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Chi-Keung Chow

Publications and source records attributed to Chi-Keung Chow.

At least 19 recordsLinked to original sources
arXiv2001

Model-Independent Predictions for Low Energy Isoscalar Heavy Baryon Observables in the Combined Heavy Quark and Large $N_c$ Expansion

Model-independent predictions for excitation energies, semileptonic form factors and electromagnetic decay rates of isoscalar heavy baryons and their low energy excited states are discussed in terms of the combined heavy quark and large $N_c$ expansion. At leading order, the observables are completely determined in terms of the known excitation energy of the first excited state of $Λ_c$. At next-to-leading order in the combined expansion all heavy baryon observables can be expressed in a model-independent way in terms of two experimentally measurable quantities. We list predictions at leading and next-to-leading order.

hep-ph↗
arXiv2001

Excited Heavy Baryons and Their Symmetries III: Phenomenology

Phenomenological applications of an effective theory of low-lying excited states of charm and bottom isoscalar baryons are discussed at leading and next-to-leading order in the combined heavy quark and large $N_c$ expansion. The combined expansion is formulated in terms of the counting parameter $λ\sim 1/m_Q, 1/N_c$; the combined expansion is in powers of $λ^{1/2}$. We work up to next-to-leading order. We obtain model-independent predictions for the excitation energies, the semileptonic form factors and electromagnetic decay rates. The spin-averaged mass of the doublet of the first orbitally excited sate of $Λ_b$ is predicted to be approximately $5920 MeV$. It is shown that in the combined limit at leading and next-to-leading order there is only one independent form factor describing $Λ_b \to Λ_c \ell \barν$; similarly, $Λ_b \to Λ_{c}^{*} \ell \barν$ and $Λ_b \to Λ_{c1} \ell \barν$ decays are described by a single independent form factor. These form factors are calculated at leading and next-to-leading order in the combined expansion. The electromagnetic decay rates of the first excited states of $Λ_c$ and $Λ_b$ are determined at leading and next-to leading order. The ratio of radiative decay rates $Γ(Λ_{c}^{*} \to Λ_c γ) / Γ(Λ_{b1} \to Λ_b γ)$ is predicted to be approximately 0.2, greatly different from the heavy quark effective theory value of unity.

hep-ph↗
arXiv2001

Excited Heavy Baryons and Their Symmetries II: Effective Theory

We develop an effective theory for heavy baryons and their excited states. The approach is based on the contracted O(8) symmetry recently shown to emerge from QCD for these states in the combined large N_c and heavy quark limits. The effective theory is based on perturbations about this limit; a power counting scheme is developed in which the small parameter is lambda^{1/2} where lambda ~ 1/N_c, Lambda /m_Q (with Lambda being a typical strong interaction scale). We derive the effective Hamiltonian for strong interactions at next-to-leading order. The next-to-leading order effective Hamiltonian depends on only two parameters beyond the known masses of the nucleon and heavy meson. We also show that the effective operators for certain electroweak transitions can be obtained with no unknown parameters at next-to-leading order.

hep-ph↗
arXiv2000

Quons in Relativistic Theories Must be Bosons or Fermions

The quon algebra describes particles, ``quons,'' that are neither fermions nor bosons using a label q that parametrizes a smooth interpolation between bosons (q = +1) and fermions (q = -1). We derive ``conservation of statistics'' relations for quons in relativistic theories, and show that in relativistic theories quons must be either bosons or fermions.

hep-th↗
arXiv2000

Excited Heavy Baryons and Their Symmetries I: Formalism

This is the first of two papers to study a new emergent symmetry which connects orbitally excited heavy baryons to the ground states in the combined heavy quark and large $N_c$ limit. The existence of this symmetry is shown in a model-independent way, and different possible realizations of the symmetry are discussed. It is also proved that this emergent symmetry commutes with the large $N_c$ spin-flavor symmetry.

hep-ph↗
arXiv2000

Quantum Coins, Dice and Children: Probability and Quantum Statistics

We discuss counterintuitive aspects of probabilities for systems of identical particles obeying quantum statistics. Quantum coins and children (two level systems) and quantum dice (many level systems) are used as examples. It is emphasized that, even in the absence of interactions, (anti)symmetrizations of multi-particle wavefunctions destroy statistical independences and often lead to dramatic departures from our intuitive expectations.

quant-ph↗
arXiv1999

Crater Property in Two-Particle Bound States: When and Why

Crater has shown that, for two particles (with masses $m_1$ and $m_2$) in a Coulombic bound state, the charge distribution is equal to the sum of the two charge distributions obtained by taking $m_1\to\infty$ and $m_2\to\infty$ respectively, while keeping the same Coulombic potential. We provide a simple scaling criterion to determine whether an arbitrary Hamiltonian possesses this property. In particular we show that, for a Coulombic system, fine structure corrections preserve this Crater property while two-particle relativistic corrections and/or hyperfine corrections may destroy it.

physics.gen-ph↗
arXiv1999

Looking For Disoriented Chiral Condensates From Pion Distributions

We suggest two methods for the detection of the formation of disoriented chiral condensates in heavy ion collisions. We show that the variance in the number of charged pions (in a suitable range of momentum space) provides a signature for the observation of a disoriented chiral condensate. The signal should be observable even if multiple domains of D$χ$C form provided the average number of pions per domain is significantly larger than unity. The variance of the number charged pions alone provides a signal which can be used even if the number of neutral pions cannot be measured in a given detector. On the other hand, the probability distribution in $R$, the proportion of neutral pions to all pions emitted in heavy ion collisions in certain kinematic regions, has been suggested as a signal of a disoriented chiral condensate. Here we note that the signature can be greatly enhanced by making suitable cuts in the data. In particular, we consider reducing the data set such that the $k$ pions with lowest $p_T$ are all neutral. We find that, given such cuts, $ $ can be substantially different from 1/3. For example, for a single D$χ$C domain without contamination due to incoherently emitted pions, $ $ is 3/5 given the pion with lowest $p_T$ is neutral, and 5/7 given the two pions with lowest $p_T$ are both neutral, {\it etc.}. The effects of multi-domain D$χ$C formation and noise due to incoherent pion emission can be systematically incorporated. Potential applications to experiments and their limitations are briefly discussed.

nucl-th↗
arXiv1999

Enhanced Signatures for Disoriented Chiral Condensates

The probability distribution in $R$, the proportion of neutral pions to all pions emitted in heavy ion collisions in certain kinematic regions, has been suggested as a signal of a disoriented chiral condensate (D$χ$C). Here we note that the signature can be greatly enhanced by making suitable cuts in the data. In particular, we consider reducing the data set such that the $k$ pions with lowest $p_T$ are all neutral. We find that, given such cuts, $ $ can be substantially different from 1/3. For example, for a single D$χ$C domain without contamination due to incoherently emitted pions, $ $ is 3/5 given the pion with lowest $p_T$ is neutral, and 5/7 given the two pions with lowest $p_T$ are both neutral, etc.. The effects of multi-domain D$χ$C formation and noise due to incoherent pion emission can be systematically incorporated. Potential applications to experiments and their limitations are briefly discussed.

nucl-th↗
arXiv1999

Signatures of Disoriented Chiral Condensates from Charged Pions

We show that the variance in the number of charged pions (in a suitable range of momentum space) provides a signature for the observation of a disoriented chiral condensate (D$χ$C). The signal should be observable even if multiple domains of D$χ$C form provided the average number of pions per domain is significantly large than unity. The variance of the number charged pions alone provides a signal which can be used even if the number of neutral pions cannot be measured in a given detector. If the neutrals can be measured, however, the fluctuations in the total number of pions provides a signature which distinguishes disoriented chiral condensates from other hypothetical sources of coherent states of pions.

nucl-th↗
arXiv1998

Discretization Errors and Rotational Symmetry: The Laplacian Operator on Non-Hypercubical Lattices

Discretizations of the Laplacian operator on non-hypercubical lattices are discussed in a systematic approach. It is shown that order $a^2$ errors always exist for discretizations involving only nearest neighbors. Among all lattices with the same density of lattice sites, the hypercubical lattices always have errors smaller than other lattices with the same number of spacetime dimensions. On the other hand, the four dimensional checkerboard lattice (also known as the Celmaster lattice) is the only lattice which is isotropic at order $a^2$. Explicit forms of the discretized Laplacian operators on root lattices are presented, and different ways of eliminating order $a^2$ errors are discussed.

hep-lat↗
arXiv1998

Hybrid Baryons in Large-N_c QCD

We study the properties and couplings of hybrid baryons in the large-$N_c$ expansion. These are color-neutral baryon states which contain in addition to $N_c$ quarks also one constituent gluon. Hybrid baryons with both symmetric and mixed symmetric orbital wave functions are considered. We introduce a Hartree description for these states, similar to the one used by Witten for ordinary baryons. It is shown that the Hartree equations for $N_c (N_c-1)$ quarks for symmetric (mixed symmetric) states in these states coincide with those in ordinary baryons in the large-$N_c$ limit. The energy due to the gluon field is of order $Λ_{QCD}$. Under the assumption of color confinement, our results prove the existence of hybrid baryons made up of heavy quarks in the large $N_c$ limit and provides a justification for the constituent gluon picture of these states. The couplings of the hybrid baryons to mesons of arbitrary spin are computed in the quark model. Using constraints from the large $N_c$ scaling laws for the meson-baryon scattering amplitudes, we write down consistency conditions for the meson couplings of the hybrid baryons. These consistency conditions are solved explicitly with results in agreement with those in the quark model for the respective couplings.

hep-ph↗
arXiv1998

Baryon Chiral Perturbation Theory in Partially Quenched Large-Nc QCD

Baryons of lower spin in partially quenched large-$N_c$ QCD are studied with particular emphasis to interpolation between standard unquenched and fully quenched limits. In large $N_c$ limit of partially quenched QCD, we calculate $Δm$, the chiral one-loop correction to baryon masses. We find that leading order contribution to $Δm$ is independent of number of ghost quarks introduced. For finite $N_c$, chiral correction $Δm$ does satisfy the Bernard--Golterman's third theorem and has no infared quenching singularity except for fully quenched limit. At large $N_c$ limit, however, we show that the third theorem is bypassed and nontrivial quenched chiral corrections do arise. In unquenched limit, we also show that standard chiral perturbation theory results are reproduced in which $η'$ loop contributions are explicitly taken into account.

hep-ph↗
arXiv1998

Quenched and Partially Quenched Chiral Perturbation Theory for Vector and Tensor Mesons

Quenched and partially quenched chiral perturbation theory for vector mesons is developed and is used to extract chiral loop correction to the $ρ$ meson mass. Connections to fully quenched and totally unquenched chiral perturbation theory results are discussed. It is also shown that (partially) quenched perturbation theory for tensor mesons can be formulated analogously, and the chiral corrections for tensor meson masses are directly proportional to their counterparts in the vector meson sector. Utilizing this observation and non-relativistic quark model, we point out that mass difference $(m_{a_2} - {3 \over 2} m_ρ)$ is ``quenching-insensitive'' in large-$N_c$ limit. This quantity may be used for normalization of mass scale in lattice QCD calculations.

hep-ph↗
arXiv1997

Aspects of Quenched Chiral Perturbation Theory for Matter Fields

Three topics about the application of quenched chiral perturbation theory to matter fields are studied. It is proved that the hairpin axial current couplings in quenched chiral perturbation theories do not contribute to the quenched chiral singularities for one chiral loop renormalization of matter field properties. The modification of mass corrections in the chiral limit due to nonzero mass splittings are studied, and selection rules for hadron decays in quenched QCD are obtained.

hep-ph↗