Quark-quark Interaction Research Articles

Implication of the PAMELA antiproton data for dark matter indirect detection at LHC

Since the PAMELA results on the ``anomalously'' high positron fraction and the lack of antiproton excess in our Galaxy, there has been a tremendous number of studies advocating new types of dark matter, with larger couplings to electrons than to quarks. This raises the question of the production of dark matter particles (and heavy associated coloured states) at LHC. Here, we explore a very simple benchmark dark matter model and show that, in spite of the agreement between the PAMELA antiproton measurements and the expected astrophysical secondary background, there is room for large couplings of a WIMP candidate to heavy quarks. Contrary to what could have been naively anticipated, the PAMELA p̄/p measurements do not challenge dark matter model building, as far as the quark sector is concerned. A quarkophillic species is therefore not forbidden. Owing to these large couplings, one would expect that a new production channel opens up at the LHC, through quark-quark and quark-gluon interactions. Alas, when the PDF of the quark is taken into account, prospects for a copious production fade away.

Quark Forces from Hadronic Spectroscopy

We consider the implications of the most general two-body quark-quark interaction Hamiltonian for the spin-flavor structure of the negative parity L = 1 excited baryons. Assuming the most general two-body quark interaction Hamiltonian, we derive two correlations among the masses and mixing angles of these states, which constrain the mixing angles, and can be used to test for the presence of three-body quark interactions. We find that the pure gluon-exchange model is disfavored by data, independently of any assumptions about hadronic wave functions.

Pion pole light-by-light contribution tog−2of the muon in a nonlocal chiral quark model

We calculate the pion-pole term of the light-by-light contribution to the g - 2 of the muon in the framework of an effective chiral quark model with instantonlike nonlocal quark-quark interaction. The full kinematic dependence of the pion-photon transition form factors is taken into account. The dependence of form factors on the pion virtuality decreases the result by about 15% in comparison to the calculation where this dependence is neglected. Further, it is demonstrated that the QCD constraints suggested by Melnikov and Vainshtein are satisfied within the model. The corresponding contributions originate from the box diagram as well from the pion-pole term. Our chiral nonlocal model result for the pion-pole light-by-light contribution to (g - 2)/2 of the muon is (6.3-6.7) × 10 -10 , which is in the ball park of other effective-model calculations.

UA(1) anomaly and $ \eta^{{\prime}}_{}$ -mass from an infrared singular quark-gluon vertex

The U A(1) problem of QCD is inevitably tied to the infrared behaviour of quarks and gluons with its most visible effect being the $ \eta^{{\prime}}_{}$ -mass. A dimensional argument of Kogut and Susskind showed that the mixing of the pseudoscalar flavour-singlet mesons with gluons can provide a screening of the Goldstone pole in this channel if the full quark-quark interaction is strongly infrared singular as ∼ 1/k 4 . We investigate this idea using previously obtained results for the Landau gauge ghost and gluon propagator, together with recent determinations for the singular behaviour of the quark-gluon vertex. We find that, even with an infrared vanishing gluon propagator, the singular structure of the quark-gluon vertex for certain kinematics is apposite for yielding a non-zero screening mass.

Permutation groupSNand largeNcexcited baryons

We study the excited baryon states for an arbitrary number of colors ${N}_{c}$ from the perspective of the permutation group ${S}_{N}$ of $N$ objects. Classifying the transformation properties of states and quark-quark interaction operators under ${S}_{N}$ allows a general analysis of the spin-flavor structure of the mass operator of these states, in terms of a few unknown constants parametrizing the unknown spatial structure. We explain how to perform the matching calculation of a general two-body quark-quark interaction onto the operators of the $1/{N}_{c}$ expansion. The inclusion of core and excited quark operators is shown to be necessary. Considering the case of the negative parity $L=1$ states transforming in the $MS$ of ${S}_{N}$, we discuss the matching of the one-gluon and the Goldstone-boson exchange interactions.

Quark Gluon Condensate, Virtuality and Susceptibility of QCD Vacuum

We study vacuum of QCD in this work. The structure of non-local quark vacuum condensate, values of various local quark and gluon vacuum condensates, quark-gluon mixed vacuum condensate, quark and gluon virtuality in QCD vacuum state, quark dynamical mass and susceptibility of QCD vacuum state to external field are predicted by use of the solutions of Dyson–Schwinger equations in “rainbow" approximation with a modeling gluon propagator and three different sets of quark-quark interaction parameters. Our theoretical predictions are in good agreement with the correspondent empirical values used widely in literature, and many other theoretical calculations. The quark propagator and self-energy functions are also obtained from the numerical solutions of Dyson–Schwinger equations. This work is centrally important for studying non-perturbative QCD, and has many important applications both in particle and nuclear physics.

1/Nccorrections to the magnetic susceptibility of the QCD vacuum

We investigate the magnetic susceptibility of the QCD vacuum with the $1/{N}_{c}$ corrections taken into account, based on the instanton vacuum. Starting from the instanton liquid model, we derive the gauged light-quark partition function in the presence of the current quark mass as well as of external Abelian vector and tensor fields. We consider the $1/{N}_{c}$ meson-loop corrections which are shown to contribute to the magnetic susceptibility by around 15% for the up (and down) quarks. We also take into account the tensor terms of the quark-quark interaction from the instanton vacuum as well as the finite-width effects, both of which are of order $\mathcal{O}(1/{N}_{c})$. The effects of the tensor terms and finite width turn out to be negligibly small. The final results for the up-quarks are given as: $\ensuremath{\chi}⟨i{\ensuremath{\psi}}^{\ifmmode\dagger\else\textdagger\fi{}}\ensuremath{\psi}{⟩}_{0}\ensuremath{\simeq}35--40\text{ }\text{ }\mathrm{MeV}$ with the quark condensate $⟨i{\ensuremath{\psi}}^{\ifmmode\dagger\else\textdagger\fi{}}\ensuremath{\psi}{⟩}_{0}$. We also discuss the pion mass dependence of the magnetic susceptibility in order to give a qualitative guideline for the chiral extrapolation of lattice data.

Ndscattering lengths from a quark-model basedNNinteraction

We calculate the doublet and quartet neutron-deuteron scattering lengths using a nonlocal nucleon-nucleon interaction fully derived from quark-quark interactions. We use as input the $\mathit{NN}{}^{1}{S}_{0}$ and ${}^{3}{S}_{1}\text{\ensuremath{-}}{}^{3}{D}_{1}$ partial waves. Our result for the quartet scattering length agrees well with the experimental value but the result for the doublet scattering length does not. However, if we take the result for the doublet scattering length together with the one for the triton binding energy they agree well with the so-called Phillips line.

A new formulation of the relativistic many-body theory of electric dipole moments of closed shell atoms

The electric dipole moments of closed-shell atoms are sensitive to the parity and time-reversal violating phenomena in the nucleus. The nuclear Schiff moment is one such property, it arises from the parity and time reversal violating quark-quark interactions and the quark-chromo electric dipole moments. We calculate the electric dipole moment of atomic 199Hg arising from the nuclear Schiff moment using the relativistic coupled-cluster theory. This is the most accurate calculation of the quantity to date. Our calculations in combination with the experiment data provide important insights to the P and T violating coupling constants at the elementary particle level. In addition, a new limit on the tensor-pseudo tensor induced atomic EDM, calculated using the relativistic coupled-cluster theory is also presented.

Preliminary study of theK¯Ninteraction in a chiral constituent quark model

A preliminary investigation of $\overline{K}N$ interaction is performed within a chiral constituent quark model by solving the resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the $S$-, $P$-, $D$-, $F$-wave $\mathit{KN}$ scattering phase shifts. The channel-coupling between $\overline{K}N,\ensuremath{\pi}\ensuremath{\Lambda}$ and $\ensuremath{\pi}\ensuremath{\Sigma}$ is considered, and the scattering phase shifts as well as the bound-state problem of $\overline{K}N$ are dynamically studied. The results show that the $S$-wave $\overline{K}N$ interaction in the isospin $I=0$ channel is attractive, and in the extended chiral SU(3) quark model such an attraction can make for a $\overline{K}N$ bound state, which appears as a $\ensuremath{\pi}\ensuremath{\Sigma}$ resonance in the coupled-channel calculation, while the chiral SU(3) quark model cannot accommodate the existence of a $\overline{K}N$ bound state. It seems that the vector meson exchanges are necessary to be introduced in the quark-quark interactions if one tries to explain the $\ensuremath{\Lambda}(1405)$ as a $\overline{K}N$ bound state or a $\ensuremath{\pi}\ensuremath{\Sigma}$-$\overline{K}N$ resonance state.

Decay width of the Θ +(1540) in 5-quark dynamical calculation

The mass and decay width of the Θ+ are calculated in a constituent quark model comprising u u d d s ¯ quarks. With the use of a one-gluon exchange quark-quark interaction, the absolute mass is calculated to be larger than 2 GeV, increasing in order of the spin-parity, 1 2 − , 3 2 + and 1 2 + ( 3 2 + ) . The characteristic feature of the wave function is also discussed.

High Energy p̄p and ppElastic Scatterings in QCD Inspired Model

We propose QCD inspired model to calculate p̄p andpp elastic scatterings at high energies in this paper. Acalculation for total cross section of p̄p and pp isperformed in which the contributions from gluon-gluon, quark-quark,and gluon-quark interactions are included. Our results show that theQCD inspired model gives a perfect fit to experimental data of totalcross section both for p̄p and pp elastic scatterings at thewhole energy region where experimental data existed at FNAL and CERN.

Color screening and quark-quark interactions in finite temperature QCD

We analyze the screening of static diquark sources in 2-flavor QCD and compare results with the screening of static quark-antiquark pairs. We show that a two quark system in a fixed color representations is screened at short distances like a single quark source in the same color representation whereas at large distances the two quarks are screened independently. At high temperatures we observe that the relative strength of the interaction in diquark and quark-antiquark systems, respectively, obeys Casimir scaling. We use this result to examine the possible existence of heavy quark-quark bound states in the high temperature phase of QCD. We find support for the existence of $bb$ states up to about $2T_c$ while $cc$ states are unlikely to be formed above $T_c$.

The signature of some promising dimeson decays

Dimesons are expected to provide important information about the effective quark-quark interaction and about production and decay mechanisms of multiquarks. The cleanest, the double-heavies, are difficult to identify. I discuss a few promising signatures for the double-charm dimesons T cc = cc u ¯ d ¯ .

Stochastic Variational Method Applied to Pentaquarks

state of Λ(1405) is lower than the energy for the (q 3 ) state, even after eliminating the contribution from the color van der Waals force due to the phenomenological linear confinement potential. The present result suggests that the Λ(1405) is a pentaquark-dominated state if the color-magnetic potential plays a leading role of the quark-quark and quark-antiquark interactions.

Few-Body Problems with Strangeness

We solve a five-body problem of pentaquark (q4 q̄) state of Λ(1405). The hamiltonian, which reproduces reasonably well the energies of ground state baryons (N, Λ, Σ, Ξ and Δ) and mesons (π, K, ρ, K*), includes kinetic energy of semi-relativistic form, linear confinement potential, and a color-magnetic interaction with Gaussian form factor. Flavor symmetry breaking (ms> mu,d) is taken into account. The energy calculated for the pentaquark state of Λ(1405) is lower than the energy for the three-quark state. The present result suggests that the Λ(1405) is a pentaquark-dominated state if the color-magnetic potential plays a leading role of the quark-quark and quark-antiquark interactions.

Condition for gapless color-antitriplet excitations in Nambu--Jona-Lasinio models

We present an exact condition for the existence of gapless quasiparticle excitations in Nambu-Jona-Lasinio models of color superconducting quark matter with a quark-quark interaction in the scalar ...

Bound state effects in transverse momentum parton distributions

We derive a nonperturbative transverse momentum distribution for partons using a potential model to describe the quark-quark interaction inside the proton. We use this distribution in the calculation of the differential cross section of ${\ensuremath{\pi}}^{0}$ production for intermediate transverse momentum values in $p\ensuremath{-}p$ collisions at high energies. Assuming a variable string tension constant for the quark-quark potential we obtain a very good description of the experimental data at different energies. The corresponding values of the mean transverse momentum of the partons are essentially lower than those obtained using a Gaussian transverse momentum parton distribution. Using the same approach we can also describe the proton production data in the Chicago-Princeton experiment. Our analysis indicates that bound state effects may be important for the description of the experimental data in proton-proton collisions.

TOWARDS THE UNDERSTANDING OF THE MESON SPECTRA

We present a quark-quark interaction for the complete study of the meson spectra, from the light to the heavy sector. We compare the quark model predictions against well-established [Formula: see text] experimental data. This allows to identify discrepancies between quark model results and experiment that may signal physics beyond conventional hadron spectroscopy.

VECTOR AND AXIAL-VECTOR CORRELATORS IN AN INSTANTON-LIKE QUARK MODEL

The behavior of the vector Adler function at spacelike momenta is studied in the framework of a covariant chiral quark model with instanton-like quark-quark interaction. This function describes the transition between the high energy asymptotically free region of almost massless current quarks to the low energy hadronized regime with massive constituent quarks. The model reproduces the Adler function and V-A correlator extracted from the ALEPH and OPAL data on hadronic τ lepton decays, transformed into the Euclidean domain via dispersion relations. The leading order contribution from hadronic part of the photon vacuum polarization to the anomalous magnetic moment of the muon, [Formula: see text], is estimated.