Strongest model-independent bound on the lifetime of Dark Matter

TL;DR

This study establishes a model-independent lower bound on dark matter lifetime, showing it must exceed approximately 160 to 200 billion years based on current cosmological observations, assuming decay into relativistic particles.

Contribution

It provides the first model-independent cosmological bound on dark matter lifetime using only decay into relativistic particles and current data.

Findings

Dark matter lifetime > 160 Gyr without BICEP2

Dark matter lifetime > 200 Gyr with BICEP2

Decay affects low-$ll$ CMB multipoles

Abstract

Dark Matter is essential for structure formation in the late Universe so it must be stable on cosmological time scales. But how stable exactly? Only assuming decays into relativistic particles, we report an otherwise model independent bound on the lifetime of Dark Matter using current cosmological data. Since these decays affect only the low-$\ell$ multipoles of the CMB, the Dark Matter lifetime is expected to correlate with the tensor-to-scalar ratio $r$ as well as curvature $\Omega_k$. We consider two models, including $r$ and $r+\Omega_k$ respectively, versus data from Planck, WMAP, WiggleZ and Baryon Acoustic Oscillations, with or without the BICEP2 data (if interpreted in terms of primordial gravitational waves). This results in a lower bound on the lifetime of CDM given by 160Gyr (without BICEP2) or 200Gyr (with BICEP2) at 95% confidence level.