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Deviation from the cosmological constant or systematic errors?

Authors

  • Shi Qi,

    Corresponding author
    1. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China
    2. Joint Center for Particle, Nuclear Physics and Cosmology, Nanjing University – Purple Mountain Observatory, Nanjing 210093, China
    3. Kavli Institute for Theoretical Physics China, CAS, Beijing 100190, China
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  • Tan Lu,

    Corresponding author
    1. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China
    2. Joint Center for Particle, Nuclear Physics and Cosmology, Nanjing University – Purple Mountain Observatory, Nanjing 210093, China
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  • Fa-Yin Wang

    Corresponding author
    1. Department of Astronomy, Nanjing University, Nanjing 210093, China
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E-mail: qishi11@gmail.com (SQ); t.lu@pmo.ac.cn (TL); fayinwang@nju.edu.cn (F-YW)

ABSTRACT

In the work of Qi, Wang & Lu, gamma-ray bursts (GRBs) are used together with an earlier Type Ia supernova (SN Ia) data set to constrain the dark energy equation of state (EOS) in a nearly model-independent way. The improvements made by including GRBs show a slight shift of the dark energy EOS toward w > −1 at redshifts z≳ 0.5. It is interesting that, when we have more SNe Ia, SNe Ia themselves also show the same trend. Motivated by the fact that both SNe Ia and GRBs seem to prefer a dark energy EOS greater than −1 at redshifts z≳ 0.5, we perform a careful investigation of this situation, including more careful treatments of measurement errors of GRBs and cross-checking the results by using different ways of including GRBs. We find that the deviation of dark energy from the cosmological constant at redshifts z≳ 0.5 is large enough that we should pay close attention to it with future observational data. Such a deviation may arise from some biasing systematic errors in the handling of SNe Ia and/or GRBs, or more interestingly from the nature of the dark energy itself.

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