Search results for "Gluon"
showing 10 items of 697 documents
Estimating the thermal photon production rate using lattice QCD
2021
We present results for the photon emission rate determined from the transverse channel vector correlator at fixed spatial momentum using two flavors of dynamical Wilson fermions at $T\sim$250 MeV. We estimate the transverse channel spectral function using the continuum extrapolated correlator by applying various fit ans\"atze with a smooth matching to the NLO perturbative result. We confront our estimate based on this channel with the latest results of our collaboration based on the difference of the transverse and longitudinal channels.
Numerical evaluation of the nonlinear Gribov-Levin-Ryskin-Mueller-Qiu evolution equations for nuclear parton distribution functions
2023
We numerically study for the first time the nonlinear GLR-MQ evolution equations for nuclear parton distribution function (nPDFs) to next-to-leading order accuracy and quantify the impact of gluon recombination at small $x$. Using the nCTEQ15 nPDFs as input, we confirm the importance of the nonlinear corrections for small $x \lesssim 10^{-3}$, whose magnitude increases with a decrease of $x$ and an increase of the atomic number $A$. We find that at $x=10^{-5}$ and for heavy nuclei, after the upward evolution from $Q_0=2$ GeV to $Q=10$ GeV, the quark singlet $\Omega(x,Q^2)$ and the gluon $G(x,Q^2)$ distributions become reduced by $9-15$%, respectively. The relative effect is much stronger fo…
Evolution of eccentricities induced by geometrical and quantum fluctuations in proton-nucleus collisions
2023
We compute the azimuthal eccentricities arising from initial stage fluctuations in high energy proton-nucleus collisions at proper times $\tau \geq 0^+$. We consider two sources of fluctuations, namely the geometrical structure of the proton and the fluctuation of color fields carried by both proton and nucleus. Describing these effects with Gaussian models allows us to analytically calculate the one- and two-point correlators of energy density, from which the eccentricities are obtained. We compute the proper time evolution of these quantities by approximating the Glasma dynamics in terms of linearized Yang-Mills equations, which we solve by assuming free field propagation and adopting the…
Analytic Form of the Two-Loop Planar Five-Gluon All-Plus-Helicity Amplitude in QCD
2015
Virtual two-loop corrections to scattering amplitudes are a key ingredient to precision physics at collider experiments. We compute the full set of planar master integrals relevant to five-point functions in massless QCD, and use these to derive an analytical expression for the two-loop five-gluon all-plus-helicity amplitude. After subtracting terms that are related to the universal infrared and ultraviolet pole structure, we obtain a remarkably simple and compact finite remainder function, consisting only of dilogarithms.
QCD and Strongly Coupled Gauge Theories: Challenges and Perspectives
2014
We dedicate this document to the memory of Mikhail Polikarpov, who passed away in July 2013. Misha worked with us for decades as a convener of the “Confinement” section of the Quark Confinement and Hadron Spectrum Series. He guided and expanded the scientific discussion of that topic, inspiring and under taking new research avenues. From its initial conception, he supported the enterprise of this document and organized Sect. 8, writing the part on confinement himself. He attracted the XIth Conference on Quark Confinement and the Hadron Spectrum to St. Petersburg (September 8-12, 2014; see http://phys.spbu.ru/confxi.html). His warm and kind personality, his high sense of humor, his ideas in …
Heavy quarkonium: progress, puzzles, and opportunities
2011
A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the $B$-factories and CLEO-c flo…
On the zero crossing of the three-gluon vertex
2016
We report on new results on the infrared behaviour of the three-gluon vertex in quenched Quantum Chormodynamics, obtained from large-volume lattice simulations. The main focus of our study is the appearance of the characteristic infrared feature known as 'zero crossing', the origin of which is intimately connected with the nonperturbative masslessness of the Faddeev-Popov ghost. The appearance of this effect is clearly visible in one of the two kinematic configurations analyzed, and its theoretical origin is discussed in the framework of Schwinger-Dyson equations. The effective coupling in the momentum subtraction scheme that corresponds to the three-gluon vertex is constructed, revealing t…
Confinement, the gluon propagator and the interquark potential for heavy mesons
2012
The interquark static potential for heavy mesons described by a massive one-gluon exchange interaction obtained from the propagator of the truncated Dyson-Schwinger equations does not reproduced the expected Cornell potential. I show that no formulation based on a finite propagator will lead to confinement of quenched QCD. I propose a mechanism based on a singular nonperturbative coupling constant which has the virtue of giving rise to a finite gluon propagator and (almost) linear confinement. The mechanism can be slightly modified to produce the screened potentials of unquenched QCD.
Jet quenching in the strongly-interacting quark–gluon plasma
2009
We propose a hybrid model for medium-induced parton energy loss, in which the hard scales in the process are treated perturbatively, while the soft scales which involve strong coupling dynamics are modeled by AdS/CFT calculations. After fitting a single parameter on R_AA for central Au+Au collisions, we are able to predict different observables like R_AA and I_AA as a function of centrality and reaction plane. We obtain a consistent picture of how jet quenching is modified if the quark-gluon plasma is strongly interacting, and we provide quantitative predictions.
Infrared facets of the three-gluon vertex
2021
We present novel lattice results for the form factors of the quenched three-gluon vertex of QCD, in two special kinematic configurations that depend on a single momentum scale. We consider three form factors, two associated with a classical tensor structure and one without tree-level counterpart, exhibiting markedly different infrared behaviors. Specifically, while the former display the typical suppression driven by a negative logarithmic singularity at the origin, the latter saturates at a small negative constant. These exceptional features are analyzed within the Schwinger-Dyson framework, with the aid of special relations obtained from the Slavnov-Taylor identities of the theory. The em…