Tachyon-dependent Chern-Simons terms and the V-QCD baryon

Abstract

The structure of the five-dimensional Tachyon-Chern-Simons action and its relevance to single-baryon states in the context of the V-QCD models for holographic QCD with backreacting flavor are analyzed. The most general form of the Tachyon-Chern-Simons 5-form, compatible with symmetries and flavor anomalies is determined. It is the sum of a non-trivial gauge-invariant 5-dimensional form and a non-invariant closed 5-form that reproduces the flavor anomalies. Single-baryon solutions of the gravity theory, arising from the DBI plus Tachyon-Chern-Simons actions are considered. The baryon is realised as a bulk axial instanton. The baryon ansatz and the field equations are derived and the boundary conditions are determined, which ensure that the solution has finite boundary energy and unit baryon charge. The boundary baryon number, which is computed from the universal (closed) part of the Tachyon-Chern-Simons action, is shown to coincide with the bulk axial instanton number.

Holographic dense QCD in the Veneziano limit

“…This required, among other things, a thorough study of the possible Chern-Simons action in the bottom-up framework, in the presence of nontrivial tachyon field. Numerical results for the soliton will appear soon [37]. After fitting the model parameters to thermodynamics, meson masses, and the pion decay constant, the classical mass of the soliton was found to be near 1 GeV, in good agreement with the observed masses of the nucleons.…”

“…The behavior of the functions at intermediate values of the dilaton can then be tuned to agree with lattice data for glueball spectra, thermodynamics of Yang-Mills [34] and full QCD [35], or experimental data for meson masses [36]. A combined, overall fit will be discussed in a future publication [37]. [38] (red dots and error bars).…”

“…The coupling of the soliton to the tachyon field, which characterizes chiral symmetry breaking, was studied in [72,73]. The setup for the baryon solution in V-QCD was established in [74]. This required, among other things, a thorough study of the possible Chern-Simons action in the bottom-up framework, in the presence of nontrivial tachyon field.…”