scholarly journals A window on infrared QCD with small expansion parameters

2021 ◽  
Author(s):  
Marcela Peláez ◽  
Urko Reinosa ◽  
Julien Serreau ◽  
Matthieu Tissier ◽  
Nicolas Wschebor
Keyword(s):  
Correlation Functions ◽  
Chemical Potential ◽  
Landau Gauge ◽  
Spontaneous Breaking ◽  
Tree Level ◽  
Coupling Constant ◽  
Long Distance ◽  
Gauge Sector ◽  
Small Parameters ◽  
Distance Properties

Abstract Lattice simulations of the QCD correlation functions in the Landau gauge have established two remarkable facts. First, the coupling constant in the gauge sector — defined, e.g., in the Taylor scheme— remains finite and moderate at all scales, suggesting that some kind of perturbative description should be valid down to infrared momenta. Second, the gluon propagator reaches a finite nonzero value at vanishing momentum, corresponding to a gluon screening mass. We review recent studies which aim at describing the long-distance properties of Landau gauge QCD by means of the perturbative Curci-Ferrari model. The latter is the simplest deformation of the Faddeev-Popov Lagrangian in the Landau gauge that includes a gluon screening mass at tree-level. There are, by now, strong evidences that this approach successfully describes many aspects of the infrared QCD dynamics. In particular, several correlation functions were computed at one- and two-loop orders and compared with ab-initio lattice simulations. The typical error is of the order of ten percent for a one-loop calculation and drops to few percents at two loops. We review such calculations in the quenched approximation as well as in the presence of dynamical quarks. In the latter case, the spontaneous breaking of the chiral symmetry requires to go beyond a coupling expansion but can still be described in a controlled approximation scheme in terms of small parameters. We also review applications of the approach to nonzero temperature and chemical potential.

scholarly journals Gauge-fixed Lattice QCD and the dispersion relation of Wilson fermions

2022 ◽  
Vol 258 ◽  
pp. 02003
Author(s):  
Giuseppe Burgio ◽  
Hannes Vogt
Keyword(s):  
Dispersion Relation ◽  
Lattice Qcd ◽  
Correlation Functions ◽  
Landau Gauge ◽  
Coulomb Gauge ◽  
Tree Level ◽  
Wilson Fermions

We show that, when investigating Wilson-fermions correlation functions on the lattice, one is bound to encounter major difficulties in defining their dispersion relation, even at tree level. The problem is indeed quite general and, although we stumbled upon it while studying Coulomb-gauge applications, it also affects gauge fixed studies in covariant gauges, including their most popular version, Landau gauge. In this paper we will discuss a solution to this problems based on a redefinition of the kinematic momentum of the fermion.

scholarly journals Gluon and ghost correlation functions of 2-color QCD at finite density

2018 ◽  
Vol 175 ◽  
pp. 07012 ◽  
Author(s):  
Ouraman Hajizadeh ◽  
Tamer Boz ◽  
Axel Maas ◽  
Jon-Ivar Skullerud
Keyword(s):  
Phase Transition ◽  
Gauge Theory ◽  
Correlation Functions ◽  
Gauge Coupling ◽  
Landau Gauge ◽  
Abelian Gauge ◽  
Finite Density ◽  
Abelian Gauge Theory ◽  
Gauge Sector ◽  
Sign Problem

2-color QCD, i. e. QCD with the gauge group SU(2), is the simplest non-Abelian gauge theory without sign problem at finite quark density. Therefore its study on the lattice is a benchmark for other non-perturbative approaches at finite density. To provide such benchmarks we determine the minimal-Landau-gauge 2-point and 3-gluon correlation functions of the gauge sector and the running gauge coupling at finite density. We observe no significant effects, except for some low-momentum screening of the gluons at and above the supposed high-density phase transition.

scholarly journals The scalar chemical potential in cosmological collider physics

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Arushi Bodas ◽  
Soubhik Kumar ◽  
Raman Sundrum
Keyword(s):  
Particle Production ◽  
Chemical Potential ◽  
Direct Detection ◽  
Heavy Particle ◽  
Scalar Particle ◽  
Energy Scale ◽  
Fine Tuning ◽  
Tree Level ◽  
Heavy Particles ◽  
Non Gaussian

Abstract Non-analyticity in co-moving momenta within the non-Gaussian bispectrum is a distinctive sign of on-shell particle production during inflation, presenting a unique opportunity for the “direct detection” of particles with masses as large as the inflationary Hubble scale (H). However, the strength of such non-analyticity ordinarily drops exponentially by a Boltzmann-like factor as masses exceed H. In this paper, we study an exception provided by a dimension-5 derivative coupling of the inflaton to heavy-particle currents, applying it specifically to the case of two real scalars. The operator has a “chemical potential” form, which harnesses the large kinetic energy scale of the inflaton, $$ {\overset{\cdot }{\phi}}_0^{1/2}\approx 60H $$ ϕ ⋅ 0 1 / 2 ≈ 60 H , to act as an efficient source of scalar particle production. Derivative couplings of inflaton ensure radiative stability of the slow-roll potential, which in turn maintains (approximate) scale-invariance of the inflationary correlations. We show that a signal not suffering Boltzmann suppression can be obtained in the bispectrum with strength fNL ∼ $$ \mathcal{O} $$ O (0.01–10) for an extended range of scalar masses $$ \lesssim {\overset{\cdot }{\phi}}_0^{1/2} $$ ≲ ϕ ⋅ 0 1 / 2 , potentially as high as 1015 GeV, within the sensitivity of upcoming LSS and more futuristic 21-cm experiments. The mechanism does not invoke any particular fine-tuning of parameters or breakdown of perturbation-theoretic control. The leading contribution appears at tree-level, which makes the calculation analytically tractable and removes the loop-suppression as compared to earlier chemical potential studies of non-zero spins. The steady particle production allows us to infer the effective mass of the heavy particles and the chemical potential from the variation in bispectrum oscillations as a function of co-moving momenta. Our analysis sets the stage for generalization to heavy bosons with non-zero spin.

scholarly journals Aspects of quantum information in finite density field theory

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Lucas Daguerre ◽  
Raimel Medina ◽  
Mario Solís ◽  
Gonzalo Torroba
Keyword(s):  
Field Theory ◽  
Quantum Information ◽  
Mutual Information ◽  
Fermi Surface ◽  
Relative Entropy ◽  
Chemical Potential ◽  
Operator Product ◽  
Dirac Fermions ◽  
Long Distance ◽  
Finite Density

Abstract We study different aspects of quantum field theory at finite density using methods from quantum information theory. For simplicity we focus on massive Dirac fermions with nonzero chemical potential, and work in 1 + 1 space-time dimensions. Using the entanglement entropy on an interval, we construct an entropic c-function that is finite. Unlike what happens in Lorentz-invariant theories, this c-function exhibits a strong violation of monotonicity; it also encodes the creation of long-range entanglement from the Fermi surface. Motivated by previous works on lattice models, we next calculate numerically the Renyi entropies and find Friedel-type oscillations; these are understood in terms of a defect operator product expansion. Furthermore, we consider the mutual information as a measure of correlation functions between different regions. Using a long-distance expansion previously developed by Cardy, we argue that the mutual information detects Fermi surface correlations already at leading order in the expansion. We also analyze the relative entropy and its Renyi generalizations in order to distinguish states with different charge and/or mass. In particular, we show that states in different superselection sectors give rise to a super-extensive behavior in the relative entropy. Finally, we discuss possible extensions to interacting theories, and argue for the relevance of some of these measures for probing non-Fermi liquids.

SCALE DEPENDENCE OF TWIST-3 CORRELATION FUNCTIONS

2011 ◽  
Vol 04 ◽  
pp. 146-156
Author(s):  
Zhong-Bo Kang ◽  
Jian-Wei Qiu
Keyword(s):  
Correlation Functions ◽  
Evolution Equations ◽  
Scale Dependence ◽  
Leading Order ◽  
Coupling Constant ◽  
Parton Distributions ◽  
Spin Asymmetries ◽  
Single Spin ◽  
Single Spin Asymmetries ◽  
Similarities And Differences

In this talk, we introduce two sets of twist-3 quark-gluon correlation functions that are relevant to transverse single spin asymmetries, and present corresponding evolution equations at the leading order in strong coupling constant, αs. The similarities and differences between the evolution of the leading power parton distributions and that of the twist-3 multiparton correlation functions are also discussed.

scholarly journals Two-flavor chiral perturbation theory at nonzero isospin: pion condensation at zero temperature

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Prabal Adhikari ◽  
Jens O. Andersen ◽  
Patrick Kneschke
Keyword(s):  
Perturbation Theory ◽  
Equation Of State ◽  
Condensed Phase ◽  
Chiral Perturbation Theory ◽  
Chemical Potential ◽  
Tree Level ◽  
Zero Temperature ◽  
Leading Order ◽  
Chiral Perturbation ◽  
Pion Condensation

Abstract In this paper, we calculate the equation of state of two-flavor finite isospin chiral perturbation theory at next-to-leading order in the pion-condensed phase at zero temperature. We show that the transition from the vacuum phase to a Bose-condensed phase is of second order. While the tree-level result has been known for some time, surprisingly quantum effects have not yet been incorporated into the equation of state.  We find that the corrections to the quantities we compute, namely the isospin density, pressure, and equation of state, increase with increasing isospin chemical potential. We compare our results to recent lattice simulations of 2 + 1 flavor QCD with physical quark masses. The agreement with the lattice results is generally good and improves somewhat as we go from leading order to next-to-leading order in $$\chi $$χPT.

Sign in / Sign up

Export Citation Format

Share Document