Bound states of bosons and fermions in a mixed vector-scalar coupling with unequal shapes for the potentials

The Klein - Gordon and the Dirac equations with vector and scalar potentials are investigated under a more general condition, V(v) + V(s) = constant. These intrinsically relativistic and isospectral problems are solved in the case of squared hyperbolic potential functions and bound states for either particles or antiparticles are found. The eigenvalues and eigenfuntions are discussed in some detail and the effective Compton wavelength is revealed to be an important physical quantity. It is revealed that a boson is better localized than a fermion when they have the same mass and are subjected to the same potentials.

Finding the Higgs boson through supersymmetry

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fermion localization on a split brane

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Indirect constraints on the triple gauge boson couplings from Z -> b(b)over-bar partial width: An update

We update the indirect bounds on anomalous triple gauge couplings coming from the non-universal one-loop contributions to the Z --> width. These bounds, which are independent of the Higgs boson mass, are in agreement with the standard model predictions for the gauge boson self-couplings since the present value of R-b agrees fairly well with the theoretical estimates. Moreover, these indirect constraints on Delta g(1)(Z) and g(5)(Z) are most stringent than the present direct bounds on these quantities, while the indirect limit on lambda(Z) is weaker than the available experimental data.

Anomalous quartic gauge boson couplings at hadron colliders

We analyze the potential of the Fermilab Tevatron and CERN Large Hadron Collider (LHC) to study anomalous quartic vector-boson interactions gamma gamma ZZ and gammaW(+)W(-). Working in the framework of SU(2)(L) circle times U(1)(Y) chiral Lagrangians, we study the production of photon pairs accompanied by l(+) l(-), l(+/-) v, and jet pairs to impose bounds on these new couplings, taking into account the unitarity constraints. We compare our findings with the indirect limits coming from precision electroweak measurements as well as with presently available direct searches at CERN LEPII. We show that the Tevatron run II can provide limits on these quartic limits which are of the same order of magnitude as the existing bounds from LEPII searches. LHC will be able to tighten considerably the direct constraints on these possible new interactions, leading to more stringent limits than the presently available indirect ones.

Black soliton in a quasi-one-dimensional trapped fermion-fermion mixture

Employing a time dependent mean-field-hydrodynamic model we study the generation of black solitons in a degenerate fermion-fermion mixture in a cigar-shaped geometry using variational and numerical solutions. The black soliton is found to be the first stationary vibrational excitation of the system and is considered to be a nonlinear continuation of the vibrational excitation of the harmonic oscillator state. We illustrate the stationary nature of the black soliton, by studying different perturbations on it after its formation.

Strength of the trilinear Higgs boson coupling in technicolor models

We discuss the strength of the trilinear Higgs boson coupling in technicolor (or composite) models in a model independent way. The coupling is determined as a function of a very general ansatz for the technicolor self-energy, and turns out to be equal or smaller than the one of the Standard Model Higgs boson depending on the dynamics of the theory. (c) 2006 Published by Elsevier B.V.

Boson-boson effective nonrelativistic potential for higher-derivative electromagnetic theories in D dimensions

The problem of computing the effective nonrelativistic potential U-D for the interaction of charged-scalar bosons, within the context of D-dimensional electromagnetism with a cutoff, is reduced to quadratures. It is shown that U-3 cannot bind a pair of identical charged-scalar bosons; nevertheless, numerical calculations indicate that boson-boson bound states do exist in the framework of three-dimensional higher-derivative electromagnetism augmented by a topological Chern-Simons term.

Four-boson scale near a Feshbach resonance

We show that an independent four-body momentum scale mu((4)) drives the tetramer binding energy for fixed trimer energy (or three-body scale mu((3))) and large scattering length (a). The three- and four-body forces from the one-channel reduction of the atomic interaction near a Feshbach resonance disentangle mu((4)) and mu((3)). The four-body independent scale is also manifested through a family of Tjon lines, with slope given by mu((4))/mu((3)) for a(-1) = 0. There is the possibility of a new renormalization group limit cycle due to the new scale.

Formation of bright solitons and soliton trains in a fermion-fermion mixture by modulational instability

We employ a time- dependent mean- field- hydrodynamic model to study the generation of bright solitons in a degenerate fermion - fermion mixture in a cigar- shaped geometry using variational and numerical methods. Due to a strong Pauli- blocking repulsion among identical spin- polarized fermions at short distances there cannot be bright solitons for repulsive interspecies interactions. Employing a linear stability analysis we demonstrate the formation of stable solitons due to modulational instability of a constant-amplitude solution of the model equations for a sufficiently attractive interspecies interaction. We perform a numerical stability analysis of these solitons and also demonstrate the formation of soliton trains by jumping the effective interspecies interaction from repulsive to attractive. These fermionic solitons can be formed and studied in laboratory with present technology.

Observing an invisible Higgs boson

Given its weak coupling to bottom quarks and tau leptons, the Higgs boson may predominantly decay into invisible particles like gravitinos, neutralinos, or gravitons. We consider the manifestation of such an invisibly decaying Higgs boson in weak boson fusion at the CERN LHC. Distinctive kinematic distributions of the two quark jets of the signal as compared to Zjj and Wjj backgrounds allow to restrict the Higgs branching ratio to 'invisible' final states to some 13% with 10 fb(-1) of data, provided events with two energetic forward jets of high dijet invariant mass and with substantial missing transverse momentum can be triggered efficiently. It is also possible to discover these particles with masses up to 480 GeV in weak boson fusion, at the 5 sigma level, provided their invisible branching ratio is close to 100%. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Cutoff-independent regularization of four-fermion interactions for color superconductivity

We implement a cutoff-independent regularization of four-fermion interactions to calculate the color-superconducting gap parameter in quark matter. The traditional cutoff regularization has difficulties for chemical potentials mu of the order of the cutoff Lambda, predicting in particular a vanishing gap at mu similar to Lambda. The proposed cutoff-independent regularization predicts a finite gap at high densities and indicates a smooth matching with the weak coupling QCD prediction for the gap at asymptotically high densities.

Search for particles decaying into a Z boson and a photon in p(p)over-bar collisions at root s=1.96 TeV

We present the results of a search for a new particle X produced in p (p) over bar collisions at root s- = 1.96 TeV and subsequently decaying to Z gamma. The search uses 0.3 fb(-1) of data collected with the DO detector at the Fermilab Tevatron Collider. We set limits on the production cross section times the branching fraction sigma(p (p) over bar -> X) x B(X -> Z gamma) that range from 0.4 to 3.5 pb at the 95% C.L. for X with invariant masses between 100 and 1000 GeV/c(2), over a wide range of X decay widths. (c) 2006 Elsevier B.V. All rights reserved.

Effective theory for trapped few-fermion systems

We apply the general principles of effective field theories to the construction of effective interactions suitable for few- and many-body calculations in a no-core shell model framework. We calculate the spectrum of systems with three and four two-component fermions in a harmonic trap. In the unitary limit, we find that three-particle results are within 10% of known semianalytical values even in small model spaces. The method is very general, and can be readily extended to other regimes, more particles, different species (e.g., protons and neutrons in nuclear physics), or more-component fermions (as well as bosons). As an illustration, we present calculations of the lowest-energy three-fermion states away from the unitary limit and find a possible inversion of parity in the ground state in the limit of trap size large compared to the scattering length. Furthermore, we investigate the lowest positive-parity states for four fermions, although we are limited by the dimensions we can currently handle in this case.

Noether and topological currents equivalence and soliton/particle correspondence in affine sl(2)((1)) Toda theory coupled to matter

A submodel of the so-called conformal affine Toda model coupled to the matter field (CATM) is defined such that its real Lagrangian has a positive-definite kinetic term for the Toda field and a usual kinetic term for the (Dirac) spinor field. After spontaneously broken the conformal symmetry by means of BRST analysis, we end up with an effective theory, the off-critical affine Toda model coupled to the matter (ATM). It is shown that the ATM model inherits the remarkable properties of the general CATM model such as the soliton solutions, the particle/soliton correspondence and the equivalence between the Noether and topological currents. The classical solitonic spectrum of the ATM model is also discussed. (C) 2001 Elsevier B.V. B.V. All rights reserved.