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Eric S. Swanson

Publications and source records attributed to Eric S. Swanson.

At least 19 recordsLinked to original sources
arXiv2026

Strong Decays of the Light Exotic $0^{+-}$ and $2^{+-}$ Hybrid Mesons

A model of hybrid meson structure based on the QCD Hamiltonian in Coulomb gauge and the use of a single constituent quasigluon is applied compute hadronic decays of mesons with exotic quantum numbers, $0^{+-}$ and $2^{+-}$. These correspond to hybrid mesons in which the gluon couples to a $q\bar{q}$ pair in an $P$-wave and can therefore be identified as orbital excitations of the exotic $1^{-+}$ state. Interestingly, we find $0^{+-}$ states to be narrow, contrary to what was found by previous calculations. This is primarily due to the suppression of the decay mode $0^{+-}\rightarrow 2^1S_0+1^1S_0$, which is unique to our model. The $2^{+-}$ states are found to be narrow, as expected.

hep-ph↗
arXiv2026

On Dispersive and Nondispersive K-matrix Formalisms

The modeling of coupled-channel effects has become increasingly important due to the availability of highly precise data for a large variety of hadronic (re)scattering processes. The K-matrix is a powerful, yet comparatively simple, method to describe scattering amplitudes, including coupled-channel effects, with the aim to interpret experimental data. Throughout the literature, a range of dispersive and nondispersive K-matrix methods are employed. Here, we compare the dispersive and nondispersive formulations in the context of the N/D method. It is shown that the methods are equivalent in the physical region under K-matrix reparameterization. Differences away from the physical region are examined. Applications to synthetic data are used to illustrate the effects of model choices concerning form factors and the application of dispersion relations, with the goal of clarifying best practices. We find no clear preference with regards to dispersive modeling. In contrast, we find that interpretational ambiguity of the bare model parameters -- and even of the form of the bare model -- is endemic, and recommend a thorough sampling of data and model spaces to assess conclusion robustness.

hep-ph↗
arXiv2025

A Primer on Functional Methods and the Schwinger-Dyson Equations

An elementary introduction to functional methods and the Schwinger-Dyson equations is presented. Emphasis is placed on practical topics not normally covered in textbooks, such as a diagrammatic method for generating equations at high order, different forms of Schwinger-Dyson equations, renormalisation, and methods for solving Schwinger-Dyson equations.

hep-ph↗
arXiv2024

Coulomb confinement in the Hamiltonian limit

The Gribov--Zwanziger scenario attributes the phenomenon of confinement to the instantaneous interaction term in the QCD Hamiltonian in the Coulomb gauge. For a static quark-antiquark pair, it leads to a potential energy that increases linearly with the distance between them. Lattice studies of the SU(2) Yang--Mills theory determined the corresponding (Coulomb) string tension for sources in the fundamental representation, $σ_{C}$, to be about three times larger than the Wilson loop string tension, $σ_F$. It is far above the Zwanziger variational bound, $σ_C \geq σ_F$. We argue that the value established in the literature is artificially inflated. We examine the lattice definition of the instantaneous potential, find the source of the string tension's enhancement, and perform its improved determination in SU(2) lattice gauge theory. We report our conservative estimate for the value of the Coulomb string tension as $σ_C/σ_F = 2.0 \pm 0.4$ and discuss its phenomenological implications.

hep-lat↗
arXiv2024

Poles and Poltergeists in $e^+ e^- \to D \bar D$ Data

A recent report of $e^+ e^- \to D\bar D$ events by the BESIII Collaboration suggests the presence of a structure $R$ at 3900~MeV\@. We argue that this structure, called $G(3900)$ in the past, is not in fact due to a new $c\bar c$ resonance, but rather naturally emerges as a threshold enhancement due to the opening of the $D^*\bar D$ channel. We further find that the appearance of this structure does not require suppression because of a radial node in the $ψ(4040)$ wave function, although a node improves fit quality. The measured $e^+ e^-$ coupling of $ψ(4040)$ is found to be substantially smaller than previously estimated. In addition, we report new corrections to the measured cross section $σ(e^+ e^- \to D\bar D)$ at energies near $ψ(3770)$.

hep-ph↗
arXiv2022

Substructure of Multiquark Hadrons (Snowmass 2021 White Paper)

In recent years there has been a rapidly growing body of experimental evidence for existence of exotic, multiquark hadrons, i.e. mesons which contain additional quarks, beyond the usual quark-antiquark pair and baryons which consist of more than three quarks. In all cases with robust evidence they contain at least one heavy quark Q=c or b, the majority including two heavy quarks. Two key theoretical questions have been triggered by these discoveries: (a) how are quarks organized inside these multiquark states -- as compact objects with all quarks within one confinement volume, interacting via color forces, perhaps with an important role played by diquarks, or as deuteron-like hadronic molecules, bound by light-meson exchange? (b) what other multiquark states should we expect? The two questions are tightly intertwined. Each of the interpretations provides a natural explanation of parts of the data, but neither explains all of the data. It is quite possible that both kinds of structures appear in Nature. It may also be the case that certain states are superpositions of the compact and molecular configurations. This Whitepaper brings together contributions from many leading practitioners in the field, representing a wide spectrum of theoretical interpretations. We discuss the importance of future experimental and phenomenological work, which will lead to better understandingof multiquark phenomena in QCD.

hep-ph↗
arXiv2021

Physics Opportunities with Meson Beams for EIC

Over the past two decades, meson photo- and electroproduction data of unprecedented quality and quantity have been measured at electromagnetic facilities worldwide. By contrast, the meson-beam data for the same hadronic final states are mostly outdated and largely of poor quality, or even non-existent, and thus provide inadequate input to help interpret, analyze, and exploit the full potential of the new electromagnetic data. To reap the full benefit of the high-precision electromagnetic data, new high-statistics data from measurements with meson beams, with good angle and energy coverage for a wide range of reactions, are critically needed to advance our knowledge in baryon and meson spectroscopy and other related areas of hadron physics. To address this situation, a state-of-the-art meson-beam facility needs to be constructed. The present letter summarizes unresolved issues in hadron physics and outlines the vast opportunities and advances that only become possible with such a facility.

nucl-ex↗
arXiv2020

Heavy Hybrid Decays in a Constituent Gluon Model

A constituent gluon model that is informed by recent lattice field theory is developed. The model is then used to compute hybrid strong decay widths, that can be useful for the GlueX collaboration at Jefferson Lab and the PANDA collaboration at FAIR. Commensurately, forthcoming data from GlueX and PANDA will test the model. Widths tend to be large except for those of the lightest hybrid $S$-wave multiplet. Selection rules, extensions, limitations, and applications are discussed.

hep-ph↗
arXiv2018

Heavy-Quark Hybrid Mass Splittings: Hyperfine and "Ultrafine"

It is argued that the heavy-quark limit of QCD requires a certain combination of hyperfine mass splittings in heavy-quark hybrid-meson multiplets to be unusually small. This observation will assist in the exploration of the heavy-quark hybrid spectrum at facilities such as PANDA. Alternatively, a large measured value for this mass splitting indicates that at least one member of the multiplet must contain significant light-quark degrees of freedom.

hep-ph↗
arXiv2017

Quarkonium $h$ States As Arbiters of Exoticity

The mass splitting between the quarkonium spin-singlet state $h$ ($J^{PC} = 1^{+-}$) and the spin average of the quarkonium spin-triplet states $χ$ ($J^{PC} = 0^{++}, 1^{++}, 2^{++}$) is seen to be astonishingly small, not only in the charmonium and bottomonium cases where the relevant masses have been measured, but in positronium as well. We find, both in nonrelativistic quark models and in NRQCD, that this hyperfine splitting is so small that it can be used as a test of the pure $Q\bar Q$ content of the states. We discuss the $2P$ states of charmonium in the vicinity of $3.9$ GeV, where the putative exotics $X(3872)$ and $X(3915)$ have been seen and a new $χ_{c0}(2P)$ candidate has been observed at Belle.

hep-ph↗
arXiv2016

Heavy-Quark QCD Exotica

This review presents an overview of the remarkable progress in the field of heavy-quark exotic hadrons over the past 15 years. It seeks to be pedagogical rather than exhaustive, summarizing both the progress and specific results of experimental discoveries, and the variety of theoretical approaches designed to explain these new states.

hep-ph↗
arXiv2016

$B$ and $B_s$ Meson Spectroscopy

Properties of bottom and bottom-strange mesons are computed in two relativized quark models. Model masses and wavefunctions are used to predict radiative transition rates and the $^3P_0$ quark pair creation model is used to compute strong decay widths. A comparison to recently observed bottom and bottom-strange states is made. We find that there are numerous excited $B$ and $B_s$ mesons that have relatively narrow widths and significant branching ratios to simple final states such as $Bπ$, $B^*π$, $BK$, and $B^*K$ that could be observed in the near future.

hep-ph↗
arXiv2015

Physics Opportunities with Meson Beams

Over the past two decades, meson photo- and electro-production data of unprecedented quality and quantity have been measured at electromagnetic facilities worldwide. By contrast, the meson-beam data for the same hadronic final states are mostly outdated and largely of poor quality, or even nonexistent, and thus provide inadequate input to help interpret, analyze, and exploit the full potential of the new electromagnetic data. To reap the full benefit of the high-precision electromagnetic data, new high-statistics data from measurements with meson beams, with good angle and energy coverage for a wide range of reactions, are critically needed to advance our knowledge in baryon and meson spectroscopy and other related areas of hadron physics. To address this situation, a state of-the-art meson-beam facility needs to be constructed. The present paper summarizes unresolved issues in hadron physics and outlines the vast opportunities and advances that only become possible with such a facility.

hep-ph↗
arXiv2014

The Gluon Propagator with Two-loop Schwinger-Dyson Equations

Gluon, ghost, and quark propagators are computed in the Schwinger-Dyson formalism. The full set of one-loop and two-loop contributions to the gap equations are evaluated for the first time. A new and efficient method for dealing with quadratic divergences is presented and a consistent renormalization method is proposed. We find that the two-loop contribution to the propagators is subleading, good fits to lattice data are possible, and reliable vertex models are important to obtaining desired ultraviolet, infrared, and gauge-symmetric behavior.

hep-ph↗
arXiv2012

Spin Zero Glueballs in the Bethe-Salpeter Formalism

The Schwinger-Dyson Bethe-Salpeter approach to the bound state problem is applied to the spin zero glueball spectrum. Although a moderately successful description of the two point functions and the glueball spectrum can be obtained, further work is required to reduce sensitivity to model truncations.

hep-ph↗
arXiv2011

Modelling DNA Response to THz Radiation

Collective response of DNA to THz electric fields is studied in a simple pair bond model. We confirm, with some caveats, a previous observation of destabilising DNA breather modes and explore the parameter-dependence of these modes. It is shown that breather modes are eliminated under reasonable physical conditions and that thermal effects are significant.

physics.bio-ph↗
arXiv2010

Confinement Models at Finite Temperature and Density

In-medium chiral symmetry breaking in confining potential models of QCD is examined. Past attempts to analyse these models have been hampered by infrared divergences that appear at non-zero temperature. We argue that previous attempts to circumvent this problem are not satisfactory and demonstrate a simple resolution. We also show that the expectation that confining models do not exhibit a chiral phase transition is incorrect. The effect of summing ring diagrams is investigated and we present the first determination of the temperature-density phase diagram for two model systems. We find that observables and the phase structure of the confinement models depend strongly on whether quark polarisation is accounted for. Finally, it appears that standard confinement models cannot adequately describe both hadron phenomenology and in-medium properties of QCD.

hep-ph↗