Robust constraints on dark energy and gravity from galaxy clustering
  data
  Galaxy clustering data provide a powerful probe of dark energy. We examine
how the constraints on the scaled expansion history of the universe,
x_h(z)=H(z)s (with s denoting the sound horizon at the drag epoch), and the
scaled angular diameter distance, x_d(z)=D_A(z)/s, depend on the methods used
to analyze the galaxy clustering data. We find that using the observed galaxy
power spectrum, P_g^{obs}(k), x_h(z) and x_d(z) are measured more accurately
and are significantly less correlated with each other, compared to using only
the information from the baryon acoustic oscillations (BAO) in P_g^{obs}(k).
Using the {x_h(z), x_d(z)} from P_g^{obs}(k) gives a DETF dark energy FoM
approximately a factor of two larger than using the {x_h(z), x_d(z)} from BAO
only; this provides a robust conservative method to go beyond BAO only in
extracting dark energy information from galaxy clustering data.
  We find that a Stage IV galaxy redshift survey, with 0.7<z<2 over 15,000
(deg)^2, can measure {x_h(z), x_d(z), f_g(z)G(z)\tilde{P}_0^{1/2}/s^4} with
high precision (where f_g(z) and G(z) are the linear growth rate and factor of
large scale structure respectively, and \tilde{P}_0 is the dimensionless
normalization of P_g^{obs}(k)), when redshift-space distortion information is
included. The measurement of f_g(z)G(z)\tilde{P}_0^{1/2}/s^4 provides a
powerful test of gravity, and significantly boosts the dark energy FoM when
general relativity is assumed.
