151 research outputs found
Collinearly improved JIMWLK evolution in Langevin form
The high-energy evolution of Wilson line operators, which at leading order is
described by the Balitsky-JIMWLK equations, receives large radiative
corrections enhanced by single and double collinear logarithms at
next-to-leading order and beyond. We propose a method for resumming such
logarithmic corrections to all orders, at the level of the Langevin formulation
of the JIMWLK equation. The ensuing, collinearly-improved Langevin equation
features generalized Wilson line operators, which depend not only upon rapidity
(the logarithm of the longitudinal momentum), but also upon the transverse size
of the color neutral projectile to which the Wilson lines belong. This
additional scale dependence is built up during the evolution, via the condition
that the successive emissions of soft gluons be ordered in time. The presence
of this transverse scale in the Langevin equation furthermore allows for the
resummation of the one-loop running coupling corrections.Comment: 24 pages, 1 figur
Building up the elliptic flow: analytical insights
In this paper, we present a fully analytical description of the early-stage
formation of elliptic flow in relativistic viscous hydrodynamics. We first
construct an elliptic deformation of Gubser flow which is a boost invariant
solution of the Navier-Stokes equation with a nontrivial transverse profile. We
then analytically calculate the momentum anisotropy of the flow as a function
of time and discuss the connection with the empirical formula by Bhalerao {\it
et al.} regarding the viscosity dependence of elliptic flow.Comment: 8 pages;v2. To be published in physics letters
On the small- behavior of the orbital angular momentum distributions in QCD
We present the numerical solution of the leading order QCD evolution equation
for the orbital angular momentum distributions of quarks and gluons and discuss
its implications for the nucleon spin sum rule. We observe that at small-,
the gluon helicity and orbital angular momentum distributions are roughly of
the same magnitude but with opposite signs, indicating a significant
cancellation between them. A similar cancellation occurs also in the quark
sector. We explain analytically the reason for this cancellation.Comment: 12 pages. v2: two figures added, version to appear in Physics Letters
Proton Spin Structure at Small-
We generalize the Bartels-Ermolaev-Ryskin approach for the structure
function at small- to determine the small- asymptotic behavior of the
orbital angular momentum distributions in QCD. We present an exact analytical
solution of the evolution equation in the double logarithmic approximation and
discuss its implications for the proton spin problem.Comment: 6 pages and 3-page appendix; v2:minor correction, references adde
Hemisphere jet mass distribution at finite
We perform the leading logarithmic resummation of nonglobal logarithms for
the single-hemisphere jet mass distribution in annihilation including
the finite- corrections. The result is compared with the previous
all-order result in the large- limit as well as fixed-order perturbative
calculations.Comment: 10 pages, 1 figure. v2: the numerical result revised after removing a
systematic error; v3: added more statistics, new fitting parameters, accepted
for publication in Phys.Lett.
Gluon polarization in the nucleon demystified
Recently, X. Chen et al. proposed a new approach to the gauge invariant
decomposition of the nucleon spin into helicity and orbital parts. The key
ingredient in their construction is the separation of the gauge field into
`physical' and `pure gauge' parts. We suggest a simple separation scheme and
show that the resulting gluon helicity coincides with the first moment of the
conventional polarized gluon distribution measurable in high energy
experiments.Comment: 6 page
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