Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 443, Issue 3, Pages 1881-1888Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stu1260
Keywords
cosmic background radiation; cosmological parameters; cosmology: observations; cosmology: theory; dark energy; early Universe
Categories
Funding
- NSF [0244990]
- John Templeton Foundation
- Direct For Mathematical & Physical Scien
- Division Of Physics [0244990] Funding Source: National Science Foundation
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In the expanding Universe, the average temperature of the cosmic microwave background (CMB) is expected to depend like T-CMB alpha(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 Sunyaev-Zeldovich effect have limited applicability and that for non-gravitational changes to the TRR, the CMB anisotropy spectrum should exhibit an additional y-type dependence.
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