Meson and glueball spectroscopy within the graviton soft wall model

The graviton soft wall model (GSW) provides a unified description of the scalar glueball and meson spectra with a unique energy scale. This success has led us to extend the analysis to the description of the spectra of other hadrons. We use this model to calculate masses of the odd and even ground states of glueballs for various spins, and show that the GSW model is able to reproduce the Regge trajectory of these systems. In addition, the spectra of the $\rho$, $a_1$ and the $\eta$ mesons will be addressed. Results are in excellent agreement with current experimental data.Furthermore such an achievement is obtained without any additional parameters. Indeed, the only two parameters appearing…

Multiphoton annihilation of monopolium

We show that due to the large coupling constant of the monopole-photon interaction the annihilation of monopole-antimonopole and monopolium into many photons must be considered experimentally. For monopole-antimonopole annihilation and lightly bound monopolium, even in the less favorable scenario, multi-photon events (four and more photons in the final state) are dominant, while for strongly bound monopolium, although two photon events are important, four and six photon events are also sizable.

Proton spin and the cheshire cat principle

Abstract We discuss the proton matrix element of the flavor-singlet axial current (FSAC), often referred to as proton spin, in terms of the chiral bag model with due account of the axial anomaly and quantum number fractionation. We conclude that the contribution due to gluons is significant for large bag radii and that it is crucial in order to establish the Cheshire cat principle.

Double parton correlations in Light-Front constituent quark models

Double parton distribution functions (dPDF) represent a tool to explore the 3D proton structure. They can be measured in high energy proton-proton and proton nucleus collisions and encode information on how partons inside a proton are correlated among each other. dPFDs are studied here in the valence quark region, by means of a constituent quark model, where two particle correlations are present without any additional prescription. This framework allows to understand the dynamical origin of the correlations and to clarify which, among the features of the results, are model independent. Use will be made of a relativistic light-front scheme, able to overcome some drawbacks of the previous cal…

η−η′(−glue) Mixing from the Chiral Lagrangian

The η − η ′ mixing from the chiral Lagrangian is reviewed. It is shown how the Feldman-Kroll-Stech ansazt can be derived from the chiral Lagrangian. The inclusion of the glueball is also discussed.

A quark model analysis of Orbital Angular Momentum

Orbital Angular Momentum (OAM) twist-two parton distributions are studied. At the low energy, hadronic, scale we calculate them for the relativistic MIT bag model and for non-relativistic potential quark models. We reach the scale of the data by leading order evolution using the OPE and 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. Sizeab…

Helicity-dependent generalized parton distributions and composite constituent quarks

An approach, recently proposed to calculate the nucleon generalized parton distributions (GPDs) in a constituent quark model (CQM) scenario, in which the constituent quarks are taken as complex systems, is used to obtain helicity-dependent GPDs. They are obtained from the wave functions of the non relativistic CQM of Isgur and Karl, convoluted with the helicity-dependent GPDs of the constituent quarks themselves. The latter are modelled by using the polarized structure functions of the constituent quark, the double distribution representation of GPDs, and a phenomenological constituent quark form factor. The present approach permits to access a kinematical range corresponding to both the Do…

Poopćene raspodjele partona i struktura sastavnog kvarka

In a scenario where the constituent quarks are composite systems, generalized parton distributions (GPDs) are built from wave functions to be evaluated in a constituent quark model (CQM), convoluted with the GPDs of the constituent quarks themselves. The approach permits to access the full kinematical range corresponding to the DGLAP and ERBL regions, so that cross-sections for deeply virtual Compton scattering can be estimated.

The effective cross section for double parton scattering within a holographic AdS/QCD approach

A first attempt to apply the AdS/QCD framework for a bottom-up approach to the evaluation of the effective cross section for double parton scattering in proton-proton collisions is presented. The main goal is the analytic evaluation of the dependence of the effective cross section on the longitudinal momenta of the involved partons, obtained within the holographic Soft-Wall model. If measured in high-energy processes at hadron colliders, this momentum dependence could open a new window on 2-parton correlations in a proton.

Quark degrees of freedom in hadronic systems

Quantum Chromodynamics (QCD) is the theory of the strong interactions. We review descriptions of hadronic systems motivated by QCD, analyzing the recent controversy between gluonic and bosonic degrees of freedom under the prism of the Cheshire Cat Principle. Our analysis leads to an optimal scheme to study hadronic properties. We proceed to extend this low energy descriptions to the deep inelastic regime.

Double parton correlations and constituent quark models: a light front approach to the valence sector

An explicit evaluation of the double parton distribution functions (dPDFs), within a relativistic Light-Front approach to constituent quark models, is presented. dPDFs encode information on the correlations between two partons inside a target and represent the non-perturbative QCD ingredient for the description of double parton scattering in proton-proton collisions, a crucial issue in the search of new Physics at the LHC. Valence dPDFs are evaluated at the low scale of the model and the perturbative scale of the experiments is reached by means of QCD evolution. The present results show that the strong correlation effects present at the scale of the model are still sizable, in the valence r…

Single Spin Asymmetry Parameter from Deeply Virtual Compton Scattering of Hadrons up to Twist-3 accuracy: I. Pion case

The study of deeply virtual Compton scattering has shown that electromagnetic gauge invariance requires, to leading order, not only twist two but additional twist three contributions. We apply this analysis and, using the Ellis-Furmanski-Petronzio factorization scheme, compute the single (electron) spin asymmetry arising in the collision of longitudinally polarized electrons with hadrons up to twist 3 accuracy. In order to simplify the kinematics we restrict the actual calculation to pions in the chiral limit. The process is described in terms of the generalized parton distribution functions which we obtain within a bag model framework.

Nucleon and delta masses in QCD

Using the positivity of the path integral measure of $QCD$ and defining a structure for the quark propagator in a background field according to the fluxon scenario for confinement, we calculate and compare the correlators for nucleon and delta. From their shape we elucidate about the origin of their mass difference, which in our simplified scenario is due to the tensor structure in the propagator. This term arises due to a dynamical mechanism which is responsible simultaneously for confinement and spontaneous chiral symmetry breaking. Finally we discuss, by comparing the calculated correlators with the Lehmann representation, the possibility that a strong CP and/or P violation occurs as a c…

Vector Mesons and Dence Skyrmion Matter

In our continuing effort to understand hadronic matter at high density, we have developed a unified field theoretic formalism for dense skyrmion matter using a single Lagrangian to describe simultaneously both matter and meson fluctuations and studied in-medium properties of hadrons. Dropping the quartic Skyrme term, we incorporate into our previous Lagrangian the vector mesons rho and omega in a form which is consistent with the symmetries of QCD. The results that we have obtained, reported here, expose a hitherto unsuspected puzzle associated with the role the omega meson plays at short distance. Since the omega meson couples to baryon density, it leads to a pseudo-gap scenario for the ch…

Further Comments on a Vanishing Singlet Axial Vector Charge

The recent suggestion of a vanishing flavor-singlet axial charge of nucleon due to a nontrivial vacuum structure is further amplified. A perturbative QCD discussion, applicable for the heavy quark contributions, relates it to the physics of the decoupling theorem. It is also shown that $g_{A}^{0}\simeq 0$ leads to a negative $\eta'$-meson-quark coupling, which has been found to be compatible with the chiral quark model phenomenology.

The baryon number two system in the Chiral Soliton Model

We study the interaction between two B = 1 states in a chiral soliton model where baryons are described as non-topological solitons. By using the hedgehog solution for the B = 1 states we construct three possible B = 2 configurations to analyze the role of the relative orientation of the hedgehog quills in the dynamics. The strong dependence of the intersoliton interaction on these relative orientations reveals that studies of dense hadronic matter using this model should take into account their implications.

Towards a unified picture of constituent and current quarks

Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We evaluate the latter at a low hadronic scale with updated phenomenological information, and we build the momentum distributions using well-known quark models. The resulting parton distributions and structure functions are evolved to the experimental scale and good agreement with the available DIS data is achieved. When compared with a similar calculation using non-composite constituent quarks, the accord with experiment of the present calculation become…

Model analysis of the world data on the pion transition form factor

We discuss the impact of recent Belle data on our description of the pion transition form factor based on the assumption that a perturbative formalism and a nonperturbative one can be matched in a physically acceptable manner at a certain hadronic scale $Q_{0}$. We discuss the implications of the different parameters of the model in comparing with world data and conclude that within experimental errors our description remains valid. Thus we can assert that the low $Q^2$ nonperturbative description together with an additional $1/Q^2$ term at the matching scale have a strong influence on the $Q^2$ behavior up to very high values of $Q^2$ .

Nucleon Structure Functions in a Constituent Quark Scenario

Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the polarized part on distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We achieve good agreement with experiments in the unpolarized as well as in the polarized case, though a good description of the recent polarized neutron data requires the introduction of one more paramater. When our results are compared with similar calculations using non-composite constituent quarks, the accord with the experiments of the present scheme is impressive. We conclude that DIS data are consistent with a low energy scenario dominat…

η−η′-glueball mixing

We have revisited glueball mixing with the pseudoscalar mesons in the MIT bag model scheme. The calculation has been performed in the spherical cavity approximation to the bag using two different fermion propagators, the cavity and the free propagators. We obtain probabilities of mixing for the $\ensuremath{\eta}$ at the level of 0.006%--2.0%, while for the ${\ensuremath{\eta}}^{\ensuremath{'}}$ one at the level of 0.6%--40%, depending on the choice of bag radius and, therefore, of the strong coupling constant. Our results differ from previous calculations. The origin of our difference stems from the treatment of the time integrations. The comparison of our calculation with experimental dat…

Gluonic contributions in the chiral hyperbag

Abstract We incorporate into a non-perturbative chiral bag model scheme the gluons and the η' in a perturbative fashion. We analyze in this context the proton matrix element for the flavor singlet axial current, where due account is taken of the anomaly, and the delta-nucleon mass difference. Our results show that the contribution due to the gluons is significant for large bag radii and that they are crucial in order to establish the Cheshire cat principle.

Medium effects in DIS from polarized nuclear targets

The behavior of the nucleon structure functions in lepton nuclei deep inelastic scattering, both polarized and unpolarized, due to nuclear structure effects is reanalyzed. The study is performed in two schemes: an x-rescaling approach, and one in which there is an increase of sea quark components in the in medium nucleon, related to the low energy N-N interaction. In view of a recent interesting experimental proposal to study the behavior of the proton spin structure functions in nuclei we proceed to compare these approaches in an effort to enlighten the possible phenomenological interest of such difficult experiment.

Hidden Dirac Monopoles

Dirac showed that the existence of one magnetic pole in the universe could offer an explanation of the discrete nature of the electric charge. Magnetic poles appear naturally in most grand unified theories. Their discovery would be of greatest importance for particle physics and cosmology. The intense experimental search carried thus far has not met with success. I proposed a universe with magnetic poles which are not observed free because they hide in deeply bound monopole--anti-monopole states named monopolium. I discuss the realization of this proposal and its consistency with known cosmological features. I furthermore analyze its implications and the experimental signatures that confirm…

Polarized Structure Functions and the Nucleon Spin

The link between the light-cone momentum distributions of constituent quark models and their corresponding parton distributions is used to study the polarized structure functions g 1 of proton and neutron. The formalism allows to analyze the effects of the structure of the quark model wave function and thus we discuss the SU (6) breaking mechanism associated with the One Gluon Exchange and large D-state admixtures originated in pionic models. We analyze the contribution to these structure functions of the gluon polarization arising from the anomaly.

Atiyah-Manton Approach to Skyrmion Matter

We propose how to approach, and report on the first results in our effort for, describing nuclear matter starting from the solitonic picture of baryons which is supposed to represent QCD for large number of colors. For this purpose, the instanton-skyrmion connection of Atiyah and Manton is exploited to describe skyrmion matter. We first modify 't Hooft's multi-instanton solution so as to suitably incorporate proper dynamical variables into the skyrmion matter and then by taking these variables as variational parameters, we show that they cover a configuration space sufficient to adequately describe the ground state properties of nuclear matter starting from the skyrmion picture. Our results…

Topological structure of dense hadronic matter

8 pages, 4 figures.-- ISI Article Identifier: 000244425500052.

The gluon spin in the chiral bag model

We study the gluon polarization contribution at the quark model renormalization scale to the proton spin, $\Gamma$, in the chiral bag model. It is evaluated by taking the expectation value of the forward matrix element of a local gluon operator in the axial gauge $A^+=0$. It is shown that the confining boundary condition for the color electric field plays an important role. When a solution satisfying the boundary condition for the color electric field, which is not the conventionally used but which we favor, is used, the $\Gamma$ has a positive value for {\it all} bag radii and its magnitude is comparable to the quark spin polarization. This results in a significant reduction in the relativ…

DIS structure functions and the double-spin asymmetry inρ0electroproduction within a Regge approach

The proton, neutron and deuteron structure functions ${F}_{2}{(x,Q}^{2})$ and ${g}_{1}{(x,Q}^{2}),$ measured at intermediate ${Q}^{2},$ are analyzed within a Regge approach. This analysis serves to fix the parameters of this scheme which are then used to calculate, in a unified Regge approach, the properties of ${\ensuremath{\rho}}^{0}$ meson electroproduction on the proton and the deuteron. In this way, the double-spin asymmetry observed at HERMES in ${\ensuremath{\rho}}^{0}$ electroproduction on the proton can be related to the anomalous behavior of the flavor-singlet part of the spin-dependent structure function ${g}_{1}{(x,Q}^{2})$ at small x.

Glueball enhancement by color deconfinement

5 pages, 4 figures.-- PACS nrs.: 14.80.-j; 24.80.+y; 25.75.Nq.-- ISI Article Identifier: 000245333000063.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0609219

Sliding Vacua in Dense Skyrmion Matter

In continuation of our systematic effort to understand hadronic matter at high density, we study dense skyrmion matter and its chiral phase structure in an effective field theory implemented with the trace anomaly of QCD applicable in the large $N_c$ limit. By incorporating a dilaton field $\chi$ associated with broken conformal symmetry of QCD into the simplest form of skyrmion Lagrangian, we simulate the effect of "sliding vacua" influenced by the presence of matter and obtain what could correspond to the ``intrinsic dependence" on the background of the system, i.e., matter density or temperature, that results when a generic chiral effective field theory of strong interactions is matched …

Analyzing the Boer-Mulders function within different quark models

A general formalism for the evaluation of time reversal odd parton distributions is applied here to calculate the Boer-Mulders function. The same formalism when applied to evaluate the Sivers function led to results which fulfill the Burkardt sum rule quite well. The calculation here has been performed for two different models of proton structure: a constituent quark model and the MIT bag model. In the latter case, important differences are found with respect to a previous evaluation in the same framework, a feature already encountered in the calculation of the Sivers function. The results obtained are consistent with the present wisdom, i.e., the contributions for the $u$ and $d$ flavors t…

The mesonic spectrum of bosonized QCD2 in the chiral limit

Abstract By studying an equivalent non-abelian bosonic theory we resolve the mesonic spectrum of quantum chromodynamics in one space-one time dimension for massless quarks. The emphasis is placed in the non-chiral sector described be colored meson fields. Two and four point functions of these fields are explicitly calculated in the large N limit. Some of the relevant issues: chiral symmetry realization, phases, anomaly saturation, etc…, are revisited.

Nuclear and partonic dynamics in the EMC effect

It has been recently confirmed that the magnitude of the EMC effect measured in the electron deep inelastic scattering is linearly related to the short-range correlation scaling factor obtained from electron inclusive scattering. By using a x-rescaling approach we are able to understand the interplay between the quark-gluon and hadronic degrees of freedom in the discussion of the EMC effect.

Double parton scattering: A study of the effective cross section within a Light-Front quark model

We present a calculation of the effective cross section $\sigma_{eff}$, an important ingredient in the description of double parton scattering in proton-proton collisions. Our theoretical approach makes use of a Light-Front quark model as framework to calculate the double parton distribution functions at low-resolution scale. QCD evolution is implemented to reach the experimental scale. The obtained $\sigma_{eff}$, when averaged over the longitudinal momentum fractions of the interacting partons, $x_i$, is consistent with the present experimental scenario. However the result of the complete calculation shows a dependence of $\sigma_{eff}$ on $x_i$, a feature not easily seen in the available…

N-quantum approach to quantum field theory at finite T and mu: the NJL model

We extend the N-quantum approach to quantum field theory to finite temperature ($T$) and chemical potential ($\mu$) and apply it to the NJL model. In this approach the Heisenberg fields are expressed using the Haag expansion while temperature and chemical potential are introduced simultaneously through a generalized Bogoliubov transformation. Known mean field results are recovered using only the first term in the Haag expansion. In addition, we find that at finite T and in the broken symmetry phase of the model the mean field approximation can not diagonalize the Hamiltonian. Inclusion of scalar and axial vector diquark channels in the SU(2)$_{rm f}$ $otimes$ SU(3)$_{\rm c}$ version of the …

Towards a Unified Description of the Baryon Spectrum and the Baryon-Baryon Interaction within a Potential Model Scheme

We study the low energy part of the nucleon and ∆ spectra by solving the Schrodinger equation for the three-quark system in the hyperspherical harmonic approach. The quark-quark hamiltonian considered includes, besides the usual one-gluon exchange, pion and sigma exchanges generated by the chiral symmetry breaking This quark-quark potential reproduces, in a Resonating Group Method calculation, the nucleon-nucleon scattering phase shifts and the deuteron properties. The baryonic spectrum obtained is quite reasonable and the resulting wave function is consistent with the ansatz used in the two baryon system.

New anomalous trajectory in Regge theory

We show that a new Regge trajectory with \alpha_{f_1} (0) \approx 1 and slope \alpha_{f_1}'(0) \approx 0 explains the features of hadron-hadron scattering and photoproduction of the rho and phi mesons at large energy and momentum transfer. This trajectory with quantum numbers P = C = +1 and odd signature can be considered as a natural partner of the Pomeron which has even signature. The odd signature of the new exchange leads to contributions to the spin-dependent cross sections, which do not vanish at large energy. The links between the anomalous properties of this trajectory, the axial anomaly and the flavor singlet axial vector f_1 (1285) meson are discussed.

Mechanism for the double-spin asymmetry in electromagnetic rho production at HERMES

We calculate the contribution of meson and pomeron exchanges to the double-spin asymmetry in $\rho$-meson electromagnetic production at HERMES energies. We show that the observed double-spin asymmetries, which are large, can be explained by the interference between the natural parity $f_2$-secondary Reggeon and the unnatural parity anomalous $f_1$ exchanges.

The pion transition form factor and the pion distribution amplitude

Recent BaBar data on the pion transition form factor, whose Q(2)-dependence is much steeper then predicted by asymptotic Quantum Chromodynamics (QCD), have caused a renewed interest in its theoretical description. We present here a formalism based on a model-independent description for low photon virtuality and a high photon virtuality description based on QCD, which match at a scale Q(0). The high photon virtuality description incorporates a flat pion distribution amplitude, phi(x) = 1, at the matching scale Q(0) and QCD evolution from Q(0) to Q > Q(0). The flat pion distribution is connected, through soft pion theorems and chiral symmetry, to the pion valence parton distribution at the sa…

Nucleon structure functions and light front dynamics

We present a quark-parton model to describe polarized and unpolarized nucleon structure functions. The twist-two matrix elements for the QCD evolution analysis of lepton-hadron scattering are calculated within a light-front covariant quark model. The relativistic effects in the three-body wave function are discussed for both the polarized and unpolarized cases. Predictions are given for the polarized gluon distributions as will be seen in future experiments.

Skyrmions at high density

The phase diagram of quantum chromodynamics is conjectured to have a rich structure containing at least three forms of matter: hadronic nuclear matter, quarkyonic matter and quark–gluon plasma. We justify the origin of the quarkyonic phase transition in a chiral-quark model and describe its formulation in terms of Skyrme crystals.

Nucleon Structure Functions and Light-Front Dynamics

We present a quark-parton model to describe polarized and unpolarized nucleon structure functions. The twist-two matrix elements for the QCD evolution analysis of lepton-hadron scattering are calculated within a light-front covariant quark model. The relativistic effects in the three-body wave function are discussed for both the polarized and unpolarized cases. Predictions are given for the polarized gluon distributions as will be seen in future experiments.

Confinement, the gluon propagator and the interquark potential for heavy mesons

The interquark static potential for heavy mesons described by a massive one-gluon exchange interaction obtained from the propagator of the truncated Dyson-Schwinger equations does not reproduced the expected Cornell potential. I show that no formulation based on a finite propagator will lead to confinement of quenched QCD. I propose a mechanism based on a singular nonperturbative coupling constant which has the virtue of giving rise to a finite gluon propagator and (almost) linear confinement. The mechanism can be slightly modified to produce the screened potentials of unquenched QCD.

Heavy meson interquark potential

The resolution of Dyson-Schwinger equations leads to the freezing of the QCD running coupling (effective charge) in the infrared, which is best understood as a dynamical generation of a gluon mass function, giving rise to a momentum dependence which is free from infrared divergences. We calculate the interquark potential for heavy mesons by assuming that it is given by a massive One Gluon Exchange potential and compare with phenomenologyical fits inspired by lattice QCD. We apply these potential forms to the description of quarkonia and conclude that, even though some aspects of the confinement mechanism are absent in the Dyson Schwinger formalism, the results for the spectrum are surprisin…

Parton distributions in a constituent quark scenario

A simple picture of the constituent quark as a composite system of point-like partons is used to construct the unpolarized and polarized parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We achieve good agreement with experiments in the unpolarized, as well as, in the polarized case. When our results are compared with similar calculations using non-composite constituent quarks, the accord with the experiments of the present scheme is impressive. We conclude that DIS data are consistent with a low energy scenario dominated by composite constituents of the nucleon.

Relativity and constituent quark structure in model calculations of parton distributions

According to recent studies, Parton Distribution Functions (PDFs) and Generalized Parton Distributions (GPDs) can be evaluated in a Constituent Quark Model (CQM) scenario, considering the constituent quarks as composite objects. In here, a fully covariant model for a system of two particles, together with its non relativistic limit, are used to calculate PDFs and GPDs. The analysis permits to realize that by no means the effects of Relativity can be simulated taking into account the structure of the constituent particles, the two effects being independent and necessary for a proper description of available high energy data in terms of CQM.

Quark exchange in deep inelastic scattering

We use a model for baryons that links the constituent structure to the deep inelastic (current) properties. The approach consists in a laboratory partonic description (based on a model of hadron structure), to which a low momentum scaleQ 0 is adscribed, which is evolved to high momenta by means of the renormalization group. A generalization of the model by means of the hadronic quark cluster decomposition, provides a description of the structure functions of nuclei and is the starting point to study the effects that the antisymmetrization at the quark level has on the structure function of a model deuteron. The analysis contains conventional and high momentum partonic components. We next st…

The spectrum of bosonized QCD2 in the chiral limit

Abstract By studying an equivalent non-abelian bosonic theory we resolve the spectrum of Quantum Chromodynamics in one space-one time dimensions for massless quarks. The emphasis is placed in the non chiral sector described by colored meson fields. Two and four point functions of these fields are explicitly calculated in the large N limit. Some of the relevant issues: chiral symmetry realization, phases, baryon spectrum, topology etc …, are revisited.

The Pion Velocity in Dense Skyrmion Matter

We have developed a field theory formalism to calculate $in$-$medium$ properties of hadrons within a unified approach that exploits a single Lagrangian to describe simultaneously both matter background and meson fluctuations. In this paper we discuss the consequences on physical observables of a possible phase transition of hadronic matter taking place in the chiral limit. We pay special attention to the pion velocity $v_\pi$, which controls, through a dispersion relation, the pion propagation in the hadronic medium. The $v_\pi$ is defined in terms of parameters related to the matrix element in matter of the axial-vector current, namely, the in-medium pion decay constants, $f_t$ and $f_s$. …

The role of the dilaton in dense skyrmion matter

In this note, we report on a remarkable and surprising interplay between the omega meson and the dilaton chi in the structure of a single skyrmion as well as in the phase structure of dense skyrmion matter which may have a potentially important consequence on the properties of compact stars. In our continuing effort to understand hadronic matter at high density, we have developed a unified field theoretic formalism for dense skyrmion matter using a single Lagrangian to describe simultaneously both matter and meson fluctuations and studied in-medium properties of hadrons. The effective theory used is the Skyrme model Lagrangian gauged with the vector mesons rho and omega, implemented with th…

Nonforward parton distributions of the pion within an effective single instanton approximation

We develop a relativistic quark model for pion structure, which incorporates the non-trivial structure of the vacuum of Quantum Chromodynamics as modelled by instantons. Pions are boundstates of quarks and the strong quark-pion vertex is determined from an instanton induced effective lagrangian. The interaction of the constituents of the pion with the external electromagnetic field is introduced in gauge invariant form. The parameters of the model, i.e., effective instanton radius and constituent quark masses, are obtained from the vacuum expectation values of the lowest dimensional quark and gluon operators and the low-energy observables of the pion. We apply the formalism to the calculati…

Scalar spectrum in a graviton soft wall model

In this study we present a unified phenomenological analysis of the scalar glueball and scalar meson spectra within an AdS/QCD framework in the bottom up approach. For this purpose we generalize the recently developed graviton soft-wall (GSW) model, which has shown an excellent agreement with the lattice QCD glueball spectrum, to a description of glueballs and mesons with a unique energy scale. In this scheme, dilatonic effects, are incorporated in the metric as a deformation of the AdS space. We apply the model also to the heavy meson spectra with success. We obtain quadratic mass equations for all scalar mesons while the glueballs satisfy an almost linear mass equation. Besides their spec…

Color-singlet states in a hadronic quark-cluster basis

We prove that any physical (color-singlet) state can be expanded in terms of a basis constructed by direct product from baryonic and/or mesonic states. The proof is based on a group-theoretical representation method due to Hund. The application of the procedure to the color degrees of freedom leads to known results, which we generalize to more complex situations. The joint application of the method to the color and flavor degrees of freedom results in our initial statement. In this way one is able to give physical meaning to a mathematical procedure. The physics behind our calculation is intimately connected with the concepts of elementarity of constituents and the spinstatistics theorem. T…

On the Delta-nucleon and rho-pi splittings: A QCD-inspired look in free hadrons versus nuclei

Relationships between mass intervals for free hadrons and in nuclei are studied in two theoretical approaches inspired by QCD: naive quark model and skyrmion model, taking one example each from mesons and baryons, that of pi-rho splitting in mesons, and nucleon-Delta splitting in baryons. Possible deconfinement effects in nuclei are examined.

Double Parton Distributions in Light-Front Constituent Quark Models

Double parton distribution functions (dPDF), accessible in high energy proton-proton and proton nucleus collisions, encode information on how partons inside a proton are correlated among each other and could represent a tool to explore the 3D proton structure. In recent papers, double parton correlations have been studied in the valence quark region, by means of constituent quark models. This framework allows to understand clearly the dynamical origin of the correlations and to establish which, among the features of the results, are model independent. Recent relevant results, obtained in a relativistic light-front scheme, able to overcome some drawbacks of previous calculations, such as the…

Monopolium: the key to monopoles

Dirac showed that the existence of one magnetic pole in the universe could offer an explanation for the discrete nature of the electric charge. Magnetic poles appear naturally in most Grand Unified Theories. Their discovery would be of greatest importance for particle physics and cosmology. The intense experimental search carried thus far has not met with success. Moreover, if the monopoles are very massive their production is outside the range of present day facilities. A way out of this impasse would be if the monopoles bind to form monopolium, a monopole- antimonopole bound state, which is so strongly bound, that it has a relatively small mass. Under these circumstances it could be produ…

Search for magnetic monopoles with the MoEDAL forward trapping detector in 2.11 fb −1 of 13 TeV proton–proton collisions at the LHC

We update our previous search for trapped magnetic monopoles in LHC Run 2 using nearly six times more integrated luminosity and including additional models for the interpretation of the data. The MoEDAL forward trapping detector, comprising 222 kg of aluminium samples, was exposed to 2.11 fb−1 of 13 TeV proton–proton collisions near the LHCb interaction point and analysed by searching for induced persistent currents after passage through a superconducting magnetometer. Magnetic charges equal to the Dirac charge or above are excluded in all samples. The results are interpreted in Drell–Yan production models for monopoles with spins 0, 1/2 and 1: in addition to standard point-like couplings, …

Color Anomaly and Flavor-Singlet Axial Charge of the Proton in the Chiral Bag: The Cheshire Cat Revisited

Quantum effects inside the chiral bag induce a color anomaly which requires a compensating surface term to prevent breakdown of color gauge invariance. We show that the presence of this surface term first discovered several years ago allows one to derive in a gauge-invariant way a chiral-bag version of the Shore-Veneziano two-component formula for the flavor-singlet axial charge of the proton. This has relevance to what is referred to as the ``proton spin problem" on the one hand and to the Cheshire-Cat phenomenon in hadron structure on the other. We show that when calculated to the leading order in the color gauge coupling and for a specific color electric monopole configuration in the bag…

Unified Approach to Dense Matter

We apply the Skyrme model to dense hadronic matter, which provides a unified approach to high density, valid in the large Nc limit. In our picture, dense hadronic matter is described by the classical soliton configuration with minimum energy for the given baryon number density. By incorporating the meson fluctuations on such ground state we obtain an effective Lagrangian for meson dynamics in a dense medium. Our starting point has been the Skyrme model defined in terms of pions, thereafter we have extended and improved the model by incorporating other degrees of freedom such as dilaton, kaons and vector mesons.

Polarized structure functions in a constituent quark scenario

Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the polarized parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. Using unpolarized data to fix the parameters we achieve good agreement with the polarization experiments for the proton, while not so for the neutron. By relaxing our assumptions for the sea distributions, we define new quark functions for the polarized case, which reproduce well the proton data and are in better agreement with the neutron data. When our results are compared with similar calculations using non-composite constituent quarks the ac…

A Unified Approach to High Density: Pion Fluctuations in Skyrmion Matter

As the first in a series of systematic work on dense hadronic matter, we study the properties of the pion in dense medium using Skyrme's effective Lagrangian as a unified theory of the hadronic interactions applicable in the large $N_c$ limit. Dense baryonic matter is described as the ground state of a skyrmion matter which appears in two differentiated phases as a function of matter density: i) at high densities as a stable cubic-centered (CC) half-skyrmion crystal; ii) at low densities as an unstable face-centered cubic (FCC) skyrmion crystal. We substitute the latter by a stable inhomogeneous phase of lumps of dense matter, which represents a naive Maxwell construction of the phase trans…

Anomalous f(1) exchange in vector meson photoproduction asymmetries

We perform an analysis of the elastic production of vector mesons with polarized photon beams at high energy in order to investigate the validity of a recently proposed dynamical mechanism based on the dominance of the f_1 trajectory at large momentum transfer. The density matrix characterizing the angular distributions of the vector meson decays is calculated within an exchange model which includes the Pomeron and the f_1. The asymmetries of these decays turn out to be very useful to disentangle the role of these exchanges since their effect depends crucially on their quantum numbers which are different. The observables analyzed are accessible with present experimental facilities.

A Quark model analysis of the Sivers function.

We develop a formalism to evaluate the Sivers function. The approach is well suited for calculations which use constituent quark models to describe the structure of the nucleon. A non-relativistic reduction of the scheme is performed and applied to the Isgur-Karl model of hadron structure. 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. This pattern is in agreement with the one found analyzing, in the same model, the impact parameter dependent generalized parton distributions. The Burkardt Sum Rule turns out to be fulfilled to a large extent. We estimate the QCD evolution of our results from the mom…

GENERALIZED PARTON DISTRIBUTIONS AND COMPOSITE CONSTITUENT QUARKS

An approach is proposed to calculate Generalized Parton Distributions (GPDs) in a Constituent Quark Model (CQM) scenario, considering the constituent quarks as complex systems. The GPDs are obtained from the wave functions of the non relativistic CQM of Isgur and Karl, convoluted with the GPDs of the constituent quarks themselves. The latter are modelled by using the structure functions of the constituent quark, the double distribution representation of GPDs, and a recently proposed phenomenological constituent quark form factor. The present approach permits to access a kinematical range corresponding to both the DGLAP and the ERBL regions, for small values of the momentum transfer and of t…

Polarized parton distributions and light-front dynamics

We present a consistent calculation of the structure functions within a light-front constituent quark model of the nucleon. Relativistic effects and the relevance of the covariance constraints are analyzed for both polarized and unpolarized parton distributions. Various models, which differ in their gluonic structure at the hadronic scale, are investigated. The results of the full covariant calculation are compared with those of a non-relativistic approximation to show the structure and magnitude of the differences.

eta - eta' - glueball mixing

We have revisited glueball mixing with the pseudoscalar mesons in the MIT bag model scheme. The calculation has been performed in the spherical cavity approximation to the bag using two different fermion propagators, the cavity and the free propagators. We obtain a very small probability of mixing for the eta at the level of $0.04-0.1% and a bigger for the eta' at the level of 4-12%. Our results differ from previous calculations in the same scheme but seem to agree with the experimental analysis. We discuss the origin of our difference which stems from the treatment of our time integrations.

Triquark correlations and pentaquarks in a QCD sum rule approach

The role of quark correlations in the description of hadron dynamics in many domains of physics, from low energy dynamics to very hot(dense) systems, is being appreciated. Strong correlations of two quarks (diquark) have been widely investigated in this respect. Recently, we have proposed a dynamical scheme to describe the $\Theta^+$ pentaquark in which also three quark correlations (triquark) were instrumental in producing a low mass exotic state. We perform a study, within the QCD sum rule approach including OPE and direct instanton contributions, of triquark correlations and obtain two quasi-bound light $ud\bar{s}$ color quark clusters of 800 MeV and 930 MeV respectively.

A quark model analysis of the transversity distribution

The feasibility of measuring chiral-odd parton distribution functions in polarized Drell-Yan and semi-inclusive experiments has renewed theoretical interest in their study. Models of hadron structure have proven succesful in describing the gross features of the chiral-even structure functions. Similar expectations support our study of the transversity parton distributions in the Isgur-Karl and MIT bag models. We confirm the diverse low x behavior of the transversity and spin structure functions at the experimental scale and show that it is fundamentally a consequence of the different behavior under evolution of these functions. The inequalities of Soffer establish constraints between data a…

Gluonic effects in vector meson photoproduction at large momentum transfers

Non-perturbative QCD mechanisms are of fundamental importance in strong interaction physics. In particular, the flavor singlet axial anomaly leads to a gluonic pole mechanism which has been shown to explain the $\eta^{\prime}$ mass, violations of the OZI rule and more recently the proton spin. We show here that the interaction derived from the gluonic pole exchange explains the high momentum transfer behavior of the photoproduction cross sections of vector mesons at JLab energies.

Scalar glueball spectrum

I discuss scenarios for scalar glueballs using arguments based on sum rules, spectral decomposition, the $\frac{1}{{N}_{c}}$ approximation, the scales of the strong interaction and the topology of the flux tubes. I analyze the phenomenological support of those scenarios and their observational implications. My investigations hint a rich low lying glueball spectrum.

The inhomogeneous phase of dense skyrmion matter

It was predicted qualitatively in ref.[1] that skyrmion matter at low density is stable in an inhomogeneous phase where skyrmions condensate into lumps while the remaining space is mostly empty. The aim of this paper is to proof quantitatively this prediction. In order to construct an inhomogeneous medium we distort the original FCC crystal to produce a phase of planar structures made of skyrmions. We implement mathematically these planar structures by means of the 't Hooft instanton solution using the Atiyah-Manton ansatz. The results of our calculation of the average density and energy confirm the prediction suggesting that the phase diagram of the dense skyrmion matter is a lot more comp…

Bag Scattering Theory

We reanalyze the procedure used thus far for the study of collision processes in the Chiral Bag Model from the point of view of scattering theory. In the present formalism thein andout states are free waves with no memory of the cavity. This feature gives rise to an observable effect consisting in a peculiar momentum dependence of the scattering amplitudes, which differs from that of previous calculations. The new procedure however does not change the magnitude of the pion-baryon coupling constants.

Quark antisymmetrization in nuclei

The half-skyrmion phase in a chiral-quark model

The Chiral Dilaton Model, where baryons arise as non-topological solitons built from the interaction of quarks and chiral mesons, shows in the high density low temperature regime a two phase scenario in the nuclear matter phase diagram. Dense soliton matter described by the Wigner–Seitz approximation generates a periodic potential in terms of the sigma and pion fields that leads to the formation of a band structure. The analysis up to three times nuclear matter density shows that soliton matter undergoes two separate phase transitions: a delocalization of the baryon number density leading to B=1/2B=1/2 structures, as in skyrmion matter, at moderate densities, and quark deconfinement at larg…

Erratum to: “A quark model analysis of orbital angular momentum” [Phys. Lett. B 460 (1999) 8–16]

Model calculations of the Sivers function satisfying the Burkardt sum rule

9 pages, 4 figures.-- ISI article identifier:000266408300028.-- ArXiv pre-print avaible at:http://arxiv.org/abs/0811.1191

Looking for magnetic monopoles at LHC with diphoton events

Magnetic monopoles have been a subject of interest since Dirac established the relation between the existence of monopoles and charge quantization. The intense experimental search carried thus far has not met with success. The Large Hadron Collider is reaching energies never achieved before allowing the search for exotic particles in the TeV mass range. In a continuing effort to discover these rare particles we propose here other ways to detect them. We study the observability of monopoles and monopolium, a monopole-antimonopole bound state, at the Large Hadron Collider in the $\gamma \gamma$ channel for monopole masses in the range 500-1000 GeV. We conclude that LHC is an ideal machine to …

Hadron correlators and the structure of the quark propagator

The structure of the quark propagator of $QCD$ in a confining background is not known. We make an Ansatz for it, as hinted by a particular mechanism for confinement, and analyze its implications in the meson and baryon correlators. We connect the various terms in the K\"allen-Lehmann representation of the quark propagator with appropriate combinations of hadron correlators, which may ultimately be calculated in lattice $QCD$. Furthermore, using the positivity of the path integral measure for vector like theories, we reanalyze some mass inequalities in our formalism. A curiosity of the analysis is that, the exotic components of the propagator (axial and tensor), produce terms in the hadron c…

A model calculation of double parton distribution functions of the pion

Two-parton correlations in the pion are investigated in terms of double parton distribution functions. A Poincar\'e covariant Light-Front framework has been adopted. As non perturbative input, the pion wave function obtained within the so-called soft-wall AdS/QCD model has been used. Results show how novel dynamical information on the structure of the pion, not accessible through one-body parton distribution, are encoded in double parton distribution functions.

Instanton induced quark dynamics and the pentaquark

We analyze the existence of the exotic $\Theta^+$ from the perspective of instanton induced quark dynamics. The 't Hooft interaction gives strong attraction in specific channels of the triquark $ud\bar s$ and diquark $ud$ configurations. In particular it leads to a light $ud\bar s$ triquark cluster, with the mass around $750 {\rm MeV}$, in the I=0, $S=1/2$ and color 3 configuration, and a light $ud$-diquark configuration, with mass $440 {\rm MeV}$, in the I=0, S=0 and color {$\bar{3}$} configuration. If we consider the pentaquark as a bound state of such triquark and diquark configurations in a relative L=1 state we obtain good agreement with the data. The small width of $\Theta^+$ has a na…

The baryonic spectrum of QCD 2 in the chiral limit

Abstract A description of the baryonic spectrum of quantum chromodynamics in one-space-one-time dimensions for massless quarks is presented. The theory has been studied in the equivalent non-abelian bosonic representation, and four-point functions of the colored meson fields under the simplifying assumption of two colors have been calculated. The crucial role of the chiral sector in providing baryon number has been unveiled. Excited baryon states appear as pseudomesonic excitations on top of the massless baryons associated with the chiral fields.

The physics programme of the MoEDAL experiment at the LHC

The MoEDAL experiment at Point 8 of the LHC ring is the seventh and newest LHC experiment. It is dedicated to the search for highly ionizing particle avatars of physics beyond the Standard Model, extending significantly the discovery horizon of the LHC. A MoEDAL discovery would have revolutionary implications for our fundamental understanding of the Microcosm. MoEDAL is an unconventional and largely passive LHC detector comprised of the largest array of Nuclear Track Detector stacks ever deployed at an accelerator, surrounding the intersection region at Point 8 on the LHC ring. Another novel feature is the use of paramagnetic trapping volumes to capture both electrically and magnetically ch…

The Proton Spin in the Chiral Bag Model : Casimir Contribution and Cheshire Cat Principle

The flavor singlet axial charge has been a source of study in the last years due to its relation to the so called {\it Proton Spin Problem}. The relevant flavor singlet axial current is anomalous, i.e., its divergence contains a piece which is the celebrated $U_A(1)$ anomaly. This anomaly is intimately associated with the $\eta^\prime$ meson, which gets its mass from it. When the gauge degrees of freedom of QCD are confined within a volume as is presently understood, the $U_A(1)$ anomaly is known to induce color anomaly leading to "leakage" of the color out of the confined volume (or bag). For consistency of the theory, this anomaly should be canceled by a boundary term. This ``color bounda…

Pseudoscalar glueball and eta-eta ' mixing

We have performed a dynamical analysis of the mixing in the pseudoscalar channel with the goal of understanding the existence and behavior of the pseudoscalar glueball. Our philosophy has not been to predict precise values of the glueball mass but to exploit an adequate effective theory to the point of breaking and to analyze which kind of mechanisms restore compatibility with data. Our study has led to analytical solutions which allow a clear understanding of the phenomena. The outcome of our calculation leads to a large mass glueball M-Theta > 2000 MeV, to a large glue content of the eta ', and to mixing angles in agreement with previous numerical studies.

Nucleon Structure Functions and Light-Front Dynamics

We present a quark-parton model to describe polarized and unpolarized nucleon structure functions. The twist-two matrix elements for the QCD evolution analysis of lepton-hadron scattering are calculated within a light-front covariant quark model. The relativistic effects in the three-body wave function are discussed for both the polarized and unpolarized cases. Predictions are given for the polarized gluon distributions as will be seen in future experiments.

Double parton correlations in constituent quark models

Double parton correlations, having effects on the double parton scattering processes occurring in high-energy hadron-hadron collisions, for example at the LHC, are studied in the valence quark region by means of constituent quark models. In this framework, two particle correlations are present without any additional prescription, at variance with what happens, for example, in independent particle models, such as the MIT bag model in its simplest version. From the present analysis, conclusions similar to the ones obtained recently in a modified version of the bag model can be drawn: correlations in the longitudinal momenta of the active quarks are found to be sizable, while those in transver…

Pure glueball states in a light-front holographic approach

A phenomenological analysis of the scalar glueball and scalar meson spectra is carried out by using the AdS/QCD framework in the bottom-up approach. The resulting spectra are in good agreement for glueballs with lattice QCD results and for mesons with PDG data. We make use of the relation between the mode functions in AdS/QCD and the wave functions in Light-Front $QCD$ to discuss the mixing of glueballs and mesons. The results of our investigation point out that above 2 GeV scalar particles will appear in almost degenerate pairs of unmixed glueball and mesons states leading to an interesting phenomenology whereby gluon dynamics could be well investigated.

Generalized parton distributions of the pion in a Bethe Salpeter approach

We calculate generalized parton distribution functions in a field theoretic formalism using a covariant Bethe-Salpeter approach for the determination of the bound-state wave function. We describe the procedure in an exact calculation in scalar Electrodynamics proving that the relevant corrections outside our scheme vanish. We extend the formalism to the Nambu--Jona-Lasinio model, a realistic theory of the pion. We go in both cases beyond all previous calculations and discover that all important features required by general physical considerations, like symmetry properties, sum rules and the polynomiality condition, are explicitly verified. We perform a numerical study of their behavior in t…

Search for Magnetic Monopoles with the MoEDAL Forward Trapping Detector in 13 TeV Proton-Proton Collisions at the LHC

MoEDAL is designed to identify new physics in the form of long-lived highly-ionising particles produced in high-energy LHC collisions. Its arrays of plastic nuclear-track detectors and aluminium trapping volumes provide two independent passive detection techniques. We present here the results of a first search for magnetic monopole production in 13 TeV proton-proton collisions using the trapping technique, extending a previous publication with 8 TeV data during LHC run-1. A total of 222 kg of MoEDAL trapping detector samples was exposed in the forward region and analysed by searching for induced persistent currents after passage through a superconducting magnetometer. Magnetic charges excee…

eta-eta ' mixing in the flavor basis and large N

The mass matrix for eta-eta' is derived in the flavor basis at O(p(4)) of the chiral Lagrangian using the large N approximation. Under certain assumptions, the mixing angle phi = 41.4 degrees and the decay constants ratio f(K)/f(pi) = 1.15 are calculated in agreement with the data. It appears that the FKS scheme arises as a special limit of the chiral Lagrangian. Their mass matrix is obtained without the hypothesis on the mixing pattern of the decay constants.

The soliton-soliton interaction in the Chiral Dilaton Model

We study the interaction between two B = 1 states in the Chiral Dilaton Model where baryons are described as nontopological solitons arising from the interaction of chiral mesons and quarks. By using the hedgehog solution for B = 1 states we construct, via a product ansatz, three possible B = 2 configurations to analyse the role of the relative orientation of the hedgehog quills in the dynamics of the soliton-soliton interaction and investigate the behavior of these solutions in the range of long/intermediate distance. One of the solutions is quite binding due to the dynamics of the pi and sigma fields at intermediate distance and should be used for nuclear matter studies. Since the product…

The pion in the graviton soft-wall model: phenomenological applications

The holographic graviton soft-wall model, introduced to describe the spectrum of scalar and tensor glueballs, is improved to incorporate the realization of chiral-symmetry as in QCD. Such a goal is achieved by including the longitudinal dynamics of QCD into the scheme. Using the relation between AdS/QCD and Light-Front dynamics, we construct the appropriate wave function for the pion which is used to calculate several pion observables. The comparison of our results with phenomenology is remarkably successful.

The physics of glueballs

Glueballs are particles whose valence degrees of freedom are gluons and therefore in their description the gauge field plays a dominant role. We review recent results in the physics of glueballs with the aim set on phenomenology and discuss the possibility of finding them in conventional hadronic experiments and in the Quark Gluon Plasma. In order to describe their properties we resort to a variety of theoretical treatments which include, lattice QCD, constituent models, AdS/QCD methods, and QCD sum rules. The review is supposed to be an informed guide to the literature. Therefore, we do not discuss in detail technical developments but refer the reader to the appropriate references.

THE PARTON DISTRIBUTIONS IN NUCLEONS: A QUARK MODEL ANALYSIS

We use a laboratory frame description based on quark model wave functions to study the parton distributions in the nucleon. The present approach incorporates two major improvements, namely, it has the correct support and the renormalization group evolution is carried out to next-to-leading order. We obtain initially the parton distributions arising from the Isgur-Karl wave function. The failure of the latter to reproduce, even approximately, the data motivates us to analyze different scenarios, i.e. additional high momentum components and nonvanishing gluon distributions at the initial scale. We conclude that in order to understand data at various scales complex models simultaneously, it i…

Quarks in nuclei

We review some properties of Quantum Chromodynamics, the theory of the hadronic interactions, which serve as guidelines to introduce low energy models of hadron structure. Among these we shall center our attention in the non relativistic quark model and the topological bag model. We present some of their applications to actual problems in experimental and theoretical nuclear physics. In particular we discuss exotic nuclei, quark matter, deep inelastic scattering, proton spin,... and their relation to such phenomena as quark Pauli blocking, strangeness enhancement, nuclear structure functions, bosonization,...

Monopolium production from photon fusion at the Large Hadron Collider

6 pages, 6 figures.-- PACS nrs.: 14.80.Hv; 95.30.Cq; 98.70.-f; 98.80.-k.-- Printed version published Aug 2009.-- ArXiv pre-print available at: http://arxiv.org/abs/0809.0272

Non-abelian gauge dynamics of slowly moving fermions

We study the dynamics generated by local gauge invariance under a non-abelianSU(N) group for two nonrelativistic particles interacting through the effect of the group charges. We describe the local gauge invariant potential which contains the exchange of infinitely many gluons. We discuss the possible implications of our result.

A model study of nuclear structure functions

We calculate the structure function for a deuteron using the hadronic quark cluster decomposition. By assuming that nuclei might be composed of quasi deuterons, we study their structure functions. The procedure enables a quantum mechanical parametrization of various scenarios, among them nuclear dynamics and nucleon swelling. Moreover it is specially suited to study quark exchange effects. We show, within a scheme where perturbative evolution effects are minimized, that the region around x=1 is very sensitive to these two mechanisms and their effects can be disentangled.

Constituent quarks and parton distributions

Abstract The high energy parton distribution when evolved to a low energy scale appears to indicate that a valence picture of hadron structure arises. We have developed a formalism based on a laboratory partonic description which connects the parton distributions with the momentum distributions of a quark model. The formalism uses Next to Leading Order evolution and has been defined to produce the right support for the parton distributions. In this scheme we have analyzed the polarized and unpolarized data and shown that well-known Quark Models lead to a qualitative description of the data. However, if one aims at a quantitative agreement, these conventional low energy models have to be cha…

Instantons and eta meson production near threshold in NN collisions

An enhancement for the $\eta$ production in proton-neutron collisions as compared with that in proton-proton scattering has been recently observed. We present a calculation for the production cross section, in proton-neutron collisions near threshold, within instanton model for the QCD vacuum and show that a specific flavor dependent nonperturbative quark-gluon interaction related to instantons is able to explain the observed enhancement.

First search for dyons with the full MoEDAL trapping detector in 13 TeV pp collisions

The MoEDAL trapping detector, consists of approximately 800 kg of aluminium volumes. It was exposed during Run-2 of the LHC program to 6.46 fb^-1 of 13 TeV proton-proton collisions at the LHCb interaction point. Evidence for dyons (particles with electric and magnetic charge) captured in the trapping detector was sought by passing the aluminium volumes comprising the detector through a SQUID magnetometer. The presence of a trapped dyon would be signalled by a persistent current induced in the SQUID magnetometer. On the basis of a Drell-Yan production model, we exclude dyons with a magnetic charge ranging up to 5 Dirac charges, and an electric charge up to 200 times the fundamental electric …

Spherical multiquark states in the chiral bag model

Abstract We study n-quark systems (n = 3, 6, 12) in the chiral bag model. In order to handle the non-linearities of the model, the hedgehog ansatz for the Goldstone pion field is used. It is found that due to “warping” of the quark orbits in the presence of mean-field pion clouds, a strong repulsion is developed when more than three quarks are put in a bag. This repulsion mechanism turns out to be close to the soliton mechanism discovered by Skyrme two decades ago. Even the magnitude of the repulsion agrees with his. It is also possible to relate the repulsion to the effective quenching of the axial charge of the multiquark system and a suggestion is made that the recently observed quenchin…

New Anomalous Exchange in Regge Phenomenology and Hard Diffraction

A new mechanism for hard diffraction based on the anomalous $f_1$ trajectory exchange, which we identify as the odd signature partner of the Pomeron, is suggested. We calculate the contribution of the $f_1$ exchange to elastic and dissociative electromagnetic production of vector mesons and show that it gives a dominant contribution to the differential cross sections at large momentum transfers.

Parton polarization and constituent quarks

Abstract A systematic study of the polarized-parton distributions is presented and related to the properties of the constituent quarks. The effects of breaking SU(6) symmetry are emphasized and the Isgur-Karl constituent model is discussed in detail. The results on the proton, neutron and deuteron structure functions are compared with the recent experimental data, and the role of the gluon polarization is pointed out. The role of the D-state admixture in the nucleon ground state is also investigated.

Parton correlations effects in double parton distribution functions

Double parton distribution functions (dPDFs), measurable in hadron-hadron collisions and encoding information on how partons inside a proton are correlated among each other, could represent a new tool to explore the three dimensional partonic structure of hadrons. In the present contribution, results of the calculations of dPFDs are presented. Phenomenological calculations of experimental observables, sensitive to dPDFs are also discussed showing how double parton correlations could be estimated in the next LHC run.

Quark degrees of freedom in hadronic systems: Partonic distributions

The role of models in Quantum Chromodynamics is to produce simple physical pictures that connect the phenomenological regularities with the underlying structure. The static properties of hadrons have provided experimental input to define a variety of very succesful Quark Models. We discuss applications of some of the most widely used of these models to the high energy regime, a scenario for which they were not proposed. The initial assumption underlying our presentation will be that gluon and sea bremsstrahlung connect the constituent quark momentum distributions with the partonic structure functions. The results obtained are encouraging but lead to the necessity of more complex structures …

QCD sum rule analysis of the pentaquark

We perform a QCD sum rule calculation to determine the mass and the parity of the lowest lying pentaquark state. We include operators up to dimension $d=13$ in the OPE and the direct instanton contributions. We find evidence for a positive parity state. The contribution from operators of dimension $d>5$ is instrumental in determining the parity of the state and achieving the convergence of the sum rule.

Skyrmions at finite density and temperature: the chiral phase transition

The Skyrme model, an effective low energy theory rooted in large $N_c$ QCD, has been applied to the study of dense matter. Matter is described by various crystal structures of skyrmions. When this system is heated, the dominating thermal degrees of freedom are the fluctuating pions. Taking these mechanisms jointly produces a description of the chiral phase transition leading to the conventional phase diagram with critical temperatures and densities in agreement with expected values.

η–η′ mixing in the flavor basis and large N

Abstract The mass matrix for η – η ′ is derived in the flavor basis at O ( p 4 ) of the chiral Lagrangian using the large N approximation. Under certain assumptions, the mixing angle ϕ = 41.4 ° and the decay constants ratio f K / f π = 1.15 are calculated in agreement with the data. It appears that the FKS scheme arises as a special limit of the chiral Lagrangian. Their mass matrix is obtained without the hypothesis on the mixing pattern of the decay constants.

Non-perturbative momentum dependence of the coupling constant and hadronic models

Models of hadron structure are associated with a hadronic scale which allows by perturbative evolution to calculate observables in the deep inelastic region. The resolution of Dyson-Schwinger equations leads to the freezing of the QCD running coupling (effective charge) in the infrared, which is best understood as a dynamical generation of a gluon mass function, giving rise to a momentum dependence which is free from infrared divergences. We use this new development to understand why perturbative treatments are working reasonably well despite the smallness of the hadronic scale.

Generalized Parton Distributions in Constituent Quark Models

An approach is proposed to calculate Generalized Parton Distributions (GPDs) in a Constituent Quark Model (CQM) scenario. These off-diagonal distributions are obtained from momentum space wave functions to be evaluated in a given non relativistic or relativized CQM. The general relations linking the twist-two GPDs to the form factors and to the leading twist quark densities are consistently recovered from our expressions. Results for the leading twist, unpolarized GPD, H, in a simple harmonic oscillator model, as well as in the Isgur and Karl model, are shown to have the general behavior found in previous estimates. NLO evolution of the obtained distributions, from the low momentum scale of…