abstract

The soliton solutions of the bosonised version of the massive Schwinger model for \(N_f =2\) in the first approximation are found. We discus scattering such solutions on each other in both elastic and non-elastic cases.

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We discuss the notion of noncommutative symmetries based on Hopf algebras in the geometric models constructed within the framework of noncommutative geometry. We introduce and discuss several notions of noncommutative symmetries and outline the construction specific examples, for instance, finite algebras and the application of symmetries in the derivation of the Dirac operator for the noncommutative torus.

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An algebraic argument based on a series of generalized Dirac equations, truncated by an “intrinsic Pauli principle”, shows that there should exist two sterile neutrinos as well as three families of leptons and quarks. Then, the influence of these additional neutrinos on neutrino oscillations is studied. As an example, a specific model of effective five-neutrino texture is proposed, where only the nearest neighbours in the sequence of five neutrinos ordered as \( \nu _s, \nu '_s, \nu _e, \nu _\mu , \nu _\tau \) are coupled through the \(5\times 5\) mass matrix. Its diagonal elements are taken as negligible in comparison with its nonzero off-diagonal entries.

abstract

A detailed study of the associated Standard Model Higgs boson production in 14 TeV \(pp\) (LHC) and 2 TeV \(p\bar p\) (Tevatron) collisions, \(WH\) with \(W\to \ell \nu \) and \(ZH\) with \(Z\to \ell \ell \), with Higgs boson decays to \(b\bar b\) pair, is presented for Higgs masses of 100 and 120 GeV. Presently, \(WH\) with \(H\to b\bar b\) production is considered to be less promising than the \(t\bar tH\) associated production for the Higgs searches at LHC. However, studies of Higgs searches at Tevatron indicate that this channel in combination with the \(WH/ZH\) channels leading to the \(E_{\rm T}^{\rm miss} + b \bar b\) signature, offers good discovery potential in the mass range 90–140 GeV. The aim of this paper is to provide several details which lead to a quantitative comparison in a consistent framework of the physics potential for these channels in both colliding scenarios. The emphasis is put on the differences in the expected signal and background rates and compositions of the backgrounds.

abstract

A detailed study of the associated Standard Model Higgs boson production in 14 TeV \(pp\) (LHC) and 2 TeV \(p\bar p\) (Tevatron) collisions, \( WH/ZH\) with \(H\to b\bar b\) decay and \({E_{\rm T}^{\rm miss} + b \bar b}\) signature, is presented for a benchmark value of the Higgs boson mass, \({m_H=100}\) GeV. The observation of these events with ATLAS at LHC is considered not to be feasible because of the overwhelming background from QCD jet events. Contrary, this signature is claimed to be promising for a Higgs boson discovery in the mass range of 90–140 GeV at the Tevatron \({p \bar p}\) collider.The aim of this paper is to provide several details which lead to a quantitative comparison in a consistent framework of the physics potential for this signature in both colliding scenarios. The emphasis is put on the differences in the expected signal and backgrounds rates and the background composition. Together with a similar study presented on the \(WH/ZH\) production with \({\ell b \bar b}\) and \({\ell \ell b \bar b}\) final states, it covers most sensitive signatures discussed in the Tevatron report for the Higgs searches in the mass range 90–140 GeV.

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The \(t\bar tb\bar b\) production is a dominant background for the SM and MSSM Higgs search in the associated production \(t\bar t H\) with \(H \to b \bar b\). This paper presents a comparison for the background rates obtained with the Monte Carlo generators: PYTHIA5.7 and CompHEP. In the case of PYTHIA the \( t \bar t\) production is generated in the hard process and the remaining two \(b\)-quarks are obtained from the partonic cascade. In the case of CompHEP an exact matrix element for \(t\bar tb\bar b\) production is used. A detailed comparison of the cross-sections and the expected acceptances is shown for several steps of the selection used for the extraction of the Higgs signal peak. The final estimates for the expected number of background events are similar in both cases with predictions from PYTHIA being even slightly higher. This comparison gives confidence in the predictions of the PYTHIA generator for the \(t\bar tb\bar b\) background.

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The structure of \(A=22\) nuclei has been studied in the framework of the collective pair approximation. The collective pairs determined by diagonalizing the Hamiltonian in the space of two nucleons with respect to the closed core of \(^{16}\)O have been considered as building blocks to expand the truncated shell-model space in terms of three pairs. It is shown that the low-lying, shell-model spectrum can be described by considering only a selected subset of all possible \(T=0\), 1 pairs.

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Motivated in part by recent experimental determinations of the \(\rho \)-meson mass in the nuclear medium, we apply the Brown–Rho scaling hypothesis in the three-nucleon system. We pay particular attention to two open problems, namely, the binding energy and the analyzing power in neutron-deuteron elastic scattering (“\(A_{y}\) puzzle”). We show that both issues can be successfully addressed by a scaling of meson masses corresponding to an average density of the three-nucleon system.

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Analysis of the clustering properties in the multiparticle final states produced in central collisions of Pb nuclei with the Ag/Br target at 158 \(A\) GeV is presented. It is mainly focused on investigation of different effects which influence the results of the search for high density phase space regions. A comparison of different clustering procedures is performed with varied cuts on the cluster size and on the number of particles per cluster. We also discuss the dependence of the obtained results on the shape of single particle distributions and on the multiplicity of produced particles.

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The event-by-event azimuthal fluctuations in high-energy heavy-ion collisions are analyzed by means of the so-called \({\mit \Phi }\)-measure. The fluctuations due to the collective transverse flow and those caused by the quantum statistics in the hadron gas are discussed in detail.

abstract

Weight function \(P(\alpha )\) in the diagonal representation of density operator, \(\rho =\int d^2\alpha P(\alpha )|\alpha \gt \lt \alpha |\), is reduced to define separately the weight functions for phase, \({\rm arg}\,(\alpha )\), and amplitude, \(|\alpha |\), which leads to concepts of phase-coherence and amplitude-coherence. For a single mode phase- -coherent field, it is shown that (i) we can have Hermitian operator of form, \(a \rho \mathrm {e} ^{i\psi }\), where \(a\) is annihilation operator and \(\psi \) is a constant, and (ii) the normally ordered characteristic function, \(\chi _N(\xi )\), is a function of only the imaginary part of \(\xi \mathrm {e} ^{i\psi }\). For a single mode amplitude-coherent field, it is shown that \(a\rho a^\dagger = ka^\dagger \), where \(a^\dagger \) is creation operator and \(k\) is a positive real constant. When the weight function for the field is non-classical, each of the reduced weight function may or may not be non-classical irrespective of the nature of the other. Examples of generation of phase-coherent and amplitude-coherent fields are given.

abstract

The \(\gamma \)-circular polarization \((P_\gamma )\) and asymmetries \((A_\gamma )\) of the parity forbidden M1 + E2 \(\gamma \)-decays: \(^{10}\)B\(^{*}\left ( J^\pi =2^{-}T=0;E_x=5.11\textrm { MeV}\right )\rightarrow \) \( ^{10}\)B\(^{*}\left ( J^\pi =1^{+}T=0;E_x=0.72\textrm { MeV}\right ) \) as well as the PNC analyzing powers for resonance reaction populating the parity \(\left ( 2^{\pm }\right ) \) doublet at 7.47 MeV have been investigated theoretically. We use the recently proposed Warburton–Brown shell model interaction. For the weak forces we discus comparatively different weak interaction models based on different assumptions for evaluating the weak meson–hadron coupling constants. The results determine a range of \(P_\gamma \)-values from which we find the most probable values: \(P_\gamma =3.7\times 10^{-4}\) for the 5.11 MeV doublet and \(A_{L(b)}\approx 0.6\times 10^{-5}\) for the 7.47 MeV doublet. These cases seem to be promising for further experimental tests of parity nonconservation in nuclei.