Weak interactions in nucleon matter

Cowell, Shannon Tracy

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https://hdl.handle.net/2142/32122 Copy

Description

Title

Weak interactions in nucleon matter

Author(s)

Cowell, Shannon Tracy

Issue Date

2004

Director of Research (if dissertation) or Advisor (if thesis)

Pandharipande, V.R.

Department of Study

Physics

Discipline

Physics

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• core-collapse supernovae
• neutrino interactions
• non- interacting Fermi gas
• hot asymmetric nucleon matter

Language

en

Abstract

Neutrino interactions play a crucial role in many astrophysical environments such as core-collapse supernovae and neutron stars. In this work, reaction rates for neutrino emission, absorption and scattering are calculated in hot asymmetric nucleon matter at densities relevant to core-collapse supernovae. We derive a consistent set of effective interactions and effective operators starting from realistic forces using correlated basis theory. These effective interactions and operators are used to calculate weak interaction rates in matter in correlated Hartree-Fock and correlated Tamm-Dancoff approximations. In general, interactions increase the range of energy transfers and shift the strength of the response to larger energy transfers as compared to non-interacting Fermi gas. In addition, at small momentum transfers, the square of the nuclear matrix element of the charge changing weak operators are quenched 20 to 25% by short-range correlations in nucleon matter. These modifications to the nuclear response significantly alter the neutrino reaction rates as compared to a non-interacting Fermi gas. At the temperature and proton fraction considered, electron capture and neutrino scattering rates are ~ 2-4 times smaller than the rates obtained for a non-interacting Fermi gas. Neutrino absorption rates in matter are reduced by Pauli blocking. However, strong interactions enhance the reaction rate, particularly at small neutrino energies. The neutrino reaction rates at equilibrium density are also calculated in the Tamm-Dancoff approximation using zero-range effective interactions with parameters chosen to reproduce the equation of state and spin-isospin susceptibilities of matter. Many modern calculations of neutrino reaction rates use this kind of effective interaction and neglect the effects of short range correlations on the nuclear matrix elements of weak operators. This treatment is inconsistent and our results indicate that reaction rates calculated in this simple approximation may be considerably overestimated.

Type of Resource

text

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http://hdl.handle.net/2142/32122

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©2004 Cowell

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