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Confused about spinors a bit

  1. Jul 3, 2010 #1
    Hi, I'm trying to teach myself a bit about spinors, mainly from reading about geometric algebra. There is something that I can't figure out though. According to GA, spinors are elements of the even graded subalgebra, so scalars, bivectors and so on. But the electromagnetic field is a bivector, but surely it's not a spinor... so how does that make sense?

    Also: When they talk about even graded elements being spinors, are they talking about spin 1/2, 1, 3/2... or something else?

    The other thing I'd like to ask about is this unclear section on wikipedia:
    I didn't really understand the bit about Clebsch-Gordon decomposition but I really don't get how [itex]\bar{\phi}\psi[/itex] can be considered as a scalar and/or a vector. I can see why it would be a scalar but not a vector as well. (BTW the latex \bars don't seem to be showing up)

    These are probably fairly basic things... I'm pretty new to it all!
  2. jcsd
  3. Jul 3, 2010 #2
    The literature on spinors can be very confusing since every person uses different notation. The way I have always understood things is that spinors in n dimensions make up the representation space of a representation of the even subalgebra of the clifford algebra. That is, even elemenets of the Clifford algebra (like bivectors) act on spinors.

    In regards to the product of spinors, I am not sure. I mean [tex]\bar \phi \psi[/tex] should be a scalar. Maybe for the other thing they meant the Kronecker product [tex]\psi \bar\phi[/tex] which is in the endomorphism space of spinors and therefore can be seen as an element of the even Clifford algebra.

    The clearest reference on spinors I have found is Ian Porteous's book "Clifford algebras and the classical groups."
  4. Jul 3, 2010 #3
    ahhhhhh ... these are the things which really makes me confused also.. in my school life i never get good marks in geometry just because i never get it correctly... nd even now after passing school i can not make out differences in this field
  5. Jul 3, 2010 #4
    That seems quite different to saying that spinors ARE elements of the even graded subalgebra. It seems to make more sense based on what I've read about representing vectors and matrices and spinors as vectors though. If even elements of the Clifford algebra act on spinors, what do they actually DO to the spinors when they act?

    The other thing why I'm not sure why spinors can be even graded elements- in 4d spacetime they have 4=2^(4/2) components, but there are 8=1/2*2^4 components in the even graded subalgebra (1 scalar, 1 pseudoscalar, 6 bivectors). So I'm kind of confused about how to connect this all up.
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