraints on the model parameters, respectively.

Figure 1

In the parameter space of the exponential chameleon model, the shadow region is allowed by the tests of the Cassini experiment, while the yellow region is allowed by the observations of PSR $\mathrm{J}1738+0333$. The combined constraints of the two experiments require $\alpha \ge 0.2$.

Figure 2

Lower bound on chameleon mass $m_s$ (upper bound on $m_s^{-1}$) as a function of the coupling constant $\beta$ from the constraints $\alpha \ge 0.2$ (green solid line) and Eq. (94) (blue dashed line).

Figure 3

Top: Upper bound on symmetron mass $m_s$ (lower bound on $m_s^{-1}$) as a function of the coupling constant $\lambda$ from the observations of PSR $\mathrm{J}1738+0333$. Bottom: In the parameter space of the symmetron model, the yellow region is allowed by the tests of Cassini experiment, while the shadow region is allowed by the observations of PSR $\mathrm{J}1738+0333$.