Updated cosmological constraints on Macroscopic Dark Matter

Cosmological observations suggest that roughly 26% of the energy content of our Universe consists of dark matter (DM), a yet unknown form of matter which manifests its presence through gravi- tational interaction. The DM played a crucial role in the evolution of the Universe, allowing the small density fluctuations present in the early Universe to grow and collapse, leading eventually to the wealth of structures (e.g., galaxies and galaxy clusters) that we observe today in the sky. However, despite knowing some basic properties of DM, its fundamental nature is still unknown and represents one of the major puzzles of both cosmology and particle physics. While there exist many theoretically motivated models which explain the dark matter as a new particle be- yond the Standard Model of particle physics, experimental evidence in laboratory searches is still lacking. It is thus important to keep an open mind on alternative scenarios, some of which could be realized within the Standard Model itself. An appealing possibility is that the dark matter consists of macroscopic-size objects, generically dubbed as Macroscopic Dark Matter (MDM) or Macros, which interact with ordinary matter predominantly via their large geometric cross-section. A possible signature of MDM is the capture of baryons from the cosmological plasma in the pre- recombination epoch, with the consequent injection of high-energy photons in the baryon-photon plasma. Without referring to any specific theoretical models, I will discuss the cosmological phe- nomenology of two distinct classes of Macros, composed either of ordinary matter or antimatter. In both scenarios, I wll also analyze the impact of a non-vanishing electric charge carried by Macros. I will focus on the following probes of MDM: the change in the baryon density between the end of the Big Bang Nucleosynthesis (BBN) and the Cosmic Microwave Background (CMB) decoupling, the production of spectral distortions in the CMB and the kinetic coupling between charged MDM and baryons at the time of recombination. While discussing these results, I will also show that future CMB spectral distortions experiments, like PIXIE and SuperPIXIE, would have the sensi- tivity to probe larger regions of the Macro parameter space: this would allow either for a possible evidence or for an improvement of the current bounds on Macros as dark matter candidates.