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Paper   IPM / Physic / 17666
School of Physics
  Title:   Negative Dark Energy Density from High Redshift Pantheon+ Supernovae
1.  M. Malekjani
2.  R. Mc Conville
3.  E. O Colgain
4.  S. Pourojaghi
5.  M.M. Sheikh-Jabbari
  Status:   Preprint
  Year:  2024
  Supported by:  IPM
Within the Friedmann-Lema\^itre-Robertson-Walker (FLRW) framework, the Hubble constant $H_0$ is an integration constant. Thus, mathematical consistency demands that $H_0$ is also observationally a constant. Building on earlier results, we demonstrate redshift evolution of flat $\Lambda$CDM cosmological parameters $(H_0, \Omega_{m})$ in Pantheon+ supernove (SN) in the redshift range $0 < z \lesssim 2.26$. We compare the whole SN sample and the SN sample split into low and high redshift subsamples demarcated by redshift $z_{\textrm{split}}$. We show that $z_{\textrm{split}}=1$ has a marginal Bayesian preference through the Akaike Information Criterion for evolution in $H_0$ (also $\Omega_m)$ compared to the whole sample. Such evolution is strictly forbidden in FLRW models. Through mock analysis, we estimate the evolution as a $ 1.4 \sigma$ effect ($p=0.08$), and the presence of $\Omega_m >1$ best fits, indicative of negative dark energy (DE) density, beyond $z_{\textrm{split}} =1$ as $1.3 \sigma$ ($p=0.1$) to $1.9 \sigma$ effects $(p=0.026$) depending on the criteria. {Finally, using complementary profile distributions we confirm a robust $> 2 \sigma$ shift in $H_0$ for SN with $z > 1$.

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