Form factors of exponential fields for two-parametric family of integrable models

A two-parametric family of integrable models (the SS model) that contains as particular cases several well known integrable quantum field theories is considered. After the quantum group restriction it describes a wide class of integrable perturbed conformal field theories. Exponential fields in the SS model are closely related to the primary fields in these perturbed theories. We use the bosonization approach to derive an integral representation for the form factors of the exponential fields in the SS model. The same representations for the sausage model and the cosine–cosine model are obtained as limiting cases. The results are tested at the special points, where the theory contains free particles.     

Purely transmitting integrable defects

Some aspects of integrable field theories possessing purely transmitting defects are described. The main example is the sine-Gordon model and several striking features of a classical field theory containing one or more defects are pointed out. Similar features appearing in the associated quantum field theory are also briefly reviewed.     

Critical dynamics in the presence of relaxing defects

The influence of defects coupling linearly to the order parameter on the critical behaviour of structural phase transitions is studied. A continuum model for the statics and dynamics is introduced and is investigated by the renormalization group theory. If the defects are slow a central peak is found, the characteristic width of which is determined by the defects. Concerning the critical behaviour the dynamical model belongs to the same universality class as the one studied previously by Grinstein, MA, and Mazenko. The concentration dependence of the central peak response is discussed inside and outside the critical region.     

Vortex structure in the presence of tilted columnar defects

It is argued that vortices in layered superconductors will be trapped by tilted columnar defects even when the external magnetic field is oriented along the c axis. For such tilted, trapped vortices the interaction at long distances becomes attractive in some directions. This must result in the formation of vortex chains with an intervortex distance of the order of the London penetration depth. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 507–511 (25 September 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Sigma models in the presence of dynamical point-like defects

Point-like Liouville integrable dynamical defects are introduced in the context of the Landau–Lifshitz and Principal Chiral (Faddeev–Reshetikhin) models. Based primarily on the underlying quadratic algebra we identify the first local integrals of motion, the associated Lax pairs as well as the relevant sewing conditions around the defect point. The involution of the integrals of motion is shown taking into account the sewing conditions.     

Angular quantization and form factors in massive integrable models

We discuss an application of the method of angular quantization to the reconstruction of form factors of local fields in massive integrable models. The general formalism is illustrated with examples of the Klein-Gordon, sinh-Gordon and Bullough-Dodd models. For the latter two models the angular quantization approach makes it possible to obtain free field representations for form factors of exponential operators. We discuss an intriguing relation between the free field representations and deformations of the Virasoro algebra. The deformation associated with the Bullough-Dodd models appears to be different from the known deformed Virasoro algebra.     

Form factors in the radiative pion decay

We perform an analysis of the form factors that rule the structure-dependent amplitude in radiative pion decay. The resonance contributions to π→eν_eγ decays are computed through the proper construction of the vector and axial-vector form factors by setting the QCD driven asymptotic properties of the three-point Green functions 〈VVP〉 and 〈VAP〉, and by demanding the smoothening of the form factors at high transfer of momentum. A comparison between theoretical and experimental determination of the form factors is also carried out. We also consider and evaluate the role played by a non-standard tensor form factor. We conclude that, at present and due to the hadronic uncertainties, the search for new physics in this process is not feasible. PACS 11.15.Pg; 12.38.-t; 12.39.Fe     

Form factors of Al

The appropriateness of Harrison's pseudo-potential for Al is re-examined by determining the model parameters from experimental data. The artificial cut-off of the form-factors is shown to be redundant. Satisfactory results are obtained from the presented scheme.     

Form factors of tetraquarks

The electric form factor of the c [`(\texts)] \overline {\text{s}} uū tetraquark with J^PC = 0⁺⁺ (M = 2691 MeV) in the field of a small and intermediate momentum transfer Q² ≤ 1 GeV² is calculated for the relativistic quark model. The charge radius of this state is determined.     

Form factors in lattice QCD

Lattice simulations of QCD have produced precise estimates for the masses of the lowest-lying hadrons which show excellent agreement with experiment. By contrast, lattice results for the vector and axial vector form factors of the nucleon show significant deviations from their experimental determination. We present results from our ongoing project to compute a variety of form factors with control over all systematic uncertainties. In the case of the pion electromagnetic form factor we employ partially twisted boundary conditions to extract the pion charge radius directly from the linear slope of the form factor near vanishing momentum transfer. In the nucleon sector we focus specifically on the possible contamination from contributions of higher excited states. We argue that summed correlation functions offer the possibility of eliminating this source of systematic error. As an illustration of the method we discuss our results for the axial charge, g _A , of the nucleon.     

Exact form factors in integrable quantum field theories: the sine-Gordon model

We provide detailed arguments on how to derive properties of generalized form factors, originally proposed by one of the authors (M.K.) and Weisz twenty years ago, solely based on the assumption of ‘maximal analyticity” and the validity of the LSZ reduction formalism. These properties constitute consistency equations which allow the explicit evaluation of the n-particle form factors once the scattering matrix is known. The equations give rise to a matrix Riemann-Hilbert problem. Exploiting the “off-shell” Bethe ansatz we propose a general formula for form factors for an odd number of particles. For the sine-Gordon model alias the massive Thirring model we exemplify the general solution for several operators. In particular we calculate the three-particle form factor of the soliton field, carry out a consistency check against the Thirring model perturbation theory and thus confirm the general formalism.     

Formation of defects in gallium phosphide grown in the presence of oxygen

The influence of oxygen introduced in the gaseous phase on the formation of defects in GaP epitaxial layers is investigated by deep-level transient spectroscopy. The extremal dependences of the concentrations of charge carriers and electron traps with energy E _c−0.24 eV on the oxygen flux are discussed. Zh. Tekh. Fiz. 67, 52–55 (September 1997)     

Form factors of soliton-creating operators in the sine-Gordon model

We propose explicit expressions for the form factors, including their normalization constants, of topologically charged (or soliton-creating) operators in the sine-Gordon model. The normalization constants, which constitute the main content of our proposal, allow one to find exact relations between the short- and long-distance asymptotics of the correlation functions. We make predictions concerning asymptotics of fermion correlation functions in the massive Thirring model, SU(2)–Thirring model with anisotropy, and in the half-filled Hubbard chain.     

Form factors of heavy mesons in QCD

We discuss logarithmic corrections to form factors of mesons built from heavy quarks. The reactions e⁺e^? → η_cγ and H → Jψγ are considered as an example. A novel feature as compared to the well-studied problem of the pion form factor is the existence of transitions between the quark-antiquark state $\text{c}\text{c}$ and the gluonic one. O(α_s) corrections are calculated exactly. An infinite series of the leading logarithmic terms (α_sln[Q²/m_c²])ⁿ is summed up with the help of the operator technique. Apart from ree results already known for quark operators, we use some new results referring to gluon operators and their mixing with those made from quarks. Two alternative derivations of the multiplicatively renormalizable operators are given. The first one reduces to a direct computation of the mixing matrix and its diagonalization, the second is based on conformal symmetry considerations.     

Form factors in the projected linear chiral sigma model

Several nucleon form factors are computed within the framework of the linear chiral soliton model. To this end variational means and projection techniques applied to generalized hedgehog quark-boson Fock states are used. In this procedure the Goldberger-Treiman relation and a virial theorem for the pion-nucleon form factor are well fulfilled demonstrating the consistency of the treatment. Both proton and neutron charge form factors are correctly reproduced, as well as the proton magnetic one. The shapes of the neutron magnetic and of the axial form factors are good but their absolute values at the origin are too large. The slopes of all the form factors at zero momentum transfer are in good agreement with the experimental data. The pion-nucleon form factor exhibits to great extent a monopole shape with a cut-off mass ofΛ=690 MeV. Electromagnetic form factors for the vertexγNΔ and the nucleon spin distribution are also evaluated and discussed.     

Form factors of boundary exponential operators in the sinh-Gordon model

Using the recently introduced boundary form factor bootstrap equations, the form factors of boundary exponential operators in the sinh-Gordon model are constructed. We also give a general method to evaluate the ultraviolet properties of boundary correlators by extending the bulk cumulant expansion to the boundary case. As an application, the ultraviolet scaling dimension and the normalization of the operators corresponding to the form factor solutions are checked against previously known results for boundary exponential operators. The construction presented in this paper can be applied to determine form factors of relevant primary boundary operators in general integrable boundary quantum field theories.     

Oxygen agglomeration at111In in silver in the presence of radiation defects

The internal oxidation process of¹¹¹In in Ag has been studied by means of the perturbed angular correlation technique. A homogeneous¹¹¹In concentration of typically 0.05 at ppm has been produced by irradiating the Ag samples with 35 MeV -particles. In particular, the effects of solving oxygen before the irradiation and of radiation induced defects have been explored. It is found that oxygen stabilizes the radiation damage by several hundred degrees. Four molecule-type complexes have been identified, consisting each of one¹¹¹In atom, vacancies and oxygen atoms, among them one with cubic environment _Q =0. The formation and desintegration kinetics of these complexes have been studied as function of the oxygen concentration and the irradiation and measuring temperature. A model is suggested which explains the oxidation process as due to diffusing oxygen and oxygen-vacancy pairs trapped by¹¹¹In.