Pion parton distributions in a nonlocal Lagrangian

2005

We use phenomenological nonlocal Lagrangians, which lead to non trivial forms for the quark propagator, to describe the pion. We define a procedure, based on the Dyson-Schwinger equations, for the calculation of the pion parton distributions at low Q^2. The obtained parton distributions fulfill all the wishful properties. Using a convolution approach we incorporate the composite character of the constituent quarks in the formalism. We evolve, using the Renormalization Group, the calculated parton distributions to the experimental scale and compare favorably with the data and draw conclusions.

Generalized parton distributions and constituent quarks

2002

An approach is described to calculate Generalized Parton Distributions (GPDs) in Constituent Quark Models (CQM). The GPDs are obtained from wave functions to be evaluated in a given CQM. The general relations linking the twist-two GPDs to the form factors and to the leading twist quark densities are recovered. Results for the leading twist, unpolarized GPD in the Isgur and Karl model are presented.

On the low-energy limit in the resonating group calculations

1977

Sivers Asymmetry for the proton and the neutron

2008

A formalism is presented to evaluate the Sivers function in constituent quark models. A non-relativistic reduction of the scheme is performed and applied to the Isgur-Karl model. The results obtained are consistent with a sizable Sivers effect and the signs for the u and d flavor contributions turn out to be opposite. The Burkardt Sum Rule is fulfilled to a large extent. After the estimate of the QCD evolution of the results from the momentum scale of the model to the experimental one, a reasonable agreement with the available data is obtained. A calculation of nuclear effects in the extraction of neutron single spin asymmetries in semi-inclusive deep inelastic scattering off 3He is also de…

On the low-energy scattering by velocity-dependent potentials

1977

Bag models and hadron structure

2008

We review the fundamental ideas leading to the basic assumptions behind the bag model description of hadron structure and explore in some detail the so called MIT bag model. We discuss the relevance of chiral symmetry and incorporate it in a bag model scheme by adding a pion field. We show perturbative techniques of calculating gluonic and pionic effects. We discuss the consequences of the solitonic nature of the hedgehog solution of the pion field and introduce the skyrmion bag model. We end up by drawing some conclusions of our study and discussing recent developments in this area.

Instantons and theΔI=1/2Rule

2001

The instanton-induced interaction leads to a significant enhancement of the Ao weak amplitude determining the DeltaI = 1/2 rule, through the contribution of operators with dimension d = 9, as we show in the weak K--> pi(pi) decay.

About two equivalent descriptions of quark antisymmetrization

1992

We analyze the wave function for a two-hadron system when the quark symmetrization principle is incorporated. Two alternative mathematical descriptions are considered. The representation method of Hund constructs a system of generators of thesinglet⊗singlet type. The method of Young-Froebenius incorporates hidden-color components in order to describe the representation basis. By taking a naive model we show that the two descriptions, are equivalent and thus no physical meaning should be attached to their mathematical differences. The results of our analysis are then applied to the more realisticN-N (deuteron) system. We end by discussing the structure of the Pauli correlations which we comp…

Quarks in Few Hadron Systems

1994

We make use of QCD-based quark models to analyze the observability of quark effects in few hadron systems. A hadron is described by a two phase picture. The dynamics of the interior (perturbative) phase consists of a mechanism to confine the elementary degrees of freedom and an asymptotic QGD type interaction. The dynamics of the exterior (non perturbative) phase is approximated by an effective mesonic lagrangian.

Implications of the restoration of chiral symmetry in bag model building

1985

We analyze via a bag model description of hadron structure the consequences of having two fundamental scales in QCD, one associated with confinement and the other with chiral-symmetry restration. The main effect is that the exterior pion field becomes weaker and, therefore, we are able to reproduce the axial-vector coupling constant.

About the realization of chiral symmetry in QCD2

1992

Two dimensional massless Quantum Chromodynamics presents many features which resemble those of the true theory. In particular the spectrum consists of mesons and baryons arranged in flavor multiplets without parity doubling. We analyze the implications of chiral symmetry, which is not spontaneously broken in two dimensions, in the spectrum and in the quark condensate. We study how parity doubling, an awaited consequence of Coleman's theorem, is avoided due to the dimensionality of space-time and confinement. We prove that a chiral phase transition is not possible in the theory.

Pionic effects in deep inelastic scattering off nuclei

1992

The structure functions calculated in the Chiral bag model reproduce quite well, after appropriate perturbative evolution to large energy scales, the experimental data. We use these results to interpret the structure of the $EMC$ data as a quenching of the pion decay constant due to the in medium behavior of the nucleon. This explanation supports recent proposals of this phenomenon whose origin is the scale invariance of the $QCD$ lagrangian.

Magnetic Monopole Search with the Full MoEDAL Trapping Detector in 13 TeV pp Collisions Interpreted in Photon-Fusion and Drell-Yan Production

2019

MoEDAL is designed to identify new physics in the form of stable or pseudostable highly ionizing particles produced in high-energy Large Hadron Collider (LHC) collisions. Here we update our previous search for magnetic monopoles in Run 2 using the full trapping detector with almost four times more material and almost twice more integrated luminosity. For the first time at the LHC, the data were interpreted in terms of photon-fusion monopole direct production in addition to the Drell-Yan-like mechanism. The MoEDAL trapping detector, consisting of 794 kg of aluminum samples installed in the forward and lateral regions, was exposed to 4.0 fb$^{-1}$ of 13 TeV proton-proton collisions at the LHC…

Orbital angular momentum parton distributions in quark models

1999

At the low energy, {\sl hadronic}, scale we calculate Orbital Angular Momentum (OAM) twist-two parton distributions for the relativistic MIT bag model and for non-relativistic quark models. We reach the scale of the data by leading order evolution in perturbative QCD. We confirm that the contribution of quarks and gluons OAM to the nucleon spin grows with $Q^2$, and it can be relevant at the experimental scale, even if it is negligible at the hadronic scale, irrespective of the model used. The sign and shape of the quark OAM distribution at high $Q^2$ may depend strongly on the relative size of the OAM and spin distributions at the hadronic scale. Sizeable quark OAM distributions at the had…

Non Perturbative One Gluon Exchange Potential from Dyson-Schwinger Equations

2012

Recent progress in the solution of Dyson-Schwinger equations of QCD allows for a non perturbative evaluation of the One Gluon Exchange (OGE) interaction. We calculate the interquark static potential for heavy mesons by assuming that it is given by this OGE interaction and we apply it to the description of charmonium.

Surgeons' fear of getting infected by COVID19: A global survey

2020

During the last three months, COVID- 19 pandemic had led to a serious backlog of operations globally, and plans for restarting operation are imperative. Recommendations for surgical activities were studied, aiming to protect the surgical staff from being infected. In the meantime, it is also important to give attention to the surgeon’s personal feeling during work. We conducted a survey to investigate global surgi- cal practices during the COVID-19 pandemic, and the surgeon’s personal feeling was also investigated in the sur- vey. In this special letter, we performed multivariate analysis to explore factors that associated with surgeon’s fear of getting infected by COVID-19.

Impact of asymptomatic COVID-19 patients in global surgical practice during the COVID-19 pandemic

2020

The rapid spread of COVID-19 has changed the global surgical care. Patients infected with COVID-19 may present without typical symptoms, and such asymptomatic patients may potentially trigger in-hospital outbreaks by transmitting the disease to health care providers and other hospitalized patients. Further, asymptomatic COVID-19 patients have worse postop- erative outcomes with an unexpectedly high morbidity and mortality, reaching 20⋅5 per cent deaths. However, we do not have objective global data on this issue. In an attempt to clarify the current global surgical practice under the COVID-19 pandemic particularly focusing on the preoperative screening of asymptomatic COVID-19 patients, we …

Search for magnetic monopoles with the MoEDAL prototype trapping detector in 8 TeV proton-proton collisions at the LHC

2016

The MoEDAL experiment is designed to search for magnetic monopoles and other highly-ionising particles produced in high-energy collisions at the LHC. The largely passive MoEDAL detector, deployed at Interaction Point 8 on the LHC ring, relies on two dedicated direct detection techniques. The first technique is based on stacks of nuclear-track detectors with surface area $\sim$18 m$^2$, sensitive to particle ionisation exceeding a high threshold. These detectors are analysed offline by optical scanning microscopes. The second technique is based on the trapping of charged particles in an array of roughly 800 kg of aluminium samples. These samples are monitored offline for the presence of trap…