GRB Hubble diagram and constraints on a \Lambda (t)CDM model
  In previous papers, a cosmological model with constant-rate particle creation
and vacuum term decaying linearly with the Hubble parameter was shown to lead
to a good concordance when tested against precise observations: the position of
the first peak in the spectrum of anisotropies of the cosmic microwave
background (CMB), the Hubble diagram for supernovas of type Ia (SNe Ia), the
distribution of large-scale structures (LSS) and the distance to the baryonic
acoustic oscillations (BAO). That model has the same number of parameters as
the spatially flat standard model and seems to alleviate some
observational/theoretical tensions appearing in the later. In this letter we
complement those tests with 109 gamma ray bursters (GRB), 59 of them with
redshifts above $z=1.4$, which permits to extend the Hubble diagram to
redshifts up to $z\approx 8$. For the calibration of the 50 GRBs with $z<1.4$
we use the 288 supernovas of the Sloan Digital Sky Survey (SDSS) project,
calibrated with the MLCS2k2 fitter, less model-dependent than other samples
like Union2. Our results show a good concordance with the previous tests and,
again, less tensions between SNe Ia and GRB best fits as compared to the
standard model.
