Fractional Dark Matter decay: cosmological imprints and observational constraints

Abstract

If a fraction f dcdm of the Dark Matter decays into invisible and massless particles (so-called "dark radiation") with the decay rate (or inverse lifetime) Γ dcdm , such decay will leave distinctive imprints on cosmological observables. With a full consideration of the Boltzmann hierarchy, we calculate the decay-induced impacts not only on the CMB but also on the redshift distortion and the kinetic Sunyaev-Zel'dovich effect, while providing detailed physical interpretations based on evaluating the evolution of gravitational potential. By using the current cosmological data with a combination of Planck 2015, Baryon Acoustic Oscillation and redshift distortion measurements which can improve the constraints, we update the 1σ bound on the fraction of decaying DM from f dcdm 5.26% to f dcdm 1.99% for the short-lived DM (assuming Γ dcdm /H 0 10 4 ). However, no constraints are improved from RSD data (f dcdm 1.03%) for the long-lived DM (i.e., Γ dcdm /H 0 10 4 ). We also find the fractional DM decay can only slightly reduce the H 0 and σ 8 tensions, which is consistent with other previous works. Furthermore, our calculations show that the kSZ effect in future would provide a further constraining power on the decaying DM.

Challenges for $Λ$CDM: An update

“…[477] and studied by Refs. [478][479][480][481][482][483][484], provides a promising scenario to relieve the Hubble constant H 0 tension (e.g. [485]).…”

Degenerate Sub-keV fermion dark matter from a solution to the Hubble tension

“…[43,44]. Also, reduction of f σ 8 in comparison with that from ΛCDM and suppression of the kinetic Sunyaev-Zel'dovich (kSZ) power spectrum were further discussed in [44] as impacts that DDM can make. (Here f is the matter growth rate, defined to be f ≡ d ln δ m /d ln a)…”

“…As phenomenological consequences, enhancement of the late integrated Sachs-Wolfe (LISW) effect for low regime ( ∼ 10) can be induced regarding CMB temperature anisotropy power spectrum. [43,44]. Also, reduction of f σ 8 in comparison with that from ΛCDM and suppression of the kinetic Sunyaev-Zel'dovich (kSZ) power spectrum were further discussed in [44] as impacts that DDM can make.…”

Arbitrating the $S_8$ discrepancy with growth rate measurements from Redshift-Space Distortions

“…It is thus worthwhile to investigate whether new physics might solve or at least alleviate the S 8 discrepancy, a possibility which has been investigated in several works. Models which have been contemplated in this sense include for example active and sterile neutrinos [43][44][45][46][47], ultra-light axions [48], decaying dark matter (DM) [49][50][51][52][53][54][55][56], extended or exotic DM and/or dark energy (DE) models and interactions [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76] including unified dark sector models [77], modified gravity models [78][79][80][81][82][83][84][85][86][87],…”