How much do charm sea quarks affect the charmonium spectrum?

The properties of charmonium states are or will be intensively studied by the B-factories Belle II and BESIII, the LHCb and PANDA experiments and at a future Super-c-tau Factory. Precise lattice calculations provide valuable input and several results have been obtained by simulating up, down and strange quarks in the sea. We investigate the impact of a charm quark in the sea on the charmonium spectrum, the renormalization group invariant charm-quark mass and the scalar charm-quark content of charmonium. The latter is obtained by the direct computation of the mass-derivatives of the charmonium masses. We do this investigation in a model, QCD with two degenerate charm quarks. The absence of light quarks allows us to reach very small lattice spacings down to 0.023 fm. By comparing to pure gauge theory we find that charm quarks in the sea affect the hyperfine splitting at a level below 2%. The most significant effects are 5% in the quark mass and 3% in the value of the charm quark content of the eta_c meson. Given that we simulate two charm quarks these estimates are upper bounds for the contribution of a single charm quark. We show that lattice spacings <0.06 fm are needed for safe continuum extrapolations of the charmonium spectrum with O(a) improved Wilson quarks. A useful relation for the projection to the desired parity of operators in two-point functions computed with twisted mass fermions is proven.Comment: 25 pages, 8 figure

Charm quark effects on the strong coupling extracted from the static force

We compute the fermionic contribution to the strong coupling $\alpha_{qq}$ extracted from the static force in Lattice QCD up to order $g^4$ in perturbation theory. This allows us to subtract the leading fermionic lattice artifacts from recent determinations of $\alpha_{qq}$ produced in simulations of two dynamical charm quarks. Moreover, by using a suitable parametrization of the $\beta_{qq}$-function, we can evaluate the charm loop effects on $\alpha_{qq}$ in the continuum limit.Comment: 8 pages, 2 figures; Proceedings of the 35th International Symposium on Lattice Field Theory, Granada, Spai

Tubi di flusso cromoelettrici in QCD

L'obiettivo principale di questo lavoro è studiare il confinamento dei quark all’interno della materia adronica. In particolare, si è esaminato il tubo di flusso cromoelettrico generato da una coppia statica quark-antiquark. Per farlo, abbiamo utilizzato gli usuali metodi numerici adoperati in Lattice QCD, considerando una discretizzazione reticolare della QCD con N_f = 2 + 1 sapori e masse dei quark fisiche. Nella prima parte del lavoro, abbiamo misurato numericamente il tubo di flusso e successivamente lo abbiamo analizzato all’interno del modello a superconduttore duale per il vuoto della QCD. Tale modello è stato finora messo alla prova per teorie di pura gauge SU(N) e sembra spiegare abbastanza bene i dati del tubo di flusso ottenuti dalle simulazioni. Nella seconda parte, abbiamo invece studiato tubi di flusso cromoelettrici introducendo nella teoria un campo magnetico esterno B⃗ uniforme e costante, orientato lungo la direzione z. L’interesse verso questo genere di studi è scaturito da un risultato trovato in un recente lavoro: è stata infatti rivelata un’anisotropia nel potenziale di una coppia quark-antiquark statica in presenza di un campo magnetico. In particolare, si è visto che la tensione di stringa sembra essere una funzione crescente (decrescente) del modulo di B⃗, nel caso in cui la coppia quark-antiquark sia disposta perpendicolarmente (parallelamente) all’orientazione del campo magnetico. Se la formazione dei tubi di flusso è responsabile del potenziale confinante tra la coppia quark-antiquark e se tale potenziale risulta anisotropo in presenza di un campo magnetico esterno, è lecito aspettarsi che questa anisotropia sia dovuta ad una deformazione del tubo di flusso. Capire come si deforma il tubo di flusso è sicuramente importante per comprendere meglio il fenomeno e rappresenta l’obiettivo di questa parte del lavoro

Flux tubes in Nf=2+1N_f=2+1 QCD with external magnetic fields

We study the behavior of the confining flux tube in $N_f=2+1$ QCD at the physical point, discretized with the stout smearing improved staggered quark action and the tree level Symanzik gauge action. We discuss how it depends on a uniform external magnetic field, showing how it displays anisotropies with respect to the magnetic field direction. Moreover, we compare the observed anisotropy pattern with that of the static quark-antiquark potential we obtained in our previous works.Comment: 8 pages, 35th International Symposium on Lattice Field Theory, Granada, Spai

Implementation of the conjugate gradient algorithm for heterogeneous systems

Lattice QCD calculations require significant computational effort, with the dominant fraction of resources typically spent in the numerical inversion of the Dirac operator. One of the simplest methods to solve such large and sparse linear systems is the conjugate gradient (CG) approach. In this work we present an implementation of CG that can be executed on different devices, including CPUs, GPUs, and FPGAs. This is achieved by using the SYCL/DPC++ framework, which allows the execution of the same source code on heterogeneous systems

Implementation of the conjugate gradient algorithm for heterogeneous systems

Lattice QCD calculations require significant computational effort, with the dominant fraction of resources typically spent in the numerical inversion of the Dirac operator. One of the simplest methods to solve such large and sparse linear systems is the conjugate gradient (CG) approach. In this work we present an implementation of CG that can be executed on different devices, including CPUs, GPUs, and FPGAs. This is achieved by using the SYCL/DPC++ framework, which allows the execution of the same source code on heterogeneous systems

Comparison of Commonly Used Sail Cloths through Photogrammetric Acquisitions, Experimental Tests and Numerical Aerodynamic Simulations

Abstract The use of polymer composites has been increasing over the years and nowadays the requirements for designing high performance and lightweight fabrics and laminates for sail manufacturing have become more stringent than ever. The present paper offers an effective methodology that enhances the understanding of the influence of fibres orientation and arrangement of panels on sail performance. Constitutive characteristics of the ten commonly used sail cloths are experimentally measured and their influence on sail dynamic performance is compared using an aerodynamic approach. As expected also in industry 4.0 the method allows to control the production process and final product optimization

Protein synthesis inhibition and loss of homeostatic functions in astrocytes from an Alzheimer's disease mouse model: a role for ER-mitochondria interaction

Deregulation of protein synthesis and ER stress/unfolded protein response (ER stress/UPR) have been reported in astrocytes. However, the relationships between protein synthesis deregulation and ER stress/UPR, as well as their role in the altered homeostatic support of Alzheimer's disease (AD) astrocytes remain poorly understood. Previously, we reported that in astrocytic cell lines from 3xTg-AD mice (3Tg-iAstro) protein synthesis was impaired and ER-mitochondria distance was reduced. Here we show that impaired protein synthesis in 3Tg-iAstro is associated with an increase of p-eIF2α and downregulation of GADD34. Although mRNA levels of ER stress/UPR markers were increased two-three-fold, we found neither activation of PERK nor downstream induction of ATF4 protein. Strikingly, the overexpression of a synthetic ER-mitochondrial linker (EML) resulted in a reduced protein synthesis and augmented p-eIF2α without any effect on ER stress/UPR marker genes. In vivo, in hippocampi of 3xTg-AD mice, reduced protein synthesis, increased p-eIF2α and downregulated GADD34 protein were found, while no increase of p-PERK or ATF4 proteins was observed, suggesting that in AD astrocytes, both in vitro and in vivo, phosphorylation of eIF2α and impairment of protein synthesis are PERK-independent. Next, we investigated the ability of 3xTg-AD astrocytes to support metabolism and function of other cells of the central nervous system. Astrocyte-conditioned medium (ACM) from 3Tg-iAstro cells significantly reduced protein synthesis rate in primary hippocampal neurons. When added as a part of pericyte/endothelial cell (EC)/astrocyte 3D co-culture, 3Tg-iAstro, but not WT-iAstro, severely impaired formation and ramification of tubules, the effect, replicated by EML overexpression in WT-iAstro cells. Finally, a chemical chaperone 4-phenylbutyric acid (4-PBA) rescued protein synthesis, p-eIF2α levels in 3Tg-iAstro cells and tubulogenesis in pericyte/EC/3Tg-iAstro co-culture. Collectively, our results suggest that a PERK-independent, p-eIF2α-associated impairment of protein synthesis compromises astrocytic homeostatic functions, and this may be caused by the altered ER-mitochondria interaction