Preprint Mathematics
Trace-perturbed minimizers of the mixed discriminant
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Overview
Abstract
For each fixed matrix size, we prove that the scalar tuple uniquely minimizes the mixed discriminant of positive semidefinite Hermitian matrices whose sum is the identity and whose individual traces are sufficiently close to one. This answers Question 1.7 of Gurvits-Leake, arXiv:2609.21083v2. The argument combines Gurvits's doubly stochastic uniqueness theorem with a positive constrained Hessian and compactness. We also record the exact region of positive definiteness of that Hessian at a scalar tuple. The global neighborhood in the theorem is qualitative and may depend on the size.
Keywords mixed discriminant · positive semidefinite matrices · Hermitian matrices · trace constraints · stability · constrained Hessian
Scope of the work
For every fixed integer n >= 1, a sufficiently small neighborhood of the uniform trace vector is considered, with sum t_i = n, ||t - 1||_1 < epsilon_n, complex Hermitian positive semidefinite n-tuples, Tr X_i = t_i, and sum X_i = I. The unique minimizer is X_i = (t_i/n)I, with normalized minimum prod(t_i)/n^n. No explicit or dimension-uniform global radius, general real-stable-polynomial result, or algorithmic improvement is asserted. The exact Hessian criterion is local and does not determine the global minimizer region; equality in that criterion is not classified by second variation.
Reproduction notes
Manuscript version 1.0, October 20, 2026; first public Archive edition 1. The publication package contains the complete four-page PDF, self-contained LaTeX source with embedded bibliography, reader build instructions, BibTeX entries, and a checksum manifest for the other four files. The proof is analytic and requires no computational certificates or data. Standard LaTeX packages are required; the README gives Tectonic and pdfLaTeX instructions. Rebuilt PDFs may differ in bytes because of compiler, font, or metadata differences.
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Author disclosures
This specialist note relies on Gurvits's earlier doubly stochastic global uniqueness theorem and standard stability and compactness arguments. The close argument in his Corollary 4.2 and the already-known simultaneously diagonalizable permanent subcase are explicitly credited. External novelty remains provisional; no worldwide priority or practical application is claimed. AI tools assisted with derivations, literature searches, proof checking, and manuscript preparation. Internal AI-assisted checks do not constitute external human refereeing or formal verification.
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Scott Schubr. (2026). Trace-perturbed minimizers of the mixed discriminant (Version 1). Luminary Research Archive. https://luminaryoddities.com/researcharchive/trace-perturbed-minimizers-of-the-mixed-discriminant/v/1
BibTeX
@techreport{luminary_trace_perturbed_minimizers_of_the_mixed_discriminant_v1,
title = {Trace-perturbed minimizers of the mixed discriminant},
author = {Scott Schubr},
year = {2026},
institution = {Luminary Research Archive},
type = {Preprint},
note = {Version 1},
url = {https://luminaryoddities.com/researcharchive/trace-perturbed-minimizers-of-the-mixed-discriminant/v/1}
}Reader correspondence
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