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Early Dark Energy and Rayleigh Scattering in the CMB

Dijkstra, Jeffrey (2023) Early Dark Energy and Rayleigh Scattering in the CMB. Bachelor's Thesis, Physics.


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Early- and late-universe observations of the Hubble constant H0 show a systematic difference between the two values, termed the Hubble tension. The inclusion of Early Dark Energy (EDE) to the early universe acting as a cosmological constant before decaying away can resolve this tension as it increases H0 inferred from the cosmic microwave background (CMB). Here Rayleigh scattering is studied in forecasts of an EDE extension to the ΛCDM model. Rayleigh scattering is a secondary CMB anisotropy caused by scattering of neutral species during recombination with a unique frequency dependency (∝ ν^4), peaking a short time after recombination, tightening constraints on the local expansion history. Here the Python branch of CAMB was modified to calculate the total single frequency Thomson + Rayleigh power spectrum. The implementation is consistent with the older Fortran Rayleigh branch to sub-percentile level. The EDE parameter forecast, with PICO noise, gives an improvement ranging 54 to 90% for Rayleigh compared to Thomson only. This is too high compared to previous studies, particularly Ωch2, H0 and fEDE. The missing cross-correlation terms in the covariance matrices and only including temperature are possible errors. However, the individual parameter errors are slightly worse than other studies due to excluding polarization effects. Upcoming development in the code, primarily including multi-frequency correlated Rayleigh signals, should clarify whether the forecasts are accurate.

Item Type: Thesis (Bachelor's Thesis)
Supervisor name: Meerburg, P.D. and Borschevsky, A.
Degree programme: Physics
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 24 Jul 2023 09:10
Last Modified: 24 Jul 2023 09:10

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