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## 4.4.2 The Vector Meson Equation Of Motion 

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There is an additional field present on the D7 brane which we have left undiscussed: it is the gauge field partner of the scalar Φ. The field strength of this gauge field enters in the standard way as 2 πα ′ F ab in the square root. The leading Lagrangian for this field, in a background configuration σ$_{0}$ is 

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There is an additional term that could be added to the DBI action: the Wess-Zumino term, which gives the coupling of the four-form C (4) to the gauge fields. It is not included here because when we calculate the equations of motion for the gauge fields, this term is only relevant for the gauge fields with a vector index on the S $^{3}$. We are only interested in states that carry 

