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The Astrophysics of Strongly Interacting Systems


Nerella, Tejaswi Venumadhav (2016) The Astrophysics of Strongly Interacting Systems. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z900001N.


This thesis presents investigations in four areas of theoretical astrophysics: the production of sterile neutrino dark matter in the early Universe, the evolution of small-scale baryon perturbations during the epoch of cosmological recombination, the effect of primordial magnetic fields on the redshifted 21-cm emission from the pre-reionization era, and the nonlinear stability of tidally deformed neutron stars.

In the first part of the thesis, we study the asymmetry-driven resonant production of 7 keV-scale sterile neutrino dark matter in the primordial Universe at temperatures T >~ 100 MeV. We report final DM phase space densities that are robust to uncertainties in the nature of the quark-hadron transition. We give transfer functions for cosmological density fluctuations that are useful for N-body simulations. We also provide a public code for the production calculation.

In the second part of the thesis, we study the instability of small-scale baryon pressure sound waves during cosmological recombination. We show that for relevant wavenumbers, inhomogenous recombination is driven by the transport of ionizing continuum and Lyman-alpha photons. We find a maximum growth factor less than ≈ 1.2 in 107 random realizations of initial conditions. The low growth factors are due to the relatively short duration of the recombination epoch.

In the third part of the thesis, we propose a method of measuring weak magnetic fields, of order 10-19 G (or 10-21 G if scaled to the present day), with large coherence lengths in the inter galactic medium prior to and during the epoch of cosmic reionization. The method utilizes the Larmor precession of spin-polarized neutral hydrogen in the triplet state of the hyperfine transition. We perform detailed calculations of the microphysics behind this effect, and take into account all the processes that affect the hyperfine transition, including radiative decays, collisions, and optical pumping by Lyman-alpha photons.

In the final part of the thesis, we study the non-linear effects of tidal deformations of neutron stars (NS) in a compact binary. We compute the largest three- and four-mode couplings among the tidal mode and high-order p- and g-modes of similar radial wavenumber. We demonstrate the near-exact cancellation of their effects, and resolve the question of the stability of the tidally deformed NS to leading order. This result is significant for the extraction of binary parameters from gravitational wave observations.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Cosmology; Dark matter; Neutrino oscillations; Non-standard-model neutrinos; Galaxy clusters; Cosmic background radiation; Intergalactic matter; Primordial magnetic fields; Cosmological recombination; Radiative transfer; Sound waves in plasmas; Neutron stars; Binary neutron stars; Tidal interactions
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Hirata, Christopher M.
Thesis Committee:
  • Bock, James J. (chair)
  • Ott, Christian D.
  • Dore, Olivier P.
  • Hirata, Christopher M.
Defense Date:18 August 2015
Non-Caltech Author Email:ntveem (AT)
Record Number:CaltechTHESIS:09042015-035149228
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 2, 5 adapted for ch. 6-7 adapted for ch. 8-10 adapted for ch. 11-13
Nerella, Tejaswi Venumadhav0000-0002-1661-2138
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9139
Deposited By: Tejaswi Nerella
Deposited On:07 Oct 2015 16:14
Last Modified:18 Aug 2017 21:06

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