Saturday, March 24, 2018

Difference between spinor and vector field




How do we distinguish spinors and vector fields? I want to know it in terms of physics with mathematical argument.



Answer



The answer to your question depends on the context, but the basic unifying theme distinguishing different kinds of fields (like vector fields, scalar fields, etc.) is how these fields transform when they are acted on by Lie Groups (and or Lie Algebras) which falls under the mathematical subject of representation theory of Lie groups and Lie algebras. Here are some examples to illustrate what I mean:


Consider a real field Vμ(x) defined on 4-dimensional Minkowski space R3,1. We say that this field is a Lorentz 4-vector field provided when it is acted on by a Lorentz transformation Λ=(Λμμν) (an element of the Lorentz Group SO(3,1)), it transforms as follows: Vμ(x)Vμ(x)=ΛμμνVν(Λ1x)


Now Consider instead a field Ψa(x) defined on 4-dimensional Minkowski space R3,1. We say that such a field is a Dirac Spinor provided when it is acted on by Lorentz transformations, it transforms as follows: Ψa(x)Ψa(x)=Rdir(Λ)aabΨb(Λ1x)

where Rdir is called the Dirac spinor representation of the Lorentz Group.


There are also other kinds of spinors, all of whom transform according to different representations of different Lie groups.


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