Light-cone Algebra Research Articles

BMS algebra from residual gauge invariance in light-cone gravity

We analyze the residual gauge freedom in gravity, in four dimensions, in the light-cone gauge, in a formulation where unphysical fields are integrated out. By checking the invariance of the light-cone Hamiltonian, we obtain a set of residual gauge transformations, which satisfy the BMS algebra realized on the two physical fields in the theory. Hence, the BMS algebra appears as a consequence of residual gauge invariance in the bulk and not just at the asymptotic boundary. We highlight the key features of the light-cone BMS algebra and discuss its connection with the quadratic form structure of the Hamiltonian.

The twisted story of worldsheet scattering in \u03b7-deformed AdS5\xd7 S5

We study the worldsheet scattering theory of the η deformation of the AdS5 × S5 superstring corresponding to the purely fermionic Dynkin diagram. This theory is a Weyl-invariant integrable deformation of the AdS5 × S5 superstring, with trigonometric quantum-deformed symmetry. We compute the two-body worldsheet S matrix of this string in the light-cone gauge at tree level to quadratic order in fermions. The result factorizes into two elementary blocks, and solves the classical Yang-Baxter equation. We also determine the corresponding exact factorized S matrix, and show that its perturbative expansion matches our tree-level results, once we correctly identify the deformed light-cone symmetry algebra of the string. Finally, we briefly revisit the computation of the corresponding S matrix for the η deformation based on the distinguished Dynkin diagram, finding a tree-level S matrix that factorizes and solves the classical Yang-Baxter equation, in contrast to previous results.

SUM RULES FOR DEEP-INELASTIC ELECTROWEAK PRODUCTION

Using light-cone algebra, various sum rules for electroweak structure functions are derived. These sum rules are examined in the context of the quark and gluon contents of the proton.

Covariant light-cone algebra

By introducing a variable lightlike vector k μ the light-cone gauge algebra of the bosonic string oscillators is rewritten in an apparently covariant form and it is shown that the apparent covariance becomes true covariance if, and only if, the parameters take the usual critical values. In particular it is shown that the k-independence of physical quantities is equivalent to the usual closure of the Lorentz group for fixed k μ and also to the zero-curvature of the light-cone-gauge surface. The connection of the k-formalism with the BRST formalism, and with other aspects of physics, notably spontaneous symmetry breaking mechanisms, is discussed.

Supersymmetric extension of the D4 bilocal current algebra

The supersymmetric extension of the Fritzch-Gell-Mann light cone algebra is introduced. It appears to be the only supersymmetry-covariant extension of the D=4 current algebra schemes for internal symmetries.

The Lund model

The Lund model, inspired by quantum chromodynamics, has provided a very promising approach to the dynamics of quark and gluon interactions. Starting with a brief reprise of basic concepts in relativity, quantum mechanics of fields and particle physics, this 1998 book discusses: the dynamics of the massless relativistic string; confinement; causality and relativistic covariance; Lund fragmentation processes; QED and QCD Bremsstrahlung; multiplicities and particle-parton distributions. Throughout the book, theory is confronted with current experimental data, and implications for future experiments are also considered. The book also explores the relationships between the Lund model and other models based on field theory (the Schwinger model, S-matrix models, light-cone algebra physics and variations of the parton model), and models based on statistical mechanics (the Feynman-Wilson gas, scaling, iterative cascade models).

Pseudoscalar electromagnetic vertex function: Quark-hadron duality.

A double-dispersion-relation model for the neutral-pseudoscalar-meson--two-photon vertex function is proposed. Several spectral-function sum rules are derived. Quark-hadron duality is established in the model, so that the low-energy behavior of the vertex function is dominated by vector-meson resonances, and the high-energy behavior of the vertex function is determined by QCD dynamics and light-cone algebra. The vertex function is then applied to study the decay processes ${\ensuremath{\pi}}^{0}$(${\ensuremath{\eta}}^{0}$)\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}, ${\ensuremath{\pi}}^{0}$(${\ensuremath{\eta}}^{0}$)\ensuremath{\rightarrow}${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$(${\ensuremath{\mu}}^{+}$\ensuremath{\mu} $^{\mathrm{\ensuremath{-}}}$), ${\ensuremath{\pi}}^{0}$(${\ensuremath{\eta}}^{0}$)\ensuremath{\rightarrow}${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$(${\ensuremath{\mu}}^{+}$\ensuremath{\mu} $^{\mathrm{\ensuremath{-}}}$)\ensuremath{\gamma}, and the scattering process ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\pi}}^{0}$(${\ensuremath{\eta}}^{0}$)\ensuremath{\gamma}.

Test of the soft-pion theorem in inclusive pion electroproduction

We show that the cross section of the deep-inelastic direct pion electroproduction in the central region can be deteermined by the use of the PCAC (partial conservation of axial-vector current) hypotheses and the light-cone current algebra in conjunction with the scaling in x for each value of x/sub B/, and that our result is consistent with the cross section of the inclusive reaction ..gamma../sub v/p ..-->.. ..pi../sup -/X.

Analysis of weak neutral currents using light-cone algebra

Using the algebra of light-cone commutators and making some simplifying assumptions, we have attempted to determine the isospin structure of a two-parameter weak hadronic neutral current. We have also computed in the light-cone model, they distributions for inclusive neutrino and antineutrino neutral current deep-inelastic interactions. Contrary to the quark-parton model, we find that both distributions have the same value.

Melosh transformation and light-cone current algebra

An investigation is made of the consequences of combining light-cone current algebra with the Melosh transformation as applied to nucleonic matrix elements of local currents and of the local limits of derivatives of bilocal currents. These lead to various sum-rule equalities and inequalities for the deep inelastic scale functions, both unpolarized and polarized.

Inclusive charmed-particle production by neutrinos in the light-cone algebra

The light-cone algebra is used to estimate the inclusive cross section for charmed-particle production by high-energy neutrinos. The results obtained are compatible with the recent experimental results on dimuon events. (AIP)

Charge Symmetry Violations in the GIM Model

The implications of the Glashow-Iliopoulos-Maiani model in the deep inelastic region are investigated using the light cone algebra. Whether we solve above or below the threshold for production of charmed particles, we find sin2θw ∼0.4. The implied charge-symmetry violation is examined. The strange and charmed quark content of the nucleon is estimated. Contributions of charmed particle production to the neutrino and antineutrino cross sections are estimated.

Hadron production in photon-photon collisions

We analyze deep-inelastic photon-photon collisions via the two-photon mechanism in electron-positron (-electron) colliding beams in a form especially suitable for experimental analysis. It is shown that by a helicity analysis similar to that used in electroproduction experiments, we can separate five of the eight structure functions describing the process ${\ensuremath{\gamma}}^{*}+{\ensuremath{\gamma}}^{*}\ensuremath{\rightarrow}\mathrm{hadrons}$. The helicity cross sections for this process and for the process with one real photon (inelastic electron-photon scattering) are related to structure functions, and are evaluated using quark light-cone algebra. There are anomalous contributions to the structure functions for the inelastic electron-photon scattering which arise both in parton as well as generalized vector-meson-dominance models. This suggests a connection between these two types of models for photon-photon scattering. Further, we use vector-meson dominance to construct a sum rule for ${\ensuremath{\sigma}}_{\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}\mathrm{hadrons}}$ from which it is estimated that roughly 20% of the cross section should be built up from higher-mass vector states. Using a spectral representation for the total transverse cross section, and the "aligned-jet" vector-dominance model we achieve a connection, via a "correspondence principle," with the parton model for the hadron multiplicities in photon-photon collisions. We also comment on inclusive pion multiplicities and the approach to scaling for photon-photon processes in the light-cone algebra.

Deep-inelastic lepton scattering in an SU(3) × U(1) gauge model

Linear relations and sum rules for deep-inelastic lepton scattering are derived in the light-cone algebra approach from a set of weak, neutral, and electromagnetic currents based on an SU(3) \ifmmode\times\else\texttimes\fi{} U(1) gauge model proposed by Schechter and Ueda.

Some neutral current effects in an SU(3)×U(1) gauge model

The anomalous magnetic moment of muon is calculated in anSU(3)×U(1) gauge model proposed by Gupta and Mani. We find the contribution due to the intermediate gauge bosons to be of the same order of magnitude as in Weinberg. Salam model. The deep-inelastic structure functions are also analysed in the same model and inequalities for the structure functions are obtained in the light-cone algebra approach.

Covariance, causality, and the refined infinite-momentum limit

The refined infinite-momentum limit approach is used in the derivation of sum rules for the real parts of current-particle forward scattering amplitudes. The sum rules are based on covariance, causality, and fixed-${q}^{2}$ unsubtracted dispersion relations in $\ensuremath{\nu}$ for the amplitudes. The fixed-mass sum rules so obtained are found to include those of the light-cone algebra. For amplitudes where the unsubtracted-dispersion-relation assumption is doubtful, the results are shown to be unaltered if once-subtracted dispersion relations are assumed instead. Convergence of the sum rules and inclusion of class-II contributions are also discussed.

Light cone, Regge contributions and large-angle scattering

The asymptotic behaviour of various three-particle vertices involving reggeons far off-mass-shell, and that of various exclusive reactions is found by using the light-cone algebra of the local and bilocal operators and supposing that the Regge contributions survive in the amplitude in the limit of large momentum transfer. The scaling behaviour (29), (34) is obtained in this way for the exclusive amplitudes. Besides, the asymptotic behaviour of hadronic form factors is obtained. The asymptotic behaviour of Regge-cut contributions and the region of applicability of the scaling behaviour (29) are found for the 2 → 2 amplitude. The relations between the dispersion contributions, Regge contributions, and those of quark diagrams, as well as the role of the signature are discussed. Predictions are given for the energy and the angular distributions for a number of two-particle reactions.

High-energy behaviour of a current amplitude and the Callan-Symanzik equations

We employ the Callan-Symanzik equations to study the high-energy behaviour of the current amplitudes for the vector-meson Compton scattering. We examine the singularity in co-ordinate space that this behaviour induces in the bilocal operator of the light-cone algebra.

Charge symmetry and neutral current in a unified model of weak and electromagnetic interactions

It is pointed out that measurement of the ratio {ie33-1} and theV — A interference term for the high-energy inclusive processes {ie33-2} + anything ({ie33-3} is the proton-neutron average) can give an estimate of the violation of charge symmetry in these processes. We then give an expression for charge symmetry violation in terms of experimentally measured structure functions above the charm threshold for the above processes for the Salam-Weinberg model. In addition, we give predictions for the neutral current for the processes {ie33-4} + anything, below and above the charm threshold for charged currents. It is pointed out that the predictions for the neutral current below the charm threshold are the same as those due to a phenomenological neutral current withSU3 structure {ie33-5}. We use light-cone algebra to obtain our results in the scaling region.

Light-cone algebra and materialization of quarks

Light-cone algebra and materialization of quarks