arXiv subjects
Publications and source records attributed to D. E. Kharzeev.
We suggest that by applying a magnetic field lying in the plane of graphene layer one may facilitate an excitonic condensation of electron-hole pairs with opposite spins and chiralities. The provided calculations yield a conservative estimate for the transition temperature $T_c \sim 0.1 B$.
A major contribution to the quest of constructing quantum dynamics of non-Abelian fieds is due to V.N. Gribov. Perturbative approach to the colour confinement, both in gluodynamics and the real world, was long considered heretic but is gaining ground. We discuss Gribov's approach to the confinement problem, centered around the role played by light quarks - the supercritical light quark confinement scenario. We also review some recent developments that are motivated, directly or indirectly, by his ideas.
The polarization of quarkonium states produced in hadron collisions exhibits strong non-perturbative effects - for example, at small transverse momentum $p_t$ charmonia appear unpolarized, in sharp contradiction to the predictions of perturbation theory. The quark--gluon plasma is expected to screen away the non-perturbative physics; therefore those quarkonia which escape from the plasma should possess polarization as predicted by perturbative QCD. We estimate the expected $J/ψ$ polarization at small $p_t$, and find that it translates into the asymmetry of the $e^+e^- (μ^+μ^-)$ angular distribution $W(θ) \sim 1 + αcos^2θ$, with $α\simeq 0.35 ÷0.4$.
Recently, several surprising experimental observations in the production of heavy quarkonium have been reported. In $e^+e^-$ annihilation at $\sqrt{s}=10.6$ GeV, Belle Collaboration finds that $J/ψ$ mesons are predominantly produced in association with an extra $\bar{c}c$ pair, with $σ(e^+e^- \to J/ψ\bar{c}c) / σ(e^+e^- \to J/ψX) = 0.59^{+0.15}_{-0.13}\pm 0.12$, and the BaBar collaboration reports that the produced $J/ψ$'s have mostly longitudinal polarization. In $\bar{p}p$ collisions at the Tevatron, the CDF Collaboration reported an excess of $J/ψ$ and $ψ^{\prime}$ mesons at high $p_{\perp}$ over the perturbative QCD predictions; non--perturbative approach of NRQCD can accomodate the magnitude of the production cross section but not the observed experimentally polarization of quarkonia. In this note we propose possible solutions to these puzzles, and devise further experimental tests.
The goal of these lectures, oriented towards the students just entering the field, is to provide an elementary introduction to QCD and the physics of nuclear interactions at high energies. We first introduce the general structure of QCD and discuss its main properties. Then we proceed to Glauber multiple scattering theory which lays the foundation for the theoretical treatment of nuclear interactions at high energies. We introduce the concept of Gribov's inelastic shadowing, crucial for the understanding of quantum formation effects. We outline the problems facing Glauber approach at high energies, and discuss how asymptotic freedom of QCD helps to resolve them, introducing the concepts of parton saturation and color glass condensate.
We consider propagation of heavy quarks in QCD matter. Because of large quark mass, the radiative quark energy loss appears to be qualitatively different from that of light quarks at all energies of practical importance. Finite quark mass effects lead to an in-medium enhancement of the heavy-to-light D/πratio at moderately large (5--10 GeV) transverse momenta. For hot QCD matter a large enhancement is expected, whose magnitude and shape are exponentially sensitive to the density of colour charges in the medium.
We have previously interpreted the various large apparent violations of the naive Okubo-Zweig-Iizuka (OZI) rule found in many channels in $\bar{p}p$ annihilation at LEAR as evidence for an intrinsic polarized $\bar{s}s$ component of the nucleon wave function. The model is further supported by new data from LEAR and elsewhere. Here we discuss in more detail the possible form of the $\bar{s}s$ component of the nucleon wave function, interpret the new data and clarify the relative roles of strangeness shake-out and rearrangement, discuss whether alternative interpretations are still allowed by the new data, and propose more tests of the model.
A large apparent violation of the OZI rule has recently been found in many channels in pbar-p annihilation LEAR. An interpretation of these data in terms of the "shake-out" and "rearrangement" of an intrinsic sbar-s component of the nucleon wave function is proposed. This gives a channel-dependent, non-universal modification of the naive OZI prediction. Within this approach, we interpret the strong excess of $ϕ$ production in S-wave pbar-p annihilations in terms of the polarization of the nucleon's sbar-s component indicated by deep inelastic lepton-nucleon scattering experiments. This interpretation could be tested by measurements of the $f_2'(1525)/f_2(1270)$ production ratio in P-wave annihilations and by experiments with polarized beams and polarized targets. We also propose a test of the intrinsic strangeness hypothesis in $ϕ$ production in high-momentum transfer processes, via a difference in constituent counting rules from gluon-mediated production.
We suggest the measurement of the integrated asymmetry of teh missing momentum distribution in (e,e$'$p)reactions to check color transparency effects at intermediate momentum transfers.
We address the problem of observed charmonium decays which should be forbidden in perturbative QCD. We examine the model in which these decays proceed through a gluonic component of the $J/Ψ$ and the $η_c$, arising from a mixing of $(c\bar c)$ and glueball states. We give some bounds on the values of the mixing angles and propose the study of the $p \bar{p} \to ϕϕ$ reaction, at $\sqrt{s} \simeq 3$ GeV, as an independent test of the model.
We suggest the measurement of the integrated asymmetry of teh missing momentum distribution in (e,e$'$p)reactions to check color transparency effects at intermediate momentum transfers.
We discuss the unexpected enhancement of the $N^*$ electroproduction on nuclei recently observed in the $(γ^*,pπ^-)$ measurement. A mechanism which is able to explain this result is proposed. To clarify the situation, we suggest to perform a new kind of experiment within well specified kinematic conditions.
The dynamics of nuclear transparency in hard nuclear reactions is studied by an expansion of the correlator of the hard scattering operator on a hadronic basis. Colour transparency appears as an effect of interference between the amplitudes corresponding to the final state interaction of different intermediate baryonic states. We find that colour transparency occurs even at moderate momentum transfers if one chooses the missing momentum of the struck nucleon by appropriate kinematics. In general, the role of the Fermi-motion is found to be crucial; without it, any effect of anomalous nuclear transparency would be impossible.