Table of contents

We evaluate the time delay in some of the established resonance regions of πN elastic scattering. In addition to the positive peaks corresponding to resonances, we identify broad regions of negative time delay or time advancement. We compare the resonance parameters determined with the time delay method with those from conventional methods and try to interpret our observation of time advancement.

Following recent work in which events which may correspond to a bound tetraneutron (⁴n) were observed, it is pointed out that from the theoretical perspective the two-body nucleon–nucleon (NN) force cannot by itself bind four neutrons, even if it could bind a dineutron. Unrealistic modifications of the NN force or introduction of unreaslistic four-nucleon force would be needed in order to bind the tetraneutron. The existence of other multineutron systems is discussed.

In a hydrodynamic model, we have analysed the direct photon data obtained by the WA98 collaboration in 158 A GeV Pb + Pb collisions. The transverse expansion of the system has been taken into account. Two scenarios have been considered: (i) the formation of quark–gluon plasma and (ii) the formation of hot hadronic gas. Both scenarios describe the data equally well. However, the hadronic gas scenario requires a very high initial temperature (∼300 MeV) and it is difficult to conceive of the existence of hadron gas at that high temperature. If, initially, the hadronic fluid possesses small radial velocity (0.2–0.3 c), the data are well explained in the hadronic gas scenario, with reasonable initial temperatures.

We consider the change of the strange-quark chemical potential in the phase diagram of nuclear matter, employing the Wilson loop and scalar quark condensate order parameters, mass-scaled partition functions and enforcing flavour conservation. Assuming the region beyond the hadronic phase to be described by massive, correlated and interacting quarks, in the spirit of lattice and effective QCD calculations, we find the strange-quark chemical potential to change sign: from positive in the hadronic phase, to zero upon deconfinement, to negative in the partonic domain. We propose this change in the sign of the strange-quark chemical potential to be an experimentally accessible order parameter and a unique, concise and well-defined indication of the quark-deconfinement phase transition in nuclear matter.

A method to extract simultaneously level densities and γ-ray transmission coefficients has for the first time been tested on light nuclei utilizing the ²⁸Si(³He,αγ)²⁷Si and ²⁸Si(³He,³He'γ)²⁸Si reactions. The extracted level densities for ²⁷Si and ²⁸Si are consistent with the level densities obtained by counting known levels in the respective nuclei. The extracted γ-ray strength in ²⁸Si agrees well with the known γ-decay properties of this nucleus. Typical nuclear temperatures are found to be T ∼ 2.4 MeV at around 7 MeV excitation energy. The entropy gap between nuclei with mass number A and A ± 1 is measured to be δS ∼ 1.0 k_B, which indicates an energy spacing between single-particle orbitals comparable with typical nuclear temperatures.

CP violating effects in the single top quark production via flavour changing neutral current (FCNC) reactions e⁺e⁻ → t and e⁺e⁻ → q (here q refers to charm and up quarks) are studied. The effective Lagrangian description of the FCNC interactions is used. A numerical analysis is performed for some next linear colliders. CP violating asymmetries for the number of q and quarks are obtained to be of order 10⁻²–10⁻³ depending on the CM energy.

The pomeron structure function is extracted from the H1 data and is subject to a leading-order QCD analysis. We compare the results obtained from the DGLAP equations with and without corrected for gluon recombination. Both cases give good fits to data but different results for the gluon distribution.

The recent TRIUMF experiment for μ⁻p → nν_μγ gave a surprising result that the induced pseudoscalar coupling constant g_P was larger than the value obtained from μ⁻p → nν_μ experiment by as much as 44%. Subsequent debates on the result gave rise to many theoretical calculations. Most of them were skeptical for the enlarged coupling constant g_P. Therefore, one needs to reexamine the theoretical analysis of the matrix element of Beder and Fearing which was exploited for the extraction of the value in the experiment. In this report we analyse the matrix element from the viewpoint of electro-magnetic coupling schemes and suggest an additional term. This additional term plays an important role in restoring the standard value of g_P.

In comparison of ground- and space-based optical detectors of ultra high energy cosmic rays (UHECR) the space-based detectors have the advantage of registering EAS, initiated by UHECR particles, at a much larger area of the atmosphere. They also have the advantages of observing EAS in a wide range of atmosphere depth including near-horizontal EAS, initiated by neutrino at depths >1000 g cm⁻². Ground-based particle detector arrays have the advantages of taking data on EAS parameters, sensitive to a primary particle mass, not determined by space detectors. Particle detectors having 100% duty cycle observe a specific UHECR source longer than the space detector with the same geometrical factor.

The recently proposed supersymmetric A₄ model of the neutrino mass matrix is modified to merge with a previously proposed axionic solution of the strong CP problem. The resulting model has only one input scale, i.e. that of A₄ symmetry breaking, which determines both the seesaw neutrino mass scale and the axion decay constant. It also solves the μ problem and conserves R parity automatically.

We describe the spontaneous ternary cold fission of ²⁵²Cf, accompanied by ⁴He, ¹⁰Be and ¹⁴C within a stationary scattering formalism. We show that the light cluster should be born in the neck region. It decays from the first resonant eigenstate in the Coulomb plus harmonic oscillator potential, centred in this region and eccentric with respect to the symmetry axis. This description gives a simple answer to the question why the averaged values in the energy spectra of emitted clusters are close to each other, in spite of different Coulomb barriers. We have shown that the angular distribution of the emitted light particle is strongly connected with its deformation and the equatorial distance. Experimental angular distributions can be explained by the spherical shapes of emitted clusters, except for a deformed ¹⁰Be. We also predicted some dependences of half-lives for such tri-nuclear systems upon potential parameters.

We perform a complete simulation of the process e⁺e⁻ → τ⁺τ⁻ν, where ν can be an electron, muon or tau neutrino, in the context of a general Higgs coupling to τ-leptons. We analyse various kinematical distributions and obtain the sensitivity regions in the parameter space that can be explored at a future e⁺e⁻ collider. In particular, inclusion of W boson fusion enhances the sensitivity significantly.

Groote and Pivovarov have noticed a possible fault in the use of sum rules involving two-point correlation functions to extract information on heavy quark parameters, due to the presence of massless contributions that invalidate the construction of moments of the spectral densities (2002 JETP Lett.75 221). Here we show how to circumvent this problem through a new definition of the moments, providing an infrared safe and consistent procedure.

Within the framework of one-loop approximation of the standard model, the probability of radiative decay of the massive Dirac neutrino ν_i → ν_j + γ in a dense medium was calculated in an intensive, external, constant magnetic field. It was found that in the case of a degenerate electron gas (important for astrophysical applications), the decay rate essentially increases due to the influence of an ultrastrong magnetic field.

We compare, for the static potential and at short distances, perturbation theory with the results of lattice simulations. We show that a renormalon-dominance picture explains why in the literature sometimes agreement, and at other times disagreement, is found between lattice simulations and perturbation theory depending on the different implementations of the latter. We also show that, within a renormalon-based scheme, perturbation theory agrees with lattice simulations.

The prompt muon contribution to the deep-sea atmospheric muon flux can serve as a tool for probing into the small-x feature of the gluon density inside of a nucleon, if the muon energy threshold could be lifted to 100 TeV. The prompt muon flux underwater is calculated taking into consideration predictions of recent charm production models in which the small-x behaviour of the gluon distribution is probed. We discuss the possibility of distinguishing the PQCD models of the charm production differing in the small-x exponent of the gluon distribution, in measurements of the muon flux at energies 10–100 TeV with neutrino telescopes.

We apply the R-matrix formalism to the ³He(n, p)³H and ⁷Be(n, p)⁷Li reactions, which play an important role in the big-bang nucleosynthesis. The cross sections are analysed along with the ⁴He and ⁸Be spectra near threshold. Neutron and proton widths of high-energy states are determined. A statistical analysis of the uncertainties provide fairly low error bars (typically 2% at the 1σ confidence level) on the reaction rates.

Unitary and analytic ten-resonance model of the nucleon electromagnetic (e.m.) structure with canonical normalizations and QCD (up to the logarithmic correction) asymptotics is constructed on the four-sheeted Riemann surface, which provides a superposition of vector–meson pole and continuum contributions in a very natural way. As a result it describes simultaneously all existing experimental space-like and time-like data on the proton e.m. form factors (ff's) and on the neutron e.m. ff's as well. A crucial factor in the latter achievement is the inclusion of a contribution of the fourth excited state of the ρ(770) meson with the parameters m_ρ'''' = 2455 ± 53 MeV, Γ_ρ'''' = 728 ± 2 MeV and (f⁽¹⁾_ρ''''NN/f_ρ'''') = 0.0549 ± 0.0005, (f⁽²⁾_ρ''''NN/f_ρ'''') = −0.0103 ± 0.0001. The pronounced effect of the two-pion continuum on the isovector spectral functions demonstrating a strong enhancement of the left wing of the ρ(770) resonance close to two-pion threshold, which was revealed by Höhler and Pietarinen by means of the nucleon ff unitarity condition more than a quarter of the century ago, is predicted by the model automatically. The model gives large values of the f^(1,2)_ϕNN coupling constants, thus indicating the violation of the OZI rule. Since in the framework of the considered model isoscalar ff's above their lowest branch point t^s₀ = 9m²_π are complex functions, the isoscalar spectral function behaviours are predicted as well.

We investigate low-energy modes of the ⁶Li(³He, p) nuclear reaction leading to a production of ⁸Be nuclei in 16.63 and 16.92 MeV excited states which may have important applications in nuclear fusion research. An extrapolation procedure developed previously is used to calculate reaction cross sections σ at energies below 1 MeV and the corresponding Maxwellian rate parameters ⟨σv⟩ in the 0–200 keV temperature range. A significant discrepancy between the present values of ⟨σv⟩ and those accepted elsewhere is marked at low temperatures. An effect of low-energy resonances associated with highly excited states in the compound nucleus ⁹B is discussed. The calculated ⁶Li + ³He reaction cross sections and rate parameters are tabulated.

The sensitivity of the present CNGS beam to the sub-dominant ν_μ ↔ ν_e oscillations in the region indicated by the atmospheric neutrino experiments is investigated. In particular, we present a revised analysis of the OPERA detector and discuss the sensitivity to θ₁₃ of ICARUS and OPERA combined. We show that the CNGS beam optimized for ν_τ appearance will improve significantly (about a factor of 5) the current limit of CHOOZ and explore most of the region sin² 2θ₁₃ ≃ (10⁻²).

A search for the second forbidden electron capture of ¹²³Te has been performed. A new technique for searches of rare nuclear decays using CdZnTe detectors has been established. After a measuring time of 195 h no signal could be found resulting in a lower half-life limit of T_1/2 > 3.2 × 10¹⁶ years (95% CL) for this process. This clearly discriminates between existing experimental results which differ by six orders of magnitude, and our data are in strong favour of the result with longer half-lives.