scholarly journals Quark propagator, instantons, and gluon propagator

1999 ◽  
Vol 60 (6) ◽  
Author(s):  
L. S. Kisslinger ◽  
M. Aw ◽  
A. Harey ◽  
O. Linsuain
Keyword(s):  
Gluon Propagator ◽  
Quark Propagator

NONPERTURBATIVE APPROACHES TO DETERMINING THE BEHAVIOR OF THE GLUON PROPAGATOR AND QUARK PROPAGATOR IN QUANTUM CHROMODYNAMICS BY SCHWINGER-DYSON EQUATIONS

1991 ◽  
Vol 06 (19) ◽  
pp. 3321-3345 ◽  
Author(s):  
A. HÄDICKE
Keyword(s):  
Quantum Chromodynamics ◽  
Gluon Propagator ◽  
Background Field ◽  
Mass Function ◽  
Field Method ◽  
Quark Propagator ◽  
Infrared Singularity ◽  
Dynamical Mass ◽  
Covariant Gauge ◽  
Background Field Method

The attempts to describe the behavior of the gluon propagator and quark propagator by using truncated Schwinger-Dyson equations and Slavnov-Taylor identities are reviewed. Special attention is paid to the problem of infrared behavior of Green’s functions. The most important attempts to calculate the gluon propagator using the axial as well as the covariant gauge are critically discussed. Furthermore, an approach concerning the gluon propagator is presented, with the background-field method as its basis. All the calculations confirm more or less the existence of an infrared singularity in the gluon propagator of the form q−4 in momentum space. The calculations to determine the behavior of the dynamical mass function of quarks, where the results concerning the gluon propagator are taken into account, show that chiral symmetry is dynamically broken. Furthermore, it turns out that there is no polelike singularity in the quark propagator. These results agree with the expectations from the confinement philosophy.

NONPERTURBATIVE QUARK PROPAGATOR APPROACH TO QCD AT LARGE DISTANCES

1994 ◽  
Vol 09 (05) ◽  
pp. 759-793 ◽  
Author(s):  
V. SH. GOGOHIA
Keyword(s):  
Gluon Propagator ◽  
Chiral Limit ◽  
Renormalization Constant ◽  
Quark Propagator ◽  
Quark Confinement ◽  
Quark Sector ◽  
Symmetry Breakdown ◽  
Gauge Fixing ◽  
Covariant Gauge ◽  
Multiplicative Renormalizability

A nonperturbative approach to QCD at large distances in the context of the Schwinger-Dyson equations and corresponding Slavnov-Taylor identity in the quark sector is presented. Making only one widely accepted assumption that the full gluon propagator becomes an infrared singular like (q2)−2 in the arbitrary covariant gauge, we find three and only three confinement-type solutions for the quark propagator (quark confinement theorem). Two of them vanish after the removal of the infrared regulation parameter. The third solution does not depend on this latter parameter, but it has no pole and it implies dynamical chiral symmetry breakdown (DCSB), which means a close connection between quark confinement and DCSB. We also show that multiplication solely by the quark infrared renormalization constant would make all the Green’s functions infrared finite (multiplicative renormalizability). The final forms of the renormalized (infrared finite) quark SD equations do not explicitly depend on a gauge-fixing parameter (“gauge invariance”). Our approach is free of ghost complications despite the fact that they play an essential role in nonperturbative dynamics. Our approach also implies the existence of a characteristic scale at which confinement, DCSB and other nonperturbative effects become essential. We solve explicitly the SD equation with corresponding ST identity for the above-mentioned IR finite quark propagator in the chiral limit and apply an effective potential in order to determine completely this solution.

scholarly journals WHAT THE INFRARED BEHAVIOR OF QCD VERTEX FUNCTIONS IN LANDAU GAUGE CAN TELL US ABOUT CONFINEMENT

2007 ◽  
Vol 16 (09) ◽  
pp. 2720-2732 ◽  
Author(s):  
R. ALKOFER ◽  
C. S. FISCHER ◽  
F. J. LLANES-ESTRADA ◽  
K. SCHWENZER
Keyword(s):  
Renormalization Group ◽  
Chiral Symmetry ◽  
Gluon Propagator ◽  
Landau Gauge ◽  
Quark Propagator ◽  
Lattice Data ◽  
Gluon Vertex ◽  
Infrared Behavior ◽  
Renormalization Group Equations ◽  
Infrared Singularities

The infrared behavior of Landau gauge QCD vertex functions is investigated employing a skeleton expansion of the Dyson–Schwinger and Renormalization Group equations. Results for the ghost-gluon, three-gluon, four-gluon and quark-gluon vertex functions are presented. Positivity violation of the gluon propagator, and thus gluon confinement, is demonstrated. Results of the Dyson–Schwinger equations for a finite volume are compared to corresponding lattice data. It is analytically demonstrated that a linear rising potential between heavy quarks can be generated by infrared singularities in the dressed quark-gluon vertex. The selfconsistent mechanism that generates these singularities necessarily entails the scalar Dirac amplitudes of the full vertex and the quark propagator. These can only be present when chiral symmetry is broken, either explicitly or dynamically.

scholarly journals Contribution of the Darwin operator to non-leptonic decays of heavy quarks

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Alexander Lenz ◽  
Maria Laura Piscopo ◽  
Aleksey V. Rusov
Keyword(s):  
Standard Technique ◽  
Quark Propagator ◽  
Leptonic Decay ◽  
Leptonic Decays ◽  
Interference Contribution ◽  
The Standard Model ◽  
Strength Tensor ◽  
Quark Flavour ◽  
Quark Decay ◽  
B Quark

Abstract We compute the Darwin operator contribution ($$ 1/{m}_b^3 $$ 1 / m b 3 correction) to the width of the inclusive non-leptonic decay of a B meson (B+, Bd or Bs), stemming from the quark flavour-changing transition b → $$ {q}_1{\overline{q}}_2{q}_3 $$ q 1 q ¯ 2 q 3 , where q1, q2 = u, c and q3 = d, s. The key ideas of the computation are the local expansion of the quark propagator in the external gluon field including terms with a covariant derivative of the gluon field strength tensor and the standard technique of the Heavy Quark Expansion (HQE). We confirm the previously known expressions of the $$ 1/{m}_b^3 $$ 1 / m b 3 contributions to the semi-leptonic decay b → $$ {q}_1\mathrm{\ell}{\overline{\nu}}_{\mathrm{\ell}} $$ q 1 ℓ ν ¯ ℓ , with ℓ = e, μ, τ and of the $$ 1/{m}_b^2 $$ 1 / m b 2 contributions to the non-leptonic modes. We find that this new term can give a sizeable correction of about −4 % to the non-leptonic decay width of a B meson. For Bd and Bs mesons this turns out to be the dominant correction to the free b-quark decay, while for the B+ meson the Darwin term gives the second most important correction — roughly 1/2 to 1/3 of the phase space enhanced Pauli interference contribution. Due to the tiny experimental uncertainties in lifetime measurements the incorporation of the Darwin term contribution is crucial for precision tests of the Standard Model.

scholarly journals THE QUARK CONDENSATE IN THE GELL-MANN-OAKES-RENNER RELATION

1996 ◽  
Vol 11 (16) ◽  
pp. 1331-1337 ◽  
Author(s):  
K. LANGFELD ◽  
C. KETTNER
Keyword(s):  
Quark Propagator ◽  
Quark Condensate ◽  
Usual Definition ◽  
Gluon Exchange ◽  
Current Mass ◽  
Definition Of

The quark condensate which enters the Gell-Mann-Oakes-Renner (GMOR) relation, is investigated in the framework of one-gluon-exchange models. The usual definition of the quark condensate via the trace of the quark propagator produces a logarithmic divergent condensate. In the product of current mass and condensate, this divergence is precisely compensated by the bare current mass. The finite value of the product in fact does not contradict the relation recently obtained by Cahill and Gunner. Therefore the GMOR relation is still satisfied.

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