Phases of new physics in the CMB

By D. Baumann, D. Green, Joel Meyers, B. Wallisch. 2015

201 citations recorded by the source corpus.

Fluctuations in the cosmic neutrino background are known to produce a phase shift in the acoustic peaks of the cosmic microwave background. It is through the sensitivity to this effect that the recent CMB data has provided a robust detection of free-streaming neutrinos. In this paper, we revisit the phase shift of the CMB anisotropy spectrum as a probe of new physics. The phase shift is particularly interesting because its physical origin is strongly constrained by the analytic properties of the Green's function of the gravitational potential. For adiabatic fluctuations, a phase shift requires modes that propagate faster than the speed of fluctuations in the photon-baryon plasma. This possibility is realized by free-streaming relativistic particles, such as neutrinos or other forms of dark radiation. Alternatively, a phase shift can arise from isocurvature fluctuations. We present simple models to illustrate each of these effects. We then provide observational constraints from the Planck temperature and polarization data on additional forms of radiation. We also forecast the capabilities of future CMB Stage IV experiments. Whenever possible, we give analytic interpretations of our results.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/7c6a496965318a5a73d0af68a3cf5287215c6415

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Citations in the corpus

Gravitational probes of dark matter physics (2017, background): “This changes the expansion history of the Universe at early times (notably changing the redshift of matterradiation equality), and thus affects acoustic horizon [493, 509, 510, 511, 512, 513].”
CMB-S4 Science Case, Reference Design, and Project Plan (2019, background): “[176, 218, 177]).”
New experimental approaches in the search for axion-like particles (2018, background): “3, updated from [283] with the QCD equation of state of [71].”
A tale of two modes: neutrino free-streaming in the early universe (2017, background): “To understand why, note that the absence of a free-streaming phase shift [12, 15, 19, 20] for models in this corner of parameter space is compensated by adjusting the angular diameter distance to the last scattering surface (via a change in H0).”