Associated neutrino mixing and neutrino oscillations in left-right electro weak gauge theory

The rare electromagnetic decay of a neutral pseudoscalar meson into a lepton pair is calculated in a bound state quark model. For heavy mesons, the leading QCD diagram is argued to be dominant allowing higher order QCD corrections to be neglected for the branching ratio of this decay to the two-photon decay. The experimentally interesting case of pion decay is treated separately, and the rates for competing processes (weak neutral currents, axions, technicolour ...) are estimated. We conclude that existing data may well allow for such contributions.     

X(3872) and Bound State Problem of D~0(D)*~0((D)~0D*~0)

We have performed a dynamical calculation of the bound state problem of D~0(D)~(*0) by considering the pion and sigma meson exchange potential.Our preliminary analysis disfavors the molecular interpretation of X(3872) if we use the experimental D~* Dπ coupling constant g=0.59 and a reasonable cutoff around 1 GeV,which is the typical hadronic scale.In contrast,there probably exists a loosely bound S-wave B (-B)~* molecular state.Such a molecular state would be rather stable since its dominant decay mode is the radiative decay through B~*→Bγ.     

Photoproduction of pion-nucleon pairs on nuclei in the Δ(1232)-resonance region

Data from three experiments performed at the linear accelerator in Saclay, the Tomsk synchrotron, and the MAMI accelerator in Mainz and devoted to studying single pion photoproduction on light nuclei that is accompanied by nucleon emission are analyzed. The behavior of respective experimental cross sections, which is inexplicable in the impulse approximation, is interpreted within a model where the formation of an intermediate quasibound isobar-nucleus state is followed by its decay to a final state involving a pion and a nucleon.     

The contribution of pion absorption with two-nucleon emission to the pion-nucleus optical potential

Four terms in the pion-nucleus optical potential which arise from pion absorption with two nucleon emission are calculated using a model in which the nucleon is treated as a bound state of a pion and a nucleon. The contribution of these terms to the reaction cross section of carbon is considered. Two of the terms give rise to a negative reaction cross section, but it is shown that the sum of the four is positive definite. We find that the absorption reaction cross sections are very sensitive to the off-shell behavior of the free pion-nucleon T-matrix.     

A Relativistic Coupled-Channel Formalism for Electromagnetic Form Factors of 2-Body Bound States

We discuss a Poincaré invariant coupled-channel formalism which is based on the point-form of relativistic quantum mechanics. Electromagnetic scattering of an electron by a 2-body bound state is treated as a 2-channel problem for a Bakamjian-Thomas-type mass operator. In this way retardation effects in the photon-exchange interaction are fully taken into account. The electromagnetic current of the 2-body bound state is then extracted from the one-photon-exchange optical potential. As an application we calculate electromagnetic pion and deuteron form factors. Wrong cluster properties, inherent in the Bakamjian-Thomas framework, are seen to cause spurious (unphysical) contributions in the current. These are separated and eliminated in an unambiguous way such that one is left with a current that has all the desired properties.     

Mesons in the Low-Energy Limit of QCDh

Quark-antiquark bound states are described within the Bethe-Salpeter approach for a class of quark models with instantaneous 4-quark interaction. Thereby decompositions of the Bethe-Salpeter vertex and wave functions according to their Lorentz structures and the particle content are used. Normalization conditions for the bound state functions are given. As an application of the general scheme, we determine the mass spectrum of low-lying mesons without expanding in energy. This calculation is performed for a special Nambu-Jona-Lasinio model which follows from the so-called QCD for hadrons, QCD_h, by a localization of the potential. Furthermore the pion and kaon decay constants are determined. We receive good agreement with the experimental data.     

Sum rules for radiative quarkonium decays from short-range interactions

Sum rules previously derived for proton decay are extended and applied to treat effects of bound states spectroscopy on radiative quarkonium decays. The transition involves boson (photon or pion) emission followed by quark annihilation. Sum rules for the contributions from different intermediate bound states are derived by using closure and the assumptions (1) that the boson emission is described by a plane wave or multipole operator which satisfies a wave equation, and (2) that the annihilation depends on the bound state wave function or its derivative at the origin.     

PROTON DECAY RATE AND THE PROTON WAVEFUNCTION

The pionic two body decay process of the proton is discussed in the SU(5) grand unification theory by using the field-current relation of the composite particle and the soft pion approximations. We connect the proton decay process with the J/ψ→pp decay amplitude and determine the wavefunction at the origin from the experimental value of the decay rate J/ψ→pp, hence we can obtain the value of the proton decay lifetime. In order to estimate the uncertainty of the proton decay lifetime due to the proton wavefunction at the origin, the lower bound of it is analysed by using an interesting model. If taking Λ_MS=200 MeV, it will be a serious test for the minimal SU(5) grand unified gauge theory. It should be noted that this method which connect the proton decay process with other relavant processes will be very useful to determine the proton decay lifetime.     

A study of transverse charge density of pions in relativistic quantum mechanics

The transverse charge density of pions is calculated based on relativistic quantum mechanics, where the pion is regarded as a quark-antiquark bound state. Corrections from the two spin-1/2 constituents and from the wave function of a quark and antiquark inside the bound system are discussed. The calculated results are compared to the results with a realistic effective Lagrangian approach as well as to that with a simple covariant model where the pion is regarded as a composite system with two scalar particles.     

Is X(3872) really a molecular state?

After taking into account both the pion and sigma meson exchange potential, we have performed a dynamical calculation of the D⁰D̄^*0 system. The σ meson exchange potential is repulsive from heavy quark symmetry and numerically important for a loosely bound system. Our analysis disfavors the interpretation of X(3872) as a loosely bound molecular state if we use the experimental D^*Dπ coupling constant g=0.59 and a reasonable cutoff around 1 GeV, which is the typical hadronic scale. Bound state solutions with negative eigenvalues for the DD̄^* system exist only with either a very large coupling constant (twice the experimental value) or a large cutoff (Λ ∼ 6 GeV or β ∼ 6 GeV²). In contrast, there probably exists a loosely bound S-wave BB̄^* molecular state. Once produced, such a molecular state would be rather stable, since its dominant decay mode is the radiative decay through B^*→Bγ. Experimental search of these states will be very interesting. PACS  12.39.Pn; 12.40.Yx; 13.75.Lb     

The Effects of the Pion String at Heavy ion Collisions

We study the possible signals of the pion string associated with the QCD chiral phase transition in LHC Pb–Pb collision at energy s=5.5 TeV.We follow the Kibble–Zurek mechanism to discuss the production and evolution of the pion string.We will show that if the QCD chiral phase transition really takes place in the LHC Pb-Pb collision process and the phase transition is in the second order,the pion string will be inevitably produced and subsequently decay.The main effect of this phenomenon is that there is a generation of a large number of pions in the final state produced by the decay of the pion string, and these pions are mostly distributed in a low momentum region with p～143MeV; also there are lots of neutral pions distributed in a low momentum region with the mean momentum at p～21MeV.     

Pion asymmetry in the three-body radiative decays of polarized hyperons

We have calculated the energy dependence of pion asymmetry relative to the direction of hyperon polarization in the three-body radiative decays of polarized hyperons, using the inner bremsstrahlung model. We find that in the low pion energy region, the pion asymmetry in the radiative decay relative to the non-radiative decay is kinematically enhanced. For certain decays, this effect could be exploited experimentally to obtain additional information about the properties of the hyperons.     

H-particle in a chiral quark model

In this paper we discuss the binding energy of the H-particle using a chiral quark model, where pion exchange plays an important role to reproduce the mass difference between the nucleon and Δ resonance. Since the main source for the bound H-particle is believed to be the color magnetic interaction, which gives the nucleon and Δ mass difference, it is very interesting to investigate whether the chiral quark model gives rise to the bound H-particle or not. We employ an extended resonating group method in order to take into account the possibility of a change of baryon wave functions when two baryons interact with each other. We found that a change of baryon size together with the Hamiltonian which consists of gluon, pseudoscalar meson and sigma meson exchange potentials gives rise to the bound H-particle. The binding energy is found to be about 25 MeV in a hybrid chiral quark model. Differences between the ordinary gluon dominant model and chiral quark models are also investigated. It is found that a pure chiral model has no bound state when the widely used sigma-quark coupling strength is employed.     

Restrictions on the cluster decay multiplicity distribution in the independent cluster emission model due to crossing symmetry and isospin invariance

We discuss multiparticle production in high energy proton-proton scattering under the assumption that all produced secondaries are pions. We take into account the pion isospin but neglect the isospin of the protons. In the first part of the paper it is shown that the multiplicity distribution of the independent cluster emission model can be derived from a unitary, crossing symmetric, isospin invariant, impact parameter model. This part is a straight forward generalization of a previous work where similar results were obtained for isospin-zero mesons. In the second part of the paper we shall discuss the restrictions on the cluster decay multiplicity distribution due to crossing symmetry in the meson variables and to isospin invariance. In particular, we shall derive a non-trivial lower bound for the dispersion of the charged particles in the cluster decay multiplicity distribution.     

The quantum skyrmion in representations of general dimension

The representations of general dimension are constructed for the SU(2) Skyrme model, treated quantum mechanically ab initio. This quantum Skyrme model has a negative mass term correction that is not present in the classical Hamiltonian. The magnitude of the quantum mechanical mass correction increases with the dimension of the representation of the SU(2) group. In the case of a 5-dimensional representation it is possible to obtain satisfactory predictions for the nucleon mass with the empirical value for the pion decay constant.     

Determination of the parity of the neutral pion via its four-electron decay

We present a new determination of the parity of the neutral pion via the double Dalitz decay pi0-->e+e-e+e-. Our sample, which consists of 30,511 candidate decays, was collected from KL-->pi0pi0pi0 decays in flight at the KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the negative pi0 parity and place a limit on scalar contributions to the pi0-->e+e-e+e- decay amplitude of less than 3.3% assuming CPT conservation. The pi0gamma*gamma* form factor is well described by a momentum-dependent model with a slope parameter fit to the final state phase-space distribution. Additionally, we have measured the branching ratio of this mode to be B(pi0-->e+e-e+e-)=(3.26+/-0.18)x10(-5).     

Pion production via isobar giant resonance formation and decay

A spin, isotopic-spin formalism for the production of pions due to decays of isobar giant resonances formed in peripheral heavy-ion collisions is presented. The projectile nucleus isobar giant resonance state is assumed to coherently form and then incoherently decay to produce the pions. Total spin and isotopic spin for the system are conserved through the concomitant excitation of the target nucleus to an isobaric analog giant resonance state. Comparisons of the predicted total pion cross sections, over a range of energies, are made with heavy-ion pion data.     

On the implications of a 17 keV neutrino

We discuss the implications of the recent measurement of a 17 keV mass component in the electron neutrino sector. Such a heavy state must decay in order to be compatible with cosmology; this requires states additional to those of the standard model. The most likely candidates are either majorons, allowing the decay into massless weakly interacting scalars, or single neutrinos, allowing the decay via the Z into light neutrinos. We show that in the latter case there is a lower bound on the lifetime in conflict with the cosmological constraints on this decay channel and on the photon plus neutrino decay channel which is also present. The extensions of the standard model needed to reduce the lifetime are considered. We analyze the mass matrix, playing particular regard to the singlet neutrino case, and discuss how it might be extended to explain the solar neutrino deficit.