Complex Geometry and Dirac Equation

S. De Leo, WA Rodrigues, J. Vaz (Dpt Fisica,Lecce and IMECC-UNICAMP)

(Submitted on 17 May 1999)

Abstract: Complex geometry represents a fundamental ingredient in the formulation of the Dirac equation by the Clifford algebra. The choice of appropriate complex geometries is strictly related to the geometric interpretation of the complex imaginary unit $i=\sqrt{-1}$. We discuss {\em two} possibilities which appear in the multivector algebra approach: the $\sigma_{123}$ and $\sigma_{21}$ complex geometries. Our formalism permits to perform a set of rules which allows an immediate translation between the complex standard Dirac theory and its version within geometric algebra. The problem concerning a double geometric interpretation for the complex imaginary unit $i=\sqrt{-1}$ is also discussed.

Comments: 11 pages, RevTex
Subjects: High Energy Physics – Theory (hep-th)
Journal reference: Int.J.Theor.Phys. 37 (1998) 2479
Report number: IMECC RP16/98
Cite as: arXiv:hep-th/9905124v1

Pauli identity and vector products: geometric, dot, wedge, and cross

Let \mathbf a and \mathbf b be two vectors in the Clifford algebra \mathcal Cl_{3,0}:

(1a)\qquad\mathbf a=a_1\mathbf e_1+a_2\mathbf e_2+a_3\mathbf e_3,
(1b)\qquad\mathbf a=b_1\mathbf e_1+b_2\mathbf e_2+b_3\mathbf e_3.

The geometric (direct) product of \mathbf a and \mathbf b is

(2)\qquad\mathbf a\mathbf b = a_1b_1\mathbf e_1\mathbf e_1+a_1b_2\mathbf e_1\mathbf e_2+a_1b_3\mathbf e_1\mathbf e_3
\qquad\qquad+ a_2b_1\mathbf e_2\mathbf e_1+a_2b_2\mathbf e_2\mathbf e_2+a_2b_3\mathbf e_2\mathbf e_3
\qquad\qquad+ a_3b_1\mathbf e_3\mathbf e_1+a_3b_2\mathbf e_3\mathbf e_2+a_3b_3\mathbf e_3\mathbf e_3

Using the orthonormality axiom, we can show that

(3)\qquad\mathbf a\mathbf b=\mathbf a\cdot\mathbf b+\mathbf a\wedge\mathbf b,

where

(4a)\qquad\mathbf a\cdot\mathbf b=a_1b_1+a_2b_2+a_3b_3,
(4b)\qquad\mathbf a\wedge\mathbf b=(a_1b_2-a_2b_1)\mathbf e_1\mathbf e_2+(a_2b_3-a_3b_2)\mathbf e_2\mathbf e_3+(a_3b_1-a_1b_3)\mathbf e_3\mathbf e_1.

In terms of the imaginary number (unit trivector) i=\mathbf e_1\mathbf e_2\mathbf e_3, we may rewrite the wedge product \mathbf a\wedge\mathbf b as

(5)\qquad\mathbf a\wedge\mathbf b=i(\mathbf a\times\mathbf b),

where

(6)\qquad \mathbf a\times\mathbf b=(a_2b_3-a_3b_2)\mathbf e_1+(a_3b_1-a_1b_3)\mathbf e_2+(a_1b_2-a_2b_1)\mathbf e_3

is the cross product of \mathbf a and \mathbf b. Substituting Eq. (5) back to Eq. (3), we obtain the familiar Pauli identity:

\mathbf a\mathbf b=\mathbf a\cdot\mathbf b+i(\mathbf a\times\mathbf b).

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