A Caltech Library Service

Stability of small-scale baryon perturbations during cosmological recombination

Venumadhav, Tejaswi and Hirata, Christopher M. (2015) Stability of small-scale baryon perturbations during cosmological recombination. Physical Review D, 91 (12). Art. No. 123009. ISSN 1550-7998.

[img] PDF - Published Version
See Usage Policy.

PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


In this paper, we study small-scale fluctuations (baryon pressure sound waves) in the baryon fluid during recombination. In particular, we look at their evolution in the presence of relative velocities between baryons and photons on large scales (k∼10^(−1)  Mpc^(−1)), which are naturally present during the era of decoupling. Previous work concluded that the fluctuations grow due to an instability of sound waves in a recombining plasma, but that the growth factor is small for typical cosmological models. These analyses model recombination in an inhomogenous universe as a perturbation to the parameters of the homogenous solution. We show that for relevant wave numbers k≳10^3  Mpc^(−1) the dynamics are significantly altered by the transport of both ionizing continuum (hν>13.6  eV) and Lyman-α photons between crests and troughs of the density perturbations. We solve the radiative transfer of photons in both these frequency ranges and incorporate the results in a perturbed three-level atom model. We conclude that the instability persists at intermediate scales. We use the results to estimate a distribution of growth rates in 10^7 random realizations of large-scale relative velocities. Our results indicate that there is no appreciable growth; out of these 10^7 realizations, the maximum growth factor we find is less than ≈1.2 at wave numbers of k≈10^3  Mpc^(−1). The instability’s low growth factors are due to the relatively short duration of the recombination epoch during which the electrons and photons are coupled.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper DOIArticle
Venumadhav, Tejaswi0000-0002-1661-2138
Hirata, Christopher M.0000-0002-2951-4932
Contact Email
Additional Information:© 2015 American Physical Society. Received 10 September 2014; published 16 June 2015. We thank Todd Thompson for bringing Shaviv’s instability to our attention, and for his careful reading of an earlier draft of this paper. We also thank Cora Dvorkin for her helpful comments on the paper, and Abhilash Mishra for useful discussions. Further, we would like to acknowledge the anonymous referee for their detailed comments, which greatly improved the paper.We express our gratitude to Julien Lesgourgues and collaborators for making the CLASS code for linear perturbations freely available. During the duration of this work, T. V. was supported by the International Fulbright Science and Technology Award, and C. H. was supported by the U.S. Department of Energy under Contract No. DE-FG03-02-ER40701, the David and Lucile Packard Foundation, the Simons Foundation, and the Alfred P. Sloan Foundation.
Funding AgencyGrant Number
International Fulbright Science and Technology AwardUNSPECIFIED
Department of Energy (DOE)DE-FG03-02-ER40701
David and Lucile Packard FoundationUNSPECIFIED
Simons FoundationUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Classification Code:PACS numbers: 95.30.Lz, 52.35.Mw, 95.30.Jx
Record Number:CaltechAUTHORS:20140930-220651879
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50132
Deposited By: Tejaswi Nerella
Deposited On:01 Oct 2014 19:29
Last Modified:17 May 2017 20:37

Repository Staff Only: item control page