Peering Beyond the Veil of Last Scattering: A View of the Universe with CMB Spectral Distortions
Year: 2026
Type: preprint
Abstract: The frequency spectrum of the cosmic microwave background is the most precise blackbody ever measured in nature, with deviations constrained at the level of almost one part per million from the COBE satellite. Nevertheless, departures away from a perfect blackbody are present in standard $Λ$CDM cosmology, lurking just beneath the surface of our current observational bounds. These spectral distortions provide invaluable information on our thermal history in both the post- and pre-recombination epochs, allowing us to peer beyond last scattering and into the primordial Universe. Here, we present an overview of the underlying physics responsible for generating CMB spectral distortions at all epochs. As an illustration of this rich physics, we review a comprehensive set of mechanisms capable of generating distortions both within and beyond the standard $Λ$CDM paradigm. We also discuss the information that can be gleaned by going beyond the monopole (sky-averaged) spectrum and exploiting the spatial information present in anisotropic spectral distortions. To supplement our discussion of the diverse science of spectral distortions, we provide an overview of the upcoming and proposed experimental landscape. We highlight that the combination of the TMS, COSMO, and BISOU experiments will provide the first discovery of a monopole $y$-type distortion within the coming decade. From space, the proposed FOSSIL experiment is forecasted to improve upon the original COBE/FIRAS measurement by roughly three orders of magnitude in sensitivity, bringing with it the detection of the $Λ$CDM $μ$-type distortion sourced by the dissipation of small scale acoustic modes in the pre-recombination plasma. With transformational measurements on the horizon, CMB spectral distortions offer a uniquely sensitive probe of the thermal history of the Universe at redshifts $z \lesssim 2 \times 10^6$.
Source: arXiv (Cornell University)
Authors: Cyr, Bryce, Aghanim, Nabila, Baker, Ethan, Battistelli, Elia Stefano, Battye, Richard, Bernal, José Luis, Chluba, Jens, Coulon, Xavier, Coulton, William, de Bernardis, Paolo, Di Valentino, Eleonora, Domènech, Guillem, Evangelista, Sara, Fabbian, Giulio, Finelli, Fabio, Hill, J. Colin, Khatri, Rishi, Kogut, Alan, Lagache, Guilaine, Liu, Hongwan, Maffei, Bruno, Majidi, Fereshteh, Maniyar, Abhishek S., Martins, C. J. A. P., Masi, Silvia, McMahon, Jeff, Paoletti, Daniela, Poulin, Vivian, Qin, Wenzer, Remazeilles, Mathieu, Rubiño-Martín, José Alberto, Sabyr, Alina, Rao, Mayuri Sathyanarayana, Sierra, Carlos, Singal, Jack, Slatyer, Tracy R., Teixeira, Elsa M., Thiele, Leander, Vacher, Léo, Watts, Duncan
Institutions: Massachusetts Institute of Technology, Centre National de la Recherche Scientifique, Université Paris-Saclay, Institut d'Astrophysique Spatiale, Boston University, Istituto Nazionale di Fisica Nucleare, Sezione di Roma I, Sapienza University of Rome, University of Manchester, Instituto de Física de Cantabria, University of Oxford, Leibniz University Hannover, Max Planck Institute for Gravitational Physics, Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Osservatorio di Astrofisica e Scienza dello Spazio, National Institute for Astrophysics, Columbia University, Tata Institute of Fundamental Research, Goddard Space Flight Center, Aix-Marseille Université, Laboratoire d’Astrophysique de Marseille, University of British Columbia, Laboratoire d'Annecy de Physique Théorique, University of Chicago, Université de Montpellier, Laboratoire Univers et Particules de Montpellier, New York University, Universidad de La Laguna, Instituto de Astrofísica de Canarias, Lawrence Berkeley National Laboratory, University of California, Berkeley, Raman Research Institute, Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, University of Richmond, Kavli Institute for the Physics and Mathematics of the Universe, University of Oslo, Laboratoire de Physique des 2 Infinis Irène Joliot-Curie, The University of Tokyo
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Award: G1532879105
OpenAlex ID: W7213431611