What does that neutrino taste like? Adding flavor helps to trace the motion of neutrinos in astrophysical systems

Neutrinos have a quantum mechanical property called “flavor”. This flavor can transform as neutrinos move through space. A major challenge is to track the physical motion of neutrinos and their changing flavor in astrophysical systems such as core-collapse supernovae and neutron star mergers. The complicated arrangement and large number of neutrinos in these systems make it almost impossible to track all or even a subset of the neutrinos.

The researchers examined a possible way to solve this challenge. The approach involves extending traditional methods of calculating neutrino motion to include quantum mechanical flavor variation. This approach reduces the complexity of calculating how neutrinos behave in complex systems

The research was published in The Astrophysical Journal AND Physics letters B diary.

A supernova or neutron star merger sends out many kinds of messengers, from photons to gravitational waves, from neutrinos to heavy elements. These messengers provide scientists with new insights into the physics of these stellar objects. However, scientists need to understand the physics of neutrinos to use these messengers. Neutrinos carry a significant fraction of the energy of these systems.

In addition, scientists need to understand the interactions involving neutrinos to predict the heavy elements produced by star explosions and stellar mergers. The angular momenta summarize the total number and flux of neutrinos in a small set of equations of motion.

Scientists can then use these equations to calculate the difference in neutrino flavor. The reduced number of equations in the angular momentum method provides a way forward for solving neutrino flavor transformation problems in compact astrophysical objects, such as merging neutron stars.

This research examined the prospects for using a semi-classical approach based on angular momentum to include quantum mechanical flavor effects in neutrino transport in a neutron star merger remnant. The researchers tested the method on a type of neutrino flavor transformation called “fast flavor,” for which angular information about the neutrinos is a known requirement for the transformation. The result was that the method captured transformation growth well and that this method warrants further exploration.