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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Lattice NRQCD study on in-medium bottomonium spectra using a novel Bayesian reconstruction approach

We present recent results on the in-medium modification of S- and P-wave bottomonium states around the deconfinement transition. Our study uses lattice QCD with N{sub f} = 2 + 1 light quark flavors to describe the non-perturbative thermal QCD medium between 140MeV < T < 249MeV and deploys lattice regularized non-relativistic QCD (NRQCD) effective field theory to capture the physics of heavy quark bound states immersed therein. The spectral functions of the {sup 3}S{sub 1} (ϒ) and {sup 3}P{sub 1} (χ{sub b1}) bottomonium states are extracted from Euclidean time Monte Carlo simulations using a novel Bayesian prescription, which provides higher accuracy than the Maximum Entropy Method. Based on a systematic comparison of interacting and free spectral functions we conclude that the ground states of both the S-wave (ϒ) and P-wave (χ{sub b1}) channel survive up to T = 249MeV. Stringent upper limits on the size of the in-medium modification of bottomonium masses and widths are provided.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Quark-antiquark bound states and QCD running coupling within infrared confinement

Bound states of spin-half and spin-one particles are studied within a relativistic quantum-field model based on the infrared confinement. The spectra of quark-antiquark and two-gluon states are determined by master equations similar to the ladder Bethe-Salpeter equations. Masses of light, intermediate and heavy mesons are estimated in a wide range of scale (from hundreds MeV up to 10 GeV). A new, independent and specific infrared-finite behavior of QCD effective coupling is revealed in the low-energy domain.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Quarkonium in Hot Medium

I review recent progress in studying quarkonium properties in hot medium as well as possible consequences for quarkonium production in heavy ion collisions. There has been considerable interest in studying quarkonia in hot medium since the publication of the famous Matsui and Satz paper. It has been argued that color screening in a deconfined QCD medium will suppress the existence of quarkonium states, signaling the formation of a quark-gluon plasma (QGP) in heavy-ion collisions. Although this idea was proposed a long time ago, first principle QCD calculations, which go beyond qualitative arguments, have been performed only recently. Such calculations include lattice QCD determinations of quarkonium correlators; potential model calculations of the quarkonium spectral functions with potentials based on lattice QCD, as well as effective field theory approaches that justify potential models and reveal new medium effects. Spectral properties of heavy quark bound states are important ingredients in modeling of heavy quarkonium production in hot medium as will be discussed later.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Bottomonium suppression in heavy-ion collisions

The thermal suppression of heavy quark bound states represents an ideal observable for determining if one has produced a quark-gluon plasma in ultrarelativistic heavy-ion collisions. In recent years, a paradigm shift has taken place in the theory of quarkonium suppression due to new first principles calculations of the thermal widths of these states. These thermal widths are large, e.g. O(20–100 MeV) for the Υ ( 1 S ) , and cause in-medium suppression of the states at temperatures below their traditionally defined disassociation temperatures. In order to apply the newly developed understanding to phenomenology, however, one must make detailed 3+1d dissipative hydrodynamical models of the plasma including the effects of finite shear viscosity. These effects include not only the modification of the time evolution of the temperature of the system, flow, etc., but also non-equilibrium modifications of the heavy quark potential itself. In this proceedings contribution, we briefly review the setup for these model calculations and present comparisons of theory with data from RHIC 200 GeV/nucleon Au-Au collisions, LHC 2.76 TeV/nucleon Pb-Pb, and LHC 5.02 TeV/nucleon Pb-Pb collisions as a function of number of participants, rapidity, and transverse momentum.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Light-front Holography - A New Approach to Relativistic Hadron Dynamics and Nonperturbative QCD

The holographic mapping of gravity in AdS space to QCD, quantized at fixed light-front time, provides a precise relation between the bound-state amplitudes in the fifth dimension of AdS space and the boost-invariant light-front wavefunctions describing the internal structure of hadrons in physical space-time. In particular, the elastic and transition form factors of the pion and the nucleons are well described in this framework. The light-front AdS/QCD holographic approach thus gives a frame-independent first approximation of the color-confining dynamics, spectroscopy, and excitation spectra of relativistic light-quark bound states in QCD. More generally, we show that the valence Fock-state wavefunctions of the eigensolutions of the light-front QCD Hamiltonian satisfy a single-variable relativistic equation of motion, analogous to the nonrelativistic radial Schroedinger equation, with an effective confining potential which systematically incorporates the effects of higher quark and gluon Fock states. The proposed method to compute the effective interaction thus resembles the two-particle-irreducible functional techniques used in quantum field theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

AdS/QCD, LIight-Front Holography, and the Non-perturbative Running Coupling

The combination of Anti-de Sitter space (AdS) methods with light-front (LF) holography provides a remarkably accurate first approximation for the spectra and wavefunctions of meson and baryon light-quark bound states. The resulting bound-state Hamiltonian equation of motion in QCD leads to relativistic light-front wave equations in terms of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. These equations of motion in physical space-time are equivalent to the equations of motion which describe the propagation of spin-J modes in anti-de Sitter (AdS) space. The eigenvalues give the hadronic spectrum, and the eigenmodes represent the probability distributions of the hadronic constituents at a given scale. A positive-sign confining dilaton background modifying AdS space gives a very good account of meson and baryon spectroscopy and form factors. The light-front holographic mapping of this model also leads to a non-perturbative effective coupling {alpha}{sub s}{sup Ads} (Q{sup 2}) which agrees with the effective charge defined by the Bjorken sum rule and lattice simulations. It displays a transition from perturbative to nonperturbative conformal regimes at a momentum scale {approx} 1 GeV. The resulting {beta}-function appears to capture the essential characteristics of the full {beta}-function of QCD, thus giving further support to the application of the gauge/gravity duality to the confining dynamics of strongly coupled QCD.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Light-Front Holography and the Light-Front Schrodinger Equation

One of the most important nonperturbative methods for solving QCD is quantization at fixed light-front time {tau} = t+z=c - Dirac's 'Front Form'. The eigenvalues of the light-front QCD Hamiltonian predict the hadron spectrum and the eigensolutions provide the light-front wavefunctions which describe hadron structure. More generally, we show that the valence Fock-state wavefunctions of the light-front QCD Hamiltonian satisfy a single-variable relativistic equation of motion, analogous to the nonrelativistic radial Schrodinger equation, with an effective confining potential U which systematically incorporates the effects of higher quark and gluon Fock states. We outline a method for computing the required potential from first principles in QCD. The holographic mapping of gravity in AdS space to QCD, quantized at fixed light-front time, yields the same light front Schrodinger equation; in fact, the soft-wall AdS/QCD approach provides a model for the light-front potential which is color-confining and reproduces well the light-hadron spectrum. One also derives via light-front holography a precise relation between the bound-state amplitudes in the fifth dimension of AdS space and the boost-invariant light-front wavefunctions describing the internal structure of hadrons in physical space-time. The elastic and transition form factors of the pion and the nucleons are found to be well described in this framework. The light-front AdS/QCD holographic approach thus gives a frame-independent first approximation of the color-confining dynamics, spectroscopy, and excitation spectra of relativistic light-quark bound states in QCD.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Relativistic description of pair production of doubly heavy baryons in e{sup +}e{sup −} annihilation

Relativistic corrections in the pair production of S-wave doubly heavy diquarks in electron-positron annihilation were calculated on the basis of perturbative QCD and the quark model. The relativistic corrections to the wave functions for quark bound states were taken into account with the aid of the Breit potential in QCD. Relativistic effects change substantially the nonrelativistic cross sections for pair diquark production. The yield of pairs of (ccq) doubly heavy baryons at B factories was estimated.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

QCD and Light-Front Holography

The soft-wall AdS/QCD model, modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics. The model predicts a zero-mass pion for zero-mass quarks and a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum L of hadrons and the radial quantum number N. Light-Front Holography maps the amplitudes which are functions of the fifth dimension variable z of anti-de Sitter space to a corresponding hadron theory quantized on the light front. The resulting Lorentz-invariant relativistic light-front wave equations are functions of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. The result is to a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryon light-quark bound states, which in turn predict the behavior of the pion and nucleon form factors. The theory implements chiral symmetry in a novel way: the effects of chiral symmetry breaking increase as one goes toward large interquark separation, consistent with spectroscopic data, and the the hadron eigenstates generally have components with different orbital angular momentum; e.g., the proton eigenstate in AdS/QCD with massless quarks has L = 0 and L = 1 light-front Fock components with equal probability. The soft-wall model also predicts the form of the non-perturbative effective coupling {alpha}{sub s}{sup AdS} (Q) and its {beta}-function which agrees with the effective coupling {alpha}{sub g1} extracted from the Bjorken sum rule. The AdS/QCD model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method in order to systematically include the QCD interaction terms. A new perspective on quark and gluon condensates is also reviewed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

QCD running coupling in low-energy region

We estimate the QCD effective charge {alpha}{sub s} in the low-energy region by exploiting the conventional meson spectrum within a relativistic quantum-field model based on analytic confinement. The ladder Bethe-Salpeter equation is solved for the masses of two-quark bound states. We found a new, independent, and specific infrared-finite behavior of QCD coupling below energy scale 1 GeV. Particularly, an infrared-fixed point is extracted at {alpha}{sub s}(0){approx_equal}0.757 for confinement scale {Lambda}=345 MeV. As an application, we estimate masses of some intermediate and heavy mesons and obtain results in reasonable agreement with recent experimental data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

William A. Bardeen: A life in physics and the legacy of the chiral anomaly

William Allan Bardeen (September 15, 1941 − November 18, 2025) was an American theoretical physicist who worked at the Fermi National Accelerator Laboratory. He is renowned for his foundational work on the chiral anomaly, the Adler-Bardeen theorem, the non-Abelian anomaly and gravitational anomalies. He was instrumental in the development of quantum chromodynamics and its applications, such as semileptonic decays and the Λ $\overline{MS}$ scheme frequently used in perturbative analysis of high energy processes involving strong interactions. Bardeen also played a major role in developing a theory of dynamical breaking of electroweak symmetry via top quark condensates, leading to one of the first composite Brout-Englert-Higgs boson models. His work on the chiral symmetry dynamics of heavy-light quark bound states correctly predicted abnormally long-lived resonances which are chiral symmetry partners of the ground state.

Hill, Christopher T. [Fermi National Accelerator L↗
DOE OSTI2011

Resonances in a finite volume

We review applications of effective field theory methods in a finite volume for the extraction of the characteristics of unstable particles from lattice QCD calculations. In particular, the scalar mesons f{sub 0}(980),a{sub 0}(980) are considered. We formulate criteria that distinguish between hadronic molecules and tightly bound quark states, as well as between the ordinary qq-bar and the tetraquark states. Using these criteria will enable one to study the nature of scalar mesons on the lattice. Further, we also formulate a procedure to calculate resonance matrix elements on the lattice by using the background field method.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗