Skip to content

GeorgeAlestas/H0_Tension_Data

Folders and files

NameName
Last commit message
Last commit date

Latest commit

 

History

32 Commits
 
 
 
 
 
 
 
 
 
 
 
 

Repository files navigation

H0 Tension, Phantom Dark Energy and Cosmological Parameter Degeneracies

Travis

This is the repository that contains the Mathematica code as well as useful comments that reproduce the figures of arxiv:2004.08363.

Abstract

Phantom dark energy ($w<-1$) can produce amplified cosmic acceleration at late times, thus increasing the value of $H_0$ favored by CMB data and releasing the tension with local measurements of $H_0$. We show that the best fit value of $H_0$ in the context of the CMB power spectrum is degenerate with a constant equation of state parameter $w$, in accordance with the approximate effective linear equation $H_0 + 30.93 w - 36.47 = 0$ ($H_0$ in $km sec^{-1} Mpc^{-1}$). This equation is derived by assuming that both $\Omega_{0 \rm m}h^2$ and $d_A=\int_0^{z_{rec}}\frac{dz}{H(z)}$ remain constant (for invariant CMB spectrum) and equal to their best fit Planck/$\Lambda$ CDM values as $H_0$, $\Omega_{0 \rm m}$ and $w$ vary. For $w=-1$, this linear degeneracy equation leads to the best fit $H_0=67.4 km sec^{-1} Mpc^{-1}$ as expected. For $w=-1.22$ the corresponding predicted CMB best fit Hubble constant is $H_0=74 km sec^{-1} Mpc^{-1}$ which is identical with the value obtained by local distance ladder measurements while the best fit matter density parameter is predicted to decrease since $\Omega_{0 \rm m}h^2$ is fixed. We verify the above $H_0-w$ degeneracy equation by fitting a $w$CDM model with fixed values of $w$ to the Planck TT spectrum showing also that the quality of fit ($\chi^2$) is similar to that of $\Lambda$ CDM. However, when including SnIa, BAO or growth data the quality of fit becomes worse than \lcdm when $w< -1$. Finally, we generalize the $H_0-w(z)$ degeneracy equation for the parametrization $w(z)=w_0+w_1 z/(1+z)$ and identify analytically the full $w_0-w_1$ parameter region (straight line) that leads to a best fit $H_0=74 km sec^{-1} Mpc^{-1}$ in the context of the Planck CMB spectrum. This exploitation of $H_0-w(z)$ degeneracy can lead to immediate identification of all parameter values of a given $w(z)$ parametrization that can potentially resolve the $H_0$ tension.

Citing the paper

If you use any of the above codes or the figures in a published work please cite the following paper:
H0 Tension, Phantom Dark Energy and Cosmological Parameter Degeneracies
George Alestas, Lavrentios Kazantzidis and Leandros Perivolaropoulos, arxiv:2004.08363

Any further questions/comments are welcome.

Authors List

George Alestas - g.alestas@uoi.gr
Lavrentios Kazantzidis - l.kazantzidis@uoi.gr
Leandros Perivolaropoulos - leandros@uoi.gr

About

This repository contains the Mathematica and MGCAMB files of arXiv:2004.08363

Topics

Resources

License

Stars

Watchers

Forks