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Larry McLerran

Publications and source records attributed to Larry McLerran.

At least 109 records · Page 6Linked to original sources
arXiv2000

Equilibration of the Gluon-Minijet Plasma at RHIC and LHC

We study the production and equilibration of the gluon-minijet plasma expected to be formed in the central region of ultrarelativistic heavy-ion collisions at the BNL-RHIC and the CERN-LHC by solving a self-consistent relativistic transport equation. We compute the minijet production within perturbative QCD. Subsequent collisions among the semi-hard partons are treated by considering the elastic gg -> gg processes with screening of the long wavelength modes taken into account. We determine the time $τ_{eq}$ where close to ideal hydrodynamic flow sets in, and find rather similar numbers for central heavy-ion collisions at BNL-RHIC and CERN-LHC energies. The number densities, energy densities and temperatures of the minijet plasma are found to be different at RHIC and LHC, e.g. $T(τ_{eq})\sim220$ MeV and 380 MeV, respectively.

hep-ph↗
arXiv2000

Diffractive Structure Function in a Quasi-Classical Approximation

We derive an expression for diffractive F_2 structure function which should be valid at small x for quasi-elastic scattering on a hadron and for quasi-elastic scattering on a large nucleus. This expression includes multiple rescatterings of the quark-antiquark pair produced by the virtual photon off the sources of color charge in a quasi-classical approximation. We find that there is a relation between such diffractive production and inclusive processes. In the former, one averages over all colors of sources before squaring the amplitude, and in the latter one first squares the amplitude and then averages it in the hadron's or nuclear wave function. We show that in the limit of a large virtuality of the photon Q^2 the diffractive structure function becomes linearly proportional to the gluon distribution of the hadron or nucleus, therefore proving that in this sense diffraction is a leading twist effect.

hep-ph↗
arXiv1999

Large Scale Rapidity Correlations in Heavy Ion Collisions

We discuss particle production mechanisms for heavy ion collisions. We present an argument demonstrating how the fluctuations of the number of produced particles in a series of classical emissions can account for KNO scaling. We predict rapidity correlations in the particle production in the event by event analysis of heavy ion collisions on the rapidity scales of the order of one over the strong coupling constant.

hep-ph↗
arXiv1999

Fock Space Distributions, Structure Functions, Higher Twists and Small x

We compute quark structure functions and the intrinsic Fock space distribution of sea quarks in a hadron wavefunction at small x. The computation is performed in an effective theory at small x where the gluon field is treated classically. At $Q^2$ large compared to an intrinsic scale associated with the density of gluons $μ^2$, large compared to the QCD scale $Λ^2_{QCD}$, and large compared to the quark mass squared $M^2$, the Fock space distribution of quarks is identical to the distribution function measured in deep inelastic scattering. For $Q^2 \le M^2$ but $Q^2 >> μ^2$, the quark distribution is computed in terms of the gluon distribution function and explicit expressions are obtained. For $Q^2 \le μ^2$ but $Q^2 >> Λ_{QCD}^2$ we obtain formal expressions for the quark distribution functions in terms of the glue. An evaluation of these requires a renormalization group analysis of the gluon distribution function in the regime of high parton density. For light quarks at high $Q^2$, the DGLAP flavor singlet evolution equations for the parton distributions are recovered. Explicit expressions are given for heavy quark structure functions at small x.

hep-ph↗
arXiv1999

Three Lectures on the Physics of Small x and High Gluon Density

In these lectures, I shall discuss small x physics and the consequences of high gluon density which arises as x decreases. I argue that an understanding of this problem would lead to knowledge of the high energy asymptotics of hadronic processes. The high gluon density should allow a first principles computation of these asymptotics from QCD.

hep-ph↗
arXiv1997

Boost covariant gluon distributions in large nuclei

It has been shown recently that there exist analytical solutions of the Yang-Mills equations for non-Abelian Weizsäcker-Williams fields which describe the distribution of gluons in large nuclei at small x. These solutions however depend on the color charge distribution at large rapidities. We here construct a model of the color charge distribution of partons in the fragmentation region and use it to compute the boost covariant momentum distributions of wee gluons. The phenomenological applications of our results are discussed.

nucl-th↗
arXiv1997

Hot Neutron Stars as a Source for Gamma Ray Bursts at Cosmological Distance Scales

We discuss the possibility that the sources for gamma ray bursts are hot neutron stars at cosmological distance scales. The temperature of such stars would be $T \sim 1 \MeV$. Such hot stars can produce an electromagnetic blast wave provided that the ratio of baryon and photon numbers $N_{B}/N_γ \le 10^{-6}$. The typical time scale for such blasts, the total luminosity, and correlation of gamma ray energy with time of arrival are shown to be roughly consistent with observation. The spectrum of photons also appears to be consistent with known data.

astro-ph↗
arXiv1997

Yang-Mills Radiation in Ultra-relativistic Nuclear Collisions

The classical Yang-Mills radiation computed in the McLerran-Venugopalan model is shown to be equivalent to the gluon bremsstrahlung distribution to lowest order in pQCD. The classical distribution is also shown to match smoothly onto the conventional pQCD mini-jet distribution at a scale characteristic of the initial parton transverse density of the system. The atomic number and energy dependence of that scale is computed from available structure function information. The limits of applicability of the classical Yang-Mills description of nuclear collisions at RHIC and LHC energies are discussed.

nucl-th↗
arXiv1996

The Intrinsic Glue Distribution at Very Small x

We compute the distribution functions for gluons at very small x and not too large values of transverse momenta. We extend the McLerran-Venugopalan model by using renormalization group methods to integrate out effects due to those gluons which generate an effective classical charge density for Weizsäcker-Williams fields. We argue that this model can be extended from the description of nuclei at small x to the description of hadrons at yet smaller values of x. This generates a Lipatov like enhancement for the intrinsic gluon distribution function and a non-trivial transverse momentum dependence as well. We estimate the transverse momentum dependence for the distribution functions, and show how the issue of unitarity is resolved in lepton-nucleus interactions.

hep-ph↗
arXiv1995

Magnetic Fields Produced by Phase Transition Bubbles in the Electroweak Phase Transition

The electroweak phase transition, if proceeding through nucleation and growth of bubbles, should generate large scale turbulent flow, which in turn generates magnetic turbulence and hence magnetic fields on the scale of turbulent flow. We discuss the seeding of this turbulent field by the motion of the dipole charge layers in the phase transition bubble walls, and estimate the strength of the produced fields.

hep-ph↗
arXiv1995

Really Computing Non-perturbative Real Time Correlation Functions

It has been argued by Grigoriev and Rubakov that one can simulate real time processes involving baryon number non-conservation at high temperature using real time evolution of classical equations, and summing over initial conditions with a classical thermal weight. It is known that such a naive algorithm is plagued by ultraviolet divergences. In quantum theory the divergences are regularized, but the corresponding graphs involve the contributions from the hard momentum region and also the new scale $\sim gT$ comes into play. We propose a modified algorithm which involves solving the classical equations of motion for the effective hard thermal loop Hamiltonian with an ultraviolet cutoff $μ\gg gT$ and integrating over initial conditions with a proper thermal weight. Such an algorithm should provide a determination of the infrared behavior of real time correlation function $ _T$ determining the baryon violation rate. Hopefully, the results obtained in this modified algorithm would be cutoff-independent.

hep-th↗
arXiv1995

Gluon Production from Non-Abelian Weizsäcker-Williams Fields in Nucleus-Nucleus Collisions

We consider the collisions of large nuclei using the theory of McLerran and Venugopalan. The two nuclei are ultra-relativistic and sources of non-abelian Weizsäcker-Williams fields. These sources are in the end averaged over all color orientations locally with a Gaussian weight. We show that there is a solution of the equations of motion for the two nucleus scattering problem where the fields are time and rapidity independent before the collision. After the collision the solution depends on proper time, but is independent of rapidity. We show how to extract the produced gluons from the classical evolution of the fields.

hep-ph↗
arXiv1995

The Gluon Propagator in non-Abelian Weizsäcker-Williams fields

We carefully compute the gluon propagator in the background of a non--Abelian Weizsäcker--Williams field. This background field is generated by the valence quarks in very large nuclei. We find contact terms in the small fluctuation equations of motion which induce corrections to a previously incorrect result for the gluon propagator in such a background field. The well known problem of the Hermiticity of certain operators in Light Cone gauge is resolved for the Weizsäcker--Williams background field. This is achieved by working in a gauge where singular terms in the equations of motion are absent and then gauge transforming the small fluctuation fields to Light Cone gauge.

hep-ph↗
arXiv1994

Green's Functions in the Color Field of a Large Nucleus

We compute the Green's functions for scalars, fermions and vectors in the color field associated with the infinite momentum frame wavefunction of a large nucleus. Expectation values of this wavefunction can be computed by integrating over random orientations of the valence quark charge density. This relates the Green's functions to correlation functions of a two dimensional, ultraviolet finite, field theory. We show how one can compute the sea quark distribution functions, and explictly compute them in the kinematic range of transverse momenta, $α_s^2 μ^2 << k_t^2 << μ^2$, where $μ^2$ is the average color charge squared per unit area. When $m_{quark}^2 << μ^2 \sim A^{1/3}$, the sea quark contribution to the infinite momentum frame wave function saturates at a value that is the same as that for massless sea quarks.

hep-ph↗
arXiv1993

Scattering in the Presence of Electroweak Phase Transition Bubble Walls

We investigate the motion of fermions in the presence of an electro\-weak phase transition bubble wall. We derive and solve the Dirac equation for such fer\-mions, and compute the transmission and reflection coefficients for fermions traveling from the symmetric to the asymmetric phases separated by the domain wall.

hep-ph↗