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The helicity of a particle is positive (" right-handed") if the direction of its spin is the same as the direction of its motion and negative ("left-handed") if opposite. Helicity is conserved. [1] That is, the helicity commutes with the Hamiltonian, and thus, in the absence of external forces, is time-invariant. It is also rotationally ...
The number of subprocesses describing a given process is so large that automatic tools have been developed to mitigate the burden of hand calculations. Interactions at HighahEnergih open a large spectrum of possible final states and consequently increase the number of processes to compute.
Helicity is a pseudo-scalar quantity: it changes sign under change from a right-handed to a left-handed frame of reference; it can be considered as a measure of the handedness (or chirality) of the flow. Helicity is one of the four known integral invariants of the Euler equations; the other three are energy, momentum and angular momentum.
In the Standard Model, using quantum field theory it is conventional to use the helicity basis to simplify calculations (of cross sections, for example).
The β decay rate calculation was developed by Fermi in 1934 and was based on Pauli's neutrino hypothesis. Fermi's Golden Rule says that the transition rate W {\displaystyle W} is given by a transition matrix element (or "amplitude") M i , f {\displaystyle M_{i,f}} weighted by the phase space and the reduced Planck constant ℏ {\displaystyle ...
These amplitudes are called MHV amplitudes, because at tree level, they violate helicity conservation to the maximum extent possible. The tree amplitudes in which all gauge bosons have the same helicity or all but one have the same helicity vanish. MHV amplitudes may be calculated very efficiently by means of the Parke–Taylor formula.
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Magnetic helicity is a gauge-dependent quantity, because can be redefined by adding a gradient to it (gauge choosing).However, for perfectly conducting boundaries or periodic systems without a net magnetic flux, the magnetic helicity contained in the whole domain is gauge invariant, [15] that is, independent of the gauge choice.