Influence of dimensionality on superconductivity in carbon nanotubes

We investigate the electronic instabilities in carbon nanotubes (CNs), looking for the break-down of the one dimensional Luttinger liquid regime due to the strong screening of the long-range part of the Coulomb repulsion. We show that such a breakdown is realized both in ultra-small single wall CNs and multi wall CNs, while a purely electronic mechanism could explain the superconductivity (SC) observed recently in ultra-small (diameter $\sim 0.4 nm$) single wall CNs ($T_c\sim 15 ^{o}K$) and entirely end-bonded multi-walled ones ($T_c\sim 12 ^{o}K$). We show that both the doping and the screening of long-range part of the electron-electron repulsion, needed to allow the SC phase, are related to the intrinsically 3D nature of the environment where the CNs operate.Comment: 5 pages, 3 figures, PACS: 71.10.Pm,74.50.+r,71.20.Tx, to appear in J. Phys. Cond. Ma

Effective gravity and OSp(N,4) invariant matter

We re-examine the OSp(N,4) invariant interacting model of massless chiral and gauge superfields, whose superconformal invariance was instrumental, both in proving the all-order no-renormalization of the mass and chiral self-interaction lagrangians, and in determining the linear superfield renormalization needed. We show that the renormalization of the gravitational action modifies only the cosmological term, without affecting higher-order tensors. This could explain why the effect of the cosmological constant is shadowed by the effects of newtonian gravity.Comment: 12 pages, LaTeX, 4 figures, PACS: 04.65.+e, substantial revisions, to appear in Phys. Rev.

A new N = 8 nonlinear supermultiplet

We construct a new off-shell $\mathcal{N}{=}8$, $d{=}1$ nonlinear supermultiplet $(\mathbf{4,8,4})$ proceeding from the nonlinear realization of the $\mathcal{N}{=}8$, $d{=}1$ superconformal group $OSp(4^{\star}|4)$ in its supercoset $\frac{OSp(4^{\star}|4)}{SU(2)_{\mathcal{R}}\otimes \left\{D,K\right\} \otimes SO(4)}$. The irreducibility constraints for the superfields automatically follow from appropriate covariant conditions on the $osp(4^{\star}|4)$-valued Cartan superforms. We present the most general sigma-model type action for $(\mathbf{4,8,4})$ supermultiplet. The relations between linear and nonlinear $(\mathbf{4,8,4})$ supermultiplets and linear $\mathcal{N}{=}8$ $(\mathbf{5,8,3})$ vector supermultiplet are discussed.Comment: 15 pages, LaTeX file, PACS numbers: 11.30.Pb, 03.65.-

N=4 supersymmetric mechanics with nonlinear chiral supermultiplet

We construct N=4 supersymmetric mechanics using the N=4 nonlinear chiral supermultiplet. The two bosonic degrees of freedom of this supermultiplet parameterize the sphere S(2) and go into the bosonic components of the standard chiral multiplet when the radius of the sphere goes to infinity. We construct the most general action and demonstrate that the nonlinearity of the supermultiplet results in the deformation of the connection, which couples the fermionic degrees of freedom with the background, and of the bosonic potential. Also a non-zero magnetic field could appear in the system.Comment: 5 page

Electronic screening and correlated superconductivity in carbon nanotubes

A theoretical analysis of the superconductivity observed recently in Carbon nanotubes is proposed. We argue that ultra-small (diameter $\sim 0.4 nm$) single wall carbon nanotubes (with transition temperature $T_c\sim 15 ^{o}K$) and entirely end-bonded multi-walled ones ($T_c\sim 12 ^{o}K$) can superconduct by an electronic mechanism, basically the same in both cases. By a Luttinger liquid -like approach, one finds enhanced superconducting correlations due to the strong screening of the long-range part of the Coulomb repulsion. Based on this finding, we perform a detailed analysis on the resulting Hubbard-like model, and calculate transition temperatures of the same order of magnitude as the measured ones.Comment: 6 pages, 1 figure, PACS: 71.10.Pm,74.50.+r,71.20.Tx, to appear in Phys. Rev.

The geometry of N=4 twisted string

We compare N=2 string and N=4 topological string within the framework of the sigma model approach. Being classically equivalent on a flat background, the theories are shown to lead to different geometries when put in a curved space. In contrast to the well studied Kaehler geometry characterising the former case, in the latter case a manifold has to admit a covariantly constant holomorphic two-form in order to support an N=4 twisted supersymmetry. This restricts the holonomy group to be a subgroup of SU(1,1) and leads to a Ricci--flat manifold. We speculate that, the N=4 topological formalism is an appropriate framework to smooth down ultraviolet divergences intrinsic to the N=2 theory.Comment: 20 pages, LaTe

Gauging N=4 Supersymmetric Mechanics

We argue that off-shell dualities between d=1 supermultiplets with different sets of physical bosonic components and the same number of fermionic ones are related to gauging some symmetries in the actions of the supermultiplets with maximal sets of physical bosons. Our gauging procedure uses off-shell superfields and so is manifestly supersymmetric. We focus on N=4 supersymmetric mechanics and show that various actions of the multiplet (3,4,1) amount to some gauge choices in the gauged superfield actions of the linear or nonlinear (4,4,0) multiplets. In particular, the conformally invariant (3,4,1) superpotential is generated by the Fayet-Iliopoulos term of the gauge superfield. We find a new nonlinear variant of the multiplet (4,4,0), such that its simplest superfield action produces the most general 4-dim hyper-K\"ahler metric with one triholomorphic isometry as the bosonic target metric. We also elaborate on some other instructive examples of N=4 superfield gaugings, including a non-abelian gauging which relates the free linear (4,4,0) multiplet to a self-interacting (1,4,3) multiplet.Comment: 32 pages, minor amendments in Sect. 2, version to appear in Nucl. Phys.

N=8 supersymmetric mechanics on the sphere S^3

Starting from quaternionic N=8 supersymmetric mechanics we perform a reduction over a bosonic radial variable, ending up with a nonlinear off-shell supermultiplet with three bosonic end eight fermionic physical degrees of freedom. The geometry of the bosonic sector of the most general sigma-model type action is described by an arbitrary function obeying the three dimensional Laplace equation on the sphere S^3. Among the bosonic components of this new supermultiplet there is a constant which gives rise to potential terms. After dualization of this constant one may come back to the supermultiplet with four physical bosons. However, this new supermultiplet is highly nonlinear. The geometry of the corresponding sigma-model action is briefly discussed.Comment: 9 pages, LaTeX file, PACS: 11.30.Pb, 03.65.-

The Common Origin of Linear and Nonlinear Chiral Multiplets in N=4 Mechanics

Elaborating on previous work (hep-th/0605211, hep-th/0611247), we show how the linear and nonlinear chiral multiplets of N=4 supersymmetric mechanics with the off-shell content (2,4,2) can be obtained by gauging three distinct two-parameter isometries of the ``root'' (4,4,0) multiplet actions. In particular, two different gauge groups, one abelian and one non-abelian, lead, albeit in a disguised form in the second case, to the same (unique) nonlinear chiral multiplet. This provides an evidence that no other nonlinear chiral N=4 multiplets exist. General sigma model type actions are discussed, together with the restricted potential terms coming from the Fayet-Iliopoulos terms associated with abelian gauge superfields. As in our previous work, we use the manifestly supersymmetric language of N=4, d=1 harmonic superspace. A novel point is the necessity to use in parallel the \lambda and \tau gauge frames, with the ``bridges'' between these two frames playing a crucial role. It is the N=4 harmonic analyticity which, though being non-manifest in the \tau frame, gives rise to both linear and nonlinear chirality constraints.Comment: 22 pages, Latex, minor corrections, to appear in Nucl. Phys.