Near-threshold radiative 3<Emphasis Type="Italic">π</Emphasis> production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

We consider the π⁺π^?π₀γ final state in electron-positron annihilation at c.m.s. energies not far from the threshold. Both initial-and final-state radiations of the hard photon are considered, but without interference between them. The amplitude for the final-state radiation is obtained by using the effective Wess-Zumino-Witten Lagrangian for pion-photon interactions valid for low energies. In real experiments, energies are never so small that ρ and ω mesons would have a negligible effect. So a phenomenological Breit-Wigner factor is introduced in the final-state radiation amplitude to account for the vector mesons' influence. Using radiative 3π production amplitudes, a Monte Carlo event generator was developed which could be useful in experimental studies.     

Lie Superalgebra Structures in <Emphasis Type="Italic">H</Emphasis><Superscript>⋅</Superscript> (<Emphasis Type="Italic">g</Emphasis>;<Emphasis Type="Italic">g</Emphasis>)

Let g=vect(M) be the Lie (super)algebra of vector fields on any connected (super)manifold M; let - be the change of parity functor, C ⁱ and H ⁱ the space of i-chains and i-cohomology. The Nijenhuis bracket makes into a Lie superalgebra that can be interpreted as the centralizer of the exterior differential considered as a vector field on the supermanifold associated with the de Rham bundle on M. A similar bracket introduces structures of DG Lie superalgebra in L ^* and for any Lie superalgebra g. We use a Mathematica-based package SuperLie (already proven useful in various problems) to explicitly describe the algebras l ^* for some simple finite dimensional Lie superalgebras g and their relatives - the nontrivial central extensions or derivation algebras of the considered simple ones.     

Ground State of <Emphasis Type="Italic">N</Emphasis> Coupled Nonlinear Schrödinger Equations in <Emphasis Type="Italic">R</Emphasis><Superscript><Emphasis Type="Italic">n</Emphasis></Superscript>,<Emphasis Type="Italic">n</Emphasis>≤3

We establish some general theorems for the existence and nonexistence of ground state solutions of steady-state N coupled nonlinear Schrödinger equations. The sign of coupling constants β _ij ’s is crucial for the existence of ground state solutions. When all β _ij ’s are positive and the matrix Σ is positively definite, there exists a ground state solution which is radially symmetric. However, if all β _ij ’s are negative, or one of β _ij ’s is negative and the matrix Σ is positively definite, there is no ground state solution. Furthermore, we find a bound state solution which is non-radially symmetric when N=3.     

The anisotropic cosmological models in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>, <Emphasis Type="Italic">T</Emphasis>) gravity with <Emphasis Type="Italic">Λ(T)</Emphasis>

The rare decay \(B\rightarrow {K^{*}}\ell ^+\ell ^-\) is a very significant mode to search for physics beyond the Standard Model (SM). The mode provides a very rich spectrum of observables obtained from the angular distribution of its decay products. The recent LHCb measured values of these observables are used to conclude an evidence of right-handed currents at the kinematic endpoint of this decay mode. As the conclusion is drawn at the maximum dilepton invariant mass square (\(q^2\)) kinematic endpoint, it relies only on heavy quark symmetries where it is valid without significant corrections.     

Scalar mesons in <Emphasis Type="Italic">η</Emphasis>′ → <Emphasis Type="Italic">ηπ</Emphasis><Superscript>0</Superscript><Emphasis Type="Italic">π</Emphasis><Superscript>0</Superscript> decay

The decay η′ → ηπ ⁰ π ⁰ is studied in the framework of isobar model. It is shown, that good agreement with the experiment is achieved if α ₀- and σ-meson contributions are taken into account. The contribution of α ₀-meson is dominant, but σ-meson is necessary to reproduce the form of the Dalitz plot. Instead of the usual Breit-Wigner form of σ-meson propagator we use parametrization of the ππ-amplitude, which satisfies analyticity, crossing, unitarity and chirality constraints. This amplitude has a pole in the complex plane, which corresponds to σ-meson and describe experimental data on ππ-scattering in K _e4 decay.     

On mass corrections to the decay <Emphasis Type="Italic">P</Emphasis> → <Emphasis Type="Italic">l</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">l</Emphasis><Superscript>−</Superscript>

The Mellin-Barnes representation is used to improve the theoretical estimate of mass corrections to the width of a light pseudoscalar meson decay into a lepton pair, P → l ⁺ l ⁻. The full resummation of the terms ln(m _l ²/Λ²)(m _l ²/Λ²) ⁿ and (m _l ²/Λ²) ⁿ to the decay amplitude is performed, where m _l is the lepton mass and Λ ≈ m _ρ is the characteristic scale of the P → γ*γ* form factor. The total effect of the mass corrections for the e ⁺ e ⁻ channel is negligible and, for the μ⁺μ⁻channel, its order is of a few percent. The text was submitted by the authors in English.     

Deviation from the standard model in the decay <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">νγ</Emphasis>

A precise investigation of radiative pion decay (π⁺ → e⁺νγ) in a pion beam from the meson factory of the Paul Scherrer Institute (Switzerland) was performed by the PIBETA Collaboration with the aid of the PIBETA detector. This resulted in finding 41 601 events of radiative pion decay in three kinematical regions. The absolute values of the branching ratio for radiative pion decay were determined in each of these regions. To a precision approximately four times higher than that known previously, the ratio of the axial-vector to the vector form factor was found to be γ ≡ F _A /F _V = 0.443 (15), the latter being fixed at F _V = 0.0259. The number of events found in the kinematical region specified by photon energies of E_γ > 55.6 MeV, positron energies of E _e > 20.0 MeV, and angles of θ_{γ, e} > 40° between the momenta of the corresponding particles (B region) was 5233. In region B, the measured branching ratio for radiative pion decay, R_π→evγ(expt) = 11.6(3) × 10^?8, proved to be smaller by eight standard deviations than that which follows from the Standard Model, R_π→evγ (theor) = 14.34(1) × 10^?8.     

The cusp effect in <Emphasis Type="Italic">η</Emphasis>′→<Emphasis Type="Italic">η</Emphasis><Emphasis Type="Italic">π</Emphasis><Emphasis Type="Italic">π</Emphasis> decays

Strong final-state interactions create a pronounced cusp in η′→η π ⁰ π ⁰ decays. We adapt and generalize the non-relativistic effective field theory framework developed for the extraction of π π scattering lengths from K→3π decays to this case. The cusp effect is predicted to have an effect of more than 8% on the decay spectrum below the π ⁺ π ⁻ threshold.     

Independent <Emphasis Type="Italic">π</Emphasis><Superscript>−</Superscript>-meson production in <Emphasis Type="Italic">pp</Emphasis> interactions

It is shown that experimental data on the multiparticle production of negatively charged pions in proton-proton interactions at \(\sqrt s \leqslant 30 GeV\) do not involve significant indications of the existence of anycorrela tions between negatively charged pions, apart from those that are associated with momentum conservation and with interference. The multiplicity distributions in rapidity intervals, forward-backward correlations, and two-particle rapidity and transverse-momentum correlations do not contradict the independent production of negatively charged pions. No constraints on the multiplicity distributions of product particles follow from their independent production.     

Dynamics of nuclear interaction in the reaction <Superscript>56</Superscript>Fe(<Emphasis Type="Italic">α</Emphasis>, <Emphasis Type="Italic">xn</Emphasis>)

The spectra and angular distributions of neutrons from the reaction ⁵⁶Fe(α, xn) were measured at the alpha-particle energies of 12.3, 16.3, 18.3, 26.8, and 45.2 MeV. The measurements were performed with time-of-flight fast-neutron spectrometers at pulsed accelerators of charged particles. The measured data were analyzed within models of equilibrium, preequilibrium, and direct reaction mechanisms. The calculations were performed by using an exact formalism of Hauser-Feshbach statistical theory. The required nuclear-level densities in nickel isotopes excited in this reaction were determined on the basis of new experimental data on low-lying levels, neutron resonances, and spectra of evaporated neutrons. The contributions of equilibrium, preequilibrium, and direct neutron emission were studied over a broad range of alpha-particle energies.     

Static spherically symmetric solution of (<Emphasis Type="Italic">R</Emphasis> ± <Emphasis Type="Italic">μ</Emphasis><Superscript>4</Superscript>/<Emphasis Type="Italic">R</Emphasis>) gravity

The static spherically symmetric solution for R ± μ ⁴/R model of f(R) gravity is investigated. We obtain the metric for space-time in the solar system that reduces to the Schwarzschild metric, when μ tends to zero. For the obtained metric, the deviation from Einstein gravity is very small. This result is different from the other results have been obtained by equivalence between f(R) gravity and scalar tensor theory. Also it is shown that the vacuum solution in the solar system depends on the shape of matter distribution which differ from the Einstein’s gravity.     

Two-photon production of vector resonance in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> collisions

A parameterization of the amplitude of the two-photon production of 1⁺⁺ and 1^?+ vector resonances V in the e ⁺ e ^? → e ⁺ e ^? V reaction has been obtained. The differential (in momentum transfer) scattering cross section dσ/dQ ² has been found for this reaction in the equivalent-photon approximation. The result obtained is model-independent.     

Investigation of the process <Emphasis Type="Italic">J/ψ</Emphasis> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> with the KEDR detector

The product of the electron width of the J/ψ meson and the probability for its decay to an electron-positron pair was measured by using data from the KEDR experiment at the VEPP-4M electron-positron collider. The result was Γ _ee × Γ _ee /Γ = 0.3392 ± 0.0068(stat.) ± 0.0063(syst.) keV.     

Pseudoscalar Higgs boson in experiments at <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> colliders

The potential of experiments at e ⁺ e ^? colliders to search for a signal of a new pseudoscalar Higgs boson and to study its CP properties is analyzed. A new Higgs boson coupling to the b quark and τ lepton, which is parameterized in a model-independent way as m _b /v(a + iγ₅ b), is chosen to be an indicator of its CP nature. We study the e ⁺ e ^? → τ⁺τ^?vv, e ⁺ e ^? → b \(\bar b\)vv, and e ⁺ e ^? → e ⁺ e ^? b \(\bar b\) processes highly sensitive to anomalous Higgs boson couplings due to the dominant contributions from the vector boson fusion processes W*W* → H and Z*Z* → H in the central region. It is shown that the study of polarization of particles in the final state could help to separate the contributions from the scalar and pseudoscalar Higgs bosons. For instance, the consideration of the cascade decays of τ leptons in the e ⁺ e ^? → τ⁺τ^?vv process allows one to determine reliably the CP state of the Higgs boson as well as the value and the sign of the b parameter. As a result of our analysis, we develop a search strategy for a signal of a new pseudoscalar Higgs boson in future experiments at linear e ⁺ e ^? colliders, which will allow one to understand the CP nature of the Higgs boson and set the bounds on its couplings to fermions.     

Process <Emphasis Type="Italic">γ</Emphasis>*<Emphasis Type="Italic">γ</Emphasis> → <Emphasis Type="Italic">σ</Emphasis> at large virtuality of <Emphasis Type="Italic">γ</Emphasis>*

The process γ*γ → σ is investigated in the framework of the SU(2)×SU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of γ* in the Euclidean kinematic domain. The asymptotic behavior of this form factor resembles the asymptotic behavior of the γ*γ → π form factor.     

Inclusive <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis> photoproduction and polarization at HERA in the <Emphasis Type="Italic">k</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript>-factorization approach

We investigate the inclusive photoproduction of J/ψ mesons at HERA within the framework of the k _T -factorization QCD approach. Our study is based on the color singlet model supplemented with the relevant off-shell matrix elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS collaborations. Special attention is put on the J/ψ polarization parameters λ and ν, which are sensitive to the production dynamics.