  We use the observed anisotropic clustering of galaxies in the Baryon
Oscillation Spectroscopic Survey (BOSS) Data Release 11 CMASS sample to measure
the linear growth rate of structure, the Hubble expansion rate and the comoving
distance scale. Our sample covers 8498 ${\rm deg}^2$ and encloses an effective
volume of 6.0 ${\rm Gpc}^3$ at an effective redshift of $\bar{z} = 0.57$. We
find $f\sigma_8 = 0.441 \pm 0.044$, $H = 93.1 \pm 3.0\ {\mathrm{km}\
\mathrm{s}^{-1} \mathrm{Mpc}^{-1}}$ and $D_{\rm A} = 1380 \pm 23\ {\rm Mpc}$
when fitting the growth and expansion rate simultaneously. When we fix the
background expansion to the one predicted by spatially-flat $\Lambda$CDM model
in agreement with recent Planck results, we find $f\sigma_8 = 0.447 \pm 0.028$
(6 per cent accuracy). While our measurements are generally consistent with the
predictions of $\Lambda$CDM and General Relativity, they mildly favor models in
which the strength of gravitational interactions is weaker than what is
predicted by General Relativity. Combining our measurements with recent cosmic
microwave background data results in tight constraints on basic cosmological
parameters and deviations from the standard cosmological model. Separately
varying these parameters, we find $w = -0.983 \pm 0.075$ (8 per cent accuracy)
and $\gamma = 0.69 \pm 0.11$ (16 per cent accuracy) for the effective equation
of state of dark energy and the growth rate index, respectively. Both
constraints are in good agreement with the standard model values of $w=-1$ and
$\gamma = 0.554$.
