Worldvolume fermion as baryon with homogeneous instantons in holographic $\mathrm{QCD}_{3}$

Abstract

(ArXiv version) We investigate holographically the effective theory of the worldvolume fermion on the flavor branes in the D3/D7 model with homogeneously smeared D(-1)-branes. As a top-down approach in gauge-gravity duality, the D(-1)-branes are instantons and violate the CP symmetry in the dual theory. In the confined geometry, we introduce a baryon vertex as a D5-brane wrapped on $S^{5}$, then identify the fermionic fluxes produced by the $N_{c}$ open strings on the D7-brane as a baryonic operator. Afterwards, we study the spectrum and the holographic correlation function of the baryonic fermion on the D7-branes. Remarkably, the fermionic spectrum is in agreement with the dispersion curves obtained from the confined correlation function, and the mass ratio of the lowest baryon and meson in our model is close to the associated experimental data. Moreover, the effective interaction terms of the holographic baryon and meson are derived and all the coupling constants take order of $N_{c}^{1/2}$ agreeing with the evaluation from the large $N_{c}$ field theory. In the deconfined geometry, the holographic correlation function is also evaluated numerically while the fermion on D7-brane is identified to plasmino instead of baryon. The dispersion curves from the deconfined correlation function basically covers the results from the hard thermal loop approximation and may imply the instanton-induced interaction with spin. Overall, this work constructs a holographic theory about baryonic fermion and mesonic boson with instantons or CP violation.