Search

The coupling constant of a vector meson with delta baryons in the AdS/QCD model is investigated. A pseudoscalar field is introduced inside the anti-de Sitter (AdS) space to break the chiral symmetry together with gauge fields with left and right chiral symmetries and the Rarita–Schwinger fields. The vector field is determined with the help of the gauge fields with left and right chiral symmetries, and profile functions for all these fields are introduced inside the AdS space. In addition, a minimal gauge and magnetic gauge Lagrangian interaction are introduced interior to the AdS space. With the help of the Lagrangian interactions and in accord with the AdS/CFТ model, the coupling constant of the vector meson with the delta baryons has been obtained in the form of an integral over the additional dimension. With the help of the software package Mathematica 7, the numerical values of the coupling constant of the vector meson with the delta baryons in the soft-wall AdS/QCD model have been determined.

We have investigated the effect of nucleon and delta resonances with spins $11/2$, $13/2$, and $15/2$ in the kaon photoproduction process $\ensuremath{\gamma}+N\ensuremath{\rightarrow}K+Y$ by using two covariant isobar models. The formalism for high-spin propagators and interaction Lagrangians were adopted from the works of Pascalutsa and Vrancx et al. The calculated scattering amplitudes were decomposed into six Lorentz- and gauge-invariant matrices, from which we calculated the cross sections and polarization observables. The unknown parameters in the amplitudes, i.e., the coupling constants and hadronic form factor cutoffs, were obtained by fitting the calculated observables to experimental data. In the $K\mathrm{\ensuremath{\Lambda}}$ channels the inclusion of $N(2600){I}_{1,11}$ and $N(2700){K}_{1,13}$ resonances improves the agreement between model calculations and experimental data significantly and reduces the dominance of resonances in the model by increasing the hadronic form factor cutoff of the Born terms. Furthermore, the inclusion of these resonances reduces the number of resonance structures in cross sections, including the structure in the ${K}^{0}\mathrm{\ensuremath{\Lambda}}$ differential cross section at $W\ensuremath{\approx}1650\text{ }\text{ }\mathrm{MeV}$, which could become a hint of the narrow resonance. In the $K\mathrm{\ensuremath{\Sigma}}$ channels the inclusion of $N(2600){I}_{1,11}$, $N(2700){K}_{1,13}$, $\mathrm{\ensuremath{\Delta}}(2420){H}_{3,11}$, $\mathrm{\ensuremath{\Delta}}(2750){I}_{3,13}$, and $\mathrm{\ensuremath{\Delta}}(2950){K}_{3,15}$ states also significantly improves the model and increases the hadronic form factor cutoff of the Born terms. However, different from the $K\mathrm{\ensuremath{\Lambda}}$ channels, the inclusion of these high-spin resonances leads to more resonance structures in the ${K}^{+}{\mathrm{\ensuremath{\Sigma}}}^{0}$ differential cross section. This investigation reveals that the second and third peaks in the ${K}^{+}{\mathrm{\ensuremath{\Sigma}}}^{0}$ differential cross section originate from the $\mathrm{\ensuremath{\Delta}}(2000){F}_{35}$ and $N(2290){G}_{19}$ resonances, respectively. We have also evaluated the resonance properties at the pole positions and using the Breit-Wigner method. In both $K\mathrm{\ensuremath{\Lambda}}$ and $K\mathrm{\ensuremath{\Sigma}}$ channels the inclusion of the high-spin baryon resonances was found to improve the agreement between the resonance properties obtained in this study and those listed by the Particle Data Group.

The vector $U$ bosons, or so-called ``dark photons,'' are one of the possible candidates for the dark matter mediators. They are supposed to interact with the standard matter via a ``vector portal'' due to the $U(1)\ensuremath{-}U(1{)}^{\ensuremath{'}}$ symmetry group mixing which might make them visible in particle and heavy-ion experiments. While there is no confirmed observation of dark photons, the detailed analysis of different experimental data allows to estimate the upper limit for the kinetic mixing parameter ${\ensuremath{\epsilon}}^{2}$ depending on the mass ${M}_{U}$ of $U$ bosons which is also unknown. In this study we present theoretical constraints on the upper limit of ${\ensuremath{\epsilon}}^{2}({M}_{U})$ in the mass range ${M}_{U}\ensuremath{\le}0.6\text{ }\text{ }\mathrm{GeV}$ from the comparison of the calculated dilepton spectra with the experimental data from the HADES collaboration at SIS18 energies where the dark photons are not observed. Our analysis is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which reproduces well the measured dilepton spectra in $p+p$, $p+A$ and $A+A$ collisions. Additionally to the different dilepton channels originating from interactions and decays of ordinary matter particles (mesons and baryons), we incorporate the decay of hypothetical $U$ bosons to dileptons, $U\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$, where the $U$ bosons themselves are produced by the Dalitz decay of pions ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}\ensuremath{\gamma}U$, $\ensuremath{\eta}$ mesons $\ensuremath{\eta}\ensuremath{\rightarrow}\ensuremath{\gamma}U$ and Delta resonances $\mathrm{\ensuremath{\Delta}}\ensuremath{\rightarrow}NU$. Our analysis can help to estimate the requested accuracy for future experimental searches of ``light'' dark photons by dilepton experiments.

Quantizing a soliton on a hypersphere, we obtain the first class Hamiltonian, and evaluate the baryon physical quantities which are in good agreement with the corresponding experimental data. In particular, we find that the predicted value for axial coupling constant is comparable to its experimental value. The prediction for delta baryon mass possessing the Weyl ordering correction obtained in the first class Dirac quantization is improved comparing with that in the second class canonical quantization performed on the hypersphere. Making use of the same input parameters associated with the baryon masses, we also investigate the hypersphere soliton and standard Skyrmion models to compare the corresponding predictions for the physical quantities effectively. Next, we evaluate the intrinsic frequencies of the pulsating baryons. We thus find that the intrinsic pulsating frequency of more massive particle is greater than that of the less massive one. We explicitly evaluate the intrinsic frequencies $\omega_{N}=0.87\times 10^{23}~{\rm sec}^{-1}$ and $\omega_{\Delta}=1.74\times 10^{23}~{\rm sec}^{-1}$ of the nucleon and delta baryon, respectively, to yield the identity $\omega_{\Delta}=2\omega_{N}$., Comment: 8 pages, title changed, version to appear in NPB

A future gamma factory at CERN or accelerator-based gamma sources elsewhere can include the possibility of energetic twisted photons, which are photons with a structured wave front that can allow a pre-defined large angular momentum along the beam direction. Twisted photons are potentially a new tool in hadronic physics, and we consider here one possibility, namely the photoproduction of $\Delta$(1232) baryons using twisted photons. We show that particular polarization amplitudes isolate the smaller partial wave amplitudes and they are measurable without interference from the terms that are otherwise dominant., Comment: 9 pages, 5 figures

In this work, we study magnetic field effects on neutron star matter containing the baryon octet and additional heavier spin 3/2 baryons (the $\Delta$'s). We make use of two different relativistic hadronic models that contain an additional vector-isovector self interaction for the mesons: one version of a relativistic mean field (RMF) model and the Chiral Mean Field (CMF) model. We find that both the additional interaction and a strong magnetic field enhance the $\Delta$ baryon population in dense matter, while decreasing the relative density of hyperons. At the same time that the vector-isovector meson interaction modifies neutron-star masses very little ($, Comment: 9 pages, 8 figures

The photoproduction of γp→K+Σ0(1385) is investigated based on an effective Lagrangian approach using the tree-level Born approximation, with the purpose of understanding the reaction mechanisms and resonance contents and their associated parameters in this reaction. In addition to the t-channel K and K*(892) exchanges, s-channel nucleon (N) exchange, u-channel Λ exchange, and generalized contact term, the exchanges of a minimum number of N and Δ resonances in the s channel are taken into account in constructing the reaction amplitudes to describe the experimental data. It is found that the most recent differential cross-section data from the CLAS Collaboration can be well reproduced by including one of the N(1895)1/2-, Δ(1900)1/2-, and Δ(1930)5/2- resonances. The reaction mechanisms of γp→K+Σ0(1385) are discussed in detail, and the predictions of the beam and target asymmetries for this reaction are given. The cross sections of γp→K0Σ+(1385) are shown to be able to further constrain the theoretical models and pin down the resonance contents for γp→K+Σ0(1385).

We investigate the hadron-quark phase transition in cold neutron stars in light of (i) the observed limits on the maximum-mass of heavy pulsars, (ii) constraints on the tidal properties inferred from the gravitational waves emitted in binary neutron-star mergers, and (iii) mass and radius constraints derived from the observation of hot spots on neutron star observed with the Neutron Star Interior Composition Explorer instrument. Special attention is directed to the possible presence of ∆(1232) baryons in neutron star matter. Our results indicate that this particle could make up a large fraction of the baryons in neutron stars and thus have a significant effect on the properties of such objects, particularly on their radii. This is partially caused by the low density appearance of ∆s for a wide range of theoretically defensible sets of meson-hyperon, SU(3) ESC08 model, and meson-∆ coupling constants. The transition of hadronic matter to quark matter, treated in the 2SC+s condensation phase, is found to occur only in neutron stars very close to the mass peak. Nevertheless, quark matter may still constitute an appreciable fraction of the stars' total matter if the phase transition is treated as Maxwell-like (sharp), in which case the neutron stars located beyond the gravitational mass peak would remain stable against gravitational collapse. In this case, the instability against gravitational collapse is shifted to a new (terminal) mass different from the maximum-mass of the stellar sequence, giving rise to stable compact objects with the same gravitational masses as those of the neutron stars on the traditional branch, but whose radii are smaller by up to 1 km. All models for the equation of state of our study fall comfortably within the bound established very recently by Annala et al., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Física La Plata

International audience; The presence of exotic hadrons, such as hyperons and Δ isobars, in the dense nuclear matter in their cores has been shown to produce important changes in the properties of neutron stars. Within the quark-meson coupling model, we show that the many-body forces generated by the change in the internal quark structure of the baryons in the strong scalar mean fields generated in dense nuclear matter prohibit the appearance of Δ isobars.

Collisions between carbon and beryllium nuclei at initial kinetic energies of carbon nuclei of 0.6, 0.95, and 2.0 GeV/nucleon have been simulated within the Liege intranuclear cascade model. Invariant proton production cross sections at an angle of 3.5° have been determined. It has been shown that the dependence of experimental invariant proton production cross sections on the cumulative variable can be explained in terms of Fermi processes of motion of nucleons in a nucleus, multiple scattering, and production of delta resonances. Results of simulation have been compared to experimental data and results obtained within the quark cluster model.

We analyse the phenomenological implications of the two-families scenario on the merger of compact stars. That scenario is based on the coexistence of both hadronic stars and strange quark stars. After discussing the classification of the possible mergers, we turn to detailed numerical simulations of the merger of two hadronic stars, i.e., "first family" stars in which delta resonances and hyperons are present, and we show results for the threshold mass of such binaries, for the mass dynamically ejected and the mass of the disk surrounding the post-merger object. We compare these results with those obtained within the one-family scenario and we conclude that relevant signatures of the two-families scenario can be suggested, in particular: the possibility of a rapid collapse to a black hole for masses even smaller than the ones associated to GW170817; during the first milliseconds, oscillations of the postmerger remnant at frequencies higher than the ones obtained in the one-family scenario; a large value of the mass dynamically ejected and a small mass of the disk, for binaries of low total mass. Finally, based on a population synthesis analysis, we present estimates of the number of mergers for: two hadronic stars; hadronic star - strange quark star; two strange quark stars. We show that for unequal mass systems and intermediate values of the total mass, the merger of a hadronic star and a strange quark star is very likely (GW170817 has a possible interpretation into this category of mergers). On the other hand, mergers of two strange quark stars are strongly suppressed., Comment: 18 pages, 16 figures

We explore the possibility of formation of $\Delta$ baryons (1232 MeV) in neutron star matter in an effective chiral model within the relativistic mean-field framework. With variation in delta-meson couplings, consistent with the constraints imposed on them, the resulting equation of state is obtained and the neutron star properties are calculated for static and spherical configuration. Within the framework of our model the critical densities of formation of $\Delta$s and the properties of neutron stars are found to be very sensitive to the iso-vector coupling compared to the scalar or vector couplings. We revisit the $\Delta$ puzzle and look for the possibility of phase transition from non-strange hadronic matter (including nucleons and $\Delta$s) to deconfined quark matter, based on QCD theories. The resultant hybrid star configurations satisfy the observational constraints on mass from the most massive pulsars PSR J1614-2230 and PSR J0348+0432 in static condition obtained with the general hydrostatic equilibrium based on GTR. Our radius estimates are well within the limits imposed from observational analysis of QLMBXs. The obtained values of $R_{1.4}$ are in agreement with the recent bounds specified from the observation of gravitational wave (GW170817)from binary neutron star merger. The constraint on baryonic mass from study of binary system PSR J0737-3039 is also satisfied with our hybrid equation of state. \noindent{Keywords: Delta baryons, Quark matter, Phase transition, Equation of State, Neutron Stars, Hybrid Stars}, Comment: 30 pages, 19 figures

We study the latest $N_f=2+1+1$ and $N_f=2$ ETMC lattice QCD simulations of the nucleon masses and extract the pion-nucleon sigma term utilizing the Feynman-Hellmann theorem in SU(2) baryon chiral perturbation theory with the extended-on-mass-shell scheme. We find that the lattice QCD data can be described quite well already at the next-to-next-to-leading order. The overall picture remains essentially the same at the next-to-next-to-next-to-leading order. Our final result is $\sigma_{\pi N}=50.2(1.2)(2.0)$ MeV, or equivalently, $f_{u/d}^N=0.0535(13)(21)$, where the first uncertainty is statistical and second is theoretical originated from chiral truncations, which is in agreement with that determined previously from the $N_f=2+1$ and $N_f=2$ lattice QCD data and that determined by the Cheng-Dashen theorem. In addition, we show that the inclusion of the virtual $\Delta(1232)$ does not change qualitatively our results., Comment: 7 pages, 2 figures, 2 tables

We consider the electromagnetic transition form factors of the Roper resonance in the framework of an effective field theory of pions, nucleons and delta and Roper resonances as explicit degrees of freedom. Due to the lack experimental data in the region of applicability of low energy effective field theory we fit available free coupling constants and compare obtained results compare to the predictions of a theoretical model., arXiv admin note: text overlap with arXiv:1606.04873 by other authors

Extending a recent suggestion for hyperon form factors to the nucleon case, dispersion theory is used to relate the low-energy vector-isovector form factors of the nucleon to the pion vector form factor. The additionally required input, i.e. the pion-nucleon scattering amplitudes are determined from relativistic next-to-leading-order (NLO) baryon chiral perturbation theory including the nucleons and optionally the Delta baryons. Two methods how to include pion rescattering are compared: (a) solving the Muskhelishvili-Omnes (MO) equation and (b) using an N/D approach. It turns out that the results differ strongly from each other. Furthermore the results are compared to a fully dispersive calculation of the (subthreshold) pion-nucleon amplitudes based on Roy-Steiner (RS) equations. In full agreement with the findings from the hyperon sector it turns out that the inclusion of Delta baryons is not an option but a necessity to obtain reasonable results. The magnetic isovector form factor depends strongly on a low-energy constant of the NLO Lagrangian. If it is adjusted such that the corresponding magnetic radius is reproduced, then the results for the corresponding pion-nucleon scattering amplitude (based on the MO equation) agree very well with the RS results. Also in the electric sector the Delta degrees of freedom are needed to obtain the correct order of magnitude for the isovector charge and the corresponding electric radius. Yet quantitative agreement is not achieved. If the subtraction constant that appears in the solution of the MO equation is not taken from nucleon+Delta chiral perturbation theory but adjusted such that the electric radius is reproduced, then one obtains also in this sector a pion-nucleon scattering amplitude that agrees well with the RS results., 12 pages, discussion and references added, results unchanged

The possible existence of $\Delta$ resonances is inspected in the cold dense matter of neutron star (NS) core in presence of the hyperons. The diverse effects of variation in $\Delta$ mass on their formation and the equation of state (EoS) are studied in this work with an effective chiral model and the resultant NS properties are calculated with the help of parameterized Tolman-Oppenheimer-Volkoff equations (PTOV) to bring out the two important features of pressure in the context of massive NSs. The $\Delta$ puzzle is re-explored and resolved taking into account the concept of modified/parameterized inertial pressure and self-gravity in case of massive pulsars like PSR J1614-2230 and PSR J0348-0432. It is seen that although the presence of exotic matter like the hyperons and the $\Delta$s softens the EoS considerably, their presence in massive NSs can be successfully explained with the theory of parameterized hydrostatic equilibrium conditions. The results of this work also satisfy the constraints on $R_{1.4}$ and $R_{1.6}$ from the gravitational wave (GW170817) detection of binary NS merger. The constraint on baryonic mass from PSR J0737-3039 is also satisfied with the solutions of the PTOV equations for all the $\Delta$ masses considered., Comment: 24 pages, 9 figures

We investigate photoproduction of $\omega$ off a nucleon target $\gamma N\to\omega N$ by using a Reggeized model where $\pi(135)+\sigma(500)+f_1(1285)+f_2(1270)$+Pomeron exchanges are included in the $t$-channel for the reaction at forward angles. The reaction mechanism at low energy is featured by the dominance of the $\pi$ exchange with the absorptive cuts introduced to modulate the pion contribution to both $\gamma p\to \omega p$ and $\gamma n\to \omega n$ reactions. Necessity of $\sigma$ exchange is illustrated in the analysis of the cross section from natural parity exchanges. Cross sections for differential, total, and spin density matrix with beam polarization are reproduced and compared with existing data on $\gamma p\to \omega p$. Scaled differential cross sections of Jefferson Lab data on $\gamma p\to \omega p$ are investigated at the production angle $\theta=90^\circ$ with the nonlinear trajectories for a saturation. Differential and total cross sections for the $\gamma n\to\omega n$ reaction are analyzed to compare with recent experimental data at the CBELSA/TAPS Collaboration. An application to the $\gamma p\to\omega\Delta^+$ reaction is presented to demonstrate the significance of the $\pi$ exchange in the total and differential cross sections., Comment: 11 pages, 12 figures, 2 tables

Recent calculations of the pion-nucleon scattering in covariant baryon chiral perturbation theory with explicit delta resonances are presented. Two-loop results of the widths of the Δ and Roper resonances are discussed in the framework of an effective field theory with nucleons, pions and the Roper and delta resonances as dynamical degrees of freedom.

The (1 + 1)-dimensional Nambu-Jona-Lasinio model describing the system of two-flavor quarks is studied in the limit of a large number of colors in the presence of a baryon chemical potential µ and an isospin chemical potential µ I . The possible formation of a nonuniform pion condensate in dense quark matter is considered for the cases of both the massive and the massless model.

We present the results of a third order calculation of the pion-nucleon scattering amplitude in a chiral effective field theory with pions, nucleons and delta resonances as explicit degrees of freedom. We work in a manifestly Lorentz invariant formulation of baryon chiral perturbation theory using dimensional regularization and the extended on-mass-shell renormalization scheme. In the delta resonance sector, the on mass-shell renormalization is realized as a complex-mass scheme. By fitting the low-energy constants of the effective Lagrangian to the $S$- and $P$-partial waves a satisfactory description of the phase shifts from the analysis of the Roy-Steiner equations is obtained. We predict the phase shifts for the $D$ and $F$ waves and compare them with the results of the analysis of the George Washington University group. The threshold parameters are calculated both in the delta-less and delta-full cases. Based on the determined low-energy constants, we discuss the pion-nucleon sigma term. Additionally, in order to determine the strangeness content of the nucleon, we calculate the octet baryon masses in the presence of decuplet resonances up to next-to-next-to-leading order in SU(3) baryon chiral perturbation theory. The octet baryon sigma terms are predicted as a byproduct of this calculation., Comment: 41 pages, 12 figures, 7 tables

At zero temperature the negative-parity ground states of the nucleon and delta baryons are non-degenerate with the positive-parity partners due to spontaneous breaking of chiral symmetry. However, chiral symmetry is expected to be restored at sufficiently high temperature, in particular when going from the hadronic to the quark-gluon plasma (QGP) phase. This would imply that channels with opposite parity become degenerate. We study the nucleon (spin $1/2$) and $\Delta$ (spin $3/2$) baryons in both parity sectors using lattice QCD. The range of temperatures spans both the hadronic and QGP phases. Using the FASTSUM anisotropic $N_f = 2 + 1$ ensembles, we analyze the correlation functions and the spectral functions using respectively exponential fits and the Maximum Entropy Method. We find clear evidence of in-medium effects in the hadronic phase, especially for the negative-parity ground state, and of parity doubling in the QGP phase., Comment: 7 pages, 3 figures. Talk presented at the 34th International Symposium on Lattice Field Theory (Lattice 2016), 24-30 July 2016, Southampton, UK

The decay of Λ -hypernuclei without π emission, known as Non-Mesonic Weak Decay (NMWD), gives an effective tool to investigate Δ S = 1 four-baryon interactions. It was theoretically suggested that the two-nucleon induced mechanism could play a substantial role in reproducing the observed NMWD decay rates and nucleon spectra, but at present no direct evidence of such a mechanism has been obtained. The FINUDA experiment, exploiting the possibility to detect both charged and neutral particles coming from the hypernucleus decay, has allowed us to deduce the relative weight of the two nucleon induced decay rate to the total NMWD rate. The value of Γ 2 N / Γ NMWD = 0.21 ± 0.07 stat − 0.02 sys + 0.03 sys has been deduced, well consistent with the previous determinations.

A non-relativistic microscopic mean field theory of finite nuclei is investigated where the nucleus is described as a collection of nucleons and delta resonances. The ground state properties of 90Zr nucleus have been investigated at equilibrium and large amplitude compression using a realistic effective baryon-baryon Hamiltonian based on Reid Soft Core (RSC) potential. The sensitivity of the ground state properties is studied, such as binding energy, nuclear radius, radial density distribution, and single particle energies to the degree of compression. It is found that the most of increasing in the nuclear energy generated under compression is used to create the massive Δ particles. For 90Zr nucleus under compression at 2.5 times density of the normal nuclear density, the excited nucleons to Δ's are increased sharply up to 14% of the total number of constituents. This result is consistent with the values extracted from relativistic heavy-ion collisions. The single particle energy levels are calculated and their behaviors under compression are examined too. A good agreement between results with effective Hamiltonian and the phenomenological shell model for the low lying single-particle spectra is obtained. A considerable reduction in compressibility for the nucleus, and softening of the equation of state with the inclusion of the Δ's in the nuclear dynamics are suggested by the results.

Based on the isospin-dependent transport model IBUU and on the scaling model according to nucleon effective mass, effects of elastic and inelastic NN scattering cross-sections on \( \pi^{{-}}_{}\)/\( \pi^{{+}}_{}\) in the neutron-rich reaction 48Ca + 48Ca at a beam energy of 400MeV/nucleon are studied. It is found that cross-section effects of both NN elastic and inelastic scatterings affect \( \Delta_{{1232}}^{}\) , \( \pi^{{-}}_{}\) and \( \pi^{{+}}_{}\) productions as well as the value of \( \pi^{{-}}_{}\)/\( \pi^{{+}}_{}\) .

The circular photon asymmetry for π 0 η photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the Δ ( 1700 ) D 33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D 33 amplitude.

The contributions of two-photon exchange in the process e+ + e− → p + including N and Δ intermediate states are estimated in a simple hadronic model. The corrections to the unpolarized cross section as well as to the polarized observables Px and Pz are evaluated. The results show the corrections to unpolarized cross section are small and the angle dependence becomes weak at small s after considering the N and Δ(1232) contributions simultaneously, while the correction to Pz is enhanced.

The angular distribution of the probability for the Δ(1232)-resonance decay Δ(1232) → Nπ versus the polarizations of baryons and the vector of dynamical nucleon polarization are calculated.

The constituent quark model (CQM) has recently been widely used for the description of the internal structure of baryons. The baryon spectrum is usually well described, although various models are quite different. However, the study of baryon spectroscopy is not sufficient to distinguish among the various forms of quark dynamics. It would be interesting to consider the effect of an extra residual interaction among the quarks, which contains a dependence on isospin (or flavor). In the chiral constituent quark model the non-confining part of the potential is provided by the interaction with the Goldstone bosons, giving rise to a spin- and isospin-dependent part which is crucial for the description of the spectrum for energies lower than 1.7 GeV. In this work we have introduced an improved form of the hyperfine interaction and isospin dependent quark potential. The resulting description of the baryon spectrum was found to be satisfactory and we not only have included confinement potential at large separations, but also color charge and non-confining hyperfine interaction potentials. This combination of potentials yields spectra which are very close to the ones obtained in experiments.

In this work we determine the critical density values of the phase transition between the hadronic to the CFL superconducting quark matter. The Delta resonances and the complete spin-1/2 baryonic octet are considered in the hadronic phase and it is observed that the delta matter inclusion in baryonic phase modifies significantly the critical conditions for the phase transition. Also, we discuss the role of the color superconducting gap on the structure properties of a formed hybrid neutron stars.

Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of $\pi^0\pi^0$ pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557~MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400~MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15\%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final state invariant masses up to $\approx$1550~MeV), where both reactions are dominated by the $N(1520)3/2^-\rightarrow \Delta(1232)3/2^+\pi$ decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an $N^{\star}\rightarrow N\sigma$ decay for the proton, while the reaction is dominated by a sequential decay via a $\Delta\pi$ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled channel analysis., Comment: accepted for publication in Eur. Phys. J. A

The first moment of longitudinal and transverse spin densities of quarks in the nucleon are calculated in a light-front constituent quark model for the different cases of quark and nucleon polarization. Significant distortions are found for the transverse spin densities. In particular the Sivers function is predicted with opposite sign for up and down quarks and the Boer-Mulders function is predicted large and negative for both up and down quarks, in agreement with lattice calculations. Quite a different spin distribution is obtained for up and down quarks in the cases of quarks and proton transversely or longitudinally polarized in the same direction., one reference added; to be published in Phys. Lett. B

The spherical Hartree-Fock approximation is applied to a no-core shell model with a realistic effective baryon-baryon interaction. The ground state properties of a heavy spherical neutron-rich doubly magic 208Pb nucleus under compression are investigated. It is found that the nucleus becomes more bound with the occurrence of Delta resonances. The creation of Delta increases as the compression is continuous. There is a considerable reduction in the compressibility when the Delta degree of freedom is activated. It is found that the Delta particle is the basic component of the 208Pb nucleus besides nucleons at the ground state without any compression. When the nucleus is compressed to about 4.31 times the ordinary density, the Delta component is sharply increased to about 14.4% of all baryons in the system. It is found that there is a radial density distribution for Delta at the ground state of 208Pb nucleus without any compression. The single particle energy levels are calculated and their behaviors are examined under compression too. A good agreement was obtained between the results of the effective Hamiltonian and the phenomenological shell model for the low lying single-particle spectra.

The N pi(0)pi(0) decays of positive-parity N* and Delta* resonances at about 2 GeV are studied at ELSA by photoproduction of two neutral pions off protons. The data reveal clear evidence for several intermediate resonances: Delta(1232), N(1520)3/2(-), and N(1680)5/2(+), with spin parities J(P) = 3/2(+), 3/2(-), and 5/2(+). The partial wave analysis (within the Bonn-Gatchina approach) identifies N(1440)1/2(+) and the N(pi pi)s (wave) (abbreviated as N sigma here) as further isobars and assigns the final states to the formation of nucleon and Delta resonances and to nonresonant contributions. We observe the know Delta(1232)pi decays of Delta(1910)1/2(+), Delta(1920)3/2(+), Delta(1905)5/2(+), Delta(1950)7/2(+), and of the corresponding spin-parity series in the nucleon sector, N(1880)1/2(+), N(1900)3/2(+), N(2000)5/2(+), and N(1990)7/2(+). For the nucleon resonances, these decay modes are reported here for the first time. Further new decay modes proceed via N(1440)1/2(pi)(+), N(1520)3/2(pi)(-) , N(1680)5/2(pi)(+), and N sigma. The latter decay modes are observed in the decay of N* resonances and at most weakly in Delta(*) decays. It is argued that these decay modes provide evidence for a 3-quark nature of N* resonances rather than a quark-diquark structure.

We determine baryon–baryon bound states in ( 3 + 1 )-dimensional SU ( 3 ) lattice QCD with two flavors, 4 × 4 spin matrices, and in an imaginary time formulation. For small hopping parameter κ > 0 and large glueball mass (strong coupling), we show the existence of three-quark isospin 1/2 particles (proton and neutron) and isospin 3/2 baryons (delta particles), with asymptotic masses − 3 ln κ and isolated dispersion curves. Baryon–baryon bound states of isospin zero are found with binding energy of order κ 2 , using a ladder approximation to a lattice Bethe–Salpeter equation. The dominant baryon–baryon interaction is an energy-independent spatial range-one attractive potential with an O ( κ 2 ) strength. There is also attraction arising from gauge field correlations associated with six overlapping bonds, but it is counterbalanced by Pauli repulsion to give a vanishing zero-range potential. The overall range-one potential results from a quark, antiquark exchange with no meson exchange interpretation; the repulsive or attractive nature of the interaction depends on the isospin and spin of the two-baryon state.

The Higgs mass value is derived from a Hamiltonian on the Lie group U(3) where we relate strong and electroweak energy scales. The baryon states of nucleon and delta resonances originate in specific Bloch wave degrees of freedom coupled to a Higgs mechanism which also gives rise to the usual gauge boson masses. The derived Higgs mass is around 125 GeV. From the same Hamiltonian we derive the relative neutron to proton mass ratio and the N and Delta mass spectra. All compare rather well with the experimental values. We predict scarce neutral flavor baryon singlets that should be visible in scattering cross sections for negative pions on protons, in photoproduction on neutrons, in neutron diffraction dissociation experiments and in invariant mass spectra of protons and negative pions in B-decays. The fundamental predictions are based on just one length scale and the fine structure constant. More particular predictions rely also on the weak mixing angle and the up-down quark flavor mixing matrix element. With differential forms on the measure-scaled wavefunction, we could generate approximate parton distribution functions for the u and d valence quarks of the proton that compare well with established experimental analysis., 18 pages, 13 figures, 3 tables

New experimental data that were obtained by the PNPI-ITEP Collaboration have resolved some discrete ambiguities in the partial-wave analysis (PWA). These results were used in the new FA02 PWA performed at George Washington University. At the same time, the FA02 PWA has revealed considerable fewer N* and Δ resonances than those listed in the RPP tables. This circumstance aggravated the known problem of so-called missing resonances. The program for further measurements of the spin rotation parameters in elastic πN scattering that are required to eliminate the remaining discrete PWA ambiguities is discussed.

The chiral quark model posits that pions couple to the axial current of constituent quarks. This chiral pion coupling governs the pion decays of baryon resonances and also implies pion and multipion interactions between the quarks. The qualitative features of this model for the description of pionic decay widths and baryon spectra are outlined. When the covariant quark model wave function for the nucleon is chosen so as to describe the empirical nucleon form factors the pion decay widths of the positive parity resonances are underpredicted. This indicates the presence of significant multiquark components in these resonances.

The photoproduction of ρ0-mesons and Δ-baryons at photon energies up to 2.6 GeV has been studied with the SAPHIR detector at the electron stretcher ELSA. Total and differential cross-sections were obtained. The decay angular distributions of ρ0-mesons show that s-channel helicity conservation, which is valid at high photon energies, is broken near threshold. The energy dependencies of the decay angular distributions in the helicity system as well as in the Gottfried-Jackson system hint at small s- or u-channel resonance contributions. For the reactions γp → Δ{++}π- and γp → Δ0π+ new data on cross-sections are presented.

The relation between strong isospin I and weak isospin i is discussed. In particular an equation between the third components I3 and i3 is given. This relation indicates that the strong isospin and weak isospin symmetries are both SU (2) subgroups of a new SU (3) symmetry underlying the structure of leptons and quarks.

The conjectured deformation of hadrons and its experimental verification offer a particularly fertile ground for understanding the intricate dynamics of their constituents and QCD at the confiment scale. The detailed study of the N → Δ transition is viewed as the preferred method of experimental investigation of this central issue in hadronic physics. A brief overview of the field is presented, followed by a presentation of the most recent results from Bates N → Δ program. The new Bates/OOPS data at Q 2 = 0.127 (GeV/c) 2 yield R SM = (-6.27 ± 0.32 stat+sys ±0.10 model )% and R EM = (-2.00±0.40 stat+sys ±0.27 mode )% and they exclude a spherical nucleon and/or Δ. The magnitude and the origin of the deformation is the focus of the ongoing and planned investigations.

An overview over the experimental research programs with photon beams is given with the focus on the electromagnetic excitation of the nucleon and the subsequent decay via mesons. Photoproduction of mesons on the free proton and on nucleons embedded in nuclei up to 1 GeV incident-photon energy are discussed.

I present an overview of recent data on Deep Inelastic Scattering at large Bjorken x and low invariant mass, W2, where parton-hadron duality was originally observed. I discuss the concept of parton-hadron duality from the perspective of perturbative QCD. Within this framework, I show that parton-hadron duality is broken for low values of W2, in the \(\Delta\)- and S11-resonance production region. A model that accounts for the anomalous scale dependence ensuing from this situation is developed.

Theoretical predictions for the magnetic moments of the physical Delta baryons are extracted from lattice QCD calculations. We utilize finite-range regulated effective field theory that is constructed to have the correct Dirac moment mass dependence in the region where the up and down quark masses are heavy. Of particular interest is the chiral nonanalytic behaviour encountered as the nucleon-pion decay channel opens. We find a Delta^++ magnetic moment (at the Delta pole) of 4.99 \pm 0.56 \mu_N. This result is within the Particle Data Group range of 3.7-7.5 \mu_N and compares well with the experimental result of Bosshard et al. of 4.52 \pm 0.51 \pm 0.45 \mu_N. The interplay between the different pion-loop contributions to the Delta^+ magnetic moment leads to the surprising result that the proton moment may exceed that of the Delta^+, contrary to conventional expectations., Comment: 7 pages, 7 figures, RevTex 4; Updated to include a recent experimental result

We compute electroweak form factors of the nucleon and photon transition form factors of non-strange baryon resonances up to the third resonance region in a model with instanton-induced interaction. The calculation is based on the Bethe-Salpeter equation for three light constituent quarks and is fully relativistic (U. L\"oring {\it et al.}, Eur. Phys. J. {\bf A10}, 309 (2001)). Static nucleon properties and photon resonance couplings are in good agreement with experiment and the $Q^2$-behaviour of the experimentally known form factors up to large momentum transfer is accounted for., Comment: 12 pages, 17 figures, submitted to Eur. Phys. J. A

The nucleon density distributions were usually described by the two-parameter Fermi shape formula. In this work, the isospin effects in the nucleon density distributions are considered, and a three-parameter formula is proposed and modified by simultaneously considering the experimental data of 885 root-mean-square (rms) charge radii and neutron skin thickness of 26 stable nuclei. The improved nucleon density formula is physically reasonable and achieves a good agreement for the charge radii and neutron skin thickness calculated with the new nucleon density formula comparing the available experimental data.

In this work we have obtained the equation of state to the highly asymmetric dense stellar matter, using the nonlinear Walecka model in the mean field approximation. We discussed the implication of changes in coupling constant of the delta baryonic resonance on the observable of the neutron star. A detailed analysis of the equation of state and of the baryonic effective mass in respect to changes in the delta coupling constants is carried out. We focus attention on a new aspect observed for pressure when varying the baryonic density of the medium; a first order phase transition like a liquid-gas phase transition was observed for an acceptable range of delta coupled constant values. We have explored the implication of this aspect for the neutron star structure and their maximum masses.

The spectrum of the SU(2) flavor baryons is studied in the frame of a relativistic chiral quark potential model based on the one-pion and one-gluon exchange mechanisms. It is argued that the ${N}^{*}$ and ${\mathrm{\ensuremath{\Delta}}}^{*}$ resonances strongly coupled to the $\ensuremath{\pi}N$ channel are identified with the orbital configurations $(1{S}_{1/2}{)}^{2}(nlj)$ with a single valence quark in the excited state ($nlj$). With the obtained selection rules based on the ``chiral constraint,'' we show that it is possible to construct a schematic periodic table of baryon resonances, consistent with the experimental data and yielding no ``missing resonances.'' A new original method for the treatment of the center of mass problem is suggested which is based on the separation of the three-quark Dirac Hamiltonian into the parts, corresponding to the Jacobi coordinates. The numerical estimations for the energy positions of the nucleon and delta baryons (up to and including F-wave ${N}^{*}$ and ${\mathrm{\ensuremath{\Delta}}}^{*}$ resonances), obtained within the field-theoretical framework by using time ordered perturbation theory, yield an overall good description of the experimental data at the level of the relativized constituent quark model of S. Capstick and W. Roberts without any fitting parameters. The only free parameter of the linear confinement potential was fitted previously by Th. Gutsche to reproduce the axial charge of the nucleon. The ground state $\mathrm{\ensuremath{\Delta}}(1232)$ is well reproduced. However, nucleon ground state and most of the radially excited baryon resonances (including Roper) are overestimated. On the contrary, the first band of the orbitally excited baryon resonances with a negative parity are underestimated. At the same time, the second band of the orbitally excited ${\mathrm{\ensuremath{\Delta}}}^{*}$ states with the negative parity are mostly overestimated, while the ${N}^{*}$ states are close to the experimental boxes. The theoretical estimations of the energy levels for the positive parity baryon resonances with $\mathrm{J}=5/2$, $7/2$ are close to the experimental data. At higher energies, where the experimental data are poor, we can extend our model schematically and predict an existence of seven ${N}^{*}$ and four ${\mathrm{\ensuremath{\Delta}}}^{*}$ new states with larger spin values.

We develop strategies for enhancing the signal/noise ratio for stochastically sampled correlation functions. The techniques are general and offer a wide range of applicability. We demonstrate the potential of the approach with a generic two-state system, and then explore the practical applicability of the method for single hadron correlators in lattice quantum chromodynamics. In the latter case, we determine the ground state energies of the pion, proton, and delta baryon, as well as the ground and first excited state energy of the rho meson using matrices of correlators computed on an exemplary ensemble of anisotropic gauge configurations. In the majority of cases, we find a modest reduction in the statistical uncertainties on extracted energies compared to conventional variational techniques. However, in the case of the delta baryon, we achieve a factor of three reduction in statistical uncertainties. The variety of outcomes achieved for single hadron correlators illustrates an inherent dependence of the method on the properties of the system under consideration and the operator basis from which the correlators are constructed., 40 pages, 21 figures; revisions made to the abstract and Section VI C, one additional figure and five tables added; published version