Fermions Bosons vertices in SM - but no SUSY

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Discussion Overview

The discussion revolves around the interactions of fermions and bosons within the framework of the Standard Model (SM) of particle physics, specifically contrasting these interactions with the transformations described by Supersymmetry (SUSY). The scope includes theoretical aspects of particle interactions, symmetry transformations, and the nature of gauge fields.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that in the Standard Model, fermions interact through exchanges of massless spin-1 particles, but they clarify that this does not imply fermions are turned into bosons during these exchanges.
  • Others emphasize that an interaction is distinct from a symmetry transformation, suggesting that the processes described in the SM do not equate to the mathematical operations of SUSY.
  • It is noted that the weak interaction is mediated by massive vector bosons, specifically the W and Z bosons, which adds complexity to the discussion of particle interactions.
  • Some participants propose that SUSY indicates the existence of bosonic partner particles for each fermion, rather than a direct transformation from fermion to boson.
  • A question is raised regarding the nature of symmetry generators and their association with particles, particularly in the context of SUSY and whether these generators manifest as interacting particles.
  • One participant mentions that gauge fields are not the generators of symmetry; rather, it is the corresponding Noether-charge operators that fulfill this role.
  • There is a reference to the behavior of the goldstino in spontaneously broken global SUSY and the gravitino in local SUSY, which can transform particles into their superpartners.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between fermions and bosons in the context of the Standard Model and SUSY. There is no consensus on whether the interactions described in the SM imply a transformation of fermions into bosons, and the discussion remains unresolved regarding the implications of symmetry transformations and their associated particles.

Contextual Notes

Participants highlight the distinction between interactions and symmetry transformations, indicating that assumptions about these concepts may vary. The discussion also touches on the role of gauge fields and Noether charges, which may require further clarification.

Lapidus
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In the Standard Model fermions interact via exchanges of massless (virtual) spin-1 particles. Fermions are turned into a boson. How is that different from the SUSY transformation that turns fermions into bosons?
 
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Lapidus said:
In the Standard Model fermions interact via exchanges of massless (virtual) spin-1 particles. Fermions are turned into a boson
Fermions are not turned into bosons in the exchange in the SM (unless in s-channel where two fermions combine into a generally off-shell boson).
 
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In addition the Orodruin's answer: An interaction (something physical happening) is not a symmetry transformation (a mathematical operation).
 
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Also note that the weak interaction is mediated by massive vector bosons, the ##W## (charged) and ##Z## (neutral) bosons.
 
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SUSY is not telling you that a fermion becomes a boson, it tells you that for each fermion there is a bosonic partner particle (super-partner). The two are related via supersymmetric transformations.
So the fact that the electron+positron annihilate let's say to 2 photons, doesn't tell you that the photon is the superpartner of the electrons/positrons (which are the selectrons)...
 
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Parhaps the question can be reformulated to how different
mfb said:
In addition the Orodruin's answer: An interaction (something physical happening) is not a symmetry transformation (a mathematical operation).

But the W and Z and gamma are symmetry transformations, generator of SU(2)xU(1), and they are particles too. It could be argued that they just happen to be particles in the defining representation of the symmetry, but then the question translates to "when do symmetries have associated particles"?

Particularly, er, specifically, what happens with the generator of supersymmetry? It seems that in this case it is not compulsed to appear as an associated particle interacting with all the others, is it? If it were, we should have diagrams where a fermion interacts with another one and becomes a boson.
 
Not the gauge fields are the generators of the symmetry but the corresponding Noether-charge operators. Of course you are right in saying that the gauge fields are Lie-algebra valued vector fields, i.e., something like ##\mathcal{A}_{\mu} =A_{\mu}^a \hat{t}^a##, where ##\hat{t}^a## are the Lie-algebra basis matrices in the representation of the field you apply the corresponding gauge-covariant derivative to, ##\mathrm{D}_{\mu} = \partial_{\mu} + \mathrm{i} g \mathcal{A}##.
 
arivero said:
what happens with the generator of supersymmetry?
See 7.5 of Stephen Martin. When global susy is spontaneously broken, the resulting goldstino can transform particles to their superpartners. In local susy, i.e. supergravity, the gravitino has this property.
 

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