The theoretical description of meson photoproduction reactions off the proton at energies around 2 GeV requires the consideration of channels involving vector mesons and baryons together with a proper implementation of unitarization. A clear example is provided by the $\gamma p \to K^0 \Sigma^+$ reaction in the energy region around the $K^\Lambda$ and $K^\Sigma$ thresholds, where the CBELSA/TAPS cross section shows a sudden drop [1]. We have developed a unitarized coupled channel model [2] that incorporates the dynamics of the vector meson-baryon interaction, which is obtained from the hidden gauge formalism. We find that the cross section in this energy region results from a delicate interference between amplitudes having $K^\Lambda$ and $K^\Sigma$ intermediate states. The sharp downfall is dictated by the presence of a nearby $N^$ resonance produced by our model, a feature that we have employed to predict its properties. We also show predictions for the complementary $\gamma n \to K^0 \Sigma^0$ reaction. Another manifestation of the importance of the vector meson-baryon dynamics may be found on the in-medium properties of the vector mesons. We have analyzed the contributions to the vector meson self-energies in nuclear matter coming from various sources [3,4]. We find that the width of the $K^$ meson at normal nuclear matter density is about $\Gamma_{K^*}$=260 MeV while that of the $\omega$ meson is $\Gamma_\omega$=121 MeV, both substantially larger than their free space values.

[1] R. Ewald et al., Phys. Lett. B713 (2012) 180. [2] A. Ramos, E. Oset, Phys. Lett. B727 (2013) 287 [3] A. Ramos, L. Tolos, R. Molina, E. Oset, Eur. Phys. J. A (2013) 49: 148. [4] L. Tolos, R. Molina, E. Oset, A. Ramos, Phys. Rev. C82 (2010) 045210