On effective actions of non-BPS branes and their higher derivative corrections

By calculating various disk level S-matrix elements and studying in details their momentum expansions, we have extracted some of the couplings in tachyon DBI action and Wess–Zumino terms of the non-BPS branes, and their higher derivative corrections. In particular, we have found that there is exact consistency between field theory and string theory tachyon pole of S-matrix element of one RR and three tachyons provided that one takes into account the fact that the tachyon vertex operator in 0 picture to be along the Pauli matrix σ₁${\sigma }_1$ whereas the tachyon in −1 picture to be along the σ₂${\sigma }_2$ direction. This internal CP factors should be included in the tachyon DBI part of the effective action.     

Solitonic branes and wrapping rules

We show that the solitonic branes of ten-dimensional IIA/IIB string theory must satisfy, upon toroidal compactification, a specific wrapping rule in order to reproduce the number of half-supersymmetric solitonic branes that follows from a supergravity analysis. The realization of this wrapping rule suggests that IIA/IIB string theory contains a whole class of so-called ??non-standard?? Kaluza-Klein monopoles.     

Sum rules for the pseudoscalar BBP couplings

In the ‘tadpole’ type mechanism of Coleman and Glashow, where all the summetry breaking effects are generated through symmetry breaking terms belonging to the same regular representation (octet in the case of SU(3) and15 in SU(4)), the strangeness changing (charm changing) effects generated through theS ₆(S ₉) tadpole must vanish. We exploit this null result to find relations between the BBP coupling constants and the baryon masses in the strange as well as charm sector.     

Berenstein-Zelevinsky triangles,elementary couplings,and fusion rules

We present a general scheme for describing (N) _k fusion rules in terms of elementary couplings, using Berenstein-Zelevinsky triangles. A fusion coupling is characterized by its corresponding tensor product coupling (i.e. its Berenstein-Zelevinsky triangle) and the threshold level at which it first appears. We show that a closed expression for this threshold level is encoded in the Berenstein-Zelevinsky triangle and an explicit method to calculate it is presented. In this way, a complete solution of (4) _k fusion rules is obtained.Work supported by NSERC (Canada).Work supported by NSERC (Canada) and FCAR (Québec).     

Selection rules for hybridization

Selection rules for the hybridization of the crystal-field levels of a magnetic ion are investigated by group theoretical methods. They appear only in a few cases. In absence of strict selection rules the possibility for drastic quantitative differences in the hybridization of different levels is discussed.This work was supported by the Deutsche Forschungsgemeinschaft through SFB 125 (Aachen-Jülich-Köln)     

Fermions on colliding branes

We study the behaviour of five-dimensional fermions localized on branes, which we describe by domain walls, when two parallel branes collide in a five-dimensional Minkowski background spacetime. We find that most fermions are localized on both branes as a whole even after collision. However, how much fermions are localized on which brane depends sensitively on the incident velocity and the coupling constants unless the fermions exist on both branes.     

Fermions on deformed thick branes

In this work we investigate the issue of fermion localization and resonances in (4,1)-deformed branes constructed with one scalar field coupled with gravity. Such models provide us branes with internal structures that turns the gravitational interaction more effective for fermions aside the brane, increasing their lifetime. The coupling between the scalar field and spinors is a necessary condition for fermions to be localized on such branes. After performing a chiral decomposition of the five-dimensional spinor we found resonances with both chiralities. The correspondence between the spectra for left and right chirality is guaranteed and Dirac fermions are realized on the brane.     

Selection rules for topology change

It is shown that there are restrictions on the possible changes of topology of space sections of the universe if this topology change takes place in a compact region which has a Lorentzian metric and spinor structure. In particular, it is impossible to create a single wormhole or attach a single handle to a spacetime but it is kinematically possible to create such wormholes in pairs. Another way of saying this is that there is a ₂ invariant for a closed oriented 3-manifold which determines whether can be the spacelike boundary of a compact manifoldM which admits a Lorentzian metric and a spinor structure. We evaluate this invariant in terms of the homology groups of and find that it is the mod2 Kervaire semi-characteristic.     

Geometry of branes on supergroups

In this note we analyze the geometry of maximally symmetric boundary conditions in Lie supergroup Wess–Zumino–Novikov–Witten models. We find that generically the worldvolume of a brane is a twisted superconjugacy class, very much like in the Lie group case. Whenever the brane is not completely delocalized in the fermionic directions a new atypical class of branes arises. We give an example of these new branes and show for type I supergroups and trivial gluing conditions that they can be naturally associated with atypical representations of the affine Lie superalgebra.     

Supergravity-induced interactions on thick branes

The gravity coupling of the symmetric space sigma model is studied in the solvable Lie algebra parametrization. The corresponding Einstein equations are derived and the energy-momentum tensor is calculated. The results are used to derive the dynamical equations of the warped five-dimensional （5D） geometry for localized bulk scalar interactions in the framework of thick brane world models. The Einstein and scalar field equations are derived for flat brane geometry in the context of minimal and non-minimal gravity-bulk scalar couplings.     

Strings and branes under microscope

It is shown that in the standard vacuum 5D Kaluza‐Klein gravity there exist wormhole‐like solutions which look like strings attached to two D‐branes. The asymptotic behaviour of the corresponding metric is investigated.     

Brownian cylinders and intersecting branes

In the paper we present a theory of random cylinders attached to branes. We analyse fluctuations and construct a theory of large deviations.     

Selection rules and superconducting correlations in carbon nanotubes

We carry out a detailed analysis of the effective interaction arising from electron-phonon scattering and its capability to produce the superconducting correlations observed in the carbon nanotubes. It is shown that certain selection rules prevent the exchange of phonons in some of the interaction channels, depending on the geometry of the nanotubes and on whether they are doped or not. In addition, we discuss the mechanism working in nanotube ropes by which the electrostatic coupling among a large number of metallic nanotubes leads to a substantial reduction in the strength of the Coulomb interaction. The scaling equation for the superconducting response function is then improved nonperturbatively, by including the exact contribution from forward-scattering processes. This allows us to estimate the boundary between superconducting and nonsuperconducting phases in the ropes, as well as to constrain the actual values of the strength of the effective attractive interaction.Received: 13 August 2003, Published online: 23 December 2003PACS: 71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.) - 73.63.Fg Nanotubes - 74.78.Na Mesoscopic and nanoscale systems