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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