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Register a new user$Lambda_{rm s}$CDM model: $Lambda$CDM model with a sign switching cosmological `constant
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Added by
\\\"Ozg\\\"ur Akarsu
Publication date
2021
fields
Physics
and research's language is
English
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Inspired by the recent conjecture that the universe has transitioned from AdS vacua to dS vacua in the late universe made via graduated dark energy, we extend the $Lambda$CDM model by a cosmological `constant ($Lambda_{rm s}$) that switches sign at certain redshift, $z_dagger$, and name it as $Lambda_{rm s}$CDM. We discuss the construction and theoretical features of this model, and find out that, when the consistency of $Lambda_{rm s}$CDM with the CMB data is ensured, (i) $z_daggergtrsim1.1$ is implied by the condition that the universe monotonically expands, (ii) $H_0$ is inversely correlated with $z_dagger$ and reaches $approx74.5~{rm km, s^{-1}, Mpc^{-1}}$ for $z_dagger=1.5$, (iii) $H(z)$ presents an excellent fit to the Ly-$alpha$ measurements provided that $z_daggerlesssim 2.34$. We further investigate the model constraints by using the full Planck CMB data, with and without BAO data. We find that the CMB data alone does not constrain $z_dagger$ but CMB+BAO dataset favors the sign switch of $Lambda_{rm s}$ providing the constraint: $z_dagger=2.44pm0.29$ (68% CL). Our analysis reveals that the lower and upper limits of $z_dagger$ are controlled by the Galaxy and Ly-$alpha$ BAO measurements, respectively, and the larger $z_{dagger}$ values imposed by the Galaxy BAO data prevent the model from achieving the highest local $H_0$ measurements. In general, $Lambda_{rm s}$CDM (i) relaxes the $H_0$ tension while being fully consistent with the TRGB measurement, (ii) removes the discrepancy with the Ly-$alpha$ measurements, (iii) relaxes the $S_8$ tension, and (iv) finds a better agreement with the BBN constraints of physical baryon density. We find no strong statistical evidence to discriminate between the $Lambda_{rm s}$CDM and $Lambda$CDM models. However, interesting and promising features of $Lambda_{rm s}$CDM provide an upper edge over $Lambda$CDM.
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