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Results tagged with helicity
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user 50583
In particle physics, helicity is the projection of the angular momentum onto the direction of momentum. For massless spin-1⁄2 particles, helicity is equivalent to the chirality operator multiplied by $\hbar/2$, so may be used for related chirality questions as well.
7
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A thought experiment about neutrinos
The two notions are only the same for massless particles - for which then helicity is also frame-invariant since massless particle have no rest frame. … Its helicity flips, sure, but its chirality - the thing the weak interaction cares about - doesn't. …
- 129k
13
votes
Accepted
Is an Anti-positron actually only a relativistic effect on the observed helicity of an elect...
The article you link is choosing to use non-standard terminology to explain how the weak force can couple to particles with a certain handedness but not others. I do something similar with "electron-1 …
- 129k
4
votes
Accepted
What is the value of $W_\mu W^\mu$ for massless particles?
There are two of them that are interchanged by parity transformations, so the "usual" massless particle gets a two-dimensional "helicity representation". …
- 129k
1
vote
How do the vector and scalar potentials transform under electromagnetic duality trnasfotmation?
On the level of the field strength tensor $F$, duality is the map $F\mapsto {\star}F$, where ${\star}$ is the Hodge dual. Maxwell's equations in vacuum are
$$ \mathrm{d}F = 0 \quad \text{and} \quad \m …
- 129k
0
votes
Adding helicities
Helicity is the projection of spin onto momentum. … If by "total helicity" you mean the projection of the total spin onto the total momentum, then this is impossible to compute from the individual helicities (take the extreme case where each individual …
- 129k
8
votes
Accepted
Helicity quantization of massless particles
Helicity is different from angular momentum because the angular momentum algebra is the Lie algebra of the massive little group $\mathrm{SO}(3)$, while helicity is for massless particles and hence must … So how does this helicity relate to $4\pi$ rotations? …
- 129k
1
vote
Accepted
Nature of Chirality: Additive or multiplicative?
The unitary representations are labeled by the mass and spin (for massive states) and helicity (for massless states), but not by anything that would lend itself to be interpreted as chirality that would … The available operator is helicity (and other spin components, of course), not chirality. …
- 129k
2
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Transverse polarizations of a massless spin 1 particle
The states with circular polarization in your basis are called helicity because they are eigenstates of the helicity operator. … For more on helicity for photons, see e.g. this answer or this answer of mine. …
- 129k
98
votes
Why is the $S_{z} =0$ state forbidden for photons?
They have helicity, which is the value of the projection of the spin operator onto the momentum operator. … And that's it - massless particles of helicity $h$ have the $h\oplus -h$ representation on their space of states, not a spin representation of $\mathrm{SO}(3)$. …
- 129k
9
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Accepted
Confusion with chirality eigenstates
Another one of these issues where careless terminology is our downfall.
Indeed, on the level of the Dirac equation, such a thing as a "left-handed electron" does not exist. Every pure electron and ev …
- 129k
36
votes
What is polarisation, spin, helicity, chirality and parity?
Helicity is the projection of the spin vector upon momentum. … It is to be noted that, for massless fermions, the chiral subspaces are precisely the eigenspaces of helicity. …
- 129k