Numerical Renormalization Group Analysis of Interacting Quantum Dots

Wilson's Numerical Renormalization Group (NRG) is so far the only nonperturbative technique that can reliably access low-energy properties of quantum impurity systems. We present a recent extension of the method, the DM-NRG, which yields highly accurate results for dynamical quantities at arbitrary frequencies and temperatures. As an application, we determine the spectrum of a quantum dot in an external magnetic field. Furthermore, we discuss magnetic impurities with orbital degeneracy, which have been inferred in recent experiments on quantum dots in an Aharonov-Bohm geometry. It is demonstrated that for spinless electrons, interference between neighbouring levels sets the low-energy scale of the system. Switching on an external field leads to a remarkable crossover into a regime dominated by orbital Kondo screening. We predict that the broadening-induced level splitting should be clearly visible in measurements of the optical absorption power. A more general model including the electron spin is studied within an extended two-band NRG procedure. We observe competition between interference and Kondo screening, similar to the situation in two-impurity models (RKKY).Comment: Invited talk at the DPG spring meeting 2001, to appear in Advances in Solid State Physics 4

Flavor Degeneracy and Effects of Disorder in Ultracold Atom Systems

Cold atoms in optical lattices offer an exciting new laboratory where quantum many-body phenomena can be realized in a highly controlled way. They can even serve as quantum simulators for notoriously difficult problems like high-temperature superconductivity. This review is focussed on recent developments and new results in multi-component systems. Fermionic atoms with SU(N) symmetry have exotic superfluid and flavor-ordered ground states. We discuss symmetry breaking, collective modes and detection issues. Bosonic multi-flavor ensembles allow for engineering of spin Hamiltonians which are interesting from a quantum computation point of view. Finally, we will address the competition of disorder and interaction in optical lattices. We present a complete phase diagram obtained within dynamical mean-field theory and discuss experimental observability of the Mott and Anderson phases.Comment: 13 pages, 9 eps figures included, Adv. Solid State Phys. (in press

Sticky Prices and Moderate Inflation

Recent evidence shows that there is great heterogeneity in the price setting frequency across sectors, and that those changing prices frequently do so even under low inflation. What happens to price setting strategies of sticky price goods under moderate inflation? We built a dataset of monthly newspaper and magazine prices for Colombia, for the period 1960-2005, an exceptional example of prolonged moderate inflation. Within this macroeconomic scenario, and the novel database, we study the frequency of price adjustment, the relative importance of time- and state-dependent theories, and their evolution as inflation declined from moderate rates to single digits.Sticky Prices, Moerate Inflation, Disinflation

DISINFLATING FROM MODERATE INFLATION

This paper studies the behavior of several macroeconomic variables during disinflationary episodes in Latin-America and the Caribbean (LAC). In particular, it focuses on disinflations from low and moderate peaks for the period 1973-2001. The methodology used for studying the average behavior of macroeconomic variables across disinflations overcomes the traditional problem of scarce long time series (of high frequency data) that has hindered the empirical research of monetary shocks in many LAC countries. Some of the important findings are as follows: (i) while GDP growth slowed down during the disinflations of the 70s and 80s, there is no evidence of this for the 90s; (ii) the trade balance significantly deteriorated during the disinflations; (iii) the nominal devaluation rate slowed down during the episodes; and (iv) the real exchange rate appreciated during the episodes.Inflation Growth Disinflation Trade Balance Exchange Rate

The current diagnosis of superficial bladder cancer must be reconsidered

The high recurrence and progression rates in superficial bladder cancer are partially related to the deficiencies of the standard conventional diagnostic modalities. Therefore, innovative noninvasive and invasive detection devices have been studied during the last decade. New diagnostic urine markers are under intensive investigation in order to exclude the presence of urothelial cancer, but the value of all these tests is still insufficiently validated in diagnosis and follow-up. With the introduction of 5-amino-levulinic acid fluorescence endoscopy, the efficacy of the detection device has been significantly improved. Flat lesions such as carcinoma in situ can be completely detected besides exophytic tumors. This is of particular importance because the fate of the patient depends to an important extent on these tumor entities. Furthermore, first experimental results using imaging devices like optical coherence tomography and confocal laser scanning microscopy promise new powerful noninvasive tools for `optical sectioning' of the bladder