CMB spectral distortions from cooling macroscopic dark matter

Abstract

We propose a new mechanism by which dark matter (DM) can affect the early and late universe. The hot interior of a macroscopic DM, or macro, can behave as a heat reservoir so that energetic photons and neutrinos are emitted from its surface and interior respectively. In this paper we focus on the spectral distortions (SDs) of the cosmic microwave background before recombination. The SDs depend on the density and the cooling processes of the interior, and the surface composition of the Macros. We use neutron stars as a model for nuclear-density Macros and find that the spectral distortions are mass-independent for fixed density. In our work, we find that, for Macros of this type that constitute 100% of the dark matter, the µ and y distortions can be near or above detection threshold for typical proposed next-generation experiments such as PIXIE.

Neutrino Cooling of Primordial Hot Regions

“…There are some observations [1] favouring their creation during the early expansion. Similar local heated areas have been hypothetically discussed earlier [2][3][4]. They could separate from the Hubble flow if their density is high enough.…”

“…There are some observations [1] indicating the existence of local heated areas in the early Universe. Hypothetical nature of local heated areas was discussed earlier [2,3,4]. Such areas can appear due to large primordial density fluctuations and can be related to the clusters of Primordial Black Holes (PBHs) [1,5,6].…”

New horizons in cosmology with spectral distortions of the cosmic microwave background

“…Using the r-type distortion we could furthermore break the degeneracy between particle yield and lifetime, should a significant distortion signal be detected [13,17]. Figure adapted from [17] More work is required, although it is already clear that in addition to the aforementioned examples distortions can meaningfully probe scenarios involving axions [189][190][191], gravitino decays [182,192], cosmic strings [193,194], DM-SMinteractions [120,172,195], macros [196] and primordial magnetic fields [197][198][199][200]. This opens a path for studying a wide range of new physics.…”

Microwave spectro-polarimetry of matter and radiation across space and time

“…This is new territory and more work is required; however, it is already clear that CMB spectral distortions can meaningfully probe scenarios involving axions [148][149][150], gravitino decays [137,151], strings [152,153], DM-SM-interactions [126,154,155], macroscopic DM [156], and primordial magnetic fields [157][158][159][160]. A CMB spectrometer that reaches the level of μ 10 −8 after foreground marginalization can rule out a vast class of particle-physics models and also allow a first detection of the guaranteed μ-distortion signal from the damping of primordial acoustic modes.…”