Transport through a double barrier in Large Radius Carbon Nanotubes in the presence of a transverse magnetic field

We discuss the Luttinger Liquid behaviour of Large Radius Carbon Nanotube e.g. the Multi Wall ones (MWNT), under the action of a transverse magnetic field $B$. Our results imply a reduction with $B$ in the value of the $bulk$ critical exponent, $\alpha_{bulk}$, for the tunneling density of states, which is in agreement with that observed in transport experiments. Then, the problem of the transport through a Quantum Dot formed by two intramolecular tunneling barriers along the MWNT, weakly coupled to Tomonaga-Luttinger liquids is studied, including the action of a strong transverse magnetic field $B$. {We predict the presence of some peaks in the conductance G versus $B$, related to the magnetic flux quantization in the ballistic regime (at a very low temperature, $T$) and also at higher $T$, where the Luttinger behaviour dominates}. The temperature dependence of the maximum $G_{max}$ of the conductance peak according to the Sequential Tunneling follows a power law, $G\propto T^{\gamma_e-1}$ with $\gamma_e$ linearly dependent on the critical exponent, $\alpha_{end}$, strongly reduced by $B$.Comment: 8 pages, 3 figures, PACS numbers: 05.60.Gg, 71.10.Pm, 73.63.-b, 71.20.Tx, 72.80.R

Large N Effects and Renormalization of the Long-Range Coulomb Interaction in Carbon Nanotubes

We develop a dimensional regularization approach to deal with the low-energy effects of the long-range Coulomb interaction in 1D electron systems. The method allows us to avoid the infrared singularities arising from the long-range Coulomb interaction at D = 1, providing at the same time insight about the fixed-points of the theory. We show that the effect of increasing the number N of subbands at the Fermi level is opposite to that of approaching the bare Coulomb interaction in the limit D --> 1. Then, we devise a double scaling limit, in which the large N effects are able to tame the singularities due to the long-range interaction. Thus, regular expressions can be obtained for all observables right at D = 1, bearing also a dependence o the doping level of the system. Our results imply a variation with N in the value of the exponent for the tunneling density of states, which is in fair agreement with that observed in different transport experiments involving carbon nanotubes. As the doping level is increased in nanotubes of large radius and multi-walled nanotubes, we predict a significant reduction of order N^{-1/2} in the critical exponent of the tunneling density of states.Comment: 16 pages, 5 figures, PACS codes: 73.40, 11.10.

Envelope solitons induced by high-order effects of light-plasma interaction

The nonlinear coupling between the light beams and non-resonant ion density perturbations in a plasma is considered, taking into account the relativistic particle mass increase and the light beam ponderomotive force. A pair of equations comprising a nonlinear Schrodinger equation for the light beams and a driven (by the light beam pressure) ion-acoustic wave response is derived. It is shown that the stationary solutions of the nonlinear equations can be represented in the form of a bright and dark/gray soliton for one-dimensional problem. We have also present a numerical analysis which shows that our bright soliton solutions are stable exclusively for the values of the parameters compatible with of our theory.Comment: 9 pages, 5 figure

Warm turbulence in the Boltzmann equation

We study the single-particle distributions of three-dimensional hard sphere gas described by the Boltzmann equation. We focus on the steady homogeneous isotropic solutions in thermodynamically open conditions, i.e. in the presence of forcing and dissipation. We observe nonequilibrium steady state solution characterized by a warm turbulence, that is an energy and particle cascade superimposed on the Maxwell-Boltzmann distribution. We use a dimensional analysis approach to relate the thermodynamic quantities of the steady state with the characteristics of the forcing and dissipation terms. In particular, we present an analytical prediction for the temperature of the system which we show to be dependent only on the forcing and dissipative scales. Numerical simulations of the Boltzmann equation support our analytical predictions.Comment: 4 pages, 5 figure

Board characteristics and financial performance in the insurance industry: An international empirical survey

There are few studies in the literature on how the characteristics of boards of directors affect the performance of insurance companies. The purpose of this research is to investigate the characteristics of a company’s board that can have a significant impact on financial performance in the insurance sector. For this purpose, we performed a dynamic pooled regression model to test the impact of a wide range of board-specific factors. The survey has been conducted on an international sample of 119 listed insurance companies operating in the period 2009-2019. The sample includes companies from three geographical areas: North America, Europe and Asia. Our findings provide evidence that board structure and board independence are the most relevant governance factors, with a potentially positive impact on insurers’ market performance. These findings indirectly outline the opportunity for insurance companies to improve corporate fair value by strengthening internal governance models through effective board policies, an adequate qualification of board members and a well-balanced membership of the board. At the same time, there is still room for improvement as regards the level of board independence by strengthening internal governance policies in order to maintain an adequate number of independent and non-executive board members. The study upgrades the evidence arising from the existing literature by providing new elements to support a deeper understanding of the effects of insurance companies’ board characteristics on financial performance. Empirical results may also have important implications for both managers and policy makers

Crossover from Luttinger liquid to Coulomb blockade regime in carbon nanotubes

We develop a theoretical approach to the low-energy properties of 1D electron systems aimed to encompass the mixed features of Luttinger liquid and Coulomb blockade behavior observed in the crossover between the two regimes. For this aim we extend the Luttinger liquid description by incorporating the effects of a discrete single-particle spectrum. The intermediate regime is characterized by a power-law behavior of the conductance, but with an exponent oscillating with the gate voltage, in agreement with recent experimental observations. Our construction also accounts naturally for the existence of a crossover in the zero-bias conductance, mediating between two temperature ranges where the power-law behavior is preserved but with different exponent.Comment: 5 pages, 3 figure

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.