Tests of the CMB temperature-redshift relation, CMB spectral distortions and why adiabatic photon production is hard

Abstract

In the expanding Universe, the average temperature of the cosmic microwave background (CMB) is expected to depend like TCMB~(1+z) on redshift z. Adiabatic photon production (or destruction) or deviations from isotropy and homogeneity could modify this scaling and several observational tests have been carried out in response. Here, we explain why `adiabatic' conditions are extremely difficult to establish in the redshift range targeted by these tests. Thus, instead of leading to a simple rescaling of the CMB temperature, a spectral distortion should be produced, which can be constrained using COBE/FIRAS. For scenarios with late photon production, tests of the temperature-redshift relation (TRR) should therefore be reinterpreted as weak spectral distortion limits, directly probing the energy dependence of the photon production process. For inhomogeneous cosmologies, an average y-type distortion is produced, but this type of distortion can be created in several other ways. Here, we briefly discuss possible effects that may help disentangling different contributions to the distortion signal, finding this to be very challenging. We furthermore argue that tests of the TRR, using the SZ effect have limited applicability and that for non-gravitational changes to the TRR the CMB anisotropy spectrum should exhibit an additional y-type dependence.

8 pages, accepted by MNRAS

References in corpus (14)

• The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From First-Year Fermi Large Area Telescope Data
• CMB Constraints on WIMP Annihilation: Energy Absorption During the Recombination Epoch
• A Test of the Copernican Principle
• CMB anisotropies seen by an off-center observer in a spherically symmetric inhomogeneous universe
• Silk damping at a redshift of a billion: a new limit on small-scale adiabatic perturbations
• Precision cosmology defeats void models for acceleration
• Lines in the cosmic microwave background spectrum from the epoch of cosmological helium recombination
• Linear kinetic Sunyaev-Zel'dovich effect and void models for acceleration
• The Signature of Proper Motion in the Microwave Sky
• 3.55 keV photon lines from axion to photon conversion in the Milky Way and M31
• Evolution of density perturbations in decaying vacuum cosmology
• Cosmological hydrogen recombination: Lyn line feedback and continuum escape
• The cosmic X-ray and gamma-ray background from dark matter annihilation
• Evolution of low-frequency features in the CMB spectrum due to stimulated Compton scattering and Doppler-broadening

Cited by in corpus (15)

• The status of varying constants: a review of the physics, searches and implications
• BBN And The CMB Constrain Neutrino Coupled Light WIMPs
• The synergy between CMB spectral distortions and anisotropies
• H0 tension or T0 tension?
• The resilience of the Etherington-Hubble relation
• Multi-interacting dark energy and its cosmological implications
• Using the cosmological recombination radiation to probe early dark energy and fundamental constant variations
• Fundamental cosmology in the E-ELT era: The status and future role of tests of fundamental coupling stability
• Sensitivity forecasts for the cosmological recombination radiation in the presence of foregrounds
• Bayesian Comparison of the Cosmic Duality Scenarios
• Constraining CMB temperature evolution with Sunyaev-Zel'dovich galaxy clusters from the Atacama Cosmology Telescope
• Scale invariant cosmology and CMB temperatures as a function of redshifts
• Cosmological impact of microwave background temperature measurements
• Resilience and implications of adiabatic CMB cooling
• Lorentzian correction for the evolution of the CMB temperature