arXiv subjects

Dennis Sivers

Publications and source records attributed to Dennis Sivers.

17 recordsLinked to original sources

arXiv2024

AI for Nuclear Physics: the EXCLAIM project

In overview of the recent activity of the newly funded EXCLusives with AI and Machine learning (EXCLAIM) collaboration is presented. The main goal of the collaboration is to develop a framework to implement AI and machine learning techniques in problems emerging from the phenomenology of high energy exclusive scattering processes from nucleons and nuclei, maximizing the information that can be extracted from various sets of experimental data, while implementing theoretical constraints from lattice QCD. A specific perspective embraced by EXCLAIM is to use the methods of theoretical physics to understand the working of ML, beyond its standardized applications to physics analyses which most often rely on industrially provided tools, in an automated way.

hep-ph↗

arXiv2021

Spherically Symmetric Chromostatic Condensates as an Introduction to the Strong Conjecture for Color Confinement

Nonlinearities imbedded in the Lagrange density for non-Abelian gauge theories produce solutions to the Yang-Mills Maxwell equations that describe spatially extended chromostatic condensates. For solutions in spherically-symmetric SU(2) the topological structures separating such condensates provide a specific solitonic description of color confinement. The strong Conjecture The confinement mechanism for QCD involves a domain wall of topological (CP-odd) charge separating the interior volume of hadrons from an exterior volume. To explain the consequences of this conjecture we describe spherically symmetric chromostatic condensates that are consistent with the interior volume of a hadron and other condensates that are consistent with exterior vacuum volume. We then demonstrate how the Yang-Mills Maxwell equations can connect the two volumes with a soliton domain wall. The preliminary phenomenological description described here does not deal explicitly either with charged fermions or with the quantization of non-Abelian dynamics.

hep-th↗

arXiv2019

SU(2) Charges with Spherical Symmetry and Confining Boundary Conditions

Applying the static Yang-Mills Maxwell equations to a simple system of SU(2) charges with spherical symmetry and confining boundary conditions provides for a demonstration of the likelihood that the confinement mechanism in non-Abelian gauge theories necessarily involves a topologically-charged domain wall consisting of a surface volume with CP-odd field strength density. The surface volume of a color-singlet system of SU(2) charges therefor describes the magnetic dual of a topological insulator. This essential topological structure in inextricably connected to the hadronic dynamics of the pion tornado. In analogy to the kink solution in the 1+1 dimensional Abelian Higgs model the classical solutions for the field equations in spherically symmetric SU(2) with this domain wall of topological charge can lead to a mass gap in the quantum system

hep-ph↗

arXiv2019

Field-Strength Descriptions for a System of Classical SU(2) Charges with Spherical Symmetry and Confining Boundary Conditions

The existence of a mechanism within the non-Abelian dynamics of QCD that confines quarks and gluons to the interior of hadrons has long been accepted empirically. To explore what this mechanism might look like, this paper examines field-strength descriptions for an extended system of SU(2) charges with spherical symmetry and imposes alternate confining boundary conditions to the time-independent Yang-Mills Maxwell equations. Three types of global solutions to the set of equations can be distinguished: types 0,1,and2. Type-0 solutions evade the nonlinear dynamics associated with the radial magnetic field to describe a topologically trivial bound state. Type-1 and type-2 solutions both require a domain wall of topological charge to separate the interior volume containing the SU(2) charge densities from the exterior volume where the boundary conditions are imposed. Type-1 solutions describe an exterior volume with a radial magnetic field while type-2 solutions contain a sterile exterior volume where all field-strengths vanish. These solutions both describe a non-Abelian "spherical dual topological insulator". the dimensional reduction associated with the imposition of spherical system of SU(2) charges can also be applied to SU(3) charges so this simple exercise is directly relevant to understanding confinement in QCD.

hep-ph↗

arXiv2015

Spin-Directed Momentum Transfers in SIDIS Baryon Production

The measurement of transverse single-spin asymmetries for baryon production in the target fragmentation region of semi-inclusive deep-inelastic scattering (SIDIS), can produce important insight into those nonperturbative aspects of QCD directly associated with confinement and with the dynamical breaking of chiral symmetry. We discuss here, interns of spin-directed momentum transfers, the powerful quantum field-theoretical constraints on the spin-orbit dynamics underlying these transverse spin observables. The spin-directed momentum shifts, originating either in the target nucleon or in the QCD jets produced in the deep inelastic scattering process, represent significant quantum entanglement effects connecting information from current fragmentation with observables in target fragmentation.

hep-ph↗

arXiv2014

Ideas in transverse spin physics

Three simple ideas about transverse spin observables are presented for the purpose of stimulating discussion. The manuscript is based on a presentation at the "Transversity 2014" workshop in Torre Chia, Sardinia, Italy on June 9-13, 2014 where approximately sixty experts on transverse spin physics had gathered to share recent results in an atmosphere of sun-drenched intensity.

hep-ph↗

arXiv2013

Kane-Pumplin-Repko Factorization: its application to precision measurements of transverse spin asymmetries and to the study of TMD evolution

This article presents a summary of overlapping presentations by the author to the QCD Evolution 2013 Workshop and to the Opportunities for Polarized Physics at Fermilab Workshop. It contains an introduction to the concept of Kane-Pumplin-Repko (KPR) factorization and descibes how this concept can be used in the analysis of high-precision measurements of parity-conserving transverse single-spin asymmetries. The discussion demonstrates that such measurements can not only probe directly for specific mechanisms that enhance our fundamental understanding of nonperturbative QCD but, because transverse spin asymmetries are unambiguously perameterized by a spin-directed momentum shift, such measurements can also be used to calibrate other phenomenological applications of transverse momentum dependent distributions (TMD's) and of TMD evolution. The calibration supplied by these measurements can thus enable the use of TMD factorization for the exploration of a broad range of other aspects of hadronic structure.

hep-ph↗

arXiv2011

The Adventure and the Prize

This article presnts a condensed summary of separate, overlapping, presentations to the Workshop on Polarized Drell-Yan Physics (Santa Fe, NM, Oct. 31-Nov.1, 2010),the GHP 2011 Worshop (Anaheim, CA, Apr.21-27, 2011) and the Transversity 2011 Workshop (Veli-Lozinj, Croatia, Aug. 29-Sep. 2, 2011) during which the author advocated for a potential experimental program based at Fermilab utilizing high-intensity polarized proton beams of 120 GeV/c to 150 GeV/c. Some possible experiments in this program are introduced briefly. Interpretations for these potential experiments are presented in terms of a hypothetical solution to the "Quantum Yang Mills Theory" problem posed by Arthur Jaffe and Edward Witten as one of the seven Millenium Prize Problems in Mathematics issued by the Clay Mathematics Institute. These comparisons illustrate the close connection between transverse spin observables and the complex dynamics of confinement and chiral symmetry breaking found in quantum chormodynamics.

hep-ph↗

arXiv2011

Quantum Number Density Asymmetries Within QCD Jets Correlated With Lambda Polarization

The observation of jets in a variety of hard-scattering processes has allowed the quantitative study of perturbative quantum chromodynamics (PQCD) by comparing detailed theoretical predictions with a wide range of experimental data. This paper examines how some important, nonperturbative, facets of QCD involving the internal dynamical structure of jets can be studied by measuring the spin orientation of Lambda particles produced in these jets. The measurement of the transverse polarization for an individual Lambda within a QCD jet permits the definition of spin-directed asymmetries in local quantum number densities in rapidity space (such as charge, strangeness and baryon number densities) involving neighboring hadrons in the jet. These asymmetries can only be generated by soft, nonperturbative dynamical mechanisms and such measurements can provide insight not otherwise accessible into the color rearrangement that occurs during the hadronization stage of the fragmentation process.

hep-ph↗

arXiv2011

Studying Spin-Orbit Dynamics using Measurements of the Proton's Polarized Gluon Asymmetry

Measurements involving the gluon spin density, Delta G=G++ - G+-, can play an important role in the quantitative understanding of proton structure. To demonstrate this, we show that the shape of the gluon asymmetry, A(x,t)=Delta G(x,t)/G(x,t), contains significant dynamical information about non-perturbative spin-orbit effects. It is instructive to use a separation A(x,t)=A_0^epsilon(x)+epsilon(x,t), where A_0^epsilon(x) is an approximately scale-invariant form that can be calculated within a given factorization prescription from the measured distributions Delta q(x,t), q(x,t) and G(x,t). Applying this separation with the J_z=1/2 sum rule provides a convenient way to determine the total amount of orbital angular momentum generated by mechanisms associated with confinement and chiral dynamics. The results are consistent with alternate non-perturbative approaches to the determination of orbital angular momentum in the proton. Our studies help to specify the accuracy that future measurements should achieve to constrain theoretical models for nucleon structure.

hep-ph↗

arXiv2009

The Fractured Boer-Mulders Effect in the Production of Polarized Baryons

The fractured Boer-Mulders functions describe an inriguing class of polarization effects for the production of baryons in the target fragmentation region of deep-inelastic processes. These functions characterize transverse momentum asymmetries related to the spin orientation for different flavors of axial vector diquarks in an unpolarized ensemble of protons just as the familiar Boer-Mulders functions characterize transverse momentum asymmetries connected to the spin orientation of quarks in unpolarized targets. The asymmetries of the fractured Boer-Mulders effect originating in the proton distribution function can be separated kinematically, both in SIDIS and in the Drell-Yan process from the asymmetries of the polarizing fracture functions generated during the soft color rearrangement of the fragmentation process. The experimental requirements for this separation are presented in this article and it is shown that the fractured Boer-Mulders effect should change sign between Drell-Yan and SIDIS while the polarizing fracture functions remain the same. Simple isospin arguments indicate the two polarization mechanisms should give significantly different results for the production of polarized lambdas and sigmas.

hep-ph↗

arXiv2008

Chiral Dynamics of the Polarizing Fracture Functions for Baryon Production

The concept of spin-directed momentum provides a useful and restrictive framework for describing dynamical mechanisms that can lead to single-spin observables. The value of this framework can be demonstrated by consideration of the polarizing fracture functions that characterize the production of polarized baryons in the target fragmentation region of semi-inclusive deep inelastic scattering from an unpolarized target. When Bjorken x is chosen large enough to indicate a hard scattering from a valence quark, the fracture function formalism dynamically selects a quark-diquark basis for baryon structure. Attention to sonstituent orbital angular momentum in the formation process and its role in contribution to the transverse momentum of the produced baryon illustrates important aspects of the generation of polarization observables.

hep-ph↗

arXiv2008

Spin-Orbit Dynamics from the Gluon Asymmetry

Determination of the orbital angular momentum of the proton is a difficult but important part of understanding fundamental structure. Insight can be gained from suitable models of the gluon asymmetry applied to the Jz = 1/2 sum rule. We have constrained the models of the asymmetry to gain possible scenarios for the angular momentum of the proton's constituents. Results and phenomenology for determining Lz are presented.

hep-ph↗

arXiv2007

Chiral Dynamics and Single-Spin Asymmetries

Parity-conserving single-spin asymmetries provide a specific measure of coherent spin-orbit dynamics in quantum chromodynamics. The origin of these effects can be traced to the interplay of chiral dynamics and confinement in the theory. The most elegant display of the relevant mechanisms occurs in the Collins functions and the polarizing fragmentation functions and fracture functions for particles with spin. In the nucleon, these same dynamical mechanisms generate virtual quantum structures leading to the Boer-Mulders functions and orbital distributions. Two complementary formalisms for these distributions appear. The familiar gauge-link formalism incorporates oll nonperturbative dynamics into nonlocal correlators. The constructive formalism introduced by the author describes distributions normalized to an intrinsic property of the nucleon, namely, the currents specified in the Bakker-Leader-Trueman sum rule. The connection between these two approaches can be explored in the process dependence of single-spin asymmetries in various hard-scattering processes. The study of the SU(2) Weyl-Dirac equation in spherical coordinates allows typical Wilson operators that determine this process dependence to be evaluated in the coordinate gauge.

hep-ph↗

arXiv2007

Coherent Spin Manipulations of a Polarized Beam With a Localized RF Magnetic Field

The coherent manipulation of spin observables in storage rings provides opportunities to test the application of some fundamental dynamical principles. In this context, it is possible to confirm, using gauge invariance and Lorentz invariance, a conjecture framed by A. M. Kondratenko concerning the "natural" or "intrinsic" resonance strength applicable to a spin rotation from a controlled Froissart-Stora sweep with an RF dipole magnet. The discussion includes a brief treatment of the "forced" component of the resonance strength associated with the effect of the betatron oscillations induced by the operation of the RF diple and a discussion of the effective resonance strength as a function of betatron tunes.

hep-ph↗

arXiv2007

Chiral Mechanisms Leading to Orbital Quantum Structures in the Nucleon

Color confinement and chiral symmetry specify some important territory for the study of hadronic physics. Any hadron can be defined as a color-singlet composite system of qurks and gluons, the fundamental fields of qcd, while the landscape of the hadronic spectrum is dominated by the fact that two quark flavors, u and d, are characterized by masses small compared to the fundamental scale of this theory. Measurements sensitive to the orbital angular momenta of the color constituents of the nucleon display the interplay of chiral dynamics and confinement in a unique manner. This pageant can be explored by an evaluation, within the context of the Georgi-Manohar chiral quark model, of the normalization of the orbital structure functions and the normalization of the Boer-Mulders functions for different quark flavors. The resolution structures in the chiral quark model represent an evaluation of Collins functions for a confined system defined by the quantum numbers of the nucleon in the constituent quark model. The orbital structure functions for antiquarks can also be specified within the basic framework of this approach while the normalization of the gluon orbital structure function requires some additional assumptions.

hep-ph↗

arXiv2006

Single-Spin Observables and Orbital Structures in Hadronic Distributions

Within the light-quark sector of the standard model, P-odd observables are generated from point-like electroweak processes while A_t- odd observables (neglecting quark mass parameters) come from dynamic spin-orbit correlations within hadrons or within larger composite systems, such as nuclei. The effects of A_t-odd dynamics can be inserted into transverse-momentum dependent constituent distribution functions and, in this paper, we construct the contribution from an orbital quark to the A_t odd quark parton distribution. Using this distribution, we examine the crucial role of initial- and final-state interactions in the observation of the scattering asymmetries in different hard-scattering processes. This construction provides a geometrical and dynamical interpretation of the Collins conjugation relation between single-spin asymmetries in semi-inclusive deep inelastic scattering and the asymmetries in Drell-Yan production. Finally, our construction allows us to display a significant difference between the calculation of a spin asymmetry generated by a hard scattering mechanism involving color-singlet exchange (such as a photon) and a calculation of an asymmetry with a hard-scattering exchange involving gluons. This leads to an appreciation of the process dependence inherent in measurements of single-spin observables.

hep-ph↗