Gluon Coupling Research Articles

One-loop phi-MHV amplitudes using the unitarity bootstrap

We consider a Higgs boson coupled to gluons via the five-dimensional effective operator HtrGμνGμν produced by considering the heavy top quark limit of the one-loop coupling of Higgs and gluons in the standard model. We treat H as the real part of a complex field that couples to the selfdual gluon field strengths and compute the one-loop corrections to amplitudes involving , two colour adjacent negative helicity gluons and an arbitrary number of positive helicity gluons - the so-called -MHV amplitudes. We use four-dimensional unitarity to construct the cut-containing contributions and the recently developed recursion relations to obtain the rational contribution for an arbitrary number of external gluons. We solve the recursion relations and give explicit results for up to four external gluons. These amplitudes are relevant for Higgs plus jet production via gluon fusion in the limit where the top quark mass is large compared to all other scales in the problem.

Phenomenology of infrared finite gluon propagator and coupling constant

We report on some recent solutions of the Dyson-Schwinger equations for the infrared behavior of the gluon propagator and coupling constant, discussing their differences and proposing that these different behaviors can be tested through hadronic phenomenology. We discuss which kind of phenomenological tests can be applied to the gluon propagator and coupling constant, how sensitive they are to the infrared region of momenta and what specific solution is preferred by the experimental data.

LARGE COMPONENT QCD AND THEORETICAL FRAMEWORK OF HEAVY QUARK EFFECTIVE FIELD THEORY

Based on a large component QCD derived directly from full QCD by integrating over the small components of quark fields with |p| < E + mQ, an alternative quantization procedure is adopted to establish a basic theoretical framework of heavy quark effective field theory (HQEFT) in the sense of effective quantum field theory. The procedure concerns quantum generators of Poincaré group, Hilbert and Fock space, anticommutations and velocity superselection rule, propagator and Feynman rules, finite mass corrections, trivialization of gluon couplings and renormalization of Wilson loop. The Lorentz invariance and discrete symmetries in HQEFT are explicitly illustrated. Some new symmetries in the infinite mass limit are discussed. Weak transition matrix elements and masses of hadrons in HQEFT are well defined to display a manifest spin-flavor symmetry and 1/mQcorrections. A simple trace formulation approach is explicitly demonstrated by using LSZ reduction formula in HQEFT, and shown to be very useful for parametrizing the transition form factors via 1/mQexpansion. As the heavy quark and antiquark fields in HQEFT are treated on the same footing in a fully symmetric way, the quark–antiquark coupling terms naturally appear and play important roles for simplifying the structure of transition matrix elements, and for understanding the introduction of "dressed heavy quark"–hadron duality. In the case that the "longitudinal" and "transverse" residual momenta of heavy quark are at the same order of power counting, HQEFT provides a consistent approach for systematically analyzing heavy quark expansion in terms of 1/mQ. Some interesting features in applications of HQEFT to heavy hadron systems are briefly outlined.

Investigation of Dilaton–Gluon Coupling Potential inCharmonium Family

The behaviour of dilaton–gluon coupling (DGC) potential is investigatedby studying charmonium spectra, annihilation rates and E1 transitionrates systematically. We find that in the non-relativistic quantumchromodynamics approximation, the charmonium properties can be describedby the DGC potential.

Is the universal string axion the QCD axion?

We consider the class of effective supergravity theories from the weakly coupled heterotic string in which local supersymmetry is broken by gaugino condensation in a hidden sector, with dilaton stabilization achieved through corrections to the classical dilaton Kähler potential. If there is a single hidden condensing (simple) gauge group, the axion is massless (up to contributions from higher dimension operators) above the QCD condensation scale. We show how the standard relation between the axion mass and its Planck scale coupling constant is modified in this class of models due to a contribution to the axion–gluon coupling that appears below the scale of supersymmetry breaking when gluinos are integrated out. In particular there is a point of enhanced symmetry in parameter space where the axion mass is suppressed. We revisit the question of the universal axion as the Peccei–Quinn axion in the light of these results, and find that the strong CP problem is avoided in most compactifications of the weakly coupled heterotic string.

Excited B mesons from the lattice

The energies of different angular momentum states of a heavy-light meson were measured on a lattice in [C. Michael, J. Peisa for UKQCD Collaboration, Phys. Rev. D 58, 34506 (1998)]. We have now repeated this study using several different lattices, quenched and unquenched, that have different physical lattice sizes, clover coefficients and quark–gluon couplings. The heavy quark is taken to be infinitely heavy, whereas the light quark mass is approximately that of the strange quark. By interpolating and extrapolating in the light quark mass we can thus compare the lattice results with B and Bs meson experiments. Most interesting is the lowest P-wave Bs state, since it is possible that it lies below the BK threshold and hence is very narrow. Unfortunately, there are no experimental results on P-wave B or Bs mesons available at present. In addition to the energy spectrum, we measured earlier also vector (charge) and scalar (matter) radial distributions of the light quark in the S-wave states of a heavy-light meson on a lattice [A.M. Green, J. Koponen, C. Michael, P. Pennanen for UKQCD Collaboration, Phys. Rev. D 65, 014512 (2002) and Eur. Phys. J. C 28, 79 (2003), hep-lat/0206015 ]. Now we are extending the study of radial distributions to P-wave states.

On the glue content in heavy quarkonia

Starting with two coupled Bethe-Salpeter equations for the quark-antiquark, and for the quark-glue-antiquark component of the quarkonium, we solve the bound state equations perturbatively. The resulting admixture of glue can be partially understood in a semiclassical way; one has, however, to take care of the different use of time ordered versus retarded Green functions. Subtle questions concerning the precise definition of the equal time wave function arise, because the wave function for the Coulomb gluon is discontinuous with respect to the relative time of the gluon. A striking feature is that a one loop non-abelian graph contributes to the same order as tree graphs, because the couplings of transverse gluons in the tree graphs are suppressed in the non-relativistic bound state, while the higher order loop graph can couple to quarks via non-suppressed Coulomb gluons. We also calculate the amplitude for quark and antiquark at zero distance in the quark-glue-antiquark component of the P-state. This quantity is of importance for annihilation decays of P-states. It shows a remarkable compensation between the tree graph and the non-abelian loop graph contribution. An extension of our results to include non-perturbative effects is possible.

Gluon coupling strength in HQCD with small cutoffs

This contribution presents the running triple-gluon-vertex coupling constant, g_lambda, in Hamiltonians for the gluons that are characterized by the size 1/lambda. The coupling constant is obtained from renormalization group equations for effective particles in canonical light-front QCD in third order perturbation theory. lambda plays the role of a finite cutoff parameter and is varied from 100 Gev down to 100 MeV.

The Effective Degree of Freedom of Low Energy QCD**The project partly supported by NSF, SED and SSTD of China, and partly by the US Department of Energy under contract W-7405-ENG-36

The adiabatic effective baryon-baryon interactions and dibaryon candidates are studied systematically with three constituent quark models based on different effective degrees of freedom: Glozman–Riska–Brown Goldstone boson exchange model based on constituent quark and Goldstone boson coupling; Fujiwara model based on constituent quark gluon coupling and Nijmegen one-boson exchange; QDCSM based on constituent quark and gluon coupling with quark delocalization and color screening. We find that the three models predicted the similar effective baryon-baryon interactions for roughly two thirds among the 64 states consisted of octet and decuplet baryons. The differences among three models and their separate characteristics are also studied.

On the dilaton and axion potentials

We extend the Vecchia–Veneziano–Witten model of quantum chromodynamics in the chiral limit and for large colour number Nc, by introducing an effective dilaton–gluon coupling from which we derive both the axion and dilaton potentials. Furthermore, using a string-inspired model, we determine a new interquark potential as a perturbative series in terms of the interquark distance r. Our potential goes beyond Dick's potential (Dick R 1999 Eur. Phys. J. C 6 701) and shares the same features as those of the Bian–Huang–Shen potential (VBHS) which depends only on odd powers of r (Bian J G, Huang T and Shen Q X 1994 Commun. Theor. Phys. 21 333).

Multiple-scale analysis and renormalization of quenched second order phase transitions

In this paper, we put forward a way to study the nucleon's thermodynamic properties such as its temperature, entropy and so on, without inputting any free parameters by human hand, even the nucleon's mass and radius. First we use the Lagrangian density of the quark gluon coupling fields to deduce the Dirac Equation of the quarks confined in the gluon fields. By boundary conditions we solve the wave functions and energy eigenvalues of the quarks, and thus get energy-momentum tensor, nucleon mass, and density of states. Then we utilize a hybrid grand canonical ensemble, to generate the temperature and chemical potentials of quarks, antiquarks of three flovars by the four conservation laws of the energy and the valence quark numbers, after which, all other thermodynamic properties are known. The only seemed free paremeter, the nucleon radius is finally determined by the grand potential minimal principle.

On the confining potential in 4D $SU(N_{\mathrm c})$ gauge theory with dilaton

Using the formal analogy between the Dick superstring inspired model and the problem of the building of an Eguchi–Hanson metric in 4D N = 2 harmonic superspace (HS), we derive a general formula for the quark–quark interaction potential V(r) including the Dick confining potential. The interquark potential V(r) depends on the dilaton–gluon coupling and may be related to the parameterization of confinement by the quark and gluon vacuum condensates. It is also shown how the axion field may be incorporated in agreement with 10D type IIB superstring requirements. Others features are also discussed.

The CP-violating triple gluon interaction in Z $\rightarrow$ 4 jets

We analyse CP-violating effects in Z $\rightarrow$ 4 jet decays, assuming the presence of a CP-violating effective triple gluon coupling. We discuss the influence of this coupling on the decay width. Furthermore, we analyse different CP-odd observables and propose strategies of a direct search for such a CP-violating GGG coupling. The present data of LEP 1 should give significant information on the coupling.

An effective field theory of QCD at high density

We derive a (Wilsonian) effective field theory of QCD at finite density by integrating out the states in the Dirac sea when the chemical potential μ≫ Λ QCD. The quark–gluon coupling is effectively (1+1)-dimensional and the theory contains four-quark operators which become relevant as we approach to the Fermi sea. By calculating the one-loop vacuum polarization tensor in the effective theory, we find the electric gluons have a screening mass, M∼ g s μ, while the static magnetic gluons are unscreened. We then investigate the gap equations for color anti-triplet Cooper pairs by including both gluon-exchange interactions and the marginal four-quark interactions in the effective theory.

Are quarks and leptons dynamically confined in four flat extra dimensions?

Rubakov and Shaposhnikov have shown that the domain wall generated by real one-component φ 4 theory extended to five flat (non-compact) dimensions can trap a massive bosonic excitation on the wall M 4; adding L D = i Σ μ=0 4 ψγ μ∂ μψ + g ψφψ likewise traps a massless left-chiral Dirac particle on the wall. Independently, Kaplan has proposed this same mechanism to generate a massless chiral fermion to circumvent no-go theorems in lattice gauge theories. We show that if the Dirac field equation is extended to (7+1) flat dimensions and the classical domain wall replaced in the four extra dimensions R 4 by a harmonic-oscillator potential plus a large constant, then “orbital” times “spin” solutions are generated in R 4 which exhibit approximate SU(4) × SU(2) symmetry. In an SU(4) = SU(3) × U(1) decomposition, the 1 and 3 irreps of SU(3) resemble singlet and triplet color, respectively, while the U(1) symmetry yields replications suggesting generation number. Doublet representations of SU(2) resemble weak isospin. Thus these representations bear some resemblance to quarks and leptons. We indicate an SU(3)-invariant coupling of gluons to these “quarks”, and a left-right symmetric coupling of the proposed quarks and “leptons” to electroweak bosons. We suggest looking for an alternate mechanism to the HO well, perhaps a (Euclidean) instanton.

Confinement from a scalar-gluon coupling in gauge theory

A model is introduced with a massive scalar coupling to the Yang--Mills term in four--dimensional gauge theory. It is shown that the resulting potential of colour sources consists of a short range Coulomb interaction and a long range confining part. Far away from the source the scalar vanishes $\sim r^{-1}$ while the potential diverges linearly $\sim r$. Up to an $N_c$--dependent factor of order 1 the tension parameter in the model is $gmf$, where $m$ denotes the mass of the scalar and $f$ is a coupling scale entering the scalar--gluon coupling.

Leptoquark pair production in hadronic interactions

The scalar and vector leptoquark pair production cross sections in hadronic collisions are calculated. In a model independent analysis we consider the most general C and P conserving couplings of gluons to both scalar and vector leptoquarks described by an effective low-energy Lagangian which obeys SU(3)c invariance. Analytical expressions are derived for the differential and integral scattering cross sections including the case of anomalous vector leptoquark couplings, K G and ΛG, to the gluon field. Numerical predictions are given for the kinematic range of the TEVATRON and LHC. The pair production cross sections are also calculated for the resolved photon contributions to at HERA and LEP ⊗ LHC, and for the process at possible future e + e − linear colliders and γγ colliders. Estimates of the search potential for scalar and vector leptoquarks at present and future high energy colliders are given.

Effects of anomalous couplings of quarks on prompt photon production

Prompt photon production is sensitive to the anomalous couplings of gluons to quarks, because it is mainly produced by quark-gluon scattering. We will examine the effects of the anomalous chromoelectric and chromomagnetic dipole moment couplings of quarks on prompt photon production. Using the data collected by CDF and D0 at the Fermilab Tevatron we put a bound on these anomalous couplings. We also estimate the sensitivity of various future high energy collider experiments to these anomalous couplings.

Dynamical perturbation theory and the auxiliary field method

By introducing auxiliary fields, which by their quantum numbers vanish in perturbation theory, we relate the dynamical perturbation theory of Pagels and Stokar and a successful gauged nonlocal constituent quark model to $U(N)$ gauge theory and to QCD. This sheds light on the duality between quark models and resonance models. We then derive the effective action in the loop expansion without dropping cubic and quartic gluon couplings.

Gluonic mesons in $J/\psi$ radiative decay

Two–gluon coupling of gluonic mesons is estimated in a spectator model to be considerably larger than that of $Q\bar{Q}$ . As an example of a gluonic meson that may be produced in $J/\psi$ radiative decay, we analyse $\eta(1760)$ . We deduce from experimental data that its branching ratio to two gluons is bounded, $0.4\pm 0.3 \stackrel{<}{\scriptstyle \sim} BR(\eta(1760)\rightarrow gg)\stackrel{<}{\scriptstyle \sim} 0.9\pm 0.3$ , consistent with a gluonic meson, but not compelling it. We propose further tests, and estimate the two–photon coupling of $\eta(1760)$ to be $1.4\pm 0.7$ keV.