ABSTRACT
As before, the quantisation for vector fields starts by expanding the field in plane waves and identifying the Fourier coefficients with creation and annihilation operators: () https://www.w3.org/1998/Math/MathML"> A μ ( x ) = ∫ d 3 k → 2 k 0 ( k → ) ( 2 π ) 3 ∑ λ ( a λ ( k → ) ε μ ( λ ) ( k → ) e − i k x + a λ † ( k → ) ε μ ( λ ) ( k → ) ∗ e i k x ) , https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429073601/03ca065d-1bf0-4218-811d-2f95276252a3/content/equ_967.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
