Relativistic calculation for the reactions\bar p d → 5πp and\bar p d → 3πp at rest

We present a fully relativistic calculation for ¯pd → 5πp and ¯pd → 3πp that includes angular momentum and spin dynamics. We calculate the inclusive proton distributions from two diagrams: the leading “tree” diagram, and the diagram for pion rescattering. Pion-nucleon rescattering proceeds through the Δ, in the RaritaSchwinger formalism, thus preserving the correct angular dependence. We use realistic parameterizations of the deuteron, keeping both theS andD states. The loop integrations for the rescattering amplitude and the phase space integrations have been done numerically. We find that the combined effects of a correct treatment of the rescattered pion and relativity are small in comparison with a simple non-relativistic calculation.     

Flavor-changing electromagnetic vertex in a non-linear Rξ gauge

We calculate the general transition q_i → q_j + γ for arbitrary quark flavors in a non-linear R_ξ gauge. The reduced number of Feynman diagrams as well as simplified Ward identities greatly facilitates this calculation. A general result with intermediate quarks of arbitrary mass is presented and the special cases s → d + γ as well as s → d + gluon are discussed.     

Four weak gauge boson production at photon linear collider and heavy Higgs signal

We study the signals and backgrounds for a heavy Higgs boson in the processes γγ → WWWW, γ → WWZZ at the proton linear collider. The results are based on the complete tree-level SM calculation for these reactions. We show that the invariant mass spectrum of central WW, ZZ pairs is sensitive to the signal from Higgs boson with a mass up to 1 TeV linear collider for integrated luminosity of 300 fb⁻¹. At 1.5 TeV PLC Higgs boson with a mass up to 700 GeV can be studied. The nonresonant longitudinal gauge boson scattering (m_H = ∞) can be detected in photon-photon collisions at e⁺e⁻ center-of-mass energy of 3 TeV.     

Dynamical calculation of the decay ψ′ → ψ + 2π

We calculate the ψ′ → ψ + 2π decay width on the basis of partial wave dispersion relations in the ππ channel. This is basically a coupled channel problem involving ππ, D$\text{D}$, etc. intermediate states. The calculation acquires anomalous thresholds due to the fact that the vertex ψ′ ψ (2π) is internally unstable. It is found that anomalous singularity contributions provide by far the most dominant contribution, which explains the rather large ψ′ → ψ + 2π decay mode. Very good agreement with the experimental width and mass distribution is achieved.     

An upper limit on the tau neutrino mass from leptonic tau decays

The partial width of the τ → e ^- v _e v _τ can be calculated from the tau mass, lifetime and branching ratio. The increasing precision on these measurements is making the partial width sensitive to the mass of the tau neutrino. We present the tau neutrino mass dependence on the partial width and show that this leads to a limit of m _r < 71 MeV at the 95% confidence level. We show that the limit is determined by the uncertainty in the tau lifetime and τ → e?v _e v _τ branching ratio. Additional measurements of these values are expected in the next few years and we show that the limit could become competitive with the direct measurements.     

Pseudoscalars and vector mesons in a unitary and self-consistently broken SU(6) W scheme

We estimate hadronic self-energy effects to “bare” pseudoscalar (P) and vector (V) meson states due to theP→PV→P, P→VV→P, V→ PP→V, V→PV→V andV→VV→V loops. We simulate higher order diagrams by consistently requiring external and internal particles to have the same mass. We find good agreement with all the experimental masses (exceptm _π), widths and mixing angles. The “bare”P andV states are heavy (≈1.26 GeV) and degenerate up to a smallm _s?m_u quark mass difference term. The “bare” coupling constants for thePPV, PVV andVVV vertices obey exact OZI rule and almost exact SU(6) _W symmetry. We use a common cut-off ofk _cm?0.7 GeV/c corresponding to a harmonic oscillator radius of ?0.7 fm for all SU(6) _W related thresholds except for the pion.     

The use of QCD in hadronic cascades between heavy quark-antiquark bound states

We argue that a perturbative calculation of the spectra and rates of hadronic transitions between heavy quark-antiquark bound states makes sense within QCD provided suitable spin-parity projections are performed. Applications are made to various kinds of cascades. We obtain the correct ψ′ → J/ψππ mass spectrum. The cascades involving the emission of at least three gluons appear very strongly suppressed as compared to those allowing two-gluon emission. Application to the ? family is made.     

Particular cases of particle production in inelastic lepton (anti) lepton scattering

As in a previous paper we consider the inclusive reactions e+e→e+e+ anything in the two photon exchange approximation. We present the complete calculation of the differential cross section dσ/dW² for the production of a state of effective mass W and we give the expression for the total cross section. We apply this to the muon pair and the pseudoscalar meson (π⁰, η and η) productions.     

Electroproduction final states as ω → 1

The successful model of Barbour and Moorhouse for pion photoproduction is extended to electroproduction and combined with recent ideas on configuration mixing or SU(6) breaking in deep inelastic electroproduction as ω → 1. We find that two consequences obtain in the current fragmentation region as ω → 1: (a) the missing mass spectrum in ep → eπ^?X and en → eπ⁺X will be featureless (phase space); (b) in ep → eM^+,0X and en → eM^0,?X for any non-strange meson M the missing hadron system will contain only octets. Hence, in particular, ep → eπΔ will vanish relative to ep → eπ⁺n as ω → 1. For K production only Λ and no Σ final states will be produced.     

Low energy constraints on N = 2 supersymmetric models

We derive constraints on the masses of mirror particles in N = 2 supersymmetric theories. We consider the K_L?K_S mass difference, the π → ev/π → μv branching ratio and the anomalous magnetic moment of the muon. The K_L?K_S mass difference gives a lower bound of 15 TeV on the mirror gauge scalar and mirror gauge fermion masses, under suitable assumptions.     

Total cross section forZ 0 production in electron proton collisions

We present an exact calculation of the total cross section π_tot of theZ ⁰ production ine ^?1+p→e ^?+Z ⁰+X processes. We find a total cross section π_tot?1.0·10^?36cm² for an energy in the center of mass of 300 GeV and aZ ⁰ mass of 90GeV, which is quite a measurable result in somee ^?1 proton collider experiments, like HERA or SPS/LEP.     

Two-nucleon production of hyperons and the search for strange dibaryons

The double charge exchange reaction³He(K^?,π ⁺)Xn was studied at 870 MeV/c. In the X missing mass range below the sigma-nucleon production threshold (2130 MeV/c²), events were detected which can be attributed to the two-nucleon process pp(K^?,π ⁺)λn. This reaction and mass range also offers good prospects for finding theI=1/2,l=1 (¹ P₁) spin-singlet dibaryon D_s suggested as the lowest massS=?1 dibaryon in the MIT Bag Model. Although the existence of the D_s is not ruled out by the present data, there is no need to invoke such an object to account for the observed events below σ production threshold. We show that the cross section level for these events is compatible with a dominant two-nucleon mechanism K^?p→π ⁰λ,π ⁰p →π ⁺n. We also offer an interpretation of the recent (K^?,K⁺) data on nuclear targets from Iijimaet al., which display a broad peak centered around a K⁺ momentum of 600 MeV/c. We find that the two-nucleon mechanism K^?N →πY,πN→K⁺Y produces cross sections which are at least an order of magnitude smaller than those observed, and we suggest that the one nucleon process K^?p →Φλ, followed by the decayΦ → K⁺K^?, accounts for the data.     

Duality diagrams and the decays of the ψ and ψ′

We apply duality diagrams to the ψ and ψ′ decays. We propose that the ψ → 3π decay is described by a Virasoro formula, and show that the low mass ππ suppression in ψ′ → ψ2π is a consequence of the threshold factor contained in the Pomeron-2π coupling. We stress the importance of the ψ and ψ′ decays for the study of heavy mesonic resonances.     

d′ production in heavy-ion collisions

The production of d′ dibaryons in heavy-ion collisions due to the elementary process NN → d′π is considered. The NN → d′π cross section is estimated using the vacuum d′ width Γ_d′ ≈ 0.5 MeV extracted from data on the double charge exchange reactions on nuclei. The d′ production rate per single collision of heavy ions is estimated at an incident beam energy of 1 A GeV within the framework of the Quantum Molecular Dynamics transport model. We suggest to analyse the invariant mass spectrum of the NNπ system in order to search for an abundance of events with the invariant mass of the d′ dibaryon. The d′ peak is found to exceed the statistical fluctuations of the background at a 6σ level for 2 × 10⁵ · A central collisions of heavy ions with the atomic number A.     

Exclusive c → s,d Semileptonic Decays of Spin-1/2 and Spin-3/2 cb Baryons

We present results for exclusive semileptonic decay widths of ground state spin-1/2 and spin-3/2  cb baryons corresponding to a c → s, d transition at the quark level. The relevance of hyperfine mixing in spin-1/2 cb baryons is shown. Our form factors are compatible with heavy quark spin symmetry constraints obtained in the infinite heavy quark mass limit.     

Calculations of the dipion contribution to the KLKS mass difference

Long range effects may well dominate the K_LK_S mass difference. The most important of these is that of the virtual two-pion intermediate state. This is computed using the most reliable presently available data on I = 0 S-wave dipion production. This is found to contribute 46±13% of the observed mass difference. The assumptions about the K → ππ interaction needed to perform this calculation are detailed and a comparison is made with other recent evaluations.     

Photoabsorption on nuclei

We calculate the total photoabsorption cross section on nuclei in the energy range from 300 MeV to 1 GeV within the framework of a semi-classical phase space model. Besides medium modifications like Fermi motion and Pauli blocking we focus on the collision broadening of the involved resonances. The resonance contributions to the elementary cross section are fixed by fits to partial wave amplitudes of pion photoproduction. The cross sections for NR → NN, needed for the calculation of collision broadening, are obtained by detailed balance from a fit to NN → NNπ cross sections. We show that a reasonable collision broadening is not able to explain the experimentally observed disappearance of the D₁₃(1520)-resonance in the photoabsorption cross section on nuclei.     

In-medium properties of the ω meson in photon induced nuclear reactions

We discuss the possibility to study the in-medium changes of the properties of the ω meson in reactions on ordinary nuclei with elementary electromagnetic probes. We present a tree-level calculation of the elementary γp→ωp process which is extended to describe also the photoproduction of medium-modified ω mesons in nuclear matter. Using a semi-classical transport approach we obtain results for e⁺e_? and π ⁰γ photoproduction off heavy nuclei in the invariant mass range of the ρ and ω mesons. Both reactions are also studied experimentally and are presently being analyzed at accelerator facilities in Bonn and at Jefferson Lab. We show that the in-medium signals expected can be as large as those obtained in heavy-ion reactions.     

Symmetry breaking and restoration in Lifshitz type theories

We consider the one-loop effective potential at zero and finite temperature in scalar field theories with anisotropic space-time scaling. For z=2, there is a symmetry breaking term induced at one loop at zero temperature and we find symmetry restoration through a first-order phase transition at high temperature. For z=3, we considered at first the case with a positive mass term at tree level and found no symmetry breaking effects induced at one loop, and then we study the case with a negative mass term at tree level where we cannot conclude about symmetry restoration effects at high temperature because of the imaginary parts that appear in the effective potential for small values of the scalar field.