Angular momentum conservation law in light-front quantum field theory

Chiu, Kelly Yu-Ju; Brodsky, Stanley J.

doi:10.1103/physrevd.95.065035

Cited by 31 publications

(44 citation statements)

References 23 publications

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“…Only one power of orbital angular momentum L z can appear at a vertex in a renormalizable theory. This leads to new rigorous selection rules for the spin dependence of scattering amplitudes [9]. One also can demonstrate an important property of quantum gravity applied to hadrons: the anomalous gravitomagnetic moment of every LF Fock state of a hadron vanishes at Q 2 = 0 [10].…”

Section: Weak Transition Form Factorsmentioning

confidence: 93%

Color Confinement and Supersymmetric Properties of Hadron Physics from Light-Front Holography

Brodsky¹

2019

J. Phys.: Conf. Ser.

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I review applications of superconformal algebra. light-front holography, and an extended form of conformal symmetry to hadron spectroscopy and dynamics. QCD is not supersymmetrical in the traditional sense -the QCD Lagrangian is based on quark and gluonic fields -not squarks nor gluinos. However, its hadronic eigensolutions conform to a representation of superconformal algebra, reflecting the underlying conformal symmetry of chiral QCD. The eigensolutions of superconformal algebra provide a unified Regge spectroscopy of meson, baryon, and tetraquarks of the same parity and twist as equal-mass members of the same 4-plet representation with a universal Regge slope. The pion qq eigenstate is composite but yet has zero mass for m q = 0. Light-Front Holography also predicts the form of the nonperturbative QCD running coupling:in agreement with the effective charge determined from measurements of the Bjorken sum rule. One also obtains viable predictions for tests of hadron dynamics such as spacelike and timelike hadronic form factors, structure functions, distribution amplitudes, and transverse momentum distributions. The combined approach of light-front holography and superconformal algebra also provides insight into the origin of the QCD mass scale and color confinement. A key tool is the dAFF principle which shows how a mass scale can appear in the Hamiltonian and the equations of motion while retaining the conformal symmetry of the action. When one applies the dAFF procedure to chiral QCD, a mass scale κ appears which determines universal Regge slopes, hadron masses in the absence of the Higgs coupling. The result is an extended conformal symmetry which has a conformally invariant action even though an underlying mass scale appears in the Hamiltonian. Although conformal symmetry is strongly broken by the heavy quark mass, the supersymmetric mechanism, which transforms mesons to baryons (and baryons to tetraquarks), still holds and gives remarkable mass degeneracies across the spectrum of light, heavy-light and double-heavy hadrons.

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Section: Weak Transition Form Factorsmentioning

confidence: 93%

Color Confinement and Supersymmetric Properties of Hadron Physics from Light-Front Holography

Brodsky¹

2019

J. Phys.: Conf. Ser.

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“…Writing p ≡ ðp − ; p ⊥ Þ for the three lightfront "spatial" components of momentum, we observe that s ∝ p, similar to the usual (Jacob-Wick) definition of helicity [46], where one would have s ∝ p for the Cartesian vector components. This choice of s μ is exactly that of "lightfront helicity" used in lightfront field theory [41,42,47], where n μ arises through the choice of time direction. Lightfront helicity states have the special property that the helicity, call it σ, is equal to the expectation value of the spin in the z-direction, σ ¼ AE1, in all Lorentz frames, so that we may talk of spin and helicity interchangeably.…”

Section: A Lightfront Helicitymentioning

confidence: 99%

Loop spin effects in intense background fields

2020

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Radiative and nonradiative electron spin-flip probabilities are analyzed in both plane wave and focused laser backgrounds. We provide a simple and physically transparent description of spin dynamics in plane waves, and demonstrate that there exists a kinematic regime in which the usual leading-order perturbative hierarchy of quantum electrodynamics is reversed, and nonradiative loop effects dominate over radiative tree-level spin flips. We show that while this loop dominance becomes suppressed in focused laser pulses due to a high sensitivity to field geometry, there is nevertheless a regime in which, in principle, loop effects on spin transitions can be discerned.

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“…In a renormalizable theory 푧 can only change by one unit at any vertex. This leads to a rigorous selection rule for amplitudes at fixed order in pQCD [52]: |Δ 푧 | ≤ in an th order perturbative expansion. This selection rule for the orbital angular momentum can be used to eliminate interaction vertices in QED and QCD and provides an upper bound on the change of orbital angular momentum in scattering processes at any fixed order in perturbation theory.…”

Section: Calculations Using Lf-time-ordered Perturbation Theory and Hmentioning

confidence: 99%

“…In a renormalizable theory, the change in orbital angular momentum is limited to Δ 푧 = 0, ±1 at each vertex [52].…”

Section: Calculations Using Lf-time-ordered Perturbation Theory and Hmentioning

confidence: 99%

Color Confinement, Hadron Dynamics, and Hadron Spectroscopy from Light-Front Holography and Superconformal Algebra

Brodsky

2018

Advances in High Energy Physics

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The QCD light-front Hamiltonian equation LF |Ψ⟩ = 2 |Ψ⟩ derived from quantization at fixed LF time = + / provides a causal, frame-independent method for computing hadron spectroscopy as well as dynamical observables such as structure functions, transverse momentum distributions, and distribution amplitudes. The QCD Lagrangian with zero quark mass has no explicit mass scale. de Alfaro, Fubini, and Furlan (dAFF) have made an important observation that a mass scale can appear in the equations of motion without affecting the conformal invariance of the action if one adds a term to the Hamiltonian proportional to the dilatation operator or the special conformal operator. If one applies the dAFF procedure to the QCD light-front Hamiltonian, it leads to a color-confining potential 4 2 for mesons, where 2 is the LF radial variable conjugate to the invariant mass squared. The same result, including spin terms, is obtained using light-front holography, the duality between light-front dynamics and AdS 5 , if one modifies the AdS 5 action by the dilatonin the fifth dimension . When one generalizes this procedure using superconformal algebra, the resulting light-front eigensolutions provide a unified Regge spectroscopy of meson, baryon, and tetraquarks, including remarkable supersymmetric relations between the masses of mesons and baryons and a universal Regge slope. The pion eigenstate has zero mass at 푞 = 0. The superconformal relations also can be extended to heavy-light quark mesons and baryons. This approach also leads to insights into the physics underlying hadronization at the amplitude level. I will also discuss the remarkable features of the Poincaré invariant, causal vacuum defined by light-front quantization and its impact on the interpretation of the cosmological constant. AdS/QCD also predicts the analytic form of the nonperturbative running couplingThe mass scale underlying hadron masses can be connected to the parameter Λ MS in the QCD running coupling by matching the nonperturbative dynamics to the perturbative QCD regime. The result is an effective coupling 푠 (2 ) defined at all momenta. One obtains empirically viable predictions for spacelike and timelike hadronic form factors, structure functions, distribution amplitudes, and transverse momentum distributions. Finally, I address the interesting question of whether the momentum sum rule is valid for nuclear structure functions.

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Angular momentum conservation law in light-front quantum field theory

Cited by 31 publications

References 23 publications

Color Confinement and Supersymmetric Properties of Hadron Physics from Light-Front Holography

Color Confinement and Supersymmetric Properties of Hadron Physics from Light-Front Holography

Loop spin effects in intense background fields

Color Confinement, Hadron Dynamics, and Hadron Spectroscopy from Light-Front Holography and Superconformal Algebra

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