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Planck 2015 constraints on spatially-flat dynamical dark energy models

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Abstract

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 \(\varLambda \)CDM and both better fit the TT + lowP + lensing + BAO data than does the standard tilted flat-\(\varLambda \)CDM model, with \(\Delta \chi ^{2} = -1.26\ (-1.60)\) for the XCDM (\(\phi \)CDM) model relative to the \(\varLambda \)CDM model. While this is a 1.1\(\sigma \) (1.3\(\sigma \)) improvement over standard \(\varLambda \)CDM and so not significant, dynamical dark energy models cannot 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.

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Notes

  1. Using a physically consistent non-flat inflation model (Gott 1982; Hawking 1984; Ratra 1985) power spectrum of energy density inhomogeneities (Ratra and Peebles 1995; Ratra 2017) to analyse the Planck 2015 cosmic microwave background (CMB) anisotropy measurements (Ade et al. 2016), Ooba et al. (2018a) find that these data do not require flat spatial hypersurfaces in the six parameter non-flat \(\varLambda \)CDM model (also see Park and Ratra 2019a,b,d). In the non-flat \(\varLambda \)CDM model, compared to the standard flat-\(\varLambda \)CDM model, there is no simple tilt option so \(n_{\mathrm{s}}\) is no longer a free parameter and it is instead replaced by the current value of the spatial curvature energy density parameter \(\varOmega _{\mathrm{k}}\). CMB anisotropy data also do not require flat spatial hypersurfaces in the seven parameter non-flat XCDM and \(\phi \)CDM inflation models (Ooba et al. 2018b,c; Park and Ratra 2018, 2019b,d). In both these models \(n_{\mathrm{s}}\) is again replaced by \(\varOmega _{\mathrm{k}}\). These models differ from the seven parameter spatially-flat XCDM and \(\phi \)CDM inflation models we study in this paper, in which \(n_{\mathrm{s}}\) is a parameter but \(\varOmega _{ \mathrm{k}}\) is not.

  2. Amongst these analyses that also make use of CMB anisotropy data, those that have used a physically consistent dynamical dark energy model such as \(\phi \)CDM (Solà et al. 2017b,c; Solà and de Cruz Pérez 2017; Gómez-Valent and Solà 2017) have performed only an approximate CMB anisotropy analysis.

  3. While XCDM is often used to model dynamical dark energy, it is not a physically consistent model as it cannot describe the evolution of energy density inhomogeneities. Also, XCDM does not accurately model \(\phi \)CDM dark energy dynamics (Podariu and Ratra 2001).

  4. Aside from CMB anisotropy measurements, many other observations have been used to constrain the \(\phi \)CDM model (see, e.g., Chen and Ratra 2004, 2011b; Samushia et al. 2007; Yashar et al. 2009; Samushia and Ratra 2010; Farooq and Ratra 2013; Pavlov et al. 2014; Avsajanishvili et al. 2015; Farooq et al. 2017; Solà et al. 2017b,c; Solà and de Cruz Pérez 2017; Zhai et al. 2017; Gómez-Valent and Solà 2017; Avsajanishvili et al. 2017; Ryan et al. 2018, 2019; Park and Ratra 2019c,d; Khadka and Ratra 2019).

  5. Our flat space \(\phi \)CDM CMB anisotropy angular power spectra differ somewhat from earlier results in Brax et al. (2000) and Mukherjee et al. (2003). We have verified that our results are accurate.

  6. We thank C.-G. Park for pointing out a numerical error in our initial CMB only \(\phi \)CDM analyses. Our corrected results here are in very good agreement with those of Park and Ratra (2018).

  7. See Penton et al. (2018) for a discussion of how observed deuterium abundances can be used to constrain spatial curvature.

  8. Closed-\(\phi \)CDM is also the best fitting of the three closed models when BAO data is included (Ooba et al. 2018c).

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Acknowledgements

We thank G. Horton-Smith and C.-G. Park for helpful discussions. We thank the referee for comments that helped us improve the paper. This work is supported by Grants-in-Aid for Scientific Research from JSPS (Nos. 16J05446 (J.O.) and 15H05890 (N.S.)). B.R. is supported in part by DOE grant DE-SC0019038.

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Correspondence to Junpei Ooba.

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Ooba, J., Ratra, B. & Sugiyama, N. Planck 2015 constraints on spatially-flat dynamical dark energy models. Astrophys Space Sci 364, 176 (2019). https://doi.org/10.1007/s10509-019-3663-4

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