DiracConjugate - Maple Help
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Physics[DiracConjugate] - compute the Dirac conjugate a given mathematical expression

Calling Sequence

DiracConjugate(psi)

Parameters

psi

-

any mathematical expression, possibly involving spinors or matrices

Description

• 

The DiracConjugate command represents and computes the Dirac conjugate of its argument; the returned result is built as follows:

  

- If  is a scalar, return its conjugate, .

  

- If  is a spinor, so defined with one spinor index using the Define command, or  is an anticommutative quantum operator (see Setup) with a spinor index, then return unevaluated, as DiracConjugate(psi), displayed as , representing , where  is the Hermitian conjugate Dagger(psi) and  is the contravariant  Dirac matrix Dgamma[~0].

  

- If  is the Dirac conjugate of - say -  , then return .

  

- If  is a Dirac matrix (represented by the Dgamma command), then return the matrix  itself, also when .

  

- If  is a Matrix - say  - return the matrix product , where  is the Dagger(M), the Hermitian conjugate of .

  

- If  is a sum of terms, return the sum of the DiracConjugate of each term.

  

- If  is a product, return , that is the product of the DiracConjugate of each of the factors with the ordering reversed.

  

- If  is one of the d_ or dAlembertian operators, return the operator applied to the DiracConjugate of the first operand of .

  

- Otherwise, return the operation unevaluated, DiracConjugate(A).

• 

The %DiracConjugate command is the inert form of DiracConjugate; that is, it represents the same mathematical operation while displaying the operation unevaluated. To evaluate the operation, use the value command.

About Spinors

• 

After loading Physics, you indicate the letter to represent a spinor index using the Setup command, for example: Setup(spinorindices = lowercaselatin). A spinor is then any symbol indexed with one spinor index, and defined as a tensor using Define. If the symbol is anticommutative, and has one spinor index, and was defined as a tensor using Define or alternatively was set as a quantum operator using Setup, then it represents a DiracSpinor,

• 

You can check whether say  is a spinor using the Library:-PhysicsType:-Spinor, as in type(psi[j], Library:-PhysicsType:-Spinor). Likewise, you can check if the object is a DiracSpinor using the Library:-PhysicsType:-DiracSpinor. Note that the object can have more than one index, but to be a spinor (Dirac or not), only one of them must be a spinor index. The related types Library:-PhysicsType:-SpinorWithoutIndices and Library:-PhysicsType:-DiracSpinorWithoutIndices return true when the argument passed to them, say , has no indices but would be a Spinor if it had a spinor index.

• 

Any tensor with more than one spinor index, is not "a spinor" but it is spinorial, for the example the Dirac matrices . You can check whether an object is spinorial using the Library:-IsSpinorial command, say as in Library:-IsSpinorial(Dgamma[mu][j,k]), which will returns true in this case, and false when the object is not spinorial. Likewise, a sum of spinorial objects, or a product of them with at least one free spinor index, is considered spinorial, for which Library:-IsSpinorial returns true.

Examples

The Dirac conjugate of a scalar is the standard conjugate

(1)

In general, the Dirac conjugate of the Dirac conjugate of an object is the object itself

(2)

The Dirac conjugate of a Dirac matrix is the Dirac matrix itself

(3)

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

(4)

Set coordinates, a quantum operator, an anticommutative prefix and a kind of letter to represent spinor indices

(5)

Define then one spinor using the  anticommutative prefix and also a generic noncommutative spinor

(6)

Take their product

(7)

Sum over the repeated indices, then take the Dirac conjugate of the sum

(8)

(9)

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

(10)

(11)

Unlike conjugate, DiracConjugate allows for constructing true scalars using contracted products of spinors

(12)

(13)

(14)

(15)

The Dirac conjugate of a Matrix

(16)

The output involves the conjugates of the components of the transpose of  multiplied at both sides by the Dirac matrix

(17)

If the matrix components are real,

(18)

(19)

(20)

The Lagrangian of QED: to load the StandardModel package, clear first the letters used to represent spinor indices

(21)

(22)

(23)

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

(24)

For Annihilation and Creation operators, DiracConjugate returns the same as the Dagger command, that is the dual, respectively.

(25)

(26)

(27)

(28)

DiracConjugate understands Commutator and AntiCommutator

(29)

(30)

(31)

(32)

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).

(33)

(34)

(35)

In the generic, non-Hermitian case:

(36)

For linear operators, differential and others, DiracConjugate is applied to the first operand.

(37)

(38)

(39)

See Also

Annihilation, AntiCommutator, Bra, Bracket, Commutator, Creation, d_, Dagger, dAlembertian, g_, Ket, Physics, Physics conventions, Physics examples, Physics Updates, Tensors - a complete guide, Mini-Course Computer Algebra for Physicists, Setup, value

Compatibility

• 

The Physics[DiracConjugate] command was introduced in Maple 2024.

• 

For more information on Maple 2024 changes, see Updates in Maple 2024.


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