Search

In this paper, we introduce a new approach to identify a bottom quark-antiquark pair inside a single jet with high transverse momentum by using the jet substructure in the center-of-mass frame of the jet. We demonstrate that the method can be used to discriminate the boosted heavy particles decaying to a 66 final state from QCD jets. Applications to searches for the standard model Higgs boson (H) decaying to bb when produced in association with a weak vector boson are also discussed. [ABSTRACT FROM AUTHOR]

We investigate the exclusive semileptonic decays J/Ψ → l+vl, where l = e,μ within the Standard Model. The relevant transition form factors are calculated in the framework of a relativistic constituent quark model with built-in infrared confinement. Our calculations predict the branching fractions B(J/Ψ→D(+)(s)l+vl) to be of the order of 10M-10 for Ds(*)-)- and 10-11 for D(*)- Most of our numerical results are consistent with other theoretical studies. However, some branching fractions are larger than those calculated in QCD sum rules approaches but smaller than those obtained in the covariant light-front quark model by a factor of about 2-3. [ABSTRACT FROM AUTHOR]

Production rates of dileptons and photons from the quark-gluon (QGP) phase are calculated taking into account effects of confinement and spontaneous chiral symmetry breaking (χSB) not far from the transition temperature Tc. We find that the production rates of dileptons with large momenta and of photons originating from the QGP around Tc are suppressed by the χSB effect. We also discuss to what extent information about details of the chiral transition, such as its characteristic temperature range and the steepness of the crossover, are reflected in these quantities. [ABSTRACT FROM AUTHOR]

The article presents a study of the one-loop matching condition for the transversity generalized quark distribution in the nonsinglet case, providing a definition of the quasitransversity generalized parton distributions (GPDs).

The article presents a study that evaluates HERMES Collaboration and the reevaluation of the strange-quark parton distribution based on kaon production in semi-inclusive deep-inelastic scattering.

We look into the signatures of the effective Y-bosonic strings in the gluonic profile due to a system of three static quarks on the lattice. The color field is calculated in pure SU(3) Yang-Mills lattice gauge theory at finite temperature with Polyakov loop operators. The analysis of the action density unveils a filled-Δ distribution. However, we found that these Δ-shaped action density profiles are structured from three Y-shaped Gaussian-like flux tubes. The geometry of the Y-shaped Gaussian flux tubes changes according to the quark configuration and temperature. The lattice data for the mean-square width of the gluonic action density have been compared to the corresponding width calculated based on the string model at finite temperature. We assume Y-string configuration with minimal length. The growth pattern of the action density of the gluonic field fits to junction fluctuations of the Y-baryonic string model for large quark separation at the considered temperatures. [ABSTRACT FROM AUTHOR]

We investigate the quark Wigner distributions in a light-cone spectator model. The Wigner distribution, as a quasidistribution function, provides the most general one-parton information in a hadron. Combining the polarization configurations, unpolarized, longitudinal polarized, or transversal polarized, of the quark and the proton, we can define 16 independent Wigner distributions at leading twist. We calculate all these Wigner distributions for the u quark and the d quark, respectively. In our calculation, both the scalar and the axial-vector spectators are included, and the Melosh-Wigner rotation effects for both the quark and the axial-vector spectator are taken into account. The results provide us a very rich picture of the quark structure in the proton. [ABSTRACT FROM AUTHOR]

In this paper the smallest thermal screening mass associated with the correlator of the CT-odd operator, ~TrFμνFμν, is determined in strongly coupled non-Abelian gauge plasmas which are holographically dual to noNconformal, bottom-up Einstein+scalar gravity theories. These holographic models are constructed to describe the thermodynamical properties of SU(Nc) plasmas near deconfinement at large Nc, and we identify this thermal mass with the Debye screening mass mD. In this class of noNconformal models with a first-order deconfinement transition at Tc the Debye screening mass mD displays the same behavior found for the expectation value of the Polyakov loop (which we also compute) jumping from zero below Tc to a nonzero value just above the transition. In the case of a crossover phase transition, mD/T has a minimum similar to that found for the speed of sound squared cs². This holographic framework is also used to evaluate mD as a fuNction of η/s in a strongly coupled conformal gauge plasma dual to Gauss-Bonnet gravity. In this case, mD/T decreases with iNcreasing η/s in accordaNce with extrapolations from weak coupling calculations. [ABSTRACT FROM AUTHOR]

We study the Abelian projection of quark confinement in SU(3) quenched lattice QCD, in terms of the dual superconductor picture. In the maximal Abelian gauge, we perform the Cartan decomposition of the non-Abelian gauge field on a 324 lattice with spacing a -- 0.058, 0.10 fm (i.e., β = 6.4, 6.0), and investigate the interquark potential V(r), the Abelian part VAbel(r), and the off-diagonal part Voff(r). For the potential analysis, we use both on-axis data and several types of off-axis data, with larger numbers of gauge configurations. Remarkably, we find almost perfect Abelian dominance of the string tension (quark-confining force) on the large-volume lattice. Also, we find a simple but nontrivial relation of V(r) ≃ VAbel(r) + Voff (r). [ABSTRACT FROM AUTHOR]

The ground state and excited spectra of barybns containing three identical heavy quarks, b or c, have been recently calculated in nonperturbative lattice QCD. The energy of positive and negative parity excitations has been determined with high precision. Lattice results constitute a unique opportunity to learn about the quark-confinement mechanism as well as elucidating our knowledge about the nature of the strong force. We analyze the nonperturbative lattice QCD results by means of heavy-quark static potentials derived using SU(3) lattice QCD. We make use of different numerical techniques for the three-body problem. [ABSTRACT FROM AUTHOR]

In the framework of the color flux-tube model with a four-body confinement potential, the lowest charged tetraquark states [Qq][Q'q'](Q = c,b,q = u,d,s) are studied by using the variational method, the Gaussian expansion method. The results indicate that some compact resonance states with three-dimensional spatial structures can be formed. These states cannot decay into two color singlet mesons Qq' and Q'q through the breakdown and recombination of color flux tubes but into QQ' and qq'. The four-body confinement potential is a crucial dynamical mechanism for the formation of these compact resonance states. The decay process is similar to that of a compound nucleus but due to the multibody color confinement. The newly observed charged states Zc(3900) and Zc(4025)/Zc(4020) can be interpreted as the S-wave tetraquark states [cu][cd] with quantum numbers IJP = 11+ and 12+, respectively. [ABSTRACT FROM AUTHOR]

The article presents a study on the mass spectra and decay properties of DS meson obtained relativistic independent quark model using a Martin-like potential for the quark confinement. The study involves spectroscopic parameters employed to further compute decay constant, electromagnetic transition and leptonic decay widths. The predicted branching ratios of the decay reported by CLEO-c, Particle Data Group and Bell collaboration are also demonstrated.

The article discusses a research that investigates the wigner functions for quark target dressed with gluon in perturbation theory. Details about the results of the combined position and momentum space information of quark distributions are noted. Also provided is the results of the computation of the different definitions of quark orbital angular momentum and spin-orbit correlations in perturbative model.

The article presents a study which examines the mass spectra and decay properties of Ds meson in a relativistic Dirac formalism. The mass spectra of the meson was obtained in the framework of the relativistic independent quark model using a Martin-like potential for the quark confinement. The decay constant, electromagnetic transition and leptonic decay widths were computed using spectroscopic parameters.

The propagation of a high-energy quark disturbs the confining QCD vacuum inducing the currents in Dirac sea. Since quarks possess electric charge, these induced vacuum quark currents act as a source of soft photon radiation. This can lead to the enhancement of the soft photon production above the expectations based on the charged hadron yields and the Low theorem. We illustrate the phenomenon by using the exactly soluble 1 + 1 dimensional massless Abelian gauge model that shares with QCD all of the ingredients involved in this mechanism: confinement, chiral symmetry breaking, axial anomaly, and the periodic 0 vacuum. We show that the propagating quark throughout the process of hadronization induces in the vacuum charged transition currents that lead to a strong resonant enhancement of the son photon yield; the Low theorem, however, remains accurate in the limit of very soft momenta. We then construct on the basis of our result a simple phenomenological model and apply it to the soft photon production in the fragmentation of jets produced in Z0 decays. We find a qualitative agreement with the recent result from the DELPHI Collaboration. [ABSTRACT FROM AUTHOR]

We calculate the scalar, axial, and pseudoscalar charges of the quark in the Schwinger-Dyson formalism of Landau gauge QCD. It is found that the dressed quark-scalar density of the valence quark is significantly enhanced against the bare-quark contribution, and the result explains qualitatively the phenomenologically known value of the pion-nucleon sigma term and also that given by lattice QCD. Moreover, we show that the Richardson's interquark potential suppresses the quark-scalar density in the Higashjima-Miransky approximation. This fact suggests that the quark-scalar density is an observable that is sensitive to quark confinement. For the quark axial charge, we find that it is suppressed due to the gluon dynamics. The result of the quenched analysis agrees qualitatively with the experimental data of the isovector axial coupling constant gA. We show that the suppression of the quenched axial charge is due to a mechanism similar to that of the quark tensor charge. In the Schwinger-Dyson equation with the leading unquenching quark-loop contribution the quark axial charge is more suppressed, due to the anomaly effect. The quark pseudoscalar density is found to be large, and is divergent as the bare quark becomes massless. This result is in agreement with the phenomenological current algebraic analysis, and explains well the dominance of the pion-pole contribution. [ABSTRACT FROM AUTHOR]

We revisit minimal supersymmetric extension of the Standard Model scenarios with light neutralino as a dark matter candidate in view of the latest LHC and dark matter direct and indirect detection experiments. We show that scenarios with a very light neutralino (~ 10 GeV) and a scalar bottom quark close in mass can satisfy all the available constraints from LEP, Tevatron, LHC, flavor and low energy experiments and provide solutions in agreement with the bulk of dark matter direct detection experiments, and in particular with the recent CDMS results. [ABSTRACT FROM AUTHOR]

We calculate the effective Polyakov line action corresponding to SU(2) lattice gauge theory on a 163 X 4 lattice via the "relative weights" method. We consider a variety of lattice couplings, ranging from β = 1.2 in the strong-coupling domain to β = 2.3 at the deconfinement transition, in order to study how the effective action evolves with β. Comparison of Polyakov line correlators computed in the effective theory and the underlying gauge theory is used to test the validity of the effective action for β > 1.4, while for β = 1.2,1.4 we can compare our effective action to the one obtained from a low-order strong-coupling expansion. Very good agreement is found at all couplings. We find that the effective action is given by a simple expression bilinear in the Polyakov lines. The range of the bilinear term, away from strong coupling, grows rapidly in lattice units as β increases. [ABSTRACT FROM AUTHOR]

A phase of strong interacting matter with deconfined quarks is expected in the core of massive neutron stars. In this article, we perform a study of the hadron-quark phase transition in cold (T=0) neutron star matter and we calculate various structural properties of hybrid stars. For the quark phase, we make use of an equation of state (EOS) derived with the field correlator method (FCM) recently extended to the case of nonzero baryon density. For the hadronic phase, we consider both pure nucleonic and hyperonic matter, and we derive the corresponding EOS within a relativistic mean field approach. We make use of measured neutron star masses, and particularly the mass M=1.97 ± 0.04M⊙ of PSR J1614-2230 to constrain the values of the gluon condensate G2, which is one of the EOS parameters within the FCM. We find that the values of G2 extracted from the mass measurement of PSR J1614-2230 are consistent with the values of the same quantity derived within the FCM from recent lattice QCD calculations of the deconfinement transition temperature at zero baryon chemical potential. The FCM thus provides a powerful tool to link numerical calculations of QCD on a space-time lattice with measured neutron star masses. [ABSTRACT FROM AUTHOR]

The maximum entropy method is used to compute the quark spectral function at nonzero temperature. We solve the gap equation of quantum chromodynamics (QCD) self-consistently, employing a rainbow kernel which phenomenologically models results from Dyson-Schwinger equations (DSE) and lattice QCD. We use the criterion of positivity restoration of the spectral function as a signal for deconfinement. Our calculation indicates that the critical temperature of deconfinement Td is slightly smaller than the one of chiral symmetry restoration Tc: Td~94%Tc in the chiral limit, and Td~96%Tc with physical light quark masses. Since these deviations are within the systematic error of our approach, it is reasonable to conclude that chiral symmetry restoration and deconfinement coincide at zero chemical potential. [ABSTRACT FROM AUTHOR]

We calculate, for the first time using unquenched lattice QCD, form factors for the rare decay ? → Kl+ l- in and beyond the Standard Model. Our lattice QCD calculation utilizes a nonrelativistic QCD formulation for the b valence quarks and the highly improved staggered quark formulation for the light valence quarks. We employ the MILC 2 + 1 asqtad ensembles. The form factor results, based on the z expansion, are valid over the full kinematic range of q². We construct the ratios fo/f+ and ft/f+, which are useful in constraining new physics and verifying effective theory form factor symmetry relations. We also discuss the calculation of Standard Model observables. [ABSTRACT FROM AUTHOR]

In lattice QCD, color confinement manifests in flux tubes. We compute in detail the quark-antiquark flux tube for pure gauge SU(3) dimension D = 3 + 1 for quark-antiquark distances R ranging from 0.4 to 1.4 fm. To increase the signal-to-noise ratio, we apply the improved multihit and extended smearing techniques. We detail the gauge-invariant squared components of the color electric and color magnetic fields both in the mediator plane between the static quark and static antiquark and in the planes of the charges. We fit the field densities with appropriate Ansätze, and we observe the screening of the color fields in all studied planes together with the quantum widening of the flux tube in the mediator plane. All components squared of the color fields are nonvanishing and are consistent with a penetration length A ~ 0.22 to 0.24 fm and an effective screening mass µ ~ 0.8 to 0.9 GeV. The quantum widening of the flux tube is well fitted with a logarithmic law in R. [ABSTRACT FROM AUTHOR]

We construct an equation of state of strange quark matter in a strong magnetic field within a confining model. The confinement is modeled by means of the Richardson potential for quark-quark interaction modified suitably to account for a strong magnetic field. We compare our results for the equation of state and magnetization of matter to those derived within the MIT bag model. The differences between these models arise mainly due to the momentum dependence of the strong interaction between quarks in the Richardson model. Specifically, we find that the magnetization of strange quark matter in this model has much more pronounced de Haas-van Alfvén oscillations than in the MIT bag model, which is the consequence of the (static) gluon-exchange structure of the confining potential. [ABSTRACT FROM AUTHOR]

We study the relativistic quark-antiquark system embedded in a magnetic field (MF). The Hamiltonian containing confinement, one gluon exchange, and spin-spin interaction is derived. We analytically follow the evolution of the lowest meson states as a function of MF strength. Calculating the one gluon exchange interaction energy 〈VOGE〉 and spin-spin contribution 〈ass〉 we have observed that these corrections remain finite at large MF, preventing the vanishing of the total ρ meson mass at some Bcrit, as previously thought. We display the ρ masses as functions of the MF in comparison with recent lattice data. [ABSTRACT FROM AUTHOR]

We study hadronic molecules formed by a heavy meson and a nucleon, DN and D*N (B̅ N and B̅ *N) systems. Respecting the heavy quark symmetry and chiral symmetry, we consider the DN-D*N (B̅ N-B̅ *N) mixing induced by the one boson exchange potential including the tensor force. We find many bound and resonant states with JP=1/2±, 3/2±, 5/2±, and 7/2- in isospin singlet channels, while we find only a few resonant states with JP=1/2- in isospin triplet channels. The analysis of DN and D*N (B̅ N and B̅ *N) molecules will be useful to study mass spectra of excited charmed (bottom) baryons with large angular momenta, when their masses are close to the DN and D*N (B̅ N and B̅ *N) thresholds. [ABSTRACT FROM AUTHOR]

We analyze geometrical scaling (GS) of negative pion multiplicity pT distributions at NA61/SHINE energies. We show that even though NA61/SHINE energies are low, one may expect to find GS in the particle spectra. We argue that qualitative behavior of ratios of multiplicities at different energies is in agreement with a simple picture of GS which is violated for pT smaller than some nonperturbative scale Λ and when larger Bjorken x of one of the scattering patrons crosses xmax above which a gluonic cloud becomes dilute and quark degrees of freedom become important. [ABSTRACT FROM AUTHOR]

In the framework of nonlocal SU(2) chiral quark models with Polyakov loop, we analyze the dependence of the deconfinement and chiral restoration critical temperatures on the explicit chiral symmetry breaking driven by the current quark mass. Our results are compared with those obtained within the standard local Polyakov-Nambu-Jona-Lasinio model and with lattice QCD calculations. For a wide range of pion masses, it is found that both deconfinement and chiral restoration critical temperatures turn out to be strongly entangled, in contrast with the corresponding results within the Polyakov-Nambu-Jona-Lasinio model. In addition, it is seen that the growth of the critical temperatures with the pion mass above the physical point is basically linear, with a slope parameter that is close to the existing lattice QCD estimates. On the other hand, we find a tendency to favor an early onset of the first order transition expected in the large quark mass limit. [ABSTRACT FROM AUTHOR]

We apply Zwanziger formalism to Cho restricted SU(2) theory to obtain the potential in a static quark-antiquark pair. Cho restricted theory is a self-consistent subset of a non-Abelian SU(2) gauge theory which tries to describe the infrared regime of Yang-Mills gauge theories. In Zwanziger formalism, a local Lagrangian depending on two electric and magnetic gauge fields is constructed for the theories where both electric and magnetic charges exist. Based on this local Lagrangian the propagator and then the potential between quarks is calculated in two limits: mcr ≪ 1 and mcr ≫ 1, where mc is the mass of the dual gauge boson and r is the distance between the quark and the antiquark. [ABSTRACT FROM AUTHOR]

Temporal quark correlation functions are analyzed in quenched lattice QCD for two values of temperature above the critical temperature (Tc) for deconfinement, T = 1.5Tc and 3Tc. A two-pole ansatz for the quark spectral function is used to determine the bare quark mass and the momentum dependence of excitation spectra on large lattices of size up to 128³ ✕ 16. The dependence of the quark correlator on these parameters as well as the finite volume dependence of the excitation energies are analyzed in detail in order to examine the reliability of our analysis. Our results suggest the existence of quasiparticle peaks in the quark spectrum. We furthermore find evidence that the dispersion relation of the plasmino mode has a minimum at nonzero momentum even in the nonperturbative region near Tc. We also elaborate on the enhancement of the quark correlator near the chiral limit which is observed at T = 1.5Tc on about half of the gauge configurations. We attribute this to the presence of near zero-modes of the fermion matrix that are associated with nontrivial topology of the gauge configurations. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of nucleón electromagnetic and axial form factors in a holographic soft-wall model. This approach is based on an action which describes hadrons with broken conformai invariance and incorporates confinement through the presence of a background dilaton field. For Nc = 3 we describe the nucleon structure in a superposition of a three-valence quark state with high Fock states including an adjustable number of partons (quarks, antiquaries and gluons) via studying the dynamics of 5D fermion fields of different scaling dimension in anti-de Sitter space. According to the gauge/gravity duality the 5D fermion fields of different scaling dimension correspond to the Fock state components with a specific number of partons. In the present application we restrict to the contribution of 3, 4 and 5 parton components in the nucleón Fock state. With a minimal number of free parameters (dilaton scale parameter, mixing parameters of partial contributions of Fock states, coupling constants in the effective Lagrangian) we achieve a reasonable agreement with data for the nucleón form factors. [ABSTRACT FROM AUTHOR]

Using the eigenmode of the Dirac operator Đ = γμDμ in quantum chromodynamics (QCD), we develop a manifestly gauge-covariant expansion and projection of the QCD operators such as the Wilson loop and the Polyakov loop. With this method, we perform a direct analysis of the correlation between confinement and chiral symmetry breaking in lattice QCD Monte Carlo calculation on 64 at β = 5.6. Even after removing the low-lying Dirac modes, which are responsible for chiral symmetry breaking, we find that the Wilson loop obeys the area law, and the slope parameter corresponding to the string tension, or confinement force, is almost unchanged. We find also that the Polyakov loop remains to be almost zero even without the low-lying Dirac modes, which indicates the Z³-unbroken confinement phase. These results indicate that one-to-one correspondence does not hold between confinement and chiral symmetry breaking in QCD. [ABSTRACT FROM AUTHOR]

The light-quark correlator in the axial-vector channel is used, in conjunction with finite energy QCD sum rules at finite temperature, in order to (a) establish a relation between chiral-symmetry restoration and deconfinement, and (b) determine the temperature behavior of the a¹(1260) width and coupling. Results indicate that deconfinement takes place at a slightly lower temperature than chiral-symmetry restoration, although this difference is not significant given the accuracy of the method. The behavior of the a¹(1260) parameters is consistent with quark-gluon deconfinement, as the width grows and the coupling decreases with increasing temperature. [ABSTRACT FROM AUTHOR]

We calculate the lattice quark propagator in Coulomb gauge from both dynamical and quenched configurations. We show that in the continuum limit both the static and the full quark propagators are multiplicatively renormalizable. From the propagator we extract the quark renormalization function Z(|p|) and the running mass M(|p|) and extrapolate the latter to the chiral limit. We find that M(|p|) practically coincides with the corresponding Landau gauge function for small momenta. The computation of M(|p|) can, however, be made more efficient in Coulomb gauge; this can lead to a better determination of the chiral mass and the quark anomalous dimension. Moreover from the structure of the full propagator we can read an expression for the dispersion relation of quarks, compatible with an IR divergent effective energy. If confirmed on larger volumes, this finding would allow one to extend the Gribov-Zwanziger confinement mechanism to the fermionic sector of QCD. [ABSTRACT FROM AUTHOR]

Nonstrange hexaquark state q3q3 spectrum is systematically studied by using the Gaussian expansion method in flux tube models with a six-body confinement potential. All the model parameters are fixed by baryon properties, so the calculation of hexaquark state q3q3 is parameter-free. It is found that some ground states of q3q3 are stable against disintegrating into a baryon and an anti-baryon. The main components of X(1835) and X(2370), which are observed in the radiative decay of J/&psgr; by BES collaboration, can be described as compact hexaquark states N8&Nmacr;8g and &Dgr;8&&Dgr;macr;8 with quantum numbers JGJPC = 0+0-+, respectively. These bound states should be color confinement resonances with three-dimensional configurations similar to a rugby ball, however, X(2120) can not be accommodated in this model approach. [ABSTRACT FROM AUTHOR]

We consider the position of the deconfining critical endpoint, where the first order transition for deconfinement is washed out by the presence of massive, dynamical quarks. We use an effective matrix model, employed previously to analyze the transition in the pure glue theory. If the parameters of the pure glue theory are unaffected by the presence of dynamical quarks, and if the quarks only contribute perturbatively, then for three colors and three degenerate quark flavors this quark mass is very heavy, mde ∼ 2.5 GeV, while the critical temperature Tde. barely changes, --1% below that in the pure glue theory. The location of the deconfining critical endpoint is a sensitive test to differentiate between effective models. For example, models with a logarithmic potential for the Polyakov loop give much smaller values of the quark mass, mde ∼ 1 GeV, and a large shift in Tde -- 10% lower than that in the pure glue theory. [ABSTRACT FROM AUTHOR]

We have been studying QCD with 2 flavors of color-sextet quarks to distinguish whether it is QCD-like or conformai. For comparison, we are now studying QCD with 3 flavors of color-sextet quarks, which is believed to be conformai in the chiral limit. Here, we present the results of simulations of lattice QCD with 3 color-sextet quarks at finite temperatures on lattices of temporal extent Nt = 4 and 6, with masses small enough to yield access to the chiral limit. As for the 2-flavor case, we find well-separated deconfinement and chiral-symmetry restoration transitions, both of which move to appreciably weaker couplings as Nt is increased from 4 to 6. If this theory is conformai, we would expect there to be a bulk chiral transition at a fixed coupling. For this reason, we conclude that for Nt = 4 and 6, the chiral and hence the deconfinement transitions are in the strong-coupling domain where the theory is essentially quenched. The similarity between the behaviors of the 2- and 3-flavor theories suggested that the Nt = 4 and 6 transitions for the 2-flavor theory also lie in the strong-coupling domain. The phase structure of both theories is very similar. [ABSTRACT FROM AUTHOR]

We present results on the chiral and deconfinement properties of the QCD transition at finite temperature. Calculations are performed with 2+1 flavors of quarks using the p4, asqtad, and HISQ/ tree actions. Lattices with temporal extent NT = 6, 8, and 12 are used to understand and control discretization errors and to reliably extrapolate estimates obtained at finite lattice spacings to the continuum limit. The chiral transition temperature is defined in terms of the phase transition in a theory with two massless flavors and analyzed using 0{N) scaling fits to the chiral condensate and susceptibility. We find consistent estimates from the HISQ/tree and asqtad actions and our main result is Tc = 154 ± 9 MeV. [ABSTRACT FROM AUTHOR]

The behavior of the Landau gauge gluon and ghost propagators is studied in pure SU(3) gauge theory at nonzero temperature on the lattice. We concentrate on the momentum range (0.6, 2.0) GeV. For the longitudinal as well as for the transverse component of the gluon propagator we extract the continuum limit. We demonstrate the smallness of finite-size and Gribov-copy effects at temperatures close to the deconfinement phase transition at T = Tc and within the restricted range of momenta. Since the longitudinal component DL(q) turns out to be most sensitive with respect to the phase transition, we propose some combinations of DL(q) signaling the transition much like "order parameters." [ABSTRACT FROM AUTHOR]

The gluonic action density is calculated in static mesons at finite temperature just below the deconfine-ment point. Our focus is to elucidate the role of vacuum ultraviolet fluctuations which are filtered using an improved smearing algorithm. In the intermediate source separation distance, where the free string picture poorly describes the flux tube width profile, we find upon reducing the vacuum action towards the classical instanton vacuum, the characteristics of the flux tube converge and compare favorably with the predictions of the free bosonic string. This result establishes a connection between the free string action and vacuum gauge fields and reveals the important role of ultraviolet physics in understanding the lattice data at this temperature scale. As a by-product of these calculations, we find the broadening of the QCD flux tube to be independent of the ultraviolet filtering at large distances. Our results exhibit a linearly divergent pattern in agreement with the string picture predictions. [ABSTRACT FROM AUTHOR]

There are good reasons that the deconfinement phase transition of pure Yang-Mills theory at finite temperature should also be reflected in the behavior of gauge-fixed gluonic correlation functions. Understanding this in detail would provide another important example of how physical information can be extracted from gauge-dependent correlations, which is not always obvious. Therefore, herein we study the behavior of the Landau-gauge gluon propagator of pure SU(2) across the phase transition in 2 + 1 and 3 + 1 dimensions in order to assess to what extend the corresponding critical behavior is reflected in these correlations. We discuss why it should emerge from a continuum perspective and test our expectations in lattice simulations. A comparison with SU(3) furthermore reveals quite clear indications for a sensitivity of the gluon propagator to the order of the transition. [ABSTRACT FROM AUTHOR]

The stability of systems containing six quarks or antiquarks is studied within a simple string model inspired by the strong-coupling regime of quantum chromodynamics and used previously for tetraquarks and pentaquarks. We discuss both six-quark (q6) and three-quark-three-antiquark (q3q3) states. The quarks are assumed to be distinguishable and thus not submitted to antisymmetrization. It is found that the ground state of (q6) is stable against dissociation into two isolated baryons. For the case of (q3q3), our results indicate the existence of a bound state very close to the threshold. The investigations are extended to (q3Q3) and (Q3q3) systems with two different constituent masses, and their stability is discussed as a function of the mass ratio. [ABSTRACT FROM AUTHOR]

The phase structure of the two-flavor Polyakov-loop extended Nambu-Jona-Lashinio model is explored at finite temperature and imaginary chemical potential with a particular emphasis on the confinement-deconfinement transition. We point out that the confined phase is characterized by a cos3μI/T dependence of the chiral condensate on the imaginary chemical potential while in the deconfined phase this dependence is given by cosμI/T and accompanied by a cusp structure induced by the Z(3) transition. We demonstrate that the phase structure of the model strongly depends on the choice of the Polyakov loop potential U. Furthermore, we find that by changing the four fermion coupling constant Gs, the location of the critical end point of the deconfinement transition can be moved into the real chemical potential region. We propose a new parameter characterizing the confinement-deconfinement transition. [ABSTRACT FROM AUTHOR]

We introduce dressed Wilson loops as a novel confinement observable. It consists of closed planar loops of arbitrary geometry but fixed area, and its expectation values decay with the latter. The construction of dressed Wilson loops is based on chiral condensates in response to magnetic and electric fields, thus linking different physical concepts. We present results for generalized condensates and dressed Wilson loops on dynamical lattice configurations and confirm the agreement with conventional Wilson loops in the limit of large probe mass. We comment on the renormalization of dressed Wilson loops. [ABSTRACT FROM AUTHOR]

We present a reanalysis of CDF data to extend limits on individual fourth-generation quark masses from particular flavor-mixing rates to the entire space of possible mixing values. Measurements from CDF have set individual limits on masses, mb' and mt', at the level of 335-385 GeV assuming specific and favorable flavor-mixing rates. We consider the space of possible values for the mixing rates and find that the CDF data imply limits of 290 GeV and greater over a wide range of mixing scenarios. We also analyze the limits from the perspective of a four-generation Cabibbo-Kobayashi-Maskawa (CKM) matrix. We find that present experimental constraints on CKM elements do not suggest further constraints on fourth-generation quark masses. [ABSTRACT FROM AUTHOR]

We develop a practical method to analyze the mixing structure of hadrons consisting of two components of quark composite and hadronic composite. As an example, we investigate the properties of the axial vector meson a1(1260) and discuss its mixing properties quantitatively. We also make reference to the large Nc procedure and its limitation for the classification of such a mixed state [ABSTRACT FROM AUTHOR]

The two-equation-of-state model is used to describe the hadron-quark phase transition in asymmetric matter formed at high density in heavy-ion collisions. For the quark phase, the three-flavor Nambu-Jona-Lasinio effective theory is used to investigate the influence of dynamical quark mass effects on the phase transition. At variance to the MIT-Bag results, with fixed-current quark masses, the main important effect of the chiral dynamics is the appearance of an end point for the coexistence zone. We show that a first-order hadron-quark phase transition may take place in the region T⊂(50-80) MeV and ρB⊂(2-4)ρ0, which is possible to be probed in the new planned facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From the isospin properties of the mixed phase, some possible signals are suggested. The importance of chiral symmetry and dynamical quark mass on the hadron-quark phase transition is stressed. The difficulty of an exact location of a critical end point comes from its appearance in a region of competition between chiral symmetry breaking and confinement, where our knowledge of effective QCD theories is still rather uncertain. [ABSTRACT FROM AUTHOR]

The CMS Collaboration at the CERN LHC has searched for the t-channel single top quark production using the spin correlation of the t-channel. The signal extraction and cross section measurement rely on the angular distribution of the charged lepton in the top quark decays, the angle between the charged lepton momentum and top spin in the top rest frame. The behavior of the angular distribution is a distinct slope for the t-channel single top (signal) while it is flat for the backgrounds. In this Brief Report, we investigate the contributions which this spin correlation may receive from a two-Higgs doublet model, a top-color assisted technicolor (TC2) and the noncommutative extension of the standard model. [ABSTRACT FROM AUTHOR]

We study the phase structure of mixed-action QCD with two Wilson sea quarks and any number of chiral valence quarks (and ghosts), starting from the chiral Lagrangian. A priori the effective theory allows for a rich phase structure, including a phase with a condensate made of sea and valence quarks. In such a phase, mass eigenstates would become admixtures of sea and valence fields, and pure-sea correlation functions would depend on the parameters of the valence sector, in contradiction with the actual setup of mixed-action simulations. Using that the spectrum of the chiral Dirac operator has a gap for nonzero quark mass we prove that spontaneous symmetry breaking of the flavor symmetries can only occur within the sea sector. This rules out a mixed condensate and implies restrictions on the low-energy constants of the effective theory. [ABSTRACT FROM AUTHOR]

The article offers information on the measurements of branching fractions, polarizations, and direct CP-violation asymmetries. The study of the branching fractions and angular distributions of B meson decays to hadronic final states without a charm quark probes. It also plays an important role in understanding CP violation in the quark sector, constraining the Cabibbo-Kobayashi-Maskawa matrix parameters.

We analyze three different new physics scenarios for ΔF=2 flavor-changing neutral currents in the quark sector in the light of recent data on neutral-meson mixing. We parametrize generic new physics contributions to Bq-Bq mixing, q=d, s, in terms of one complex quantity Δq, while three parameters ΔKtt, ΔKct, and ΔKcc are needed to describe K-K mixing. In scenario I, we consider uncorrelated new physics contributions in the Bd, Bs, and K sectors. In this scenario, it is only possible to constrain the parameters Δd and Δs whereas there are no nontrivial constraints on the kaon parameters. In scenario II, we study the case of minimal flavor violation (MFV) and small bottom Yukawa coupling, where Δ=Δd=Δs=ΔKtt. We show that Δ must then be real, so that no new CP phases can be accommodated, and express the remaining parameters ΔKcc and ΔKct in terms of Δ in this scenario. Scenario III is the generic MFV case with large bottom Yukawa couplings. In this case, the kaon sector is uncorrelated to the Bd and Bs sectors. As in the second scenario one has Δd=Δs=Δ, however, now with a complex parameter Δ. Our quantitative analyses consist of global Cabibbo-Kobayashi-Maskawa (CKM) fits within the Rfit frequentist statistical approach, determining the standard model parameters and the new physics parameters of the studied scenarios simultaneously. We find that the recent measurements indicating discrepancies with the standard model are well accommodated in Scenarios I and III with new mixing phases, with a slight preference for Scenario I that permits different new CP phases in the Bd and Bs systems. Within our statistical framework, we find evidence of new physics in both Bd and Bs systems. The standard model hypothesis Δd=Δs=1 is disfavored with p-values of 3.6σ and 3.3σ in Scenarios I and III, respectively. We also present an exhaustive list of numerical predictions in each scenario. In particular, we predict the CP phase in Bs→J/ψϕ and the difference between the Bs and Bd semileptonic asymmetries, which will be both measured by the LHCb experiment. [ABSTRACT FROM AUTHOR]