Hadrons as holograms

We review our recent work on four topics in strong-interaction physics from the perspective of the gauge/gravity correspondence. In particular, we discuss (i) the construction of the ``metric soft wall'' dual for holographic QCD which reproduces the observed linear square-mass trajectories of radially and orbitally excited (light-quark) hadrons, (ii) an extension of the metric soft wall which encodes diquark correlations holographically and additionally leads to an excellent description of the empirical nucleon excitation spectrum, (iii) an AdS/QCD dual that emerges as a new solution of 5d Einstein-dilaton gravity with a specifically derived potential and realizes the area law of the Wilson loop and (approximately) linear meson trajectories dynamically, and finally (iv) the calculation of glueball correlation functions and decay constants in both the hard- and dilaton soft-wall gravity duals, as well as a quantitative analysis of their QCD-relevant physics content.