|Manu||Date: Tuesday, 15-December-2020, 9:36 AM | Message # 1|
Are primordial magnetic field theories getting in a twist?
by Anna Demming , Phys.org
In cosmic voids where the density of galaxies is far lower than standard, astronomers have observed weak magnetic fields that may provide a window into the early universe. The fields 10-17-10-10 G in magnitude with large coherence lengths of up to megaparsecs are thought to have their origins in the early universe, but so far it is unclear when or how they were generated. One hypothesis is that an imbalance in the numbers of "left-handed" and "right-handed" fermions may be at the heart of it, as this could give rise to helical magnetic fields. But so far there has been no detailed analysis as to how the evolution of the numbers of left- and right-handed fermions might stack up against this hypothesis. Now a collaboration of researchers in Europe report a more rigorous analysis of this chirality imbalance with surprising results.
The handedness or chirality of fermions is a fundamental property of quantum particles (relevant for the description of the weak interaction between them). "For massless fermions it coincides with the particle's helicity, i.e. the projection of the particle's spin on the direction of its movement," explains Oleksandr Sobol, a postdoctoral researcher at the Ecole Polytechnique Fédérale de Lausanne in Swtizerland and the University of Kyiv, and corresponding author on this latest report. "However, for real massive fermions there is no simple analogy."
Oleksandr explains that certain processes can flip the chirality, which tends to even out the imbalance in fermion chirality over time. So far cosmologists have relied on an estimate of this decay rate based on the simplest reactions involved in these processes. According to these principles the decay rate is proportional to the square of a fundamental constant known as the fine structure constant, which quantifies the strength of electromagnetic interactions between fundamental particles. However, one of the things this estimate fails to take into account is the way particles in a plasma differ from particles in a vacuum. It turns out that this has a significant impact on calculations of the probability of one of the scattering processes that can flip a particle's chirality.
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