Probing the cosmographic parameters to distinguish between dark energy
  and modified gravity models
  In this paper we investigate the deceleration, jerk and snap parameters to
distinguish between the dark energy and modified gravity models by using high
redshift gamma-ray bursts (GRBs) and supernovae (SNe). We first derive the
expressions of deceleration, jerk and snap parameters in dark energy and
modified gravity models. In order to constrain the cosmographic parameters, we
calibrate the GRB luminosity relations without assuming any cosmological models
using SNe Ia. Then we constrain the models (including dark energy and modified
gravity models) parameters using type Ia supernovae and gamma-ray bursts.
Finally we calculate the cosmographic parameters. GRBs can extend the redshift
- distance relation up to high redshifts, because they can be detected to high
redshifts.We find that the statefinder pair (r,s) could not be used to
distinguish between some dark energy and modified gravity models, but these
models could be differentiated by the snap parameter. Using the
model-independent constraints on cosmographic parameters, we conclude that the
\LambdaCDM model is consistent with the current data.
