Hadron Structure Within the Point Form of Relativistic Quantum Mechanics

We present an outline of recent developments in the field of hadron form-factor calculations within constituent-quark models using the point form of relativistic quantum mechanics. Our method to calculate currents and form factors is exemplified by means of the weak B → D transition. We present results for weak B → D transition form factors in the space- and the time-like momentum-transfer region. We discuss how wrong cluster properties, which one has to deal with when employing relativistic quantum mechanics, affect these form factors and we estimate the role non-valence, Z-graph contributions may play for decay kinematics.     

Strange form factors of the proton: a new analysis of the ν (ovrarr/BC) data of the BNL-734 experiment

We consider ratios of elastiv ν(ovrarr/BC)-proton cross sections measured by the Brookhaven BNL-734 experiment and use them to obtain the neutral current (NC) over charged current (CC) neutrino-antineutrino asymmetry. We discuss the sensitivity of these ratios and of the asymmetry to the electric, magnetic and axial strange form factors of the nucleon and to the axial cutoff mass M_A. We show that the effects of the nuclear structure and interactions on the asymmetry and, in general, on ratios of cross sections are negligible. We find some restrictions on the possible values of the parameters characterizing the strange form factors. We show that a precise measurement of the neutrino-antineutrino asymmetry would allow the extraction of the axial and vector magnetic strange form factors in a model independent way. The neutrino-antineutrino asymmetry turns out to be almost independent on the electric strange form factor and on the axial cutoff mass.     

CP violation and top quark decays

We investigate how to testCP invariance in the weak decay of top quarks. A prediction ofCP violation from the Standard Model is made by an explicit calculation. The effect is very small as expected. We then use a form factor approach to parametrize possible new interactions ofCP violation. The differences between the form factor approach and an effective Lagrangian approach are discussed. The sensitivity of ourCP-odd observables to the form factors is estimated.     

A Combined Study of the Pion’s Static Properties and form Factors

We study consistently the pion’s static observables and the elastic and γ* γ → π ⁰ transition form factors within a light-front model. Consistency requires that all calculations are performed within a given model with the same and single adjusted length or mass-scale parameter of the associated pion bound-state wave function. Our results agree well with all extent data including recent Belle data on the γ* γ → π ⁰ form factor at large q ², yet the BaBar data on this transition form factor resists a sensible comparison. We relax the initial constraint on the bound-state wave function and show the BaBar data can partially be accommodated. This, however, comes at the cost of a hard elastic form factor not in agreement with experiment. Moreover, the pion charge radius is about 40 % smaller than its experimentally determined value. It is argued that a decreasing charge radius produces an ever harder form factor with a bound-state amplitude difficultly reconcilable with soft QCD. We also discuss why vector dominance type models for the photon-quark vertex, based on analyticity and crossing symmetry, are unlikely to reproduce the litigious transition form factor data.     

N-string vertex,canonical forms and bosonization

We give the field representation of the canonical forms for the operators which generate the projective transformation. This representation is also applicable in formulating the N-string vertex of Lovelace and Olive. It shows that they have the properties of a transition operator. Requiring the same properties for the ghost sector in bosonized form we construct the BRST invariant canonical form and the N-string vertex. We consider the (N − 3) b-ghost insertion. We show that the resulting vertex with (N − 3) parameters corresponding to the location of the ghosts is symmetric with respect to the N strings and it gives the proper integration measure.     

Form factors of exponential operators and exact wave function renormalization constant in the Bullough-Dodd model

We compute the form factors of exponential operators e^kgϕ(x) in the two-dimensional integrable Bullough-Dodd model (a₂⁽²⁾ affine Toda field theory). These form factors are selected among the solutions of general non-derivative scalar operators by their asymptotic cluster property. Through analytical continuation to complex values of the coupling constant these solutions permit to compute the form factors of scaling relevant primary fields in the lightest-breather sector of integrable /gf_1,2 and /gf_1,5 deformations of conformal minimal models. We also obtain the exact wave-function renormalization constant Z(g) of the model and the properly normalized form factors of the operators ϕ(x) and : ϕ²(x) :.     

Quark model analysis of semileptonicD decays intoK andK *

We derive the form factors governing the decaysD→Kev andD→K ^* ev in the framework of a relativistic constituent quark model. Our results agree with the recently measured form factors and the data for rates at the level of the present experimental uncertainty.     

Bag-model form factors and Hartree-Fock approximation to the σωπ model

We evaluate form factors for the scattering ofσ, ω andπ mesons from nucleons described by the MIT bag model. These form factors are then written covariantly and used for nuclear matter in the Hartree-Fock approximation to theσω model of quantum hadrodynamics with pions. For fixed parameters (meson couplings and masses) the inclusion of these form factors results in more binding at a higher saturation density. After refitting the parameters to reproduce the empirical saturation properties, the result is very close to that without form factors.     

Global analysis of the strangeness vector and axial form factors of the nucleon and their uncertainties

We have studied the strangeness contribution to the elastic vector and axial form factors of the nucleon, using all available electroweak elastic scattering data sensitive to these contributions. Specifically, we combine ??p and $\bar{\nu} p$ elastic scattering cross sections from Brookhaven E734 with parity-violating asymmetries in elastic ep scattering, and quasi-elastic ed and e ⁴He scattering, observed in the SAMPLE, HAPPEx, G0 and PVA4 experiments. We are able not only to determine these form factors at individual values of momentum-transfer (Q ²), as has been done recently, but also to fit the Q ²-dependence of these form factors using simple functional forms. We present the results of these fits using existing data.     

The applicability of perturbative QCD to the pion form factor and the pionic wavefunction

We reanalyse the pionic form factor by using perturbative QCD theory and contributions from endpoint regions. We find that the perturbative QCD can be applied to the pionic form factor asQ ²>4 GeV² and they become unreliable asQ ²≦4 GeV². Therefore the applicability of perturbative QCD to the form factor is questionable only asQ ²≦4 GeV².     

One-loop generated anomalous gauge couplings

We compute, at one loop, the CP-violating anomalous trilinear gauge-boson form factors which couple theW (or theZ) to the photon and theZ. In order to see which form factors are generated by which types of underlying interactions, we work with as general an underlying model as is possible. After identifying which form factors can arise at one loop in a completely general renormalizable model of spin-half and spin-zero particles, we provide explicit formulae for the induced form factors in a very broad class of such models. Our results include some previous calculations as special cases, and we identify errors in some of these.     

Production of D*+(2010) mesons by high energy neutrinos from the Tevatron

We discuss some issues arising in the search for CP violation in the decays Z → τ⁺ τ^? and Z → bb?X. The form-factor and the effective Lagrangian approach to parametrize CP-violating effects are compared. We emphasize the interest to study both real and imaginary parts of CP-violating form factors like the weak dipole moment form factor ${d_?u^Z}={(m_Z^2)}$ of the τ-lepton. We propose an “optimal” way to search for CP violation when Z → bb?X events have to be selected on a statistical basis from the total number of Z hadronic decays.     

The role of gluon-gluon shadowing in smallx-behaviour of structure functions

We consider influence of gluon shadowing effects on the proton structure function in the smallx interval. These effects are noticeable in the HERA kinematical region. The explicit form of the gluon distribution in the proton depend significantly on the form of used boundary condition atQ ²=Q ₀ ² . We consider also difference of results obtained with the help of Kuraev-Lipatov-Fadin and Altarelli-Parisi evolution equations.     

Nucleon magnetic form factors in the cloudy bag model

The nucleon magnetic moments and magnetic form factors have been calculated in the cloudy bag model. The πNN, πNΔ, γπ form factors and the CM corrections have been taken into account. We obtained very good results for these quantities.     

Polarized parity violating electron scattering on 3He

We calculate the asymmetry parameters, A, and figures-of-merit for polarized parity violating electron scattering from ³He via the reaction, e⁻ +³ He → e⁻ +³ He. We do this explicitly forv incident electron energies of 1.0 GeV and 4.0 GeV. We find a sharp and unexpected variation in A due to cancellations between the weak and electromagnetic form factors caused by the different q² dependences of these form factors. We find that at small angles, the asymmetry may be obtained to reasonably high accuracy for all energies considered and that the interesting region where the asymmetry has its first maximum and minimum is accessible for electron energies of 1 GeV or higher. In addition we find that the asymmetry and figures-of-merit are in the range of those for other proposed target nuclei. We also consider the possibility of strange quark contributions to the asymmetry and show that at the first maxima and minima, possible contributions of the strange quark current vector form factors cause large variations in the asymmetry which might be observed.     

The extended Nambu-Jona-Lasinio model with separable interaction: Low energy pion physics and pion-nucleon form factor

A Lagrangian formulation of the Nambu-Jona-Lasinio model with separable interaction is given. The electromagnetic interaction is introduced in a nonminimal way to the nonlocal quark current. Various choices of the vertex form factors characterizing the composite structure of mesons and baryon are investigated. We find that the physical observables depend very weakly on form factor shapes. We calculate the πNN form factor considering nucleon as a three-quark system.     

A minimal size for granular superconductors

We investigate the minimal size of small superconducting grains by means of a Ginzburg–Landau model confined to a sphere of radius R. This model is supposed to describe a material in the form of a ball, whose transition temperature when presented in bulk form, T₀, is known. We obtain an equation for the critical temperature as a function of R and of T₀, allowing us to obtain a minimal radius of the sphere below which no superconducting transition exists. An estimate of values of minimal radii for different materials is done.     

Universal amplitude ratios in the two-dimensional q-state Potts model and percolation from quantum field theory

We consider the scaling limit of the two-dimensional q-state Potts model for q ⩽ 4. We use the exact scattering theory proposed by Chim and Zamolodchikov to determine the one-and two-kink form factors of the energy, order and disorder operators in the model. Correlation functions and universal combinations of critical amplitudes are then computed within the two-kink approximation in the form factor approach. Very good agreement is found whenever comparison with exact results is possible. We finally consider the limit q → 1 which is related to the isotropic percolation problem. Although this case presents a serious technical difficulty, we predict a value close to 74 for the ratio of the mean cluster size amplitudes above and below the percolation threshold. Previous estimates for this quantity range from 14 to 220.     

Spiky strings on NS5-branes

We study rigidly rotating strings in the near-horizon geometry of a stack of Neveu-Schwarz (NS) 5-branes. We solve the Nambu-Goto action of the fundamental string in the presence of a NS-NS two form (Bμν) and find out limiting cases corresponding to magnon and spike like solutions.