Electromagnetic form factors from the fifth dimension

Abstract

We analyse various $U(1{)}_{EM}$ form factors of mesons at strong coupling in an $\mathcal{N}=2$ flavored version of $\mathcal{N}=4$ $SYM$ which becomes conformal in the UV. The quark mass breaks the conformal symmetry in the IR and generates a mass gap. In the appropriate limit, the gravity dual is described in terms of probe $D7$-branes in $Ad{S}_5\times S^5$. By studying the $D7$ fluctuations we find the suitable terms in a "meson effective theory" which allow us to compute the desired form factors, namely the $\gamma \pi \rho$ and $\gamma f_0\rho$ transition form factors. At large $q^2$ we find perfect agreement with the naive parton model counting, which is a consequence of the conformal nature of both QCD and our model in the UV. By using the same tools, we can compute the ${\gamma }^{\ast }{\gamma }^{\ast }\pi$ form factor. However this channel is more subtle and comparisons to the QCD result are more involved.

34 pages, 6 figures, pdflatex. References and clarifications added

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• Virtual Compton Scattering off a Spinless Target in AdS/QCD
• Deep inelastic scattering off a plasma with flavour from D3-D7 brane model
• Generalized baryon form factors and proton structure functions in the Sakai-Sugimoto model
• High--Energy Photon--Hadron Scattering in Holographic QCD
• The Virtual Photon Structure Functions and AdS/QCD Correspondence
• Holography for General Gauge Mediation
• Deep Inelastic Scattering in Holographic AdS/QCD Models
• Gauge Mediated Supersymmetry Breaking in Five Dimensions
• ADS/CFT Applied To Vector Meson Emission From A Heavy Accelerated Nucleus