Physics & Astronomy ETDs


Sajad Abbar

Publication Date



A star with a mass larger than 8−10 solar masses can end its life in a supernova ex- plosion and possibly form a neutron star. In this dissertation, I study two important aspects of the physics of supernovae and neutron stars. In the first part, I consider neutrino flavor oscillations in supernovae. Neutrino flavor oscillations in the presence of ambient neutrinos is nonlinear in nature which leads to interesting phenomenology that has not been well understood. This phenomenon in the supernova context has been studied in the so-called neutrino Bulb model which is a restricted, stationary supernova model and which possesses the (spatial) spherical symmetry about the center of the supernova and the (directional) axial symmetry around the radial direction. By studying the problem of the neutrino oscillations in a two dimensional toy model, the so-called neutrino Line model, I show that the spatial symmetries can be broken spontaneously in a dense neutrino gas. Using a time-dependent version of the neutrino Bulb model, I also show that the stationarity of a neutrino gas can be broken spontaneously as well. In the second part, I compute the thermal conductivity of the neutron star crust. I use the quantum Monte Carlo (QMC) technique to calculate the static structure function S(q) of a one-component ion lattice and use it to compute the thermal conductivity κ of high-density solid matter expected in the neutron star crust. By making detailed comparisons with the results obtained using one-phonon approximation (OPA), and the multi-phonon harmonic approximation, we assess the temperature regime where S(q) from QMC can be used directly to calculate κ. We also com- pare the QMC results to those obtained using the classical Monte Carlo technique to quantitatively assess the magnitude of the quantum corrections. We show that the quantum effects become relevant at temperature T < 0.3 ΩP, where ΩP is the ion plasma frequency. At T ≃ 0.1 ΩP the quantum effects suppress κ by about 30%. The comparison with the results of the OPA indicates that dynamical information beyond the static structure is needed when T < 0.1 ΩP.

Degree Name


Level of Degree


Department Name

Physics & Astronomy

First Advisor

Duan, Huaiy

First Committee Member (Chair)

Allahverdi, Rouzbeh

Second Committee Member

Miyake, Akimasa

Third Committee Member

Reddy, Sanjay




neutrino, supernovae, neutron star, dense matter

Document Type