Abstract
We study a class of decaying dark matter models as a possible resolution to
the observed discrepancies between early- and late-time probes of the universe.
This class of models, dubbed DDM, characterizes the evolution of comoving dark
matter density with two extra parameters. We investigate how DDM affects key
cosmological observables such as the CMB temperature and matter power spectra.
Combining 3x2pt data from Year 1 of the Dark Energy Survey,Planck-2018 CMB
temperature and polarization data, Supernova (SN) Type Ia data from Pantheon,
and BAO data from BOSS DR12, MGS and 6dFGS, we place new constraints on the
amount of dark matter that has decayed and the rate with which it converts to
dark radiation. The fraction of the decayed dark matter in units of the current
amount of dark matter, $\zeta$, is constrained at 68% confidence level to be
<0.32 for DES-Y1 3x2pt data, <0.030 for CMB+SN+BAO data, and <0.037 for the
combined dataset. The probability that the DES and CMB+SN+BAO datasets are
concordant increases from 4% for the $Łambda$CDM model to 8% (less tension)
for DDM. Moreover, tension in $S_8=\sigma_8Ømega_m/0.3$ between DES-Y1
3x2pt and CMB+SN+BAO is reduced from 2.3$\sigma$ to 1.9$\sigma$. We find no
reduction in the Hubble tension when the combined data is compared to
distance-ladder measurements in the DDM model. The maximum-posterior
goodness-of-fit statistics of DDM and $Łambda$CDM are comparable, indicating
no preference for the DDM cosmology over $Łambda$CDM.
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