Direct Instantons and Nucleon Magnetic Moments

We calculate the leading direct-instanton contributions to the operator product expansion of the nucleon correlator in a magnetic background field and set up improved QCD sum rules for the nucleon magnetic moments. Remarkably, the instanton contributions are found to affect only those sum rules which had previously been considered unstable. The new sum rules show good stability and reproduce the experimental values of the nucleon magnetic moments with values of $\chi$, the quark condensate magnetic susceptibility, consistent with other estimates.Comment: 15 pages, 2 figure

Glottocodes: identifiers linking families, languages and dialects

Glottocodes constitute the backbone identification system for the language, dialect and family inventory Glottolog(https://glottolog.org). In this paper, we summarize the motivation and history behind the system of glottocodes and describe theprinciples and practices of data curation, technical infrastructure and update/version-tracking systematics. Since our understandingof the target domain—the dialects, languages and language families of the entire world—is continually evolving, changesand updates are relatively common. The resulting data is assessed in terms of the FAIR (Findable, Accessible, Interoperable,Reusable) Guiding Principles for scientific data management and stewardship. As such the glottocode-system responds to animportant challenge in the realm of Linguistic Linked Data with numerous NLP applications.1. Introduction 2. Motivation and History 3. Glottolog data curation 3.1. Glottolog data is findable 3.2. Glottolog data is accessible 3.3. Glottolog data is interoperable 3.4. Glottolog data is reusable 4. Policies governing glottocode assignment 5. Glottolog versioning 6. Conclusio

Vacuum structure and string tension in Yang-Mills dimeron ensembles

We numerically simulate ensembles of SU(2) Yang-Mills dimeron solutions with a statistical weight determined by the classical action and perform a comprehensive analysis of their properties. In particular, we examine the extent to which these ensembles capture topological and confinement properties of the Yang-Mills vacuum. This further allows us to test the classic picture of meron-induced quark confinement as triggered by dimeron dissociation. At small bare couplings, spacial, topological-charge and color correlations among the dimerons generate a short-range order which screens topological charges. With increasing coupling this order weakens rapidly, however, in part because the dimerons gradually dissociate into their meron constituents. Monitoring confinement properties by evaluating Wilson-loop expectation values, we find the growing disorder due to these progressively liberated merons to generate a finite and (with the coupling) increasing string tension. The short-distance behavior of the static quark-antiquark potential, on the other hand, is dominated by small, "instanton-like" dimerons. String tension, action density and topological susceptibility of the dimeron ensembles in the physical coupling region turn out to be of the order of standard values. Hence the above results demonstrate without reliance on weak-coupling or low-density approximations that the dissociating dimeron component in the Yang-Mills vacuum can indeed produce a meron-populated confining phase. The density of coexisting, hardly dissociated and thus instanton-like dimerons seems to remain large enough, on the other hand, to reproduce much of the additional phenomenology successfully accounted for by non-confining instanton vacuum models. Hence dimeron ensembles should provide an efficient basis for a rather complete description of the Yang-Mills vacuum.Comment: 36 pages, 17 figure

Gauge-invariant and infrared-improved variational analysis of the Yang-Mills vacuum wave functional

We study a gauge-invariant variational framework for the Yang-Mills vacuum wave functional. Our approach is built on gauge-averaged Gaussian trial functionals which substantially extend previously used trial bases in the infrared by implementing a general low-momentum expansion for the vacuum-field dispersion (which is taken to be analytic at zero momentum). When completed by the perturbative Yang-Mills dispersion at high momenta, this results in a significantly enlarged trial functional space which incorporates both dynamical mass generation and asymptotic freedom. After casting the dynamics associated with these wave functionals into an effective action for collections of soft vacuum-field orbits, the leading infrared improvements manifest themselves as four-gradient interactions. Those turn out to significantly lower the minimal vacuum energy density, thus indicating a clear overall improvement of the vacuum description. The dimensional transmutation mechanism and the dynamically generated mass scale remain almost quantitatively robust, however, which ensures that our prediction for the gluon condensate is consistent with standard values. Further results include a finite group velocity for the soft gluonic modes due to the higher-gradient corrections and indications for a negative differential color resistance of the Yang-Mills vacuum.Comment: 47 pages, 5 figures (vs2 contains a few minor stylistic adjustments to match the published version

The Strangeness Radius and Magnetic Moment of the Nucleon Revisited

We update Jaffe's estimate of the strange isoscalar radius and magnetic moment of the nucleon. We make use of a recent dispersion--theoretical fit to the nucleon electromagnetic form factors and an improved description of symmetry breaking in the vector nonet. We find $\mu_s = -0.24 \pm 0.03$~n.m. and $r_s^2 = 0.21 \pm 0.03$~fm$^2$. The strange formfactor $F_2^s (t)$ follows a dipole with a cut--off mass of 1.46~GeV, $F_2^s (t)= \mu_s (1-t/2.14 \, {\rm GeV}^2 )^{-2}$. These numbers should be considered as upper limits on the strange vector current matrix--elements in the nucleon.Comment: 8 pp, LaTeX, uses epsf, 1 figure in separate fil