Decaying dark matter and the tension in σ8

Kari Enqvist, Seshadri Nadathur, Toyokazu Sekiguchi, Tomo Takahashi

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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, σ8. 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 Γ. From the combined CMB+WL data, we obtain a lower
bound Γ−1 ≥ 97 Gyr at 95 % C.L, which is less tight than the constraint from CMB alone.
Original languageEnglish
Article number067
Number of pages18
JournalJournal of Cosmology and Astroparticle Physics
Issue number9
Publication statusPublished - 29 Sept 2015


  • cosmological simulations
  • particle physics - cosmology connection
  • cosmological parameters from LSS
  • weak gravitational lensing


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