Low-energy theorem and OPE in the conformal window of massless QCD

We develop a new technique, based on a low-energy theorem (LET) of NSVZ type derived in arXiv:1701.07833, for the nonperturbative investigation of SU(N) QCD with N${}_f$ massless quarks - or, more generally, of massless QCD-like theories - in phases where the beta function, $\beta(g)$, with $g=g(\mu)$ the renormalized gauge coupling, admits an isolated zero, $g_*$, in the infrared (IR) or ultraviolet (UV). We point out that the LET sets constraints on 3-point correlators involving the insertion of $Tr\, F^2$, its anomalous dimension $\gamma_{F^2}$, and the anomalous dimensions of multiplicatively renormalizable operators at $g_*$. These constraints intertwine with the exact conformal scaling for $g(\mu)\rightarrow g_*$ with $\mu\neq 0,+\infty$ fixed and the IR/UV asymptotics - which may or may not coincide with the IR/UV limit of the aforementioned conformal scaling - for $\Lambda_{\scriptscriptstyle{IR/UV}}$ fixed. In the conformal case we also discuss how the LET for bare correlators is the rationale for the existence in massless QCD of the mysterious divergent contact term in the OPE of $Tr\,F^2$ with itself discovered in perturbation theory in arXiv:1209.1516, arXiv:1407.6921 and computed to all orders in arXiv:1601.08094. Specifically, if $\gamma_{F^2}$ does not vanish, the divergent contact term in the rhs of the LET for the 2-point correlator of $Tr\,F^2$ has to match - and we verify by direct computation that it actually does - the divergence in the lhs due to the nontrivial anomalous dimension of $Tr\,F^2$. Hence, remarkably, the additive renormalization due to the divergent contact term in the rhs is related by the LET to the multiplicative renormalization in the lhs, in such a way that a suitably renormalized version of the LET has no ambiguity for additive renormalization.Comment: 91 pages, no figures. We have replaced the conformal ansatz in the former eq. (7.3) with the ansatz for the exact solution of the Callan-Symanzik equation and extensively rewritten the pape

Conserved vector current in QCD-like theories and the gradient flow

We present analytical results for the Euclidean 2-point correlator of the flavor-singlet vector current evolved by the gradient flow at next-to-leading order ($O(g^2)$) in perturbatively massless QCD-like theories. We show that the evolved 2-point correlator requires multiplicative renormalization, in contrast to the nonevolved case, and confirm, in agreement with other results in the literature, that such renormalization ought to be identified with a universal renormalization of the evolved elementary fermion field in all evolved fermion-bilinear currents, whereas the gauge coupling renormalizes as usual. We explicitly derive the asymptotic solution of the Callan-Symanzik equation for the connected 2-point correlators of these evolved currents in the limit of small gradient-flow time $\sqrt{t}$, at fixed separation $|x-y|$. Incidentally, this computation determines the leading coefficient of the operator-product expansion (OPE) in the small $t$ limit for the evolved currents in terms of their local nonevolved counterpart. Our computation also implies that, in the evolved case, conservation of the vector current, hence transversality of the corresponding 2-point correlator, is no longer related to the nonrenormalization, in contrast to the nonevolved case. Indeed, for small flow time the evolved vector current is conserved up to $O(t)$ softly violating effects, despite its $t$-dependent nonvanishing anomalous dimension.Comment: 42 pages, 7 figure

Emerg Infect Dis

The present work is devoted to the study of stone beads and pendants from Bronze Age sites in Sicily and the Aeolian Islands. Macroscopic geological examination made it possible to identify the rock types and in some cases their probable provenance. A chronological and typological analysis of the objects as well as graphic and photographic documentation completes the study of the stone artifacts. Comparative research throughout the Mediterranean allows the distinction between local groups of beads and pendants (i.e. of local production and distribution) and groups of Near Eastern objects (mainly in carnelian) that arrived in Italy through Aegean contacts. This work enables a chronological classification of these objects, some of which arrived in Sicily via Mediterranean sea routes. As a result, it is possible to discuss in depth some issues regarding Aegean imports in Italy and the changing socio-economic role that ornaments played in the indigenous communities during the Bronze Age

Informed classification of sweeteners/bitterants compounds via explainable machine learning

Perception of taste is an emergent phenomenon arising from complex molecular interactions between chemical compounds and specific taste receptors. Among all the taste perceptions, the dichotomy of sweet and bitter tastes has been the subject of several machine learning studies for classification purposes. While previous studies have provided accurate sweeteners/bitterants classifiers, there is ample scope to enhance these models by enriching the understanding of the molecular basis of bitter-sweet tastes. Towards these goals, our study focuses on the development and testing of several machine learning strategies coupled with the novel SHapley Additive exPlanations (SHAP) for a rational sweetness/bitterness classification. This allows the identification of the chemical descriptors of interest by allowing a more informed approach toward the rational design and screening of sweeteners/bitterants. To support future research in this field, we make all datasets and machine learning models publicly available and present an easy-to-use code for bitter-sweet taste prediction

PAMAM and PPI dendrimers as potential anti-cancer drug carriers: a computational investigation

Photodynamic therapy (PDT) is a promising technique for several types of anti-cancer therapy, exploiting a photosensitizer, a light source and oxygen. The present work computationally investigates the properties of poly(amidoamine) (PAMAM) and poly(propyleneimine) (PPI) dendrimers of generation 3 and 4 as potential nanoscale drug delivery systems for Rose Bengal (RB), a candidate photosensitizer for PDT

Machine Learning Aided Molecular Modelling of Taste to Identify Food Fingerprints

Nature has developed fascinating mechanisms for selecting and monitoring nutrients through refined systems for food intake and uptake. One of the most important is the sense of taste. Taste is an emergent property involving a complex network of multilevel biological interactions beginning with the activation of specific protein receptors as a consequence of interaction with food molecules. In this context, crucial information about the mechanisms underlying the functioning of taste can be obtained by using molecular mechanistic modelling and machine learning tools borrowed from the field of drug design and the study of structural biology and protein biophysics. The ultimate goal is to develop predictive models capable of studying the intricate connection of molecular, sub-cellular and cellular phenomena underlying the complex biological mechanisms that regulate the relationships between food constituents and perceived taste. Artificial intelligence-driven digital tools for taste prediction and the study of molecular features of the interaction between food molecules and taste receptors have been recently developed by our group. Such tools are the operating engines of the decision support tool developed during the VIRTUOUS project (https://virtuoush2020.com). In this work, these tools were used to generate molecular fingerprints of coffee starting from its chemical composition. Through methods that integrate molecular modelling techniques and machine learning, molecules extracted from coffee were characterized in terms of binding affinity, specificity, and selectivity toward bitter receptors. The targeting ability of coffee-extracted molecules for human TAS2Rs was studied with an atomistic resolution to obtain a virtual fingerprint that links the molecular structure of food ingredients with their bitter profile. The study fits within the digital transition vision that leverages modelling and computational approaches to develop decision-supporting tools for developing solutions in the areas of nutrition, health and the modern food industry

Theoretical status of epsilon'/epsilon

We review the theory of epsilon'/epsilon and present an updated phenomenological analysis using hadronic matrix elements from lattice QCD. The present status of the computation of epsilon'/epsilon, considering various approaches to the matrix-element evaluation, is critically discussed.Comment: 22 pages, 2 eps figures, based on the talks given by M.C. at "Les Rencontres de Physique de la Vallee d'Aoste", La Thuile (Italy), 27 February-4 March 2000 and by G.M. at the "XXXVth Rencontres de Moriond", Les Arcs 1800 (France), 11-18 March 200