The Dirac conjugate of a scalar is the standard conjugate
In general, the Dirac conjugate of the Dirac conjugate of an object is the object itself
The Dirac conjugate of a Dirac matrix is the Dirac matrix itself
Note the display is different from the display of conjugate: the above has the bar in black and bold, instead of blue and thin as in (1)
The Dirac conjugate of is also equal to itself
Set coordinates, a quantum operator, an anticommutative prefix and a kind of letter to represent spinor indices
Define then one spinor using the anticommutative prefix and also a generic noncommutative spinor
Take their product
Sum over the repeated indices, then take the Dirac conjugate of the sum
This result is expressed in terms of the conjugate of the spinor components of and . Reversing the order of operations results in the same: take first the Dirac conjugate of the product , then sum over the repeated indices
Unlike conjugate, DiracConjugate allows for constructing true scalars using contracted products of spinors
The Dirac conjugate of a Matrix
The output involves the conjugates of the components of the transpose of multiplied at both sides by the Dirac matrix
If the matrix components are real,
The Lagrangian of QED: to load the StandardModel package, clear first the letters used to represent spinor indices
This Lagrangian is a scalar, constructed as a sum of products, where each term and each product involves noncommutative objects; the first term includes the contracted spinor product of the DiracConjugate of the electron field . Computing the Dirac conjugate of this Lagrangian is thus expected to result in several intermediate computations such that, at the end, the result is the same Lagrangian
For Annihilation and Creation operators, DiracConjugate returns the same as the Dagger command, that is the dual, respectively.
DiracConjugate understands Commutator and AntiCommutator
Thus, the DiracConjugate of an AntiCommutator of Hermitian operators is equal to itself (however, the product of two Hermitian operators is Hermitian only if they commute).
In the generic, non-Hermitian case:
For linear operators, differential and others, DiracConjugate is applied to the first operand.