Spatial Wilson loops in the classical field of high-energy heavy-ion collisions

It has been previously shown numerically that the expectation value of the magnetic Wilson loop at the initial time of a heavy-ion collision exhibits area law scaling. This was obtained for a classical non-Abelian gauge field in the forward light cone and for loops of area $A\gtrsim 2/Q_s^2$. Here, we present an analytic calculation of the spatial Wilson loop in the classical field of a collision within perturbation theory. It corresponds to a diagram with two sources, for both projectile and target, whose field is evaluated at second order in the gauge potential. The leading non-trivial contribution to the magnetic loop in perturbation theory is proportional to the square of its area.Comment: 4 pages, 4 figures. v2: minor revisions, new version to appear in PR

KNO scaling from a nearly Gaussian action for small-x gluons

Transverse momentum integrated multiplicities in the central region of pp collisions at LHC energies satisfy Koba-Nielsen-Olesen scaling. We attempt to relate this finding to multiplicity distributions of soft gluons. KNO scaling emerges if the effective theory describing color charge fluctuations at a scale on the order of the saturation momentum is approximately Gaussian. From an evolution equation for quantum corrections which includes both saturation as well as fluctuations we find that evolution with the QCD \beta-function satisfies KNO scaling while fixed-coupling evolution does not. Thus, non-linear saturation effects and running-coupling evolution are both required in order to reproduce geometric scaling of the DIS cross section and KNO scaling of virtual dipoles in a hadron wave function.Comment: Notes based on various presentations delivered by the authors in spring/summer 201

Magnetic flux loop in high-energy heavy-ion collisions

We consider the expectation value of a magnetic flux loop in the immediate forward light cone of collisions of heavy nuclei at high energies. Such collisions are characterized by a non-linear scale Q_s where color fields become strong. We find that loops of area greater than ~2/Q_s^2 exhibit area law behavior, which determines the scale of elementary flux excitations ("vortices"). We also estimate the magnetic string tension, sigma_M = 0.12 Q_s^2. By the time t ~ 1/Q_s even small loops satisfy an area law. We describe corrections to the propagator of semi-hard gluons at very early times in the background of fluctuating magnetic fields.Comment: 4 pages, 5 figures; v2: added plot of Z(N) part of loop in fig.1; v3: added magnetic loop for asymmetric projectile/target saturation momenta, estimate of vortex density, and an appendix; v4: corrected outline of perturbative calculation of Wilson loop; to appear in PR

IRBIT a Master Regulator of Cell Physiology

(excerpt) Hormones and neurotransmitters regulate cell functions by binding to their receptors, which activate intracellular signaling and produce the physiological response [1]. There are several intracellular pathways, including but not limited to, leading to the activation of protein kinases, phosphatases and increase in intracellular calcium (Ca2+) [1]

Two-gluon correlations and initial conditions for small-x evolution

We derive the effective action of the hard large-x valence charges up to fourth order in their density. Such non-Gaussian weight functionals contribute at leading order in N_c to the connected two-gluon production diagrams which determine di-hadron correlations. The corresponding diagrams are not necessarily (highly) suppressed by the density of valence charges since their infrared divergences differ from those obtained in a Gaussian theory. Therefore, it appears prudent to include such higher dimensional operators when determining initial ensembles for JIMWLK evolution of higher n-point functions of Wilson lines.Comment: 12 pages; v2: fixed layou

Medium-induced gluon radiation in hard forward parton scattering in the saturation formalism

We derive the medium-induced, coherent gluon radiation spectrum associated with the hard forward scattering of an energetic parton off a nucleus, in the saturation formalism and within the Gaussian approximation for the relevant correlators of Wilson lines. The calculation reproduces the simple expression for the spectrum previously obtained in the opacity expansion formalism, and rigorously specifies its validity range. The connection between the calculations in the opacity expansion and saturation formalisms is made apparent. This study may serve as a first step in order to implement consistently induced coherent energy loss and gluon shadowing in `saturation-based models' of hadron nuclear suppression in proton-nucleus collisions.Comment: 25 pages, 2 figure

TMD gluon distributions at small x in the CGC theory

We review recent progress in the description of unpolarized transverse-momentum-dependent (TMD) gluon distributions at small $x$ in the color glass condensate (CGC) effective theory. We discuss the origin of the non-universality of TMD gluon distributions in the TMD factorization framework and in the CGC theory and the equivalence of the two approaches in their overlapping domain of validity. We show some applications of this equivalence, including recent results on the behavior of TMD gluon distributions at small $x$, and on the study of gluon saturation. We discuss recent advances in the unification of the TMD evolution and the non-linear small-$x$ evolution of gluon distributions.Comment: Invited review article for the International Journal of Modern Physics E (Nuclear Physics). Version accepted for publication. 28 pages, 9 figure

Initial conditions in high-energy collisions

This thesis is focused on the initial stages of high-energy collisions in the saturation regime. We start by extending the McLerran-Venugopalan distribution of color sources in the initial wave-function of nuclei in heavy-ion collisions. We derive a fourth-order operator in the action and discuss its relevance for the description of color charge distributions in protons in high-energy experiments. We calculate the dipole scattering amplitude in proton-proton collisions with the quartic action and find an agreement with experimental data. We also obtain a modification to the fluctuation parameter of the negative binomial distribution of particle multiplicities in proton-proton experiments. The result implies an advancement of the fourth-order action towards Gaussian when the energy is increased. Finally, we calculate perturbatively the expectation value of the magnetic Wilson loop operator in the first moments of heavy-ion collisions. For the magnetic flux we obtain a first non-trivial term that is proportional to the square of the area of the loop. The result is close to numerical calculations for small area loops