We determine constraints on spatially-flat tilted dynamical dark energy XCDM and \phi CDM inflation models by analyzing Planck 2015 cosmic microwave background ( CMB ) anisotropy data and baryon acoustic oscillation ( BAO ) distance measurements .
XCDM is a simple and widely used but physically inconsistent parameterization of dynamical dark energy , while the \phi CDM model is a physically consistent one in which a scalar field \phi with an inverse power-law potential energy density powers the currently accelerating cosmological expansion .
Both these models have one additional parameter compared to standard \Lambda CDM and both better fit the TT + lowP + lensing + BAO data than does the standard tilted flat- \Lambda CDM model , with \Delta \chi ^ { 2 } = -1.26 ( -1.60 ) for the XCDM ( \phi CDM ) model relative to the \Lambda CDM model .
While this is a 1.1 \sigma ( 1.3 \sigma ) improvement over standard \Lambda CDM and so not significant , dynamical dark energy models can not be ruled out .
In addition , both dynamical dark energy models reduce the tension between the Planck 2015 CMB anisotropy and the weak lensing \sigma _ { 8 } constraints .