arXiv subjects

D. E. Kharzeev

Publications and source records attributed to D. E. Kharzeev.

At least 19 recordsLinked to original sources

arXiv2023

Hot QCD White Paper

Hot QCD physics studies the nuclear strong force under extreme temperature and densities. Experimentally these conditions are achieved via high-energy collisions of heavy ions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). In the past decade, a unique and substantial suite of data was collected at RHIC and the LHC, probing hydrodynamics at the nucleon scale, the temperature dependence of the transport properties of quark-gluon plasma, the phase diagram of nuclear matter, the interaction of quarks and gluons at different scales and much more. This document, as part of the 2023 nuclear science long range planning process, was written to review the progress in hot QCD since the 2015 Long Range Plan for Nuclear Science, as well as highlight the realization of previous recommendations, and present opportunities for the next decade, building on the accomplishments and investments made in theoretical developments and the construction of new detectors. Furthermore, this document provides additional context to support the recommendations voted on at the Joint Hot and Cold QCD Town Hall Meeting, which are reported in a separate document.

nucl-ex↗

arXiv2020

Charge-dependent flow induced by electromagnetic fields in heavy ion collisions

The colliding heavy ions create extremely strong magnetic and electric fields that significantly affect the evolution of the produced quark-gluon plasma (QGP). The knowledge of these fields is essential for establishing the role of topological fluctuations in the QGP through the chiral magnetic effect and related anomaly-induced phenomena. In this talk, we describe our work on the evolution of the QGP in electric and magnetic fields in the framework of hydrodynamics supplemented, in a perturbative fashion, by the dynamical electromagnetism. The evolution of the QGP fluid is described within the iEBE-VISHNU framework. We find that the electromagnetically induced currents result in a charge-odd directed flow $Δv_1$ and a charge-odd $Δv_3$ flow both of which are odd in rapidity. While the predicted magnitude of these charge-odd flows agrees with the data from RHIC and LHC, the sign of the predicted asymmetry between the flows of positive and negative hadrons is opposite to the data.

hep-ph↗

arXiv2019

Chiral Magnetic Josephson junction: a base for low-noise superconducting qubits?

Superconducting materials with non-centrosymmetric lattices lacking the space inversion symmetry are known to exhibit a variety of interesting parity-breaking phenomena, including the anomalous Josephson effect. Here we consider a Josephson junction consisting of two non-centrosymmetric superconductors (NCSs) connected by a uniaxial ferromagnet, and demonstrate that it exhibits a direct analog of the Chiral Magnetic Effect observed in Dirac and Weyl semimetals. We propose to use this "Chiral Magnetic Josephson junction" (CMJ junction) as an element of a qubit with a Hamiltonian tunable by the ferromagnet's magnetization. The CMJ junction allows to avoid the use of an offset magnetic flux in inductively shunted qubits, thus enabling a simpler and more robust architecture. The resulting"`chiral magnetic qubit" is protected from the noise caused by fluctuations in magnetization when the easy axis of the uniaxial ferromagnet is directed across the junction.

cond-mat.supr-con↗

arXiv2018

Chiral propulsion by electromagnetic fields

We consider the propulsion of micron-scale chiral objects by electromagnetic fields in fluids - a problem with broad applications in microfluidics, pharmaceutics, and biomedicine. Because of the small size of the moving objects, the propulsion can be described by the Stokes equation possessing the time-reversal invariance. We propose a method of evaluating the propulsion velocity based on the Green's function of the Stokes equation. As an illustration, we first use it to provide a simple derivation of the classic Stokes law for a sphere moving in a viscous fluid. We then use this method for describing the propulsion of helical bodies, evaluate the propulsion velocity, and find that it does not depend on the viscosity of the fluid as long as the Reynolds number remains small. As an application, we describe recent experimental results on the propulsion of nano-propellers by electromagnetic fields in water, with a good agreement with the data. We also discuss applications to optofluidic chiral sorting of molecules by rotating electromagnetic fields and circularly polarized light.

cond-mat.soft↗

arXiv2017

Thermal radiation and entanglement in proton-proton collisions at the LHC

The origin of the apparent thermalization in high-energy collisions is investigated using the data of the ATLAS and CMS Collaborations at the LHC. For this purpose, we analyze the transverse momentum distributions in the following proton-proton collision processes, all at $\sqrt{s} = 13$ TeV: i) inclusive inelastic $pp$ collisions; ii) single- and double-diffractive Drell-Yan production $pp \to μ^+ μ^- X$; and iii) Higgs boson production. We confirm the relation between the effective temperature and the hard scattering scale observed at lower energies, and find that it extends even to the Higgs boson production process. In addition we find that the thermal component disappears in diffractive events (even though many charged hadrons are still produced). We discuss the implications of our study for the mechanism of multi-particle production -- in particular, we test the hypothesis about the link between quantum entanglement and thermalization in high-energy collisions.

hep-ph↗

arXiv2016

Chiral Magnetic and Vortical Effects in High-Energy Nuclear Collisions --- A Status Report

The interplay of quantum anomalies with magnetic field and vorticity results in a variety of novel non-dissipative transport phenomena in systems with chiral fermions, including the quark-gluon plasma. Among them is the Chiral Magnetic Effect (CME) -- the generation of electric current along an external magnetic field induced by chirality imbalance. Because the chirality imbalance is related to the global topology of gauge fields, the CME current is topologically protected and hence non-dissipative even in the presence of strong interactions. As a result, the CME and related quantum phenomena affect the hydrodynamical and transport behavior of strongly coupled quark-gluon plasma, and can be studied in relativistic heavy ion collisions where strong magnetic fields are created by the colliding ions. Evidence for the CME and related phenomena has been reported by the STAR Collaboration at Relativistic Heavy Ion Collider at BNL, and by the ALICE Collaboration at the Large Hadron Collider at CERN. The goal of the present review is to provide an elementary introduction into the physics of anomalous chiral effects, to describe the current status of experimental studies in heavy ion physics, and to outline the future work, both in experiment and theory, needed to eliminate the existing uncertainties in the interpretation of the data.

hep-ph↗

arXiv2014

Nuclear modification of the J/Psi transverse momentum distributions in high energy pA and AA collisions

We evaluate the transverse momentum spectrum of J/Psi (up to semi-hard momenta) in pA and AA collisions taking into account only the initial state effects, but resumming them to all orders in α_s^2 A^{1/3}. In our previous papers we noticed that cold nuclear matter effects alone could not explain the experimental data on rapidity and centrality dependencies of the J/Psi yield in AA collisions indicating the existence of an additional suppression mechanism. Our present calculations indicate that the discrepancy persists and even increases at semi-hard transverse momenta, implying a significant final state effect on J/Psi production in this kinematical domain. The QCD dipole model we employ is only marginally applicable for J/Psi production at mid-rapidity at RHIC energies but its use is justified in the forward rapidity region. At LHC energies we can quantitatively evaluate the magnitude of cold nuclear matter effects in the entire kinematical region of interest. We present our calculations of J/Psi transverse momentum spectra in pA and AA collisions at LHC and RHIC energies.

hep-ph↗

arXiv2012

From the chiral magnetic wave to the charge dependence of elliptic flow

The quark-gluon plasma formed in heavy ion collisions contains charged chiral fermions evolving in an external magnetic field. At finite density of electric charge or baryon number (resulting either from nuclear stopping or from fluctuations), the triangle anomaly induces in the plasma the Chiral Magnetic Wave (CMW). The CMW first induces a separation of the right and left chiral charges along the magnetic field; the resulting dipolar axial charge density in turn induces the oppositely directed vector charge currents leading to an electric quadrupole moment of the quark-gluon plasma. Boosted by the strong collective flow, the electric quadrupole moment translates into the charge dependence of the elliptic flow coefficients, so that $v_2(π^+) < v_2(π^-)$ (at positive net charge). Using the latest quantitative simulations of the produced magnetic field and solving the CMW equation, we make further quantitative estimates of the produced $v_2$ splitting and its centrality dependence. We compare the results with the available experimental data.

hep-ph↗

arXiv2011

Gluon saturation effects on the color singlet J/Psi production in high energy dA and AA collisions

We derive the formulae for the cross section of J/Psi production in high energy pA and AA collisions taking into account the gluon saturation/color glass condensate effects. We then perform the numerical calculations of the corresponding nuclear modification factors and find a good agreement between our calculations and the experimental data on J/Psi production in dA collisions. We also observe that cold nuclear modification effects alone cannot describe the data on J/Psi production in AA collisions. Additional final state suppression (at RHIC) and enhancement (at LHC) mechanisms are required to explain the experimental observations.

hep-ph↗

arXiv2010

Magnetic-Field-Induced insulator-conductor transition in SU(2) quenched lattice gauge theory

We study the correlator of two vector currents in quenched $SU\lr{2}$ lattice gauge theory with a chirally invariant lattice Dirac operator with a constant external magnetic field. It is found that in the confinement phase the correlator of the components of the current parallel to the magnetic field decays much slower than in the absence of a magnetic field, while for other components the correlation length slightly decreases. We apply the maximal entropy method to extract the corresponding spectral function. In the limit of zero frequency this spectral function yields the electric conductivity of the quenched theory. We find that in the confinement phase the external magnetic field induces nonzero electric conductivity along the direction of the field, transforming the system from an insulator into an anisotropic conductor. In the deconfinement phase the conductivity does not exhibit any sizable dependence on the magnetic field.

hep-lat↗

arXiv2009

D-instantons and multiparticle production in N=4 SYM

N=4 Super-symmetric Yang-Mills theory (N=4 SYM) in the strong coupling regime has been successfully applied (through the AdS/CFT correspondence) to the description of strongly coupled plasma which is a multiparticle state. Yet, the high-energy scattering in the strong coupling limit of N=4 SYM is purely elastic, so this multiparticle final state can never be produced: this is because in this limit the theory is dual to weak supergravity, and the dominant interaction is the elastic graviton exchange. Here we propose a resolution of this dilemma by considering the contribution of D-instantons in $AdS_5$ bulk space to the scattering amplitude. We argue that D-instantons coupled to dilatons and axions are responsible for multiparticle production in strongly coupled N=4 SYM, and the corresponding cross section increases with energy. We evaluate the intercept and the slope of the corresponding Pomeron trajectory in terms of the typical size of the D-instanton, and argue that the resulting physical picture may resemble the real world.

hep-ph↗

arXiv2009

Topologically induced local P and CP violation in hot QCD

Very stringent experimental bounds exist on the amount of P and CP violation in strong interactions. Nevertheless, the presence of non-Abelian topological solutions and the axial anomaly make the issue of CP invariance in QCD non-trivial ("the strong CP problem"). Even in the absence of a global P and CP violation the fluctuations of topological charge in the QCD vacuum are expected to play an important role in the breaking of chiral symmetry, and in the mass spectrum and other properties of hadrons. Here I argue that topological fluctuations in hot QCD matter can become directly observable in the presence of a very intense external magnetic field by inducing local P- and CP- odd effects. These local parity-violating phenomena can be described by using the Maxwell-Chern-Simons, or axion, electrodynamics as an effective theory. Local P and CP violation in hot QCD matter can be observed in experiment through the "chiral magnetic effect" - the separation of electric charge along the axis of magnetic field that is created by the colliding relativistic ions. There is a recent evidence for the electric charge separation relative to the reaction plane of heavy ion collisions from the STAR Collaboration at RHIC.

hep-ph↗

arXiv2009

Spin-polarized transport through domain wall in magnetized graphene

Atomically thin two-dimensional layer of honeycomb crystalline carbon known as graphene is a promising system for electronics. It has a point-like Fermi surface, which is very sensitive to external potentials. In particular, Zeeman magnetic field parallel to the graphene layer splits electron bands and creates fully spin-polarized and geometrically congruent circular Fermi surfaces of particle and hole type. In the presence of electric field, particles and holes with opposite spins drift in opposite direction. These phenomena are likely to be of interest for developing graphene-based spintronic devices. A domain wall (DW) separating regions with opposite spin polarizations is a basic element of such a device. Here we consider a ballistic passage of spin-polarized charge carriers through DW in graphene. We also discuss the analogy between the generation of spin currents in graphene and in relativistic quark-gluon plasma, where the spin-polarized current is responsible for the phenomenon of charge separation studied recently at RHIC.

cond-mat.mes-hall↗

arXiv2009

Hot and dense matter: from RHIC to LHC: Theoretical overview

Relativistic heavy ion physics studies the phenomena that occur when a very large (in units of QCD scale $Λ_{\rm QCD}$) amount of energy is deposited into a large (in units of $Λ^{-3}_{\rm QCD}$) volume, creating an extended in space and time domain with an energy density that is large in units of $Λ^{4}_{\rm QCD}$. This includes the mechanism by which the energy is deposited (likely a transformation of the colliding Lorentz-contracted "gluon walls" into the strong longitudinal color fields); approach to thermalization; and the static and dynamical properties of the created quark-gluon plasma. Of particular interest is the fate of symmetries (e.g. chiral $SU_L(3) \times SU_R(3)$, scale, and discrete ${\cal P}$ and ${\cal CP}$ invariances) in hot and dense QCD matter. At present, the program at RHIC has entered a stage where new discoveries are enabled by high precision of the measurements; moreover, an array of new capabilities will soon be available due to the numerous and significant upgrades. Very importantly, we will soon have access to unprecedented energies of colliding ions at the LHC. In addition, future RHIC runs at low energies, FAIR at GSI and NICA at JINR will make possible the studies of QCD matter at high baryon density. I will describe the current status of theoretical knowledge about hot QCD, and the ways in which it may be expected to improve in the near future.

hep-ph↗

arXiv2008

Parton energy loss at strong coupling and the universal bound

The apparent universality of jet quenching observed in heavy ion collisions at RHIC for light and heavy quarks, as well as for quarks and gluons, is very puzzling and calls for a theoretical explanation. Recently it has been proposed that the synchrotron--like radiation at strong coupling gives rise to a universal bound on the energy of a parton escaping from the medium. Since this bound appears quite low, almost all of the observed particles at high transverse momentum have to originate from the surface of the hot fireball. Here I make a first attempt of checking this scenario against the RHIC data and formulate a "Universal Bound Model" of jet quenching that can be further tested at RHIC and LHC.

hep-ph↗

arXiv2008

Universal upper bound on the energy of a parton escaping from the strongly coupled quark-gluon matter

It has been shown through the AdS/CFT correspondence that the energy loss of a fast quark in a strongly coupled ${\cal N}=4$ SUSY Yang--Mills matter in the large N limit is given by the classical Lienard formula. I demonstrate that under quite natural assumptions about the dynamics of heavy ion collisions this leads to a universal (i.e. independent of the initial parton energy, but dependent on flavor and centrality) upper bound on the energy of the partons escaping from the plasma. This bound is a Yang--Mills analog of the Pomeranchuk bound in classical electrodynamics, where it is a consequence of radiation in a strong external field acting on a relativistic charge. Since as a result the massive constituent partons are slowed down to a velocity v < c, the angular distribution of the emitted radiation exhibits a broad "dead cone". If the properties of conformal and QCD matter at strong coupling are qualitatively similar, the existence of this universal upper bound would have dramatic implications for heavy ion experiments.

hep-ph↗

arXiv2007

Spontaneous symmetry breakings in graphene subjected to in-plane magnetic field

Application of the magnetic field parallel to the plane of the graphene sheet leads to the formation of electron- and hole-like Fermi surfaces. Such situation is shown to be unstable with respect to the formation of an excitonic condensate even for an arbitrary weak magnetic field and interaction strength. At temperatures lower than the mean-field temperature the order parameter amplitude is formed. The order parameter itself is a U(2) matrix allowing for the combined rotations in the spin and valley spaces. These rotations smoothly interpolate between site and bond centered spin density waves and spin flux states. The trigonal warping, short range interactions, and the three particle Umklapp processes freeze some degrees of freedom at temperatures much smaller than the mean-field transition temperature and make either Berezinskii-Kosterlitz-Thouless (driven either by vortices or half-vortices) or Ising type transitions possible. Strong logarithmic renormalization for the coupling constants of these terms by the Coulomb interaction are calculated within one-loop renormalization group. It is found that in the presence of the Coulomb interaction some short range interaction terms become much greater than one might expect from the naive dimensionality counting.

cond-mat.mes-hall↗

arXiv2007

Theoretical issues in J/psi suppression

Two decades ago Matsui and Satz suggested that Debye screening in the quark-gluon plasma would result in J/psi suppression in heavy ion collisions. Much has happened in the subsequent years, and the picture of quark-gluon plasma at present is rapidly evolving - what does it imply for the J/psi suppression? What are the recent RHIC and SPS results trying to tell us? What else has to be done? This talk is an attempt to address these questions.

hep-ph↗