25 research outputs found
Cosmological Perturbations at Second Order and Recombination Perturbed
We derive the full set of second-order equations governing the evolution of
cosmological perturbations, including the effects of the first-order electron
number density perturbations, \delta_e. We provide a detailed analysis of the
perturbations to the recombination history of the universe and show that a
perturbed version of the Peebles effective 3-level atom is sufficient for
obtaining the evolution of \delta_e for comoving wavenumbers smaller than
1Mpc^{-1}. We calculate rigorously the perturbations to the Ly\alpha escape
probability and show that to a good approximation it is governed by the local
baryon velocity divergence. For modes shorter than the photon diffusion scale,
we find that \delta_e is enhanced during recombination by a factor of roughly 5
relative to other first-order quantities sourcing the CMB anisotropies at
second order. Using these results, in a companion paper we calculate the CMB
bispectrum generated during recombination.Comment: 47 pages, 6 figure
Towards an Optimal Reconstruction of Baryon Oscillations
The Baryon Acoustic Oscillations (BAO) in the large-scale structure of the
universe leave a distinct peak in the two-point correlation function of the
matter distribution. That acoustic peak is smeared and shifted by bulk flows
and non-linear evolution. However, it has been shown that it is still possible
to sharpen the peak and remove its shift by undoing the effects of the bulk
flows. We propose an improvement to the standard acoustic peak reconstruction.
Contrary to the standard approach, the new scheme has no free parameters,
treats the large-scale modes consistently, and uses optimal filters to extract
the BAO information. At redshift of zero, the reconstructed linear matter power
spectrum leads to a markedly improved sharpening of the reconstructed acoustic
peak compared to standard reconstruction.Comment: 20 pages, 5 figures; footnote adde
Quantum field theory of scalar cosmological perturbations
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (leaf 55).Using canonical quantization we show that the spectrum of the scalar cosmological fluctuations as calculated until now is not correct. We derive the correct expression for the spectrum, and show that our correct treatment alleviates the fine-tuning problem in inflation.by Svetlin Valentinov Tassev.S.B
Estimating CDM Particle Trajectories in the Mildly Non-Linear Regime of Structure Formation. Implications for the Density Field in Real and Redshift Space
We obtain approximations for the CDM particle trajectories starting from
Lagrangian Perturbation Theory. These estimates for the CDM trajectories result
in approximations for the density in real and redshift space, as well as for
the momentum density that are better than what standard Eulerian and Lagrangian
perturbation theory give. For the real space density, we find that our proposed
approximation gives a good cross-correlation (>95%) with the non-linear density
down to scales almost twice smaller than the non-linear scale, and six times
smaller than the corresponding scale obtained using linear theory. This allows
for a speed-up of an order of magnitude or more in the scanning of the
cosmological parameter space with N-body simulations for the scales relevant
for the baryon acoustic oscillations. Possible future applications of our
method include baryon acoustic peak reconstruction, building mock galaxy
catalogs, momentum field reconstruction.Comment: 25 pages, 11 figures; reference adde