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Michael Lublinsky

Publications and source records attributed to Michael Lublinsky.

At least 19 recordsLinked to original sources
arXiv2026

Running coupling effects in the anti-collinear resummation in high energy evolution

We study the effects of the running of the QCD coupling on the anti-collinear resummation in JIMWLK evolution in the linear (BFKL) regime. We determine the appropriate scale choice for the coupling entering the JIMWLK kernel, and derive the anti-collinearly resummed BFKL kernel, which includes running-coupling effects both in the resummation equation (i.e. DGLAP) and in the JIMWLK kernel proper. We find that the running of the coupling generally further slows down BFKL evolution, as expected. Surprisingly however the value of the generalized characteristic function at $\gamma=1$ is unaffected by the running coupling owing to subtle cancellations. We develop an approximation that allows us to use the generalized characteristic function to study the BFKL Green's function. Within this approximation we find that the Pomeron intercept in the anti-collinear regime is significantly reduced by both, the resummation and the running of the coupling.

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arXiv2026

Chiral Plasma under Strong Magnetic Fields: A Holographic Analysis of Transport Phenomena

Chiral plasma appears in several areas of physics, historically starting from primordial plasma in the early Universe, then in quark-gluon plasma produced in heavy ion collisions, and, more recently, in Dirac and Weyl semimetals. The major signature of the plasma is the non-conservation of the axial current due to the chiral anomaly and the emergence of new, anomaly-induced transport phenomena. In this paper, we study the plasma exposed to arbitrarily strong constant magnetic and weak electric fields. Employing all-order gradient resummation, we write down constitutive relations for electric and axial currents parameterized by thirteen momentum- and magnetic- field-dependent transport coefficient functions. The latter are computed utilizing a theoretical lab for a realistic plasma, namely a holographic $U(1)_V \times U(1)_A$ Maxwell--Chern--Simons theory in Schwarzschild--AdS$_5$, in the probe limit. As an application, we revisit the phenomena of negative magnetoresistance and chiral magnetic waves, beyond the naive hydrodynamic limit.

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arXiv2026

Anti-collinear resummation in JIMWLK evolution in the linear regime

The recently-proposed resummation procedure for anti-collinear logarithms in the JIMWLK kernel~\cite{Kovner:2023vsy} is studied in the linear (BFKL) regime in the fixed-coupling approximation. Simple closed form expressions for the resummed momentum space kernel and characteristic function $\chi(n,\gamma)$ are found. We find that the anti-collinear pole in the leading order characteristic function at $\gamma=1$ disappears, and instead $\chi(\gamma=1)=\frac{12}{11}\frac{\pi}{\alpha_sN_c}$ for $n_F=0$. Comparison with the known NLO BFKL eigenvalue, with the target-Bjorken limit ($Q_T\gg Q_P$) of the $\gamma^*(Q_P)+\gamma^*(Q_T)$-scattering amplitude and with the ``all-poles'' resummation prescription are presented.

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arXiv2025

Sakai-Sugimoto Model in an Off-Shell: Chiral Lagrangian to All Orders

The Sakai-Sugimoto holographic model is famous for implementing the approximate chiral symmetry of QCD and reproducing the Chiral Lagrangian in a top-down approach. In this manuscript, we revisit the model in a formalism that is somewhat different from the original work by Sakai and Sugimoto: We start by identifying boundary degrees of freedom and splitting the bulk equations of motion into dynamical ones and constraints. The former are then solved to all orders in derivatives of the boundary fields. The constraints are left unsolved, leaving the dynamical degrees of freedom off-shell. This approach enables us to systematically derive the effective action of the boundary theory. The derived effective action is very rich in physics: it contains an $U(N_f)$ multiplet of massless pseudoscalars interacting (via trilinear and higher terms) with towers of massive (axial-)vector mesons. In contrast to the previous studies, our effective action is non-local. The original Chiral Lagrangian is recovered as its local expansion in small $\pi$-meson momenta (derivative expansion). We particularly zoom in on the values of four derivative terms couplings, the low energy constants, and compare those with the ones reported in the literature.

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arXiv2024

Born-Oppenheimer Renormalization group for High Energy Scattering: the Modified BFKL, or where did it all go?

We continue exploring the Born-Oppenheimer renormalization group generating evolution in frequency of physical observables. In this paper we study the evolution of the total cross section for dilute-dilute scattering retaining only eikonal emissions. We derive and analyze the analog of the BFKL equation in this framework. The frequency evolution has a very strong effect on the solutions of the BO-BFKL equation, slowing down the evolution of the scattering amplitude in a spectacular fashion: the intercept of the Pomeron is decreased by about a factor of three relative to the canonical LO BFKL result. The anomalous dimension is also modified significantly - from the BFKL value of one it goes down to the negative value of $\approx-0.2$. Introducing saturation boundary as a proxy for the full saturation dynamics, we find that the dependence of the saturation momentum on rapidity $\eta$ becomes quite weak with $Q^2_s\sim e^{a\bar\alpha_s\eta}$ with $a\approx 0.784$ as opposed to the BFKL value $a=4.88$. Our results underscore the necessity to take into account the DGLAP effects in the high energy evolution. This is left for future work.

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arXiv2024

Born-Oppenheimer Renormalization group for High Energy Scattering: the Setup and the Wave Function

We develop an approach to QCD evolution based on the sequential Born-Oppenheimer approximations that include higher and higher frequency modes as the evolution parameter is increased. This Born-Oppenheimer renormalization group is a general approach which is valid for the high energy evolution as well as the evolution in transverse resolution scale $Q^2$. In the former case it yields the frequency ordered formulation of high energy evolution, which includes both the eikonal splittings which produce gluons with low longitudinal momentum, and the DGLAP-like splittings which produce partons with high transverse momentum. In this, first paper of the series we lay out the formulation of the approach, and derive the expression for the evolved wave function of a hadronic state. We also discuss the form of the $S$-matrix which is consistent with the frequency ordering.

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arXiv2024

Born-Oppenheimer Renormalization group for High Energy Scattering: CSS, DGLAP and all that

In \cite{one}, we have introduced the Born-Oppenheimer (BO) renormalization group approach to high energy hadronic collisions and derived the BO approximation for the light cone wave function of a fast moving projectile hadron. In this second paper, we utilize this wave function to derive the BO evolution of partonic distributions in the hadron -- the gluon transverse momentum and integrated parton distributions (TMD and PDF respectively). The evolution equation for the TMD contains a linear and a nonlinear term. The linear term reproduces the Collins-Soper-Sterman (CSS) equation with a physical relation between the transverse and longitudinal resolution scales. We explain how this equivalence arises, even though the BO and CSS cascades are somewhat different in structures. The nonlinear term in the evolution has a very appealing physical meaning: it is a correction due to stimulated emission, which enhances emission of gluons (bosons) into states with a nonzero occupation. For the evolution of the PDF we again find a linear and nonlinear term. At not very small Bjorken $x$, the linear term recovers the DGLAP equation in the leading logarithmic approximation. At small $x$ however there are contributions from gluon splittings which are in the BFKL kinematics leading to a modification of the DGLAP equation. The nonlinear terms have the same physical origin as in the equation for the TMD -- the stimulated emission corrections. Interestingly the nonlinear corrections are the most important for the virtual terms, so that the net correction to the DGLAP is negative and mimics shadowing, although the physical origin of the nonlinearity is very different.

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arXiv2024

The CSS Hamiltonian: high energy evolution of rapidity dependent observables

We consider evolution of observables which depend on a small but fixed value of longitudinal momentum fraction $x$, to high rapidity, such that $\eta>\ln 1/x$. We show that this evolution is not given by the JIMWLK (or BK) equation. We derive the evolution Hamiltonian - $H_{CSS-JIMWLK}$ which generates this evolution in the cases of dilute and dense projectile wave function. The two limits yield identical results for $H_{CSS-JIMWLK}$. We show that the resulting evolution for the gluon TMD is identical to the (double logarithmic) perturbative Collins-Soper-Sterman evolution equation in the longitudinal resolution parameter at a fixed and very large transverse resolution.

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arXiv2024

High energy scattering in the Unitary Toy Model

We continue exploring the Unitary Toy Model (UTM) as a playground for high energy collisions in QCD. Our new approach is based on the diagonalization of the evolution Hamiltonian. Part of the spectrum can be identified with intercepts of dressed Pomerons. Analogously to QCD, a multi-Pomeron expansion of the $S$-matrix is badly divergent asymptotic series. Yet we succeeded to establish resummation procedures resulting in a well behaved $S$-matrix. In addition the Hamiltonian possesses negative eigenvalues, which dominate the approach of the $S$-matrix to saturation. We are hopeful that important lessons about BFKL-based Pomeron calculus could be taken from the toy world to real QCD.

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arXiv2024

On running coupling in the JIMWLK evolution and its Langevin formulation

Various conventional running coupling prescriptions reproducing $β_ 0$-dependent terms of NLO JIMWLK are reviewed and found to be theoretically inconsistent: the JIMWLK evolution Hamiltonian with running coupling violates the requirement of positive semidefiniteness. This requirement appears to be tightly related to the possibility of having a Langevin formulation for the evolution. We also review the scheme that attributes a part of $β_0$-dependent terms to the DGLAP evolution of the projectile. The remaining $β_0$-dependent contributions sum up into so-called the ``daughter dipole'' prescription, which leads to a manifestly positive semidefinite Hamiltonian.

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arXiv2023

Not all that is $β_0$ is $β$-function: the DGLAP resummation and the running coupling in NLO JIMWLK

We reanalyze the origin of the large transverse logarithms associated with the QCD one loop beta-function coefficient in the NLO JIMWLK Hamiltonian. We show that some of these terms are not associated with the running of the QCD coupling constant but rather with the DGLAP evolution. The DGLAP-like resummation of these logarithms is mandatory within the JIMWLK Hamiltonian, as long as the color correlation length in the projectile is larger than that in the target. This regime in fact covers the whole range of rapidities at which JIMWLK evolution is supposed to be applicable. We derive the RG equation that resums these logarithms to all orders in alpha_s in the JIMWLK Hamiltonian. This is a nonlinear equation for the eikonal scattering matrix S(x). We solve this equation and perform the DGLAP resummation in two simple cases: the dilute limit, where both the projectile and the target are far from saturation, and the saturated regime, where the target correlation length also determines its saturation momentum.

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arXiv2023

Single inclusive particle production at next-to-leading order in proton-nucleus collisions at forward rapidities: hybrid approach meets TMD factorization

We revisit the calculation of the cross section for forward inclusive single hadron production in $pA$ collisions within the hybrid approach. We show that the proper framework to perform this calculation beyond leading order is not the collinear factorization, as has been assumed so far, but the TMD factorized framework. Within the TMD factorized approach we show that all the large transverse logarithms appearing in the fixed order calculation, are resummed into the evolution of the TMD PDFs and TMD FFs with factorization scale. The resulting expressions, when written in terms of TMDs evolved to the appropriate, physically well understood factorization scale, contain no additional large logarithms. The absence of any large logarithms in the resummed result should ensure positivity of the cross section and eradicate the persistent problem that have plagued the previous attempts at calculating this observable in the hybrid approach.

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arXiv2022

NLO JIMWLK evolution with massive quarks

NLO evolution of the Jalilian-Marian-Iancu-McLerran-Weigert-Leonidov-Kovner (JIMWLK) equation with massless quarks was derived a few years ago. We make a step further to compute the evolution kernels focusing on the effects due to finite quark masses. To this goal, the light-cone wave function of a fast moving dilute hadronic projectile is computed up to ${\cal O}(g^3)$ in QCD coupling constant. Compared with the massless case, a new IR divergence emerges, which is eventually canceled by a mass dependent counter term. Our results extend the theoretical tools used in physics of gluon saturation and aim at improving precision in future phenomenological applications.

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arXiv2021

Correlations between azimuthal asymmetries and multiplicity and mean transverse momentum in small collisions systems in the CGC

Considering a dilute-dense situation suitable for pA collisions, we compute in the Color Glass Condensate the correlation between azimuthal asymmetries, specifically the squared second Fourier coefficient $v_2^2$, and the total multiplicity in the event. We also analyse the correlation between $v_2^2$ and the mean squared transverse momentum of particles in the event. In both cases, we find that the correlations are generally very small, consistent with the observations. We also note an interesting sharp change in the value of $v_2^2$ and its correlations as a function of the width of the transverse momentum bin, related with a change of the dominance of Bose and HBT quantum correlations.

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arXiv2021

Magnetic monopole in a chiral plasma: chiral dyon

The placement of a magnetic monopole into an electrically-neutral chiral plasma with a non-zero axial density results in an electric polarization of the matter. The electric current produced by the chiral magnetic effect is balanced by charge diffusion and Ohmic dissipation, which generates a non-trivial charge distribution. In turn, the latter induces a separation of chiralities along the magnetic field of the monopole due to the chiral separation effect. We find the stationary states of such a system, with vanishing total electric current and stationary axial current balanced by the chiral anomaly. In this solution, the monopole becomes "dressed" with an electric charge that is proportional to the averaged chiral density of the matter -- forming a chiral dyon. The interplay between the chiral effects on the one hand, and presence of magnetic field of the monopole on the other, may affect the evolution of the monopole density in the early Universe, contribute to the process of baryogenesis, and can also be instrumental for detection of relic monopoles using chiral materials.

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arXiv2021

All order effective action for charge diffusion from Schwinger-Keldysh holography

An effective action for diffusion of a conserved $U(1)$ charge is derived to all orders in the derivative expansion within a holographic model dual to the Schwinger-Keldysh closed time path. A systematic approach to solution of the 5D Maxwell equations in a doubled Schwarzschild-AdS$_5$ black brane geometry is developed. Constitutive relation for the stochastic charge current is shown to have a term induced by thermal fluctuations (coloured noise). All transport coefficient functions parameterising the effective action and constitutive relations are computed analytically in the hydrodynamic expansion, and then numerically for finite momenta.

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arXiv2020

Angular correlations in pA collisions from CGC: multiplicity and mean transverse momentum dependence of $v_2$

Within the dense-dilute Color Glass Condensate approach, and using the Golec-Biernat-Wuesthoff model for the dipole scattering amplitude, we calculate $v_2^2$ as well as the correlations between $v_2^2$ and both the total multiplicity and the mean transverse momentum of produced particles. We find that the correlations are generally very small consistent with the observations. We note an interesting sharp change in the value of $v^2_2$ as well as of its correlations as a function of the width of the transverse momentum bin. This crossover is associated with the change from Bose enhancement dominance of the correlation for narrow bin to HBT dominated correlations for larger bin width.

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