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Neutrino Processes in Dense Matter with Strong Magnetic Fields

Mentor:

Mia Kumamoto (mialk@uw.edu) and Sanjay Reddy

Student:

Catherine Welch

Project Description:

Reactions that produce neutrinos are important for cooling and transport properties in the dense matter found in neutron stars. The rates of these reactions depend on the detailed kinematics of neutrons, protons, and electrons. In particular, momentum conservation requires the so-called triangle inequality |k_n| < |k_p| + |k_e| to be satisfied for β decay to occur. This constraint can be lifted by including spectator particles in the reaction which are present only to conserve momentum, resulting in a slower reaction. In the presence of strong magnetic fields, the proton and electron energy levels are quantized and wave-functions are modified to be a superposition of many momentum eigenstates. Low energy particles having access to high momentum states means that β decay can occur at lower densities than would normally be allowed without spectator particles.

The student will learn basic relativistic quantum mechanics (calculating reaction rates from Feynman diagrams, weak interactions, electromagnetic modifications to Dirac equation) and apply these to the problem of neutrino cooling in highly magnetized neutron star matter. The main reaction of interest is the direct Urca process (n → p+e+ν and p+e → n+ν), exploring the details of the effects of a strong magnetic field on charged particle wavefunctions, dispersions, and neutrino emissivity.