Discovering and studying bileptons with e−e− collisions

We analyze the prospects for discovering and unraveling the nature of doubly charged bileptons at a linear collider of the next generation running in its e⁻e⁻ mode. We stress the importance of initial state radiation, beam spread and polarization, and compute the discovery bounds. The gauge nature of vector bileptons can be determined by studying hard photon emission.     

TeV-scale bileptons, see-saw type II and lepton flavor violation in core-collapse supernova

Electrons and electron neutrinos in the inner core of the core-collapse supernova are highly degenerate and therefore numerous during a few seconds of explosion. In contrast, leptons of other flavors are non-degenerate and therefore relatively scarce. This is due to lepton flavor conservation. If this conservation law is broken by some non-standard interactions, ν _e are converted to ν _μ , ν _τ , and e are converted to μ. This affects the supernova dynamics and the supernova neutrino signal. We consider lepton flavor violating interactions mediated by scalar bileptons, i.e. heavy scalars with lepton number 2. It is shown that in case of TeV-mass bileptons the electron Fermi gas is equilibrated with non-electron species inside the inner supernova core at a time scale ～(1–100) ms. In particular, a scalar triplet which generates neutrino masses through the see-saw type II mechanism is considered. It is found that the supernova core is sensitive to yet unprobed values of masses and couplings of the triplet.     

Bilepton production in $ e^-\gamma $ collisions

We study the production of bileptons, new gauge bosons of lepton number two, in the minimal 3-3-1 model in high energy collisions. If the bilepton masses are in the range of 300 GeV the reaction will give observable cross-sections in future colliders.Received: 5 August 2003, Published online: 23 March 2004Dang Van Soa: On leave of absence from Department of Physics, Hanoi University of Education, Hanoi, VietnamHoang Ngoc Long: On leave of absence from Institute of Physics, NCST, P.O. Box 429, Bo Ho, Hanoi 10000, Vietnam     

Bilepton contributions to the neutrinoless double beta decay in the economical 3-3-1 model

A new bound of the mixing angle between charged gauge bosons (the standard-model W and the bilepton Y) in the economical 3-3-1 model is given. Possible contributions of the charged bileptons to the neutrinoless double beta ((ββ)_0ν) decay are discussed. We show that the (ββ)_0ν decay in this model is due to both the Majorana 〈M _ν〉 _L and Dirac 〈M _ν 〉_D neutrino masses. If the mixing angle is in the range of the ratio of neutrino masses 〈M _ν 〉 _L /〈M _ν 〉_D, the Majorana and Dirac masses are comparable to each other and both may give the main contribution to the decay. As a result, constraints on the bilepton mass are given. The article is published in the original.     

\mu-e conversion in nuclei in the left-right supersymmetric model

We investigate the contributions to conversion in nuclei in a supersymmetric model with left-right symmetry, motivated by the new data on neutrino oscillations. We study the dependence of the conversion rate on the various parameters of the model, and show that light-mass or large scenarios are severely restricted. We analyse the effect of several popular mecahnisms of neutrino mixing on the conversion rate as well as the influence of the right-handed scale on the conversion rate. We compare the conversion rate to the branching ratio for and discuss their relative accessibility at future experiments, their sensitivity to various parameters of the model, as well as their relative importance in providing signals for new Physics. Received: 31 May 2000 / Published online: 31 August 2000     

Symplectic Structures on Gauge Theory

We study certain natural differential forms and their equivariant extensions on the space of connections. These forms are defined using the family local index theorem. When the base manifold is symplectic, they define a family of symplectic forms on the space of connections. We will explain their relationships with the Einstein metric and the stability of vector bundles. These forms also determine primary and secondary characteristic forms (and their higher level generalizations). Received: 27 February 1996 / Accepted: 7 July 1997     

On Kreimer's Hopf algebra structure of Feynman graphs

We reinvestigate Kreimer's Hopf algebra structure of perturbative quantum field theories with a special emphasis on overlapping divergences. Kreimer first disentangles overlapping divergences into a linear combination of disjoint and nested ones and then tackles that linear combination by the Hopf algebra operations. We present a formulation where the Hopf algebra operations are directly defined on any type of divergence. We explain the precise relation to Kreimer's Hopf algebra and obtain thereby a characterization of their primitive elements. Received: 9 July 1998 / Revised version: 21 September 1998 / Published online: 19 November 1998     

Diffraction at HERA and the confinement problem

We discuss HERA data on the high energy behavior of the total cross section and on diffraction in deep inelastic scattering. We outline their novelty in comparison with diffraction in high energy hadron-hadron scattering. As a physical picture, we propose an interpretation in terms of QCD radiation at small and large distances: a careful study of the transition between the two extremes represents a new approach to the QCD confinement problem. Received: 7 December 2000 / Published online: 6 April 2001     

Magnetic properties of spin-orbital polarons in lightly doped cobaltates

We present a numerical treatment of a spin-orbital-polaron model for NaxCoO2 at small hole concentration (0.7 < x 1). We demonstrate how the polarons account for the peculiar magnetic properties of this layered compound: They explain the large susceptibility; their internal degrees of freedom lead both to a negative Curie-Weiss temperature and yet to a ferromagnetic intralayer interaction, thereby resolving a puzzling contradiction between these observations. We make specific predictions on the momentum and energy location of excitations resulting from the internal degrees of freedom of the polaron, and discuss their impact on spin-wave damping.     

Generalized parton distributions

We discuss how generalized parton distributions (GPDs) enter in a variety of hard exclusive processes such as deeply virtual Compton scattering (DVCS) and hard meson electroproduction reactions on the nucleon. We show some key observables which are sensitive to the various hadron structure aspects of the GPDs, and discuss their experimental status.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Fz Elastic and Compton scattering - 13.60.Le Meson production - 12.38.Bx Perturbative calculations     

Pomeron-Odderon interference effects in electroproduction of two pions

We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction of a pair. We calculate these asymmetries, originating from both longitudinal and transverse polarizations of the virtual photon, in the framework of QCD and in the Born approximation, in a kinematical domain accessible to HERA experiments. We predict a sizable charge asymmetry with a characteristic dependence on the invariant mass of the pair, which makes this observable very important for establishing the magnitude of the Odderon exchange in hard processes. The single-spin asymmetry turns out to be rather small. We briefly discuss future improvements of our calculations and their possible effects on the results. Received: 18 July 2002 / Published online: 25 October 2002     

Interaction of two-dimensional spatial incoherent solitons in photorefractive medium

We present a review of our recent theoretical and experimental results on the interaction of incoherent two-dimensional solitary beams in PR SBN crystals. We show that the inherent anisotropy of PR nonlinearity strongly affects the interaction between solitons. Theoretical and experimental results reveal that solitons interacting in a plane perpendicular to the direction of external biasing field always attract, whereas those colliding in a plane of the field exhibit anomalous behaviour. They may experience both attractive and repulsive forces, depending on their mutual separation. We also show that this anisotropy results in the complicated topology of soliton trajectories, featuring periodic collisions, prolonged mutual spiraling and collapse, depending on the initial conditions. Received: 16 November 1998 / Revised version: 12 February 1999 / Published online: 12 April 1999     

Unequal twins: probability distributions do not determine everything

It is the common lore to assume that knowing the equation for the probability distribution function (PDF) of a stochastic model as a function of time tells the whole picture defining all other characteristics of the model. We show that this is not the case by comparing two exactly solvable models of anomalous diffusion due to geometric constraints: the comb model and the random walk on a random walk. We show that though the two models have exactly the same PDFs, they differ in other respects, like their first passage time distributions, their autocorrelation functions, and their aging properties.     

A next-to-leading order study of pion-pair production and comparison with E706 data

We discuss the production of pion pairs with a large invariant mass in hadronic collisions. We present a study based on a perturbative QCD calculation at full next-to-leading order accuracy, implemented in the computer programme DIPHOX. We provide a comparison of various predictions with the corresponding observables measured by the E706 fixed target experiment. Discrepancies between data and next-to-leading order calculation are carefully analysed. We classify the theoretical next-to-leading order distributions with respect to their infrared sensitivity, and explain which distributions need improvements. Further, we comment on the energy scale dependences of non pertubative effects. Received: 8 November 2001 / Published online: 5 April 2002     

Quadratic Bosonic and Free White Noises

We discuss the meaning of renormalization used for deriving quadratic bosonic commutation relations introduced by Accardi [ALV] and find a representation of these relations on an interacting Fock space. Also, we investigate classical stochastic processes which can be constructed from noncommutative quadratic white noise. We postulate quadratic free white noise commutation relations and find their representation on an interacting Fock space. Received: 23 August 1999 / Accepted: 8 December 1999     

Baryonic masses based on the NJL model

We employ the Nambu-Jona-Lasinio model to determine the vacuum pressure on the quarks in a baryon and hence their density inside. Then we estimate the baryonic masses by implementing the local density approximation for the mean-field quark energies obtained in a uniform and isotropic system. We obtain a fair agreement with the experimental masses. Received: 27 September 2002 / Accepted: 4 October 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: giacosa@tphys.physik.uni-tuebingen.de Communicated by A. Molinari     

Calibrations and Intersecting Branes

We investigate the solutions of Nambu–Goto-type actions associated with calibrations. We determine the supersymmetry preserved by these solutions using the contact set of the calibration and examine their bulk interpretation as intersecting branes. We show that the supersymmetry preserved by such solutions is closely related to the spinor singlets of the subgroup G of Spin (9,1) or Spin (10,1) that rotates the tangent spaces of the brane. We find that the supersymmetry projections of the worldvolume solutions are precisely those of the associated bulk configurations. We also investigate the supersymmetric solutions of a Born–Infeld action. We show that in some cases this problem again reduces to counting spinor singlets of a subgroup of Spin (9,1) acting on the associated spinor representations. We also find new worldvolume solutions which preserve 1/8 of the supersymmetry of the bulk and give their bulk interpretation. Received: 20 May 1998 / Accepted: 16 November 1998     

Bosonic quartic couplings at LEP2

We list the set of and conserving anomalous quartic vector bosons self-couplings which can be tested at LEP2 through triple vector boson production. We show how this set can be embedded in manifestly gauge invariant operators exhibiting an global symmetry. We derive bounds on these various couplings and show the most relevant distributions that can enhance their contribution. We also find that an collider running at 500 GeV can improve the LEP2 limits by as much as three-orders of magnitude. Received: 9 September 1999 / Revised version: 19 October 1999 / Published online: 17 February 2000     

Permutation invariant algebras, a Fock space realization and the Calogero model

We study permutation invariant oscillator algebras and their Fock space representations using three equivalent techniques, i.e. (i) a normally ordered expansion in creation and annihilation operators, (ii) the action of annihilation operators on monomial states in Fock space and (iii) Gram matrices of inner products in Fock space. We separately discuss permutation invariant algebras which possess hermitean number operators and permutation invariant algebras which possess non-hermitean number operators. The results of a general analysis are applied to the -extended Heisenberg algebra, underlying the M-body Calogero model. Particular attention is devoted to the analysis of Gram matrices for the Calogero model. We discuss their structure, eigenvalues and eigenstates. We obtain a general condition for positivity of eigenvalues, meaning that all norms of states in Fock space are positive if this condition is satisfied. We find a universal critical point at which the reduction of the physical degrees of freedom occurs. We construct dual operators, leading to the ordinary Heisenberg algebra of free Bose oscillators. From the Fock-space point of view, we briefly discuss the existence of a mapping from the Calogero oscillators to the free Bose oscillators and vice versa. Received: 26 July 2001 / Revised version: 9 January 2002 / Published online: 12 April 2002