arXiv subjects

Kai Schwenzer

Publications and source records attributed to Kai Schwenzer.

44 records · Page 3Linked to original sources

arXiv2007

Nonperturbative quark-gluon dynamics

We summarize recent results on the nonperturbative quark-gluon interaction in Landau gauge QCD. Our analytical analysis of the infrared behaviour of the quark-gluon vertex reveals infrared singularities, which lead to an infrared divergent running coupling and a linear rising quark-antiquark potential when chiral symmetry is broken. In the chirally symmetric case we find an infrared fixed point of the coupling and, correspondingly, a Coulomb potential. These findings provide a new link betwen dynamical chiral symmetry breaking and confinement.

hep-ph↗

arXiv2007

Dynamically induced scalar quark confinement: A link between chiral symmetry breaking and confinement

Employing functional approaches the infrared behaviour of Landau gauge QCD vertex functions is investigated. Results for the ghost-gluon, three-gluon and quark-gluon vertex functions are presented. As can be analytically shown a linear rising potential between heavy quarks is generated by infrared singularities in the dressed quark-gluon vertex. The selfconsistent mechanism that generates these singularities implies the existence of scalar Dirac amplitudes of the full vertex and the quark propagator. These amplitudes can only be present when chiral symmetry is broken, either explicitly or dynamically. The corresponding relations thus constitute a novel mechanism that directly links chiral symmetry breaking with confinement.

hep-ph↗

arXiv2007

Lower dimensional Yang-Mills theory as a laboratory to study the infrared regime

Lattice studies of the infrared regime of gauge theories are complicated by the required extensive limits, the performed gauge fixing and the demand for high statistics. Using a general power counting scheme for the infrared limit of Landau gauge SU(N) Yang-Mills theory in arbitrary dimensions we show that the infrared behavior of Greens functions is both qualitatively and quantitatively similar in two, three and four spacetime dimensions. Therefore, lower dimensional lattice simulations can serve as a simplified laboratory to analyze the presently applied approximations and to obtain first results for higher correlation functions.

hep-ph↗

arXiv2006

Low Energy Dynamics in Ultradegenerate QCD Matter

We study the low energy behavior of QCD Green functions in the limit that the baryon chemical potential is much larger than the QCD scale parameter $Λ_QCD$. We show that there is a systematic low energy expansion in powers of $(ω/m)^{1/3}$, where $ω$ is the energy and $m$ is the screening scale. This expansion is valid even if the effective quark-gluon coupling $g$ is not small. The expansion is purely perturbative in the magnetic regime $|\vec{k}| \gg k_0$. If the external momenta and energies satisfy $k_0 \sim |\vec{k}|$, planar, abelian ladder diagrams involving the full quark propagator have to be resummed but the corresponding Dyson-Schwinger equations are closed.

hep-ph↗

arXiv2005

Neutrino Emission from Ungapped Quark Matter

We study neutrino emission from a normal, ungapped, quark phase in the core of a compact star. Neutrino emission from non-interacting quark matter leads to an emissivity that scales as $ε\sim T^7$. We show that the emissivity is enhanced by a combination of Fermi liquid and non-Fermi liquid effects. Fermi liquid effects lead to an emissivity that scales as $ε\sim α_s T^6$, as originally shown by Iwamoto. We demonstrate that non-Fermi liquid effects further enhance the rate, leading to $ε\sim α_s^3 T^6\log(m/T)^2$, where $m$ is the electric screening scale and $m\gg T$ under the conditions found in compact stars. We show, however, that combined with non-Fermi liquid effects in the specific heat the enhancement in the emissivity only leads to a modest reduction in the temperature of the star at late times. Our results confirm existing bounds on the presence of ungapped quark matter in compact stars. We also discuss neutrino emission from superconducting phases with ungapped fermionic excitations.

astro-ph↗

arXiv2004

Non-Fermi Liquid Effects in QCD at High Density

We study non-Fermi liquid effects due to the exchange of unscreened magnetic gluons in high density QCD by using an effective field theory. A one-loop calculation gives the well known result that magnetic gluons lead to a logarithmic enhancement in the fermion self energy near the Fermi surface. The self energy is of the form $Σ(ω)\sim ωγ\log(ω)$, where $ω$ is the energy of the fermion, $γ=O(g^2)$, and $g$ is the coupling constant. Using an analysis of the Dyson-Schwinger equations we show that, in the weak coupling limit, this result is not modified by higher order corrections even in the regime where the logarithm is large, $γ\log(ω)\sim 1$. We also show that this result is consistent with the renormalization group equation in the high density effective field theory.

hep-ph↗

arXiv2004

Linking the Quark Meson Model with QCD at High Temperature

We model the transition of a system of quarks and gluons at high energies to a system of quarks and mesons at low energies in a consistent renormalization group approach. Flow equations interpolate between the physics of the high-temperature degrees of freedom and the low-temperature dynamics at a scale of 1 GeV. We also discuss the dependence of the equation of state on baryon density and compare our results with recent lattice gauge simulations.

hep-ph↗

arXiv2003

Resolution-dependent quark masses from meson correlators

We explore the impact of a resolution-dependent constituent quark mass, as recently applied to diffractive meson production, in QCD correlation functions of several spin-0 and spin-1 meson channels. We compare the resulting correlators with experimental and lattice data, analyze the virtues and limitations of the approach, and discuss the channel dependence of the obtained effective quark masses.

hep-ph↗