Constraints on dark energy from the Ly{\alpha} forest baryon acoustic
  oscillations measurement of the redshift 2.3 Hubble parameter
  We use the Busca et al. (2012) measurement of the Hubble parameter at
redshift z = 2.3 in conjunction with 21 lower z measurements, from Simon et al.
(2005), Gaztanaga et al. (2009), Stern et al. (2010), and Moresco et al.
(2012), to place constraints on model parameters of constant and time-evolving
dark energy cosmological models. The inclusion of the new Busca et al. (2012)
measurement results in H(z) constraints significantly more restrictive than
those derived by Farooq et al. (2012). These H(z) constraints are now more
restrictive than those that follow from current Type Ia supernova (SNIa)
apparent magnitude measurements (Suzuki et al. 2012). The H(z) constraints by
themselves require an accelerating cosmological expansion at about 2-sigma
confidence level, depending on cosmological model and Hubble constant prior
used in the analysis. A joint analysis of H(z), baryon acoustic oscillation
peak length scale, and SNIa data favors a spatially-flat cosmological model
currently dominated by a time-independent cosmological constant but does not
exclude slowly-evolving dark energy density.
