Correlated transport and non-Fermi liquid behavior in single-wall carbon nanotubes

We derive the effective low-energy theory for single-wall carbon nanotubes including the Coulomb interactions among electrons. The generic model found here consists of two spin-1/2 fermion chains which are coupled by the interaction. We analyze the theory using bosonization, renormalization-group techniques, and Majorana refermionization. Several experimentally relevant consequences of the breakdown of Fermi liquid theory observed here are discussed in detail, e.g., magnetic instabilities, anomalous conductance laws, and impurity screening profiles.Comment: 23 pages REVTeX, incl 5 figs, to appear in Europ.Phys.Journal

Endogenous Product versus Process Innovation and a Firm’s Propensity to Export

This paper provides an empirical analysis of the effects of new product versus process innovations on export propensity at the firm level. Product innovation is a key factor for successful market entry in models of creative destruction and Schumpeterian growth. Process innovation helps securing a firm’s market position given the characteristics of its product supply. Both modes of innovation are expected to raise a firm’s propensity to export. According to new trade theory, we conjecture that product innovation is relatively more important in that regard. We investigate these hypotheses in a rich survey panel data set with information about new innovations of either type. With a set of indicators regarding innovation motives and impediments and continuous variables at the firm and industry level at hand, we may determine the probability of launching new innovations and their impact on export propensity at the firm level through a double treatment approach.product innovation, process innovation, propensity to export, multiple treatment effects estimation

Artifical atoms in interacting graphene quantum dots

We describe the theory of few Coulomb-correlated electrons in a magnetic quantum dot formed in graphene. While the corresponding nonrelativistic (Schr\"odinger) problem is well understood, a naive generalization to graphene's "relativistic" (Dirac-Weyl) spectrum encounters divergencies and is ill-defined. We employ Sucher's projection formalism to overcome these problems. Exact diagonalization results for the two-electron quantum dot, i.e., the artificial helium atom in graphene, are presented.Comment: 4+ pages, 2 figure

Exact solution of the three-boson problem at vanishing energy

A zero range approach is used to model resonant two-body interactions between three identical bosons. A dimensionless phase parametrizes the three-body boundary condition while the scattering length enters the Bethe-Peierls boundary condition. The model is solved exactly at zero energy for any value of the scattering length, positive or negative. From this solution, an analytical expression for the rate of three-body recombination to the universal shallow dimer is extracted.Comment: 12 page

Absorptive capacity and the growth and investment effects of regional transfers : a regression discontinuity design with heterogeneous treatment effects

Researchers often estimate average treatment effects of programs without investigating heterogeneity across units. Yet, individuals, firms, regions, or countries vary in their ability, e.g., to utilize transfers. We analyze Objective 1 Structural Funds transfers of the European Commission to regions of EU member states below a certain income level by way of a regression discontinuity design with systematically heterogeneous treatment effects. Only about 30% and 21% of the regions - those with sufficient human capital and good-enough institutions - are able to turn transfers into faster per-capita income growth and per-capita investment. In general, the variance of the treatment effect is much bigger than its mean

How Low Business Tax Rates Attract Multinational Headquarters: Municipality-Level Evidence from Germany

Most existing empirical evidence on the impact of profit taxation on multinational firm activity is based on cross-country data. One major drawback of such data is that countries differ not only with regard to taxes but along other dimensions which might be hard to capture by means of observable characteristics. We compile a database of more than 11,000 municipalities in Germany to analyze the sensitivity of the location decisions of foreign MNEs with respect to business tax rates which are levied directly by the municipalities. Using count data models suited for cross-sectional and panel data, we find that higher business tax rates have a negative effect on the number of foreign MNE headquarters, after controlling for other determinants of firm location decisions. On average, a one-percent reduction of the municipal business tax rate (equivalent to a decline by about 0.14 percentage points) leads to an increase in the number of headquarters of foreign MNEs by about 0.05. Hence, the average municipality needs to reduce its business tax rate by 20% to attract one foreign MNE.multinational firms, profit taxation, regional public finance, count data

Interaction-induced harmonic frequency mixing in quantum dots

We show that harmonic frequency mixing in quantum dots coupled to two leads under the influence of time-dependent voltages of different frequency is dominated by interaction effects. This offers a unique and direct spectroscopic tool to access correlations, and holds promise for efficient frequency mixing in nano-devices. Explicit results are provided for an Anderson dot and for a molecular level with phonon-mediated interactions.Comment: 4 pages, 2 figures, accepted for publication in Phys.Rev.Let