PhysLean Documentation

PhysLean.QFT.PerturbationTheory.FieldOpAlgebra.TimeContraction

Time contractions #

We define the state algebra of a field structure to be the free algebra generated by the states.

For a field specification 𝓕, and φ and ψ elements of 𝓕.FieldOp, the element of 𝓕.FieldOpAlgebra, timeContract φ ψ is defined to be 𝓣(φψ) - 𝓝(φψ).

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    For a field specification 𝓕, and φ and ψ elements of 𝓕.FieldOp, if φ and ψ are time-ordered then

    timeContract φ ψ = [anPart φ, ofFieldOp ψ]ₛ.

    For a field specification 𝓕, and φ and ψ elements of 𝓕.FieldOp, if φ and ψ are not time-ordered then

    timeContract φ ψ = 𝓢(𝓕 |>ₛ φ, 𝓕 |>ₛ ψ) • [anPart ψ, ofFieldOp φ]ₛ.

    For a field specification 𝓕, and φ and ψ elements of 𝓕.FieldOp, then timeContract φ ψ is in the center of 𝓕.FieldOpAlgebra.