On Dp-Dp+4 systems, QCD dual and phenomenology

TL;DR

The paper advances a program to realize a holographic dual of large-$N$ QCD using brane configurations, centering on D4-D8 and D3-D7 constructions. It identifies a candidate QCD dual, a system of $D3-(D7-ar{D7}(D5))-D7'$, but notes that an explicit supergravity solution for the full setup is not available; supersymmetry is broken via a $D7-ar{D7}$ condensation to a D5, motivating an exploration of Standard Model embeddings through TeV-scale string theory. The work develops a domain-wall–QFT perspective (DW-QFT) for nonconformal branes and relies on Hull duality to discuss UV completions in M theory, outlining how various M-brane and T-dual frames could encode the decoupled field theory. In the phenomenology section, it analyzes D3-D7-O(7) based Lagrangians and the prospects for TeV-scale strings, including orientifold-induced spectra; it concludes that while a brane-world approach remains appealing, achieving a realistic SM content without invoking problematic additional fields or mass scales is difficult. Overall, the paper maps a concrete holographic route to QCD while candidly exposing substantial technical and phenomenological barriers to a fully realistic string-theoretic Standard Model embedding.

Abstract

D4-D8 and D3-D7 systems are studied and a possible holographic dual of large N QCD (SU(N) gauge fields and fundamental quarks) is sought. A candidate system is found, for which however no explicit solution is available. Susy is broken by having a $D7-\bar{D7}$ condensing to a D5. The mechanism for supersymmetry breaking is then used to try to construct a Standard Model embedding. One can either obtain too few low energy fields or too many. The construction requires TeV scale string theory.