Weak gravitational lensing as a method to constrain unstable dark matter

Mei-Yu Wang and Andrew R. Zentner

Phys. Rev. D 82, 123507 – Published 2 December 2010

Abstract

The nature of the dark matter remains a mystery. The possibility of an unstable dark matter particle decaying to invisible daughter particles has been explored many times in the past few decades. Meanwhile, weak gravitational lensing shear has gained a lot of attention as a probe of dark energy, though it was previously considered a dark matter probe. Weak lensing is a useful tool for constraining the stability of the dark matter. In the coming decade a number of large galaxy imaging surveys will be undertaken and will measure the statistics of cosmological weak lensing with unprecedented precision. Weak lensing statistics are sensitive to unstable dark matter in at least two ways. Dark matter decays alter the matter power spectrum and change the angular diameter distance-redshift relation. We show how measurements of weak lensing shear correlations may provide the most restrictive, model-independent constraints on the lifetime of unstable dark matter. Our results rely on assumptions regarding nonlinear evolution of density fluctuations in scenarios of unstable dark matter and one of our aims is to stimulate interest in theoretical work on nonlinear structure growth in unstable dark matter models.

Received 24 September 2010

DOI:https://doi.org/10.1103/PhysRevD.82.123507

Authors & Affiliations

Mei-Yu Wang^* and Andrew R. Zentner^†

Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA

^*mew56+@pitt.edu
^†zentner@pitt.edu

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Issue

Vol. 82, Iss. 12 — 15 December 2010

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Images

Figure 1
Fractional difference of shear lensing autospectra with and without halo mass loss due to dark matter decay. In this panel, we choose a dark matter lifetime of $τ = 500 Gyr$ for illustrative purposes. From top to bottom, lines are for the autospectra of sources in the first tomographic redshift bin ( $0 \leq z_{p} < 0.6$ ) to the fifth tomographic redshift bin ( $2.4 \leq z_{p} < 3.0$ ). In this panel, both spectra are computed using a halo model. For comparison, note that the differences between the halo model and the Smith et al. [61] relation can be as much as 20% with the maximum discrepancy near $ℓ \sim 1000$ .Reuse & Permissions
Figure 2
Relative difference in the linear potential power spectra between DDM and stable dark matter models at $z = 4$ (top) and $z = 0$ (bottom). The solid lines show a model with $τ_{DDM} = 10^{3} Gyr$ while the dashed lines have $τ_{DDM} = 300 Gyr$ . The dashed-dotted lines show the influence of a non-negligible neutrino mass with $\sum_{i} m_{ν_{i}} = 0.3 eV$ .Reuse & Permissions
Figure 3
Relative differences in comoving angular diameter distance between models with DDM and stable dark matter as a function of scale factor. The solid line represents a model with $τ_{DDM} = 10^{3} Gyr$ and the dashed line shows a model with $τ_{DDM} = 300 Gyr$ .Reuse & Permissions
Figure 4
Relative modification to linear lensing convergence power spectra caused by DDM. The lines shows the convergence power spectra for galaxies in our third redshift bin (galaxies with photometric redshifts $1.2 \leq z_{p} < 1.8$ ) in a model with finite $τ_{DDM}$ compared to a model of stable dark matter. The solid line shows the power spectrum residual in a model with $τ_{DDM} = 1000 Gyr$ , and the dashed line shows the same power spectrum residual with $τ_{DDM} = 300 Gyr$ .Reuse & Permissions
Figure 5
Marginalized $1 σ$ constraint contours for dark matter decay rate against other varying cosmological parameters in our model. In this illustrative example, we show contours from our linear power spectrum, $ℓ_{\max} = 300$ , Wide survey calculations. The outer contours were computed using our contemporary priors while the inner contours were computed assuming Planck-level priors. This example is useful because degeneracies are most significant in the linear power spectrum calculations. Notice that the degeneracy between dark matter lifetime and neutrino mass is relatively insignificant for contemporary priors, but is the most important remaining degeneracy with Planck prior constraints. The crosses designate fiducial parameter values.Reuse & Permissions

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