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S. M. H. Wong

Publications and source records attributed to S. M. H. Wong.

At least 19 recordsLinked to original sources
arXiv2006

On Kolmogorov Wave Turbulence in QCD

We investigate Kolmogorov wave turbulence in QCD or, in other words, we calculate the spectrum of gluons as a function of time, f_k(t), in the presence of a source which feeds in energy density in the infrared region at a constant rate. We find an early, an intermediate and a late time form for the gluon spectrum. Wave turbulence in QCD turns out to be somewhat different than the turbulence in the case of ϕ^4-type theories studied by Zakharov, L'vov and Falkovich. The hope is that a good understanding of QCD wave turbulence might lead to a better understanding of the instability problem in the early stages of the evolution after a heavy ion collision.

hep-ph↗
arXiv2005

A Modified "Bottom-up" Thermalization in Heavy Ion Collisions

In the initial stage of the bottom-up picture of thermalization in heavy ion collisions, the gluon distribution is highly anisotropic which can give rise to plasma instability. This has not been taken account in the original paper. It is shown that in the presence of instability there are scaling solutions, which depend on one parameter, that match smoothly onto the late stage of bottom-up when thermalization takes place.

hep-ph↗
arXiv2005

A Possible Modified "bottom-up" Thermalization in Heavy Ion Collisions

We present a possible scaling solution to pre-equilibrium evolution which interpolates between the instability present in the dense gluon system produced immediately after a heavy ion collision and the final equilibration which occurs later. Our solution depends on a single parameter $δ$. Depending on the value of $δ$, our proposed solution matches onto the bottom-up picture either at an intermediate stage or toward the end of the evolution given by bottom-up. We discuss in detail the reasons why we believe our solution is self-consistent, and we also point out why it is difficult to actually prove consistency.

hep-ph↗
arXiv2005

On the Projectile-Target Duality of the Color Glass Condensate in the Dipole Picture

Recently Kovner and Lublinsky proposed a set of equations which can be viewed as dual to JIMWLK evolution. We show that these dual equations have a natural dipole-like structure, as conjectured by Kovner and Lublinsky. In the high energy large N_c limit these evolution equations reduce to equations previously derived in the dipole model. We also show that the dual evolution kernel is scheme dependent, although its action on the weight functional describing a high energy state gives a unique result.

hep-ph↗
arXiv2005

Extension of the JIMWLK Equation in the Low Gluon Density Region

It has recently been realized that the Balitsky-JIMWLK equations have serious shortcomings as equations to be used in small-x evolution near the unitarity limit. A recent generalization of the Balitsky equations has been given which corrects these shortcomings. In this paper we present an equivalent discussion, but in terms of the JIMWLK equation where we show that a new (fourth order functional derivative) term should be included. We also present a stochastic version of the new equation which, however, has some unusual mathematical aspects which are not as yet well understood.

hep-ph↗
arXiv2004

Out-of-Equilibrium Collinear Enhanced Equilibration in the Bottom-Up Thermalization Scenario in Heavy Ion Collisions

Experimental measurement of the elliptic flow parameter $v_2$ and hydrodynamic model together showed that thermalization in the central region at the Relativistic Heavy Ion Collider to be perplexingly fast. This is a mystery in itself since none of the numerical perturbative QCD models are able to achieve such a feat. By exploiting a theoretical oversight on collinear processes in an out-of-equilibrium system it is argued that, in the bottom-up thermalization scenario, equilibration can proceed at a higher rate than what is expected in the conventional perturbative QCD picture.

hep-ph↗
arXiv2002

Equivalence of Classical Skyrmions and Coherent States of Baryons I. Constrained Quantization on the SU(2) and SO(3) manifolds

In the Skyrme model, the Lagrangian can be quantized in several ways using the collective coordinate approach. Not all of which produce quantum states that can be interpreted as physical particles. For example the SU(2) collective coordinate approach produces both integral and half-integral spin and isospin states. Only half of these are the physical baryons. Less well known is the fact that it is equally possible to quantize the system using the SO(3) collective coordinates. This produces only unphysical integral spin and isospin states. To fulfill the goal of being able to express a classical skyrmion as a coherent state of baryons directly in terms of the baryon states, surprisingly a combination of both collective coordinate approaches is required. To prepare for the subsequent application to skyrmion formation through disoriented chiral condensates in heavy ion collisions, the Skyrme model is rigorously quantized using the Dirac prescription for constrained systems. This is shown for both the SU(2) as well as the SO(3) collective coordinate approach.

hep-ph↗
arXiv2002

Equivalence of Classical Skyrmions and Coherent States of Baryons II. Baryonic Coherent State Construction on Compact Manifolds

In connection with the possibility of skyrmion production from small domain disoriented chiral condensates formation from heavy ion collisions, the direct relation of a classical skyrmion to baryon states is examined. It is argued that a skyrmion is a coherent state of baryons. The collective coordinate approach of quantization means that the physical baryon states exist not in flat space but on a compact manifold. This requires the construction of coherent states in such a curve space. Using the techniques associated with the Segal-Bargmann transform also known as the coherent state transform used for example in the study of the classical limit of quantum gravity, such states can be constructed in the context of the Skyrme model. They are made up directly of baryon states on S^3 but with quantum operators on the SO(3) manifold. In terms of wavefunctions, they are a superposition of the analytic baryon wavefunctions of Adkins, Nappi and Witten. The distribution of the baryon states in terms of the relative probabilities of the baryons inside a skyrmion can therefore be determined.

hep-ph↗
arXiv2002

Elliptic Flow from a Transversally Thermalized Fireball

The agreement of elliptic flow data at RHIC at central rapidity with the hydrodynamic model has led to the conclusion of very rapid thermalization. This conclusion is based on the intuitive argument that hydrodynamics, which assumes instantaneous local thermalization, produces the largest possible elliptic flow values and that the data seem to saturate this limit. We here investigate the question whether incompletely thermalized viscous systems may actually produce more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast primordial longitudinal expansion of the reaction zone, we investigate a toy model which exhibits thermalization only in the transverse directions but undergoes collisionless free-streaming expansion in the longitudinal direction. For collisions at RHIC energies, elliptic flow results from the model are compared with those from hydrodynamics. With the final particle yield and $\kt$-distribution fixed, the transversally thermalized model is shown not to be able to produce the measured amount of elliptic flow. This investigation provides further support for very rapid local kinetic equilibration at RHIC. It also yields interesting novel results for the elliptic flow of massless particles such as direct photons.

hep-ph↗
arXiv2002

What exactly is a Skyrmion?

Skyrmions are well known to be baryons because their topological charge has been positively identified with the baryon number. Beyond that their identity has never been clear. In view of the possibility of skyrmion production through Disoriented Chiral Condensates in heavy ion collisions, the exact identity of the skyrmion must be resolved before they can be identified in experiments. It is shown that skyrmions are not individual baryons but coherent states of known baryons and higher resonances on a compact manifold associated with the spin and flavor symmetry group. An outline of how to calculate exactly the probability amplitudes of the superposition of physical baryon and excited baryon states that make up the skyrmion is given.

hep-ph↗
arXiv2002

Possible Evidence of Disoriented Chiral Condensates from the Anomaly in Omega and AntiOmega Abundances at the SPS

No conventional picture of nucleus-nucleus collisions has yet been able to explain the abundance of Omega and AntiOmega in central collisions between Pb nuclei at 158 A GeV at the CERN SPS. We argue that such a deviation from predictions of statistical thermal models and numerical simulations is evidence that they are produced as topological defects in the form of skyrmions arising from the formation of disoriented chiral condensates. The estimated domain size falls in the right range to be consistent with the so far non-observation of DCC from the distribution of neutral pions.

hep-ph↗
arXiv2001

Disentangling the Imaginary-Time Formalism at Finite Temperature

We rewrite the imaginary-time formalism of finite temperature field theory in a form that all graphs used in calculating physical processes do not have any loops. Any production of a particle from a heat bath which is itself not thermalized or the decay and absorption of a similar particle in the bath is expressed entirely in terms of the sum of particle interaction processes. These are themselves very general in meaning. They can be straight forward interactions or the more subtle and less well-known purely interference processes that do not have a counter part in the vacuum.

hep-ph↗
arXiv2001

Two-Loop Self-Energy and Multiple Scattering at Finite Temperature

One and two loop self-energies are worked out explicitly for a heavy scalar field interacting weakly with a light self-interacting scalar field at finite temperature. The ring/daisy diagrams and a set of necklace diagrams can be summed simultaneously. This simple model serves to illustrate the connection between multi-loop self-energy diagrams and multiple scattering in a medium.

hep-th↗
arXiv2001

Is Anomalous Production of Omega and anti-Omega Evidence for Disoriented Chiral Condensates?

No conventional picture of nucleus-nucleus collisions has yet been able to explain the abundance of Omega and anti-Omega hyperons in central collisions between Pb nuclei at 158 A GeV at the CERN SPS. We argue that this is evidence that they are produced as topological defects arising from the formation of disoriented chiral condensates (DCC) with an average domain size of about 2 fm.

nucl-th↗
arXiv2000

Bremsstrahlung from a Microscopic Model of Relativistic Heavy Ion Collisions

We compute bremsstrahlung arising from the acceleration of individual charged baryons and mesons during the time evolution of high-energy Au+Au collisions at the Relativistic Heavy Ion Collider using a microscopic transport model. We elucidate the connection between bremsstrahlung and charge stopping by colliding artificial pure proton on pure neutron nuclei. From the intensity of low energy bremsstrahlung, the time scale and the degree of stopping could be accurately extracted without measuring any hadronic observables.

hep-ph↗
arXiv2000

Color Octet Contribution in Exclusive P-Wave Charmonium Decay

Recent advances in our understanding of the higher-wave quarkonia have generated much interests in quarkonium physics. However most are devoted to inclusive decays and productions. Experimental data of several two-body exclusive decay channels of P-wave charmonia such as ππand p \bar p are available and some have recently been re-measured by the BES collaboration. It is not clear from the outset that color octet is needed for these exclusive channels. Indeed only color singlet has been used in the past and reasonable agreement with data was found. Contrary to these old results, we provide theoretical arguments for the inclusion of color octet and perform explicit calculations to back this up.

hep-ph↗
arXiv2000

Color Screening Effects on Hadronization in Relativistic Heavy Ion Collisions

The effects of color screening on the hadronization of a parton plasma into a hadron gas are examined at the energies of the relativistic heavy ion collider. It is found to have the tendency to prevent hadronization and therefore delaying the conversion of the partons into a hadron gas. Because of the continual expansion, the resulting hadron gas number densities are lower when screening is included. This should reduce the hadronic noise to genuine signals of the quark-gluon plasma. In this sense, color screening is favorable and should be included in numerical models. In any case, we advocate that numerical models should allow the confining forces and color screening to act on each other so as to undergo the phase transition in a natural way. Hadronization is also shown to seriously disrupt parton equilibration and is yet another reason why full parton chemical equilibration should not be expected.

hep-ph↗