Within a chiral quark model, we evaluate the good cross section in the Euclidean space in the vector - axial vector channel, proposed recently by Ma and Qiu as means to extract the so far elusive ...parton distribution functions of the pion from lattice QCD. Our results are remarkably simple at the quark model scale and agree well, after the necessary QCD evolution, with the most recent lattice calculations at the scale μ∼2 GeV for various values of the lattice pion mass. Comparisons are made as functions of the Ioffe time variable. We also comment on the information on the lowest moments in the momentum fraction x, generically extractable from such analyses, as well as on the inaccessibility of the x→1 limit from the present data.
Off-shell effects in generalized parton distributions (GPDs) of the pion, appearing, e.g., in the Sullivan process, are considered. Due to the lack of crossing symmetry, the moments of GPDs involve ...also odd powers of the skewness (longitudinal momentum transfer) parameter, which results in emergence of new off-shell form factors. With current-algebra techniques, we derive exact relations between the four off-shell gravitational form factors of the pion, in analogy to the electromagnetic case. Our results place stringent constraints on the off-shell GPDs of the pion. We provide an explicit realization in terms of a chiral quark model, where we show that the off-shell effects in GPDs are potentially significant in modeling physical processes and should not be neglected.
We evaluate nonperturbatively the quark quasidistribution amplitude and the valence quark quasidistribution function of the pion in the framework of chiral quark models, namely the Nambu–Jona-Lasinio ...model and the Spectral Quark Model. We arrive at simple analytic expressions, where the nonperturbative dependence on the longitudinal momentum of the pion can be explicitly assessed. The model results for the quark quasidistribution amplitude of the pion compare favorably to the data obtained from the Euclidean lattice simulations. The quark distribution amplitude, arising in the limit of infinite longitudinal momentum of the pion, agrees, after suitable QCD evolution, to the recent data extracted from Euclidean lattices, as well as to the old data from transverse lattice simulations.
Baryonic content of the pion Sanchez-Puertas, Pablo; Ruiz Arriola, Enrique; Broniowski, Wojciech
Physics letters. B,
11/2021, Letnik:
822
Journal Article
Recenzirano
Odprti dostop
The baryon form factor of charged pions arises since isospin symmetry is broken. We obtain estimates for this basic property in two phenomenological ways: from simple constituent quark models with ...unequal up and down quark masses, and from fitting to e+e−→π+π− data. All our methods yield a positive π+ baryon mean square radius of (0.03−0.04fm)2. Hence, a picture emerges where the outer region has a net baryon, and the inner region a net antibaryon density, both compensating each other such that the total baryon number is zero. For π− the effect is opposite.
The parton quasidistribution functions (QDFs) of Ji have been found by Radyushkin to be directly related to the transverse momentum distributions (TMDs), to the pseudodistributions, and to the ...Ioffe-time distributions (ITDs). This makes the QDF results at finite longitudinal momentum of the hadron interesting in their own right. Moreover, the QDF-TMD relation provides a gateway to the pertinent QCD evolution, with respect to the resolution scale Q, for the QDFs. Using the Kwieciński evolution equations and well established parametrizations at a low initial scale, we analyze the QCD evolution of quark and gluon QDF components of the proton and the pion. We discuss the resulting breaking of the longitudinal-transverse factorization and show that it has little impact on QDFs at the relatively low scales presently accessible on the lattice, but the effect is visible in reduced ITDs at sufficiently large values of the Ioffe time. Sum rules involving derivatives of ITDs and moments of the parton distribution functions (PDFs) are applied to the European Twisted Mass Collaboration lattice data. This allows us for a lattice determination of the transverse-momentum width of the TMDs from QDF studies.
The valence double parton distribution of the pion is analyzed in the framework of chiral quark models, where in the chiral limit factorization between the longitudinal and transverse degrees of ...freedom occurs. This feature leads, at the quark-model scale, to a particularly simple distribution of the form D ( x 1 , x 2 , q ) = δ ( 1 − x 1 − x 2 ) F ( q ) , where x 1 , 2 are the longitudinal momentum fractions carried by the valence quark and antiquark and q is their relative transverse momentum. For q = 0 this result complies immediately with the Gaunt-Sterling sum rules. The Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution to higher scales is carried out in terms of the Mellin moments. We then explore its role on the longitudinal correlation quantified with the ratio of the double distribution to the product of single distributions, D ( x 1 , x 2 , q = 0 ) / D ( x 1 ) D ( x 2 ) . We point out that the ratios of moments ⟨ x n 1 x m 2 ⟩ / ⟨ x n 1 ⟩ ⟨ x m 2 ⟩ are independent of the evolution, providing particularly suitable measures to be tested in the upcoming lattice simulations. The transverse form factor F ( q ) and its Fourier conjugate in the relative transverse coordinate b are obtained in variants of the Nambu–Jona-Lasinio model with the spectral and Pauli-Villars regularizations. The results are valid in the soft-momentum domain. Interestingly, with the spectral regularization of the model, the effective cross section for the double parton scattering of pions is exactly equal to the geometric cross section, σ eff = π ⟨ b 2 ⟩ , and yields about 20 mb.
Abstract Background and Aims Older patients with antineutrophil cytoplasmic autoantibody-associated vasculitis (AAV) commonly experience renal impairment and poor prognosis. The European Vasculitis ...Study Group trials showed that approximately 16.7% and 22.5% of older patients with AAV suffered from end-stage renal disease (ESRD) in 5- and 10-year durations. The aim of this study was to analyze differences in course and outcome of patients with AAV with respect to age. Method This retrospective observational study included patients with diagnosis of AAV and biopsy proven renal involvement between 2000-2021. Patients were divided into two groups according to age: ≥65 or <65 years old. We recorded baseline characteristics and clinical data during follow-up. Response was defined as a BVAS reduction of at least 50% or BVAS of 0, while receiving prednisone dose higher than 4 mg; and remission as BVAS of 0 while receiving prednisone dose of 4 mg or less. Results We included 42 patients with AAV diagnosis, 47.6% of which were 65 years-old or older. Mean age of the older age group was 77 ± 8 years. No differences were found between older and younger patients at baseline (BVAS, FFS extra-renal symptoms, serum creatinine at diagnosis, hematuria), Patients > 65 years were significantly more likely to present p-ANCA positive MPA, as shown in Table 1. There was no difference in initial or maintenance immunosuppressive therapy between the two groups. No differences were found between older and younger patients with regard to treatment response. Although we found no statistical differences, older patients had worse renal outcomes. The older adult group had a higher mortality rate, p 0.01. The average time to death was 27 months for patients over 65 years and 34.5 in those who were younger (p 0.71). Conclusion No differences were found between older and younger patients with regard to treatment response. However, mortality was higher during follow-up in the group of older patients. Our results suggest that more attention should be paid to older patients with severe renal impairment.
Abstract Background and Aims Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of rare but potentially serious diseases with high mortality. Renal involvement is ...frequent in AAV with patients developing end-stage renal disease (ESRD) or becoming dependent on dialysis in up to 23% of patients. Several studies suggest the presence of clinical factors as predictors of survival in these diseases. The objective of this study was to analyze clinical evolution of AAV and to identify potential risk factors for developing renal events (ESRD or dialysis) and death in patients with AAV, with special attention to the implications that the presence of myeloperoxidase (MPO) or proteinase 3 (PR3) antibodies at diagnosis may have on the disease progression. Method We conducted a retrospective observational study of patients under follow-up for AAV. We considered only those with a confirmed diagnosis of AAV through renal biopsy for the present study. We collected clinical and laboratory variables at the time of disease presentation. We divided the patients based on the presence of MPO or PR3. Subsequently, we analyzed the patients' progression towards the occurrence of renal events (ESRD or dialysis) and mortality. Results Out of the 42 studied patients, 29 were MPO-positive and 13 were PR3-positive. We observed statistically significant differences in age and the frequency of hypertension, with the MPO group being older and more hypertensive than the PR3 group. On the contrary, PR3-positive patients exhibited a higher percentage of diabetes and increased severity of vasculitis at diagnosis as measured by the Birmingham Vasculitis Activity Score (BVAS). While most MPO-positive patients met criteria for microscopic polyangiitis (MPA), all PR3-positive patients met criteria for granulomatosis with polyangiitis (GPA) according to the ACR/EULAR 2022 guidelines. There were no statistically significant differences regarding clinical or laboratory variables analyzed, neither with induction nor maintenance treatment. We did not observe differences in the progression towards renal events or mortality between groups. However, we did observe a higher percentage of disease recurrence among PR3-positive patients (Table 1). Conclusion There were no statistically significant differences observed in the progression towards renal events (ESRD and dialysis) or mortality regardless of MPO or PR3 antibodies.
Scope
We evaluated the protective effect of extra virgin olive oil (EVOO) in high‐fat diets (HFDs) on the inflammatory response and liver damage in a nonalcoholic fatty liver disease (NAFLD) mouse ...model.
Methods and results
C57BL/6J mice were fed a standard diet or a lard‐based HFD (HFD‐L) for 12 wk to develop NAFLD. HFD‐fed mice were then divided into four groups and fed for 24 wk with the following: HFD‐L, HFD‐EVOO, HFD based on phenolics‐rich EVOO, and reversion (standard diet). HFD‐L‐induced metabolic disorders were alleviated by replacement of lard with EVOO. EVOO diets improved plasma lipid profile and reduced body weight, plasma and epididymal fat INF‐γ, IL‐6 and leptin levels, and macrophage infiltration. Moreover, NAFLD activity scores were reduced. The liver lipid composition showed an increase in MUFAs, especially oleic acid, and a decrease in saturated fatty acids. Hepatic adiponutrin and Cd36 gene expression was upregulated in the EVOO groups. Liver ingenuity pathway analysis revealed in EVOO groups regulation of proteins involved in lipid metabolism, small molecule biochemistry, gastrointestinal disease, and liver regeneration.
Conclusion
Dietary EVOO could repair HFD‐induced hepatic damage, possibly via an anti‐inflammatory effect in adipose tissue and modifications in the liver lipid composition and signaling pathways.
Dietary fat may be an important modifiable factor involved in nonalcoholic fatty liver disease. The protective effect of extra virgin olive oil (EVOO) in high‐fat diets on the inflammatory response and liver damage is evaluated in a nonalcoholic fatty liver disease mouse model. EVOO diets improve plasma lipid profile, plasma and fat inflammation; ameliorate liver damage; increase MUFAs liver levels; and modify liver protein expression. Dietary EVOO could repair high‐fat diet induced hepatic damage via an anti‐inflammatory effect and changes in the liver lipid composition and signaling pathways.
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