# COSMO-15, the 19th annual International Conference on Particle Physics and Cosmology

7-11 September 2015
Warsaw, Poland
Europe/Zurich timezone

## Decaying Dark Matter and the Discrepancy in sigma_8

10 Sep 2015, 14:40
20m
Main Hall ()

### Speaker

Toyokazu Sekiguchi (University of Helsinki, Finland)

### Description

We consider decaying dark matter (DDM) as a resolution to the possible tension between cosmic microwave background (CMB) and weak lensing (WL) based determinations of the amplitude of matter fluctuations, $\sigma_8$. We perform N-body simulations in a model where dark matter decays into dark radiation and develop an accurate fitting formula for the non-linear matter power spectrum, which enables us to test the DDM model by the combined measurements of CMB, WL and the baryon acoustic oscillation (BAO). We employ a Markov chain Monte Carlo analysis to examine the overlap of posterior distributions of the cosmological parameters, comparing CMB alone with WL+BAO. We find an overlap that is significantly larger in the DDM model than in the standard CDM model. This may be hinting at DDM, although current data is not constraining enough to unambiguously favour a non-zero dark matter decay rate $\Gamma$. From the combined CMB+WL data, we obtain a lower bound $\Gamma^{-1}>97$ Gyr at 95 % C.L, which is less tight than the constraint from CMB alone.

### Presentation Materials

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