Search

The baryon form factor of charged pions arises since isospin symmetry is broken. We obtain estimates for this basic property in two phenomenological ways: from simple constituent quark models with unequal up and down quark masses, and from fitting to e+e−→π+π−data. All our methods yield a positive π+baryon mean square radius of (0.03 −0.04fm)2. Hence, a picture emerges where the outer region has a net baryon, and the inner region a net antibaryon density, both compensating each other such that the total baryon number is zero. For π−the effect is opposite., European H2020 MSCA-COFUND 754510,824093,H2020-INFRAIA-2018-1, Polish National Science Centre 2018/31/B/ST2/01022, Generalitat de Catalunya 2017SGR1069, Ministerio de Economía y Competitividad FPA2017-86989-P,SEV-2016-0588 MINECO, European Regional Development Fund FIS2017-85053-C2-1-P ERDF, Junta de Andalucía FQM-225

Chiral and pion superfluidity phase transitions are studied within NJL model. The model parameters are fitted by pion mass and decay constant together with recent isospin density from lattice QCD. Dense and cold QCD matter suffered the first order chiral phase transition during the quark chemical potential increase. Based on the studies of phase structures, the equation of states (EoS) of dense QCD matter is calculated with the conditions of β equilibrium and electric charge neutrality. Take the EoS as input, the mass-radius relation of up-down quark stars is predicted, which is consistent with recent observations of heaviest mass and radius of 1.4M⊙.

We show that the experimental data of transverse momentum ( p T ) spectra of identified hadrons released recently by ALICE collaboration for p–Pb collisions at s N N = 5.02 TeV exhibit a distinct universal behavior — the quark number scaling. We further show that the scaling is a direct consequence of quark (re-)combination mechanism of hadronization and can be regarded as a strong indication of the existence of the underlying source with constituent quark degree of freedom for the production of hadrons in p–Pb collisions at such high energies. We make also predictions for production of other hadrons.

While the constituent quark model (CQM), in which the quarks are assumed to be the complex objects, is used to calculate the parton distribution functions of the iso-scalar lithium-6 (6Li) nucleus, the u–d constituent quark distribution functions of the 6Li nucleus are evaluated from the valence quark exchange formalism (VQEF) for the A = 6 iso-scalar system. After computing the valence quark, sea quark, and gluon distribution functions in the constituent quark exchange model (CQEM, i.e., CQM + VQEF ), the nucleus structure function is calculated for the 6Li nucleus at the leading order (LO) and the next-to-leading-order (NLO) levels to extract the European muon collaboration (EMC) ratio, at different hard scales, using the standard Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGALP) evolution equations. The outcomes are compared with those of our previous works and the available NMC experimental data, and various physical points are discussed. It is observed that the present EMC ratios are considerably improved compared with those of our previous works, in which only the valence quark distributions were considered to calculate the EMC ratio, and are closer to the NMC data. Finally, it is concluded that at a given appropriate hard scale, the LO approximation may be enough for calculating the nucleus EMC ratio.

As an improvement of the QCD sum rule method to study modifications of light vector mesons in nuclear matter and/or at finite temperature, we calculate the Wilson coefficients of all independent gluonic non-scalar operators up to dimension 6 in the operator product expansion (OPE) of the vector channel for light quarks. To obtain the gluon part of the light quark OPE from the heavy quark one, we also compute the heavy quark expansion of the relevant quark condensates. Together with the results for the quark operators that are already available in the literature, this completes the OPE of the vector channel in a hot or dense medium for operators up to dimension 6., 6 pages, no figure

We calculate the single-spin asymmetries A L W ± of W ± bosons produced in polarized pp collisions with the valence part of the up and down quark helicity distributions modeled by the light-cone quark-spectator–diquark model while the sea part helicity distributions of the up and down quarks treated as parametrization. Comparing our results with those from experimental data at RHIC, we find that the helicity distributions of sea quarks play an important role in the determination of the shapes of A L W ± . It is shown that A L W − is sensitive to Δ u ¯ , while A L W + to Δ d ¯ intuitively. The experimental data of the polarized structure functions and the sum of helicities are also important to constrain the sizes of quark helicity distributions both for the sea part and the valence part of the nucleon.

In this study, firstly we have studied the behavior of quark and strange quark matter for a ( n + 2 ) -dimensional Friedmann–Robertson–Walker (FRW) universe which is homogeneous and isotropic in creation field (C-field) cosmology. Using the deceleration parameter two different exact solutions of the modified Einstein equations in C-field cosmology are obtained. In addition, we obtain exact solutions of the quark and strange quark matter for a ( n + 2 )-dimensional homogeneous and isotropic static Einstein universe (SEU) and a maximally symmetric de Sitter vacuum universe in four dimensions. Also, using C ˙ = 0 in C-field theory, we get the SEU and de Sitter vacuum universes in Riemann geometry. Finally, some physical and kinematical quantities are discussed.

We propose a radiatively induced quark and lepton mass model in the first and second generation with extra $U(1)$ gauge symmetry and vector-like fermions. Then we analyze the allowed regions which simultaneously satisfy the FCNCs for the quark sector, LFVs including $\mu-e$ conversion, the quark mass and mixing, and the lepton mass and mixing. Also we estimate the typical value for the $(g-2)_\mu$ in our model., Comment: 18 pages, 1 figure, 3 tables; figures are updated, accepted version for publication in Physics Letters B

Tuning effect in particle masses manifests itself in integer relations between masses of leptons, quarks, meson and baryons. It includes also dimensionless relation between such well-known SM-parameters as masses of the muon and Z-boson, mμ/MZ=115.910−5 coinciding with the QED radiative correction α/2π=115.910−5 considered for the electron mass me by V. Belokurov and D. Shirkov. Integer presentation of particle masses (n=1,13,16,17,18,115) for values mμ, fπ, mπ, ΔMΔ, neutron mass and (n=3x16, n=3x18) for constituent quarks M"q=mp,mω/2=780 MeV and Mq=3ΔMΔ=mΞ/3=441 MeV were found with the period δ=16me. More accurate relations with δ were found from precise ratio mn/me=1838.6836605(11). The shift δmn=161.65(6) keV of neutron mass from 115δ-me accounts integer ratio δmN/δmn=8(1.0001(1)) with nucleon mass splitting. With fundamental boson masses the parameters Mq=3ΔMΔ=mΞ/3=441 MeV and M"q =mρ/2=388.8(2) MeV are in ratios MZ/Mq=LZ=206.8 and MW/M"q =LW=207.3 coinciding with lepton ratio L=mμ/me=1316-1=207.

The real, interacting elementary particle always consits of a 'bare' particle and a cloud of virtual particles mediating a self-interaction and/or the bond inside a composite object. In this letter we discuss the question of spin content of the virtual cloud in two different cases: electron and quark. Further, the quark spin is discussed in the context of proton spin, which is generated by the interplay of quarks and virtual gluons. We present a general constraint on the gluon contribution and make a comparison with the experimental data., Comment: 8 pages, 3 figures, 1 table, the final and enlarged version is accepted to Phys.Lett.B

The distribution of the QCD topological charge can be described by cumulants, with the lowest one being the topological susceptibility. The vacuum energy density in a theta-vacuum is the generating function for these cumulants. In this paper, we derive the vacuum energy density in SU(2) chiral perturbation theory up to next-to-leading order keeping different up and down quark masses, which can be used to calculate any cumulant of the topological charge distribution. We also give the expression for the case of SU(N) with degenerate quark masses. In this case, all cumulants depend on the same linear combination of low-energy constants and chiral logarithm, and thus there are sum rules between the N-flavor quark condensate and the cumulants free of next-to-leading order corrections., match the version published in PLB

The supersymmetric (SUSY) minimal SO(10) model is a well-motivated grand unified theory, where the Standard Model (SM) fermions have Yukawa couplings with only one ${\bf 10}$-plet and one $\overline{\bf 126}$-plet Higgs fields and it is highly non-trivial if the realistic quark and lepton mass matrices can be reproduced in this context. It has been known that the best fit for all the SM fermion mass matrices is achieved by a vacuum expectation value of the $\overline{\bf 126}$-plet Higgs field being at the intermediate scale of around ${\cal O}(10^{13})$ GeV. Under the presence of the SO(10) symmetry breaking at the intermediate scale, the successful SM gauge coupling unification is at risk and likely to be spoiled. Recently, it has been shown that the low-energy fermion mass matrices, except for the down-quark mass predicted to be too low, are very well-fitted without the intermediate scale. In order to resolve the too-low down quark mass while keeping the other fittings intact, we consider SUSY threshold corrections to reproduce the right down quark mass. It turns out that this requires flavor-dependent soft parameters. Motivated by this fact, we calculate particle mass spectra at low energies with flavor-dependent sfermion masses at the grand unification scale. We present a benchmark particle mass spectrum which satisfies a variety of phenomenological constraints, in particular, the observed SM-like Higgs boson mass of around 125 GeV and the relic abundance of the neutralino dark matter as well as the experimental result of the muon anomalous magnetic moment. In the resultant mass spectrum, sleptons in the first and second generations, bino and winos are all light, and this scenario can be tested at the LHC Run-2 in the near future., Comment: 20 pages, 2 figures. To be published in Physics Letters B

At large momentum transfers the photon interacts with the charges and spins of the constituent partons in a hadron. It is expected that the neutral kaon can acquire finite electromagnetic form factors because its wave function is affected by the order of magnitude difference between the mass of the strange quark and that of the down quark, or flavor SU ( 3 ) breaking. We report on the first measurement of the form factor of neutral kaons at the large timelike momentum transfer of | Q 2 | = 17.4 GeV 2 by measuring the cross section for e + e − → K S K L at s = 4.17 GeV using CLEO-c data with an integrated luminosity of 586 pb−1. We obtain F K S K L ( 17.4 GeV 2 ) = 5.3 × 10 − 3 , with a 90% C.L. interval of ( 2.9 – 8.2 ) × 10 − 3 . This is nearly an order of magnitude smaller than F K + K − ( 17.4 GeV 2 ) = ( 44 ± 1 ) × 10 − 3 , and indicates that the effect of SU ( 3 ) breaking is small. In turn, this makes it unlikely that the recently observed strong violation of the pQCD prediction, F π + π − ( | Q 2 | ) / F K + K − ( | Q 2 | ) = f π 2 / f K 2 , which is based on the assumption of similar wave functions for the pions and kaons, can be attributed to SU ( 3 ) breaking alone.

Just after the phase transition from hadronic to quark matter in neutron stars, weak interactions drive quark matter to thermal and chemical equilibrium. We calculate the reaction rate and the neutrino emissivity for all the relevant weak interaction processes in hot and dense quark matter and solve the Boltzmann equation in order to describe the time evolution of the system. We find that the neutrino emissivity per baryon is very large, leading to an energy release per baryon of 10–60 MeV in the form of neutrinos.

A new parametrization for improved quark mass density-dependent (IQMDD) model by including omega tensor and non-linear omega-rho couplings has been proposed. By employing this model, the ground-state properties of finite nuclei, the saturation properties of the nuclear matter and the equation of state (EOS) of neutron star matter are studied. It has been shown that this model is able to provide a good description not only for the ground-state properties of finite nuclei but also for the saturation properties of the nuclear matter. The results obtained by using the new IQMDD model are compared with the relativistic mean field model and experimental findings. (c) 2013 Elsevier B.V. All rights reserved.

We show that the main features of the pattern of fermion masses and mixing can be expressed in terms of simple relations among weak-basis invariants. In the quark sector, we identify the weak-basis invariants which signal the observed alignment of the up and down quark mass matrices in flavour space. In the lepton sector, we indicate how a set of conditions on weak-basis invariants can lead to an approximate tribimaximal lepton mixing matrix. We also show the usefulness of these invariants in the study of specific ans\"atze for the flavour structure of fermion mass matrices., Comment: 16 pages, 1 figure

The recent observation of the pulsar PSR J1614-2230 with a mass of 1.97 ± 0.04 M ⊙ gives a strong constraint on the equation of state (EoS) of the dense matter in compact stars. In this work, we calculate the maximum mass of quark stars with the density-dependent quark mass model, and explore the parameter ranges for this model fully, by considering the constraints of absolute stability of strange quark matter and the mass of PSR J1614-2230. Without the color-superconductivity, the maximum mass of unpaired quark stars is more sensitive to the parameter C, and complies with the constraints within the range of 96 MeV fm - 3 ≲ C ≲ 130 MeV fm - 3 . The largest mass can reach 2.25 M ⊙ at C ≃ 96.54 MeV fm - 3 and m s 0 ≃ 145 MeV . For the quark stars composed of the quark matter in color-flavor locked (CFL) phase, we can obtain quite large maximum masses at a sufficiently high gap value, but the value of m s 0 is very important in deciding the maximum mass of the CFL quark stars.

We study in detail the effect of the finite current quark mass on chiral symmetry breaking, in the framework of truncated Coulomb gauge QCD with a linear confining quark-antiquark potential. In the chiral limit of massless current quarks, the breaking of chiral symmetry is spontaneous. But for a finite current quark mass, some dynamical symmetry breaking continues to add to the explicit breaking caused by the quark mass. Moreover, using as order parameter the mass gap, i. e. the quark mass at vanishing moment or the quark condensate, a finite quark mass transforms the chiral symmetry breaking from a phase transition into a crossover. For the study of the QCD phase diagram it thus is relevant to determine how the current quark mass affects chiral symmetry breaking. Since the current quark masses of the six standard flavours u, d, s, c, b, t span over five orders of magnitude from 1.5 MeV to 171 GeV, we develop an accurate numerical method to study the running quark mass gap and the quark vacuum energy density from very small to very large current quark masses., Comment: 24 pages, 5 figures, 3 tables

Heavy quark jet quenching in high energy nuclear collisions became a decisive tool to distinguish between theories based on Standard Model perturbative QCD and AdS/CFT gravity dual models. The momentum independence and inverse quark mass dependence of the drag coefficient in AdS/CFT differs substantially from the characteristic log ( p T / M ) / p T variation of the heavy quark drag in QCD, which was obtained from early calculations. The latest pQCD efforts on heavy quark energy loss include color magnetic dynamical effects and final size non-static coherence effects in perturbative quark gluon plasmas and the obtained results are much closer to the experimental data for heavy quarks. We discuss our recent understanding of heavy quark quenching and summarize the measurable quantities to distinguish between the pQCD and AdS/CFT scenarios.

The vacuum polarization of a quark, when considered in terms of the external momentum q^2, is a function of the Stieltjes type. Consequently, the mathematical theory of Pade Approximants assures that the full function, at any finite value of q^2 away from the physical cut, can be reconstructed from its low-energy power expansion around q^2=0. We illustrate this point by applying this theory to the vacuum polarization of a heavy quark and obtain the value of the constant K^(2) governing the threshold expansion at order O(alpha_s^2)., 9 pages, 4 figures

The light anti-quark and quark distribution in the proton, as well as the neutron to proton ratio of the structure functions, extracted from experimental data, are well fitted by a statistical model of linear-confined quarks. The parameters of the model are given by a temperature, which is adjusted by the Gottfried sum-rule violation, and two chemical potentials given by the corresponding up ( u ) and down ( d ) quark normalizations in the nucleon. The quark energy levels are generated by a relativistic linear-confined scalar plus vector potential.

Recently reported massive compact stars ( M ∼ 2 M ⊙ ) have provided strong constraints on the properties of the ultradense matter beyond the saturation nuclear density. Therefore, realistic quark or hybrid star models must be compatible with these observational data. Some used equations of state (EoS) describing quark matter are in general too soft and hence are not suitable to explain the stability of high compact star masses. In this work, we present the calculations of static spherically symmetric quark star structure by using an equation of state which takes into account the superconducting colour-flavour locked phase of the strange quark matter. In addition, some fundamental aspects of QCD (asymptotic freedom and confinement) are considered by means of a phenomenological description of the deconfined quark phase, the density-dependent quark mass model. We discuss the influence of the obtained quark matter equation of state on the mass-radius relationship of quark stars. Massive quark stars are found due to the stiffness of the equation of state, when reasonable values of the superconducting gap, taken as a free parameter, are used.

I discuss heavy flavor production at hadronic facilities. I present total cross sections and differential distributions for top quark, bottom quark, and charm quark production at the Tevatron and LHC colliders, and at fixed-target experiments such as HERA-B. The calculations include complete next-to-leading order corrections as well as higher-order soft-gluon corrections which are important near kinematical threshold., Comment: 6 pages, 7 figures; invited talk at PANIC 2008, Eilat, Israel, November 9-14, 2008

Chiral perturbation theory in the two-flavour sector allows one to analyse Green functions in qcd in a limit where the strange quark mass is considered to be large in comparison to the external momenta and to the light quark masses m u and m d . In this framework, the low-energy constants of SU ( 2 ) R × SU ( 2 ) L depend on the value of the heavy quark masses. In a recent article, we have worked out, for the coupling constants l i which occur at order p 4 in the chiral expansion, the dependence on the strange quark mass at two-loop accuracy. Here, we provide analogous relations for some of the couplings c i which are relevant at order p 6 . To keep the calculations somewhat reasonable in size, we consider only those 28 couplings which enter the Green functions built from vector and axial vector quark currents in the chiral limit m u = m d = 0 , m s ≠ 0 . This provides the matching for 27 linear combinations of the 28 couplings.

Densities in compact stars may be such that quarks are no longer confined in hadrons, but instead behave as weakly interacting particles. In this regime perturbative calculations are possible. Yet, due to high pressures and an attractive channel in the strong force, condensation of quarks in a superfluid state is likely. This can have interesting consequences for magnetic fields, especially in relation to the discovery of slow-period free precession in a compact star. In this proceedings there will be a discussion of the mass-radius relations of compact stars made from quark matter and magnetic field behaviour in compact stars with a quark matter core., 4 pages, 2 images. To be published in the proceedings of SEWM 2008, Nucl. Phys. A, in print

We outline the key elements of a recent calculation aimed at determining the equation of state of deconfined (but unpaired) quark matter at zero temperature and high density, using finite quark masses. The computation is performed in perturbation theory up to three loops, and necessitates the development and application of some novel computational tools. In this talk, we introduce the basic features of these new techniques and review the main sources of motivation for considering finite quark mass effects in perturbation theory. We outline the key elements of a recent calculation aimed at determining the equation of state of deconfined (but unpaired) quark matter at zero temperature and high density, using finite quark masses. The computation is performed in perturbation theory up to three loops, and necessitates the development and application of some novel computational tools. In this talk, we introduce the basic features of these new techniques and review the main sources of motivation for considering finite mass effects in perturbation theory. We outline the key elements of a recent calculation aimed at determining the equation of state of deconfined (but unpaired) quark matter at zero temperature and high density, using finite quark masses. The computation is performed in perturbation theory up to three loops, and necessitates the development and application of some novel computational tools. In this talk, we introduce the basic features of these new techniques and review the main sources of motivation for considering finite quark mass effects in perturbation theory.

We calculate potentials between a proton and a $\Xi^0$ (hyperon with strangeness -2) through the equal-time Bethe-Salpeter wave function, employing quenched lattice QCD simulations with the plaquette gauge action and the Wilson quark action on (4.5 fm)^4 lattice at the lattice spacing $a \simeq 0.14$ fm. The ud quark mass in our study corresponds to $m_{\pi}\simeq 0.37$ and 0.51 GeV, while the s quark mass corresponds to the physical value of $m_K$. The central $p \Xi^0$ potential has a strong (weak) repulsive core in the $^1S_0$ ($^3S_1$) channel for $r \lsim 0.6$ fm, while the potential has attractive well at the medium and long distances (0.6 fm $\lsim r \lsim 1.2$ fm) in both channels. The sign of the $p \Xi^0$ scattering length and its quark mass dependence indicate a net attraction in both channels at low energies., Comment: 10 gages, 4 figures, version accepted for publication in Physics Letters B

The scale dependence in perturbative QCD remains on obstacle to making precise tests of the theory. To over come the scale ambiguity while people are usually using the standard M S ¯ approach with a physical choice of renormalization scale, we try to employ the approach of complete RG-improvement. In this approach all ultraviolet logarithms involving the dimensionful parameter, Q , on which the observable depends are resummed, thereby building the correct Q -dependence. Based on these two approaches, sea quark densities in the nucleon are analyzed. To achieve the asymmetry of these densities, chiral quark model is used. To avoid from the unaccepted Q 2 behavior of sea densities inside the constituent quark, we assume that the free parameter which exists in the vertex function of boson-quark splitting function, is Q 2 -dependence. Using un-symmetrized sea densities of the nucleon, the Gottfried sum rule is calculated in these two approaches. The result of the latter one is very close to the reported experimental value.

I discuss several new results from lattice heavy quark physics that have appeared in the last year.

We evaluate lower bounds on the sum of the up and down quark masses. The bounds follow from the constraints provided by the dispersion relation obeyed by the two--point function of the scalar current density when combined with properties of the scalar spectral function at long--distances and perturbative QCD at short--distances. Our results point to values of $m_u+m_d$ somewhat higher than those reported recently in the literature using lattice QCD simulations., Comment: 7 pages, 3figures. A few sentences have been added to improve clarity. One reference added. To be published in PLB

A new kind microscopic resonance, the color confinement multi quark resonance is proposed and studied. The quark delocalization color screening model is compared to one of the chiral quark model, the Salamanca model, and a new mechanism of the intermediate range NN interaction, the mutual distortion of interacting nucleons, is checked to be similar to the σ meson exchange.

We consider correlations in hot and dense quark matter within the framework of light front quantization. We have computed the masses of two-body boundstates M 2 ( T , μ ) in the pionic and scalar diquark channel using a T-matrix approach. The quark interaction is given by a NJL model. The gap equation is generalized to finite temperature T and quark chemical potential μ and we determine the medium dependent quark mass. Further we calculate the critical temperature of two flavor color superconductivity.

The search for new phases of strange quark matter inside neutron stars has recently received a lot of attention since it has been shown that the attractive nature of the one gluon exchange interaction in QCD may produce a superconducting phase in quark matter. We study an extended version of the Chromodielectric model with a BCS quark pairing implemented, and analyze the superconducting color flavor locked phase. We show that the inclusion in the free energy density of a negative term of the diquark condensate ensures the stability of quark matter. We explore the implications of our results in the structure of compact quark stars and explicitly show that CFL stars can be absolutely stable and more compact than strange stars.

We present results for the light quark masses obtained from a lattice QCD simulation with N f = 2 degenerate Wilson dynamical quark flavours. The sea quark masses of our lattice, of spacing a ≃ 0.06 fm , are relatively heavy, i.e., they cover the range corresponding to 0.60 ≲ M P / M V ≲ 0.75 . After implementing the non-perturbative RI-MOM method to renormalise quark masses, we obtain m ud MS ¯ ( 2 GeV ) = 4.3 ± 0.4 −0 +1.1 MeV , and m s MS ¯ ( 2 GeV ) = 101 ± 8 −0 +25 MeV , which are about 15% larger than they would be if renormalised perturbatively. In addition, we show that the above results are compatible with those obtained in a quenched simulation with a similar lattice.

It was pointed out in 1984 by Witten that strange quark matter (SQM) – matter made of up, down, and strange quarks (rather than just up and down, as are protons and neutrons) – might well be stable and the lowest energy state of matter. The reason is that it would be electrically neutral and have less Pauli-Principle repulsion. Binding would increase with numbers of quarks, and might not begin below thousands. It would have nuclear density. Neutron stars would be strange quark stars; and it might conceivably constitute dark matter. One way to detect ton-range SQM nuggets (SQNs) would be from seismic signals they would make passing through the Earth. We give a rough estimate on the relative advantage of attempting to detect SQNs on the Moon over Earth (about 50 times more detections).

Triple-quark elastic scattering amplitudes from perturbative QCD are first calculated and then used in a transport equation to study the thermalization of quark matter. By examining momentum isotropy to which the transport equation leads, we can determine thermalization time and offer an initial thermal quark distribution function. With an anisotropic initial quark distribution, which is relevant to quark matter initially created in a central Au-Au collision at \sqrt {s_{NN}}=200 GeV, the transport equation gives a time of the order of 1.8 fm/c for quark matter itself to thermalize by the triple-quark scatterings., Comment: 19 pages, 4 figures, 1 table, LaTex, define u12,u13,u21,u23,u31,u32

The running of renormalized quark masses is computed in lattice QCD with two flavors of massless O(a) improved Wilson quarks. The regularization and flavor independent factor that relates running quark masses to the renormalization group invariant ones is evaluated in the Schroedinger Functional scheme. Using existing data for the scale r_0 and the pseudoscalar meson masses, we define a reference quark mass in QCD with two degenerate quark flavors. We then compute the renormalization group invariant reference quark mass at three different lattice spacings. Our estimate for the continuum value is converted to the strange quark mass with the help of chiral perturbation theory., Comment: 25 pages, 6 figures; sections 1 and 4 rearranged, minor change to the summary plot

The transition between the hadronic phase and the quark gluon plasma phase at nonzero temperature and quark chemical potentials is studied within the large-Nc expansion of QCD., Comment: 5 pages

We study the phase diagram of dense, locally neutral three-flavor quark matter as a function of the strange quark mass, the quark chemical potential, and the temperature, employing a general nine-parameter ansatz for the gap matrix. At zero temperature and small values of the strange quark mass, the ground state of matter corresponds to the color-flavor-locked (CFL) phase. At some critical value of the strange quark mass, this is replaced by the recently proposed gapless CFL (gCFL) phase. We also find several other phases, for instance, a metallic CFL (mCFL) phase, a so-called uSC phase where all colors of up quarks are paired, as well as the standard two-flavor color-superconducting (2SC) phase and the gapless 2SC (g2SC) phase., 14 pages, 11 figures, references added; the version accepted for publication in Nucl. Phys. A

We suggest an approach to explain the observed pattern of the neutrino masses and mixing which employs the weakly broken quark-lepton symmetry and does not require introduction of an ad hoc symmetry of the neutrino sector. The mass matrices are nearly equal for all quarks and leptons. They have very small determinants and hierarchical form with expansion parameter lambda = 0.26. The latter can be realized, e.g., in the model with U(1) family symmetry. The symmetry is broken at the lambda^2 level. Large lepton mixing appears as a result of summation of the neutrino and charged lepton rotations which diagonalize the mass matrices in contrast with quark sector where the up quarks and down quarks rotations cancel each other. We show that the flip of the sign of rotation in the lepton sector is a result of the seesaw mechanism which also enhances the neutrino mixing. In this approach one expects, in general, deviation of the 2-3 mixing from maximal, s_{13} \sim (1-3) lambda^2, hierarchical neutrino mass spectrum, and m_{ee} < 10^{-2} eV. The scenario is consistent with the thermal leptogenesis and (in SUSY context) bounds on lepton number violating processes, like mu to e gamma., 25 pages, one figure, ReVTeX4, Nucl. Phys. B version

We compute the b quark mass from dynamical lattice QCD with clover quarks. The calculation is done at a fixed lattice spacing with sea quark masses as low as half the strange quark mass. Our final result is m_b(m_b} = 4.25(2)(11) GeV, where the first error is statistical and the last error is the systematic uncertainty., 10 pages

A dynamical quark model of hadron and nucleus structure is proposed. It is shown in the framework of the model, called the Strongly Correlated Quark Model, that quarks and nucleons inside nuclei are arranged in crystal–like structure.

Helicity-dependent generalized parton distributions of the nucleon are derived from the overlap representation of generalized parton distributions using light-cone wave functions obtained in constituent quark models. Results from two different quark models are used also to study the angular momentum sum rule and the spin asymmetry in polarized electron scattering., 20 pages, 5 figures, 2 tables

The chiral SU(3) quark model is extended to include coupling between vector chiral field and quarks. By using this model, the phase shifts of NN scattering for different partial waves are studied. The results are very similar to those of the chiral SU(3) quark model calculation, in which one gluon exchange (OGE) plays dominate role in the short range part of the quark-quark interactions. Only in the $^1S_0$ case, the one channel phase shifts of the extended chiral SU(3) quark model are obviously improved., 15 pages, 6 figures

The recently discovered pentaquark $\Theta^+$ is described within the chiral constituent quark model. Within this picture the flavor-spin interaction between valence quarks inverts the $(1s)^4$ and $(1s)^3(1p)$ levels of the four-quark subsystem and consequently the lowest-lying pentaquark is a positive parity, I=0, J=1/2 state of the flavor antidecuplet, similar to the soliton model prediction. Contrary to the soliton model, however, the quark picture predicts its spin-orbit partner with $J=3/2$. Different interpolating fields intended for lattice calculations of $\Theta^+$ are constructed, which have a maximal overlap with this baryon if it is indeed a quark excitation in the 5Q system., Comment: 9 pp

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 examine whether the O(a) improved quark action on anisotropic lattices can be used as a framework for the heavy quark, which enables precision computation of matrix elements of heavy-light mesons. To this end, it is crucial to verify that a mass independent and nonperturbative tuning of the parameters is possible. As a first step, we observe the dispersion relation of heavy-light mesons on a quenched lattice using the action which is nonperturbatively tuned only for the leading terms. We also apply the action to a calculation of heavy-light decay constants in the charm quark mass region.

Theoretical predictions are given for the light-flavor sea-quark distributions in the nucleon including the strange quark ones on the basis of the flavor SU(3) version of the chiral quark soliton model. Careful account is taken of the SU(3) symmetry breaking effects due to the mass difference between the strange and nonstrange quarks, which is the only one parameter necessary for the flavor SU(3) generalization of the model. A particular emphasis of study is put on the light-flavor sea-quark asymmetry as well as the particle-antiparticle asymmetry of the strange quark distributions in the nucleon.