R-parity and conservation of angular momentum

[Ken41]

Assuming R-pairity and thus the creation/destruction of supersymmetric particles happens in pairs,
how is angular momentum conserved when a particle and its supersymmetric partner have different spin by 1/2?

 

[fzero]

It depends on the process, but angular momentum will be conserved in ways that are already familiar from SM processes. For example, in the SM, we can have processes like $gg\rightarrow q \bar{q}$. At tree-level, there is a diagram

$g$ ^^^^^^^^^^^^^^^^---------------------- $q$
$\hspace{3.65cm}$ |
$\hspace{3.65cm}$ |
$\hspace{3.65cm}$ |
$g$ ^^^^^^^^^^^^^^^^---------------------- $\bar{q}$

Angular momentum is conserved because the initial state can have $J = 0,1,2,\ldots$ and so can the final state.

In the MSSM, the same diagram can describe gluino production $gg\rightarrow \tilde{g} \bar{\tilde{g}}$. It is also easy to add additional vertices to produce a 1-loop diagram with squarks or a squark + $q\bar{q}$ in the final state

 

[Ken41]

Thanks for responding! Is it obvious why in your example, gg→g̃ barg̃ , ( where NN->SS) , the reverse reaction (SS->NN) would not be allowed? The R- parity would not change, so CPT stays the same...

 

[fzero]

Thanks for responding! Is it obvious why in your example, gg→g̃ barg̃ , ( where NN->SS) , the reverse reaction (SS->NN) would not be allowed? The R- parity would not change, so CPT stays the same...

The reverse reaction would be allowed. The R-parity of $\tilde{g}$ is $-1$, but the R-partity is multiplicative, so for a system of two of them it is $1$. In general, R-parity is conserved by particle-antiparticle annihilation for all SUSY particles.

 

[ohwilleke]

More generally, any Feynman diagram's truth or falsity is never changed by rotating the diagram.

 

[member 11137]

Assuming R-pairity and thus the creation/destruction of supersymmetric particles happens in pairs,
how is angular momentum conserved when a particle and its supersymmetric partner have different spin by 1/2?

Do you know this document: "m_T2: the truth behind the glamour", arXiv:hep-ph/0304226v1, 23 April 2003? Perhaps you might be interested by it.