Interpreting cosmological tensions from the effective field theory of torsional gravity. (arXiv:1909.06388v1 [astro-ph.CO])

Interpreting cosmological tensions from the effective field theory of torsional gravity. (arXiv:1909.06388v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yan_S/0/1/0/all/0/1">Sheng-Feng Yan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_P/0/1/0/all/0/1">Pierre Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chen_J/0/1/0/all/0/1">Jie-Wen Chen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_X/0/1/0/all/0/1">Xin-Zhe Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cai_Y/0/1/0/all/0/1">Yi-Fu Cai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Saridakis_E/0/1/0/all/0/1">Emmanuel N. Saridakis</a>

Cosmological tensions can arise within $Lambda$CDM scenario amongst
different observational windows, such as measurements of the $H_0$ and
$sigma_8$ parameters. These tensions, if finally confirmed by measurements,
may indicate new physics beyond the standard paradigm. In this Letter, we
report how to alleviate both the $H_0$ and $sigma_8$ tensions simultaneously
within torsional gravity from the perspective of effective field theory (EFT).
We apply the EFT approach, which allows to investigate the evolution equations
at the background and perturbation levels in a systematic way, and examine the
conditions followed by the coefficients of various possibly involved operators
such that cosmological tensions can be relaxed. Following these observations we
construct concrete models of Lagrangians of torsional gravity. Specifically, we
consider the parametrization $f(T)=-T -2Lambda/M_P^2 +alpha T^beta$, where
two out of the three parameters are independent (in which an additional term of
the form $cT^{1/2}$ can be added). This model can efficiently fit observations
solving all statistical tensions. To our knowledge, this is the first time
where a modified gravity theory can alleviate both $H_0$ and $sigma_8$
tensions simultaneously, hence offering an additional argument in favor of
gravitational modification.

Cosmological tensions can arise within $Lambda$CDM scenario amongst
different observational windows, such as measurements of the $H_0$ and
$sigma_8$ parameters. These tensions, if finally confirmed by measurements,
may indicate new physics beyond the standard paradigm. In this Letter, we
report how to alleviate both the $H_0$ and $sigma_8$ tensions simultaneously
within torsional gravity from the perspective of effective field theory (EFT).
We apply the EFT approach, which allows to investigate the evolution equations
at the background and perturbation levels in a systematic way, and examine the
conditions followed by the coefficients of various possibly involved operators
such that cosmological tensions can be relaxed. Following these observations we
construct concrete models of Lagrangians of torsional gravity. Specifically, we
consider the parametrization $f(T)=-T -2Lambda/M_P^2 +alpha T^beta$, where
two out of the three parameters are independent (in which an additional term of
the form $cT^{1/2}$ can be added). This model can efficiently fit observations
solving all statistical tensions. To our knowledge, this is the first time
where a modified gravity theory can alleviate both $H_0$ and $sigma_8$
tensions simultaneously, hence offering an additional argument in favor of
gravitational modification.

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