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Weighing the Neutrinos with the Galaxy Shape-Shape Correlations

The galaxies form and evolve in the early epochs through the anisotropic merging process along the primary narrow filaments, in the direction of which their shapes become elongated and intrinsically aligned. The nonlinear evolution of the cosmic web broadens the primary filaments, by entangling them with multiple secondary filaments, which has an effect of reducing the anisotropy of the merging process and in consequence weakens the galaxy shape-shape correlations in the later epochs. Assuming that the degree of the nonlinearity and complexity of the cosmic web depends on the nature of dark matter, we propose a hypothesis that the galaxy shape-shape correlation function, $η(r)$, may be a powerful complimentary probe of the total neutrino mass, $M_ν$. Testing this hypothesis against a high resolution N-body simulation, we show that the $M_ν$-dependence of $η(r)$ at $z=0$ is sensitive enough to distinguish between $M_ν=0.0$ eV and $M_ν=0.1$ eV. We also show that the differences in $η(r)$ at $r\le 5\,h^{-1}$Mpc between the models with massless and massive neutrinos cannot be explained by their differences in the small-scale density powers, $σ_{8}$, which implies that the galaxy shape-shape correlation function has a potential to break the notorious cosmic degeneracy between $M_ν$ and $σ_{8}$.