Maximilian Haensch | Searcharxiv

arXiv2026

Positivity properties of observables in planar maximally supersymmetric Yang-Mills theory

We study positivity properties of exact observables in planar N=4 super Yang-Mills as functions of the 't Hooft coupling. Motivated by analogous results in quantum mechanics, we ask whether such observables admit a once-subtracted dispersion representation in the coupling over a positive spectral measure. Our main result is that this property, also known as the Stieltjes property, holds for a broad class of exact observables. We prove it analytically, through integral representations, for the octagon anomalous dimension, the logarithm of the circular Wilson loop, the Bremsstrahlung function, and anomalous dimensions in the BMN limit, and we provide numerical evidence for the cusp and tilted cusp anomalous dimensions. We also identify quantities for which the Stieltjes property does not hold, and study the weaker positivity property of complete monotonicity. The Stieltjes property yields two powerful consequences: it lets us turn perturbative input into rigorous non-perturbative bounds, and bootstrap perturbative coefficients. We also show how the strong-coupling expansion and its non-perturbative corrections can be recovered from the once-subtracted dispersion representation via a Mellin-Barnes representation and outline a method to estimate the strong-coupling expansion from weak-coupling data.

hep-th↗

arXiv2024

Medium induced mixing, spatial modulations and critical modes in QCD

The mixing between the chiral condensate and the density in hot and dense QCD matter is familiar. We show that the mixing relevant for the ground state is considerably more extensive, and in particular also involves gluonic degrees of freedom. As a result, the Hessian of the QCD effective action is non-Hermitian, but retains a symmetry under combined charge- and complex conjugation. This can lead to complex-conjugate pairs of eigenvalues of this Hessian, signaling regimes with spatially modulated correlations. Furthermore, based on the analytic structure of the quark determinant at a chiral critical point, we demonstrate that the corresponding massless critical mode is composed of the chiral condensate, the density and the Polyakov loops. Due to an avoided crossing, the critical mode turns out to be disconnected from the chiral condensate in vacuum. We present general arguments for all these features and illustrate them through explicit model calculations.

hep-ph↗