Hints of dark energy anisotropic stress using Machine Learning. (arXiv:2001.11420v3 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Arjona_R/0/1/0/all/0/1">Rubén Arjona</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nesseris_S/0/1/0/all/0/1">Savvas Nesseris</a>
Recent analyses of the Planck data and quasars at high redshifts have
suggested possible deviations from the flat $Lambda$ cold dark matter model
($Lambda$CDM), where $Lambda$ is the cosmological constant. Here we use
machine learning methods to investigate any possible deviations from
$Lambda$CDM at both low and high redshifts by using the latest cosmological
data. Specifically, we apply the Genetic Algorithms to explore the nature of
dark energy (DE) in a model independent fashion by reconstructing its equation
of state $w(z)$, the growth index of matter density perturbations $gamma(z)$,
the linear DE anisotropic stress $eta_textrm{DE}(z)$ and the adiabatic sound
speed $c_textrm{s,DE}^2(z)$ of DE perturbations. We find a $sim2sigma$
deviation of $w(z)$ from -1 at high redshifts, the adiabatic sound speed is
negative at the $sim2.5sigma$ level at $z=0.1$ and a $sim2sigma$ deviation
of the anisotropic stress from unity at low redshifts and $sim4 sigma$ at
high redshifts. These results hint towards either the presence of an
non-adiabatic component in the DE sound speed or the presence of DE anisotropic
stress, thus hinting at possible deviations from the $Lambda$CDM model.
Recent analyses of the Planck data and quasars at high redshifts have
suggested possible deviations from the flat $Lambda$ cold dark matter model
($Lambda$CDM), where $Lambda$ is the cosmological constant. Here we use
machine learning methods to investigate any possible deviations from
$Lambda$CDM at both low and high redshifts by using the latest cosmological
data. Specifically, we apply the Genetic Algorithms to explore the nature of
dark energy (DE) in a model independent fashion by reconstructing its equation
of state $w(z)$, the growth index of matter density perturbations $gamma(z)$,
the linear DE anisotropic stress $eta_textrm{DE}(z)$ and the adiabatic sound
speed $c_textrm{s,DE}^2(z)$ of DE perturbations. We find a $sim2sigma$
deviation of $w(z)$ from -1 at high redshifts, the adiabatic sound speed is
negative at the $sim2.5sigma$ level at $z=0.1$ and a $sim2sigma$ deviation
of the anisotropic stress from unity at low redshifts and $sim4 sigma$ at
high redshifts. These results hint towards either the presence of an
non-adiabatic component in the DE sound speed or the presence of DE anisotropic
stress, thus hinting at possible deviations from the $Lambda$CDM model.
http://arxiv.org/icons/sfx.gif
