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Register a new userOn the Quark-Quark Superconducting Pairing Induced by Instantons in QCD
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The superconducting pairing of quarks induced by instantons in QCD is studied by means of the functional integral method. The integral equation determining the critical temperature of the superconducting phase transition is established. It is shown that the Bose condensate of diquarks consists of color antitriplet $(bar{3}) $ scalar diquarks
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By means of the functional integral method we show that in the case of the quark-antiquark pairing at zero temperature and zero chemical potential (in the vacuum) the singlet pairing is more preferable than that with the color-flavor locking (CFL)
We use over-improved stout-link smearing to investigate the presence and nature of instantons on the lattice. We find that smearing can remove short-range effects with little damage to the long-range structure of the gauge field, and that after around 50 sweeps this process is complete. There are more significant risks for very high levels of smearing beyond 100 sweeps. We are thus able to produce gauge configurations dominated by instanton effects. We then calculate the overlap quark propagator on these configurations, and thus the non-perturbative mass function. We find that smeared configurations reproduce the majority of dynamical mass generation, and conclude that instantons are primarily responsible for the dynamical generation of mass.
In response to the growing need for theoretical tools that can be used in QCD to describe and understand the dynamics of gluons in hadrons in the Minkowski space-time, the renormalization group procedure for effective particles (RGPEP) is shown in the simplest available context of heavy quarkonia to exhibit a welcome degree of universality in the first approximation it yields once one assumes that beyond perturbation theory gluons obtain effective mass. Namely, in the second-order terms, the Coulomb potential with Breit-Fermi spin couplings in the effective quark-antiquark component of a heavy quarkonium, is corrected in one-flavor QCD by a spin-independent harmonic oscillator term that does not depend on the assumed effective gluon mass or the choice of the RGPEP generator. The new generator we use here is much simpler than the ones used before and has the advantage of being suitable for studies of the effective gluon dynamics at higher orders than the second and beyond the perturbative expansion.
We perform the first studies of various inter-quark potentials in SU(3)$_{rm c}$ lattice QCD. From the accurate lattice calculation for more than 300 different patterns of three-quark (3Q) systems, we find that the static 3Q potential $V_{rm 3Q}$ is well described by Y-Ansatz, i.e., the Coulomb plus Y-type linear potential. Quark confinement mechanism in baryons is also investigated in maximally-Abelian projected QCD. We next study the multi-quark potentials $V_{n{rm Q}}$ ($n$=4,5) in SU(3)$_{rm c}$ lattice QCD, and find that they are well described by the one-gluon-exchange Coulomb plus multi-Y type linear potential, which supports the flux-tube picture even for the multi-quarks. Finally, we study the heavy-heavy-light quark (QQq) potential both in lattice QCD and in a lattice-QCD-based quark model.
We consider electroweak corrections to the relation between the running $overline{mathrm{MS}}$ mass $m_b$ of the $b$ quark in the five-flavor QCD$times$QED effective theory and its counterpart in the Standard Model (SM). As a bridge between the two parameters, we use the pole mass $M_b$ of the $b$ quark, which can be calculated in both models. The running mass is not a fundamental parameter of the SM Lagrangian, but the product of the running Yukawa coupling $y_b$ and the Higgs vacuum expectation value. Since there exist different prescriptions to define the latter, the relations considered in the paper involve a certain amount of freedom. All the definitions can be related to each other in perturbation theory. Nevertheless, we argue in favor of a certain gauge-independent prescription and provide a relation which can be directly used to deduce the value of the Yukawa coupling of the $b$ quark at the electroweak scale from its effective QCD running mass. This approach allows one to resum large logarithms $ln(m_b/M_t)$ systematically. Numerical analysis shows that, indeed, the corrections to the proposed relation are much smaller than those between $y_b$ and $M_b$.
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