TY - JOUR
T1 - Difficulties distinguishing dark energy from modified gravity via redshift distortions
AU - Simpson, Fergus
AU - Peacock, John A.
PY - 2010/2/3
Y1 - 2010/2/3
N2 - The bulk motion of galaxies induced by the growth of cosmic structure
offers a rare opportunity to test the validity of general relativity
across cosmological scales. However, modified gravity can be degenerate
in its effect with the unknown values of cosmological parameters. More
seriously, even the “observed” value of the redshift-space
distortions used to measure the fluctuation growth rate depends on the
assumed cosmological parameters (the Alcock-Paczynski effect). We give a
full analysis of these issues, showing how to combine redshift-space
distortions with baryon acoustic oscillations and CMB data, in order to
obtain joint constraints on deviations from general relativity and on
the equation of state of dark energy while allowing for factors such as
nonzero curvature. In particular we note that the evolution of
Ωm(z), along with the Alcock-Paczynski effect, produces
a degeneracy between the equation of state w and the modified growth
parameter γ. Typically, the total marginalized error on either of
these parameters will be larger by a factor ≃2 compared to the
conditional error where one or the other is held fixed. We argue that
future missions should be judged by their figure of merit as defined in
the wp-γ plane, and note that the inclusion of spatial
curvature can degrade this value by an order of magnitude.
AB - The bulk motion of galaxies induced by the growth of cosmic structure
offers a rare opportunity to test the validity of general relativity
across cosmological scales. However, modified gravity can be degenerate
in its effect with the unknown values of cosmological parameters. More
seriously, even the “observed” value of the redshift-space
distortions used to measure the fluctuation growth rate depends on the
assumed cosmological parameters (the Alcock-Paczynski effect). We give a
full analysis of these issues, showing how to combine redshift-space
distortions with baryon acoustic oscillations and CMB data, in order to
obtain joint constraints on deviations from general relativity and on
the equation of state of dark energy while allowing for factors such as
nonzero curvature. In particular we note that the evolution of
Ωm(z), along with the Alcock-Paczynski effect, produces
a degeneracy between the equation of state w and the modified growth
parameter γ. Typically, the total marginalized error on either of
these parameters will be larger by a factor ≃2 compared to the
conditional error where one or the other is held fixed. We argue that
future missions should be judged by their figure of merit as defined in
the wp-γ plane, and note that the inclusion of spatial
curvature can degrade this value by an order of magnitude.
UR - http://www.scopus.com/inward/record.url?scp=77749330075&partnerID=8YFLogxK
U2 - 10.1103/PhysRevD.81.043512
DO - 10.1103/PhysRevD.81.043512
M3 - Article
VL - 81
JO - Physical Review D
JF - Physical Review D
SN - 1550-7998
IS - 4
M1 - 043512
ER -