456 research outputs found
Optimal polarisation equations in FLRW universes
This paper presents the linearised Boltzmann equation for photons for scalar,
vector and tensor perturbations in flat, open and closed FLRW cosmologies. We
show that E- and B-mode polarisation for all types can be computed using only a
single hierarchy. This was previously shown explicitly for tensor modes in flat
cosmologies but not for vectors, and not for non-flat cosmologies.Comment: 27 pages, prepared for submission to JCAP. Matches published versio
The effective gravitational decoupling between dark matter and the CMB
We present a detailed and self-contained analytical derivation of the
evolution of sub-horizon cosmological perturbations before decoupling, based on
previous work by S. Weinberg. These solutions are valid in the minimal LCDM
scenario, to first order in perturbation theory, in the tight-coupling limit
and neglecting neutrino shear stress. We compare them to exact numerical
solutions computed by a Boltzmann code, and we find the two to be in very good
agreement. The analytic solutions show explicitly that CDM and the
baryon-photon fluid effectively behave as separate self-gravitating fluids
until the epoch of baryon drag. This in turn leads to the surprising conclusion
that the CMB is much less sensitive to the clustering properties of minimally
coupled Dark Matter models than what would be naively expected.Comment: 23 pages, 8 figures, 2 references added, few sentences clarifie
How secret interactions can reconcile sterile neutrinos with cosmology
Short baseline neutrino oscillation experiments have shown hints of the
existence of additional sterile neutrinos in the eV mass range. However, such
neutrinos seem incompatible with cosmology because they have too large an
impact on cosmic structure formation. Here we show that new interactions in the
sterile neutrino sector can prevent their production in the early Universe and
reconcile short baseline oscillation experiments with cosmology.Comment: 4 pages, 5 figures, prepared for submission to PR
Student Engagement: The Effects of Goals, Personality, Relations, and Society
Undergraduate
Applie
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