Parity nonconservation and stellar collapse
ACCORDING to the current theory, the evolution of sufficiently massive stars leads eventually to gravitational instability and collapse. After thermonuclear burning has stopped, dense stellar cores become unstable and collapse to form neutron stars (pulsars) or black holes. In both cases energy of the order of 0.1 Mc2 is released, mostly in the form of neutrinos and gravitational waves. As the radius of the core decreases, its magnetic field grows (magnetic flux is conserved) and can reach huge values of order 1012–1013 G. Even greater azimuthal fields (∼3 × 1015 G) can be generated by differential rotation of the core1. It will be shown here that neutrino emission in the collapse is asymmetric, as a result of parity nonconservation in weak interactions. Neutrinos and antineutrinos are emitted preferentially in the direction parallel to the local magnetic field of the collapsing core.
Investigating the effect of a magnetic field on beta decay
The effect of an external magnetic field on theβ-decay process of a neutron is analyzed in detail. The spin effects within this process are studied, as is the final mass of the neutrino. Results of computer-based experiments are presented.
Coherent effects of a weak neutral current
If there is a weak neutral current, then the elastic scattering process &+A &+A should have a sharp coherent forward peak just as e+A -e+A does. Experiments to observe this peak can give important information on the isospin structure of the neutral current. The experiments are very difficult, although the estimated cross sections (about 10 38 cm2 on carbon) are favorable. The coherent cross sections (in contrast to incoherent) are almost energy-independent. Therefore, energies as low as 100 MeV may be suitable. Quasicoherent nuclear excitation processes v+A v+ A*provide possible tests of the conservation of the weak neutral current. Because of strong coherent effects at very low energies, the nuclear elastic scattering process may be important in inhibiting cooling by neutrino emission in stellar collapse and neutron stars.