LOW-ENERGY BEHAVIOR OF FEW-PARTICLE SCATTERING-AMPLITUDES IN 2 DIMENSIONS

A study of the analytic behavior of different few-particle scattering amplitudes at low energies in two space dimensions is presented. Such a study is of use in modeling and understanding different few-particle processes at low energies. A detailed discussion of the energy and the momentum dependence of the partial-wave on-the-energy-shell and off-the-energy-shell two-particle t matrices is given. These t-matrix elements tend to zero as the energy and momentum variables tend to zero. The multiple-scattering series is used to show that the connected three-to-three amplitudes diverge in the low-energy-momentum limit. Unitarity relations are used to show that the connected two-to-three and one-to-three amplitudes have specific logarithmic singularities at the m-particle breakup threshold. The subenergy singularity in the two-to-three amplitudes is also studied, and comments are made on some applications of the present study in different problems of ph cal interest.

MODEL INDEPENDENCE OF SCATTERING OF 3 IDENTICAL BOSONS IN 2 DIMENSIONS

Within the framework of scattering integral equations in momentum space, we present numerical results of scattering of three identical bosons at low energies in two dimensions for short-range separable potentials. An analysis of the present numerical results reveals the three-particle scattering observables to be independent of potential shape provided the low-energy two-particle binding energy and scattering length are held fixed throughout the investigation. We think that the present conclusion of model independence will be valid for any potential, local or nonlocal, whose range is much smaller than the size of the two-particle bound state.

Comment on Casimir force in compact non-commutative extra dimensions and radius stabilization

We call attention to a series of mistakes in a paper by S. Nam recently published in this journal (J. High Energy Phys. 10 (2000) 044).

Influence of various implant platform configurations on peri-implant tissue dimensions: an experimental study in dog

AimTo evaluate the influence (i) of various implant platform configurations and (ii) of implant surface characteristics on peri-implant tissue dimensions in a dog model.Material and methodsMandibular premolars and first molars were extracted bilaterally in six Labrador dogs. After 3 months of healing, two implants, one with a turned and a second with a moderately rough surface, were installed on each side of the mandible in the premolar region. on the right side of the mandible, implants with a tapered and enlarged platform were used, while standard cylindrical implants were installed in the left side of the mandible. Abutments with the diameter of the cylindrical implants were used resulting in a mismatch of 0.25 mm at the tapered implant sites. The flaps were sutured to allow a non-submerged healing. After 4 months, the animals were sacrificed and ground sections were obtained for histometric assessment.ResultsAll implants were completely osseointegrated. A minimal buccal bone resorption was observed for both implant configurations and surface topographies. Considering the animals as the statistical unit, no significant differences were found at the buccal aspect in relation to bone levels and soft tissue dimensions. The surface topographies did not influence the outcomes either.ConclusionsThe present study failed to show differences in peri-implant tissue dimensions when a mismatch of 0.25 mm from a tapered platform to an abutment was applied. The surface topographies influence a neither marginal bone resorption or peri-implant soft tissue dimension.To cite this article:Baffone GM, Botticelli D, Pantani F, Cardoso LC, Schweikert MT, Lang NP. Influence of various implant platform configurations on peri-implant tissue dimensions: an experimental study in dog.Clin. Oral Impl. Res. 22, 2011; 438-444.

Comorbidity of obsessive-compulsive disorder and personality disorders. A Brazilian controlled study

The aim of this study was to evaluate the presence of personality disorders (PDs) in 40 patients with obsessive-compulsive disorder (DSM-III-R criteria) from the Medical School of Botucatu (UNESP), Sao Paulo, Brazil. It is a case-control study. Patients were 24 women and 16 men, 16-68 years old, referred to our outpatient psychiatric service for treatment. Controls were 40 nonpsychiatric outpatients matched to the cases by sex, age and marital status. The instrument used was the Portuguese version of the Structured Interview for DSM-III-R Personality Disorders (SIDP-R). All interviews (n = 80) were made simultaneously by 2 raters, with independent scoring, so that the interrater reliability of the instrument could also be assessed (kappa statistics). The consensual axis II diagnoses in the OCD group were: avoidant (52.5%, κ = 0.80), dependent (40%, κ = 0.84), histrionic (20%, κ = 0.83), paranoid (20%, κ = 0.74), obsessive-compulsive (17.5%, κ = 0.86), narcissistic (7.5%, κ = 1.00), schizotypal (5%, κ = 0.65), passive-aggressive (5%, κ = 0.79) and self-defeating (5%, κ 0.55). At least one PD diagnosis was made in 70% of the patients, while only 6 controls had a PD diagnosis (p < 0.01). A great deal of diagnostic overlap was found in the OCD group (57.5% had two or more PDs), especially between avoidant and dependent PDs. The features of these two PDs may be secondary to the OCD. The study also suggests that there is not a close relationship between OCD and obsessive-compulsive personality disorder (OCPD). Patients with OCPD or even 3 or 4 O-C traits had significantly less insight into their obsessions and compulsions (p < 0.01).

Faddeev-jackiw formalism for A topological-like oscillator in planar dimensions

The problem of a harmonic oscillator coupling to an electromagnetic potential plus a topological-like (Chern-Simons) massive term, in two-dimensional space, is studied in the light of the symplectic formalism proposed by Faddeev and Jackiw for constrained systems.

Extra dimensions in superstring theory

It was earlier shown that an SO(9,1) θα spinor variable can be constructed from RNS matter and ghost fields. θα has a bosonic world-sheet super-partner λα which plays the role of a twistor variable, satisfying λΓμ λ = ∂xμ + iθΓμ ∂θ. For Type IIA superstrings, the left-moving [θL α, λL α] and right-moving [θRα, λRα] can be combined into 32-component SO(10,1) spinors [θA, λA]. This suggests that λAΓAB 11 λB = 2λL αλRα can be interpreted as momentum in the eleventh direction. Evidence for this interpretation comes from the zero-momentum vertex operators of the Type IIA superstring and from consideration of DD-branes. As in the work of Bars, one finds an SO(10,2) structure for the Type IIA superstring and an SO(9, 1) × SO(2, 1) structure for the Type IIB superstring. © 1997 Elsevier Science B.V.

Universal scaling in BCS superconductivity in three dimensions in non-s waves

The solutions of a renormalized BCS equation are studied in three space dimensions in s, p and d waves for finite-range separable potentials in the weak to medium coupling region. In the weak-coupling limit, the present BCS model yields a small coherence length ξ and a large critical temperature, T c, appropriate for some high-T c materials. The BCS gap, T c, ξ and specific heat C s(T c) as a function of zero-temperature condensation energy are found to exhibit potential-independent universal scalings. The entropy, specific heat, spin susceptibility and penetration depth as a function of temperature exhibit universal scaling below T c in p and d waves.

Remarks on fermion-boson equivalence in three dimensions

Starting from a decomposition of the self-dual field in (2 + 1) dimensions, we build up an alternative quantum theory which consists of a self-dual model coupled to a Maxwell-generalized Chern-Simons theory. We discuss the fermion-boson equivalence of this quantum theory by comparing it with the Thirring model. Using these results we were able to compute the mass of the bosonized fermions up to third order in 1/m. Some problems related to the number of poles of the effective propagator are also addressed.

Effective action for QED in 2+1 dimensions at finite temperature

Both the parity-breaking and parity-invariant parts of the effective action for the gauge field in QED 3 with massive fermions at finite temperature are obtained exactly. This is feasible because we use a particular configuration of the background gauge field, namely a constant magnetic field and a time-dependent time component of the background gauge field. Our results allow us to compute exactly physically interesting quantities such as the induced charge density and fermion condensate whose dependence on the temperature, fermion mass and gauge field is discussed. ©1999 The American Physical Society.

Relativistic quantum thermodynamics of ideal gases in two dimensions

In this work we study the behavior of relativistic ideal Bose and Fermi gases in two space dimensions. Making use of polylogarithm functions we derive a closed and unified expression for their densities. It is shown that both type of gases are essentially inequivalent, and only in the non-relativistic limit the spinless and equal mass Bose and Fermi gases are equivalent as known in the literature.

Class of self-dual models in three dimensions

In the present paper we introduce a hierarchical class of self-dual models in three dimensions, inspired in the original self-dual theory of Towsend-Pilch-Nieuwenhuizen. The basic strategy is to explore the powerful property of the duality transformations in order to generate a new field. The generalized propagator can be written in terms of the primitive one (first order), and also the respective order and disorder correlation functions. Some conclusions about the charge screening and magnetic flux were established. ©1999 The American Physical Society.