Economic cycles in the United States and in the euro area : determinants, scale and linkages

This article analyses the business cycles observed in the euro area and in the United States on the basis of the estimated results of a general equilibrium model. In the first place it is shown that the cyclical movements in both economies show strong similarities : there are no significant divergences in the behavioural parameters of either the private sector or the monetary authorities, while also the various exogenous shocks, being the driving force behind the business cycles in this model, prove to be comparable in terms of scale and persistence. On the basis of the estimated models, the observed cyclical movements may be ascribed to various types of exogenous shocks, such as innovations in productivity, the labour supply, consumer preferences or economic policy. In the short term, the business cycles appear mainly to have been generated by demand shocks (preference and investment shocks, exogenous demand shocks and monetary shocks). During recession periods simultaneous demand shocks in consumption and investment spending appear to play an important part. In the long term, shocks affecting the labour supply and productivity are the driving forces. As to the inflation developments, especially temporary mark-up shocks prevail in the short term, although in the long term inflation is primarily a monetary phenomenon and is being guided by the inflation target of the central bank. The limited effect of monetary shocks on the real economy does not imply that monetary policy is insignificant. The systematic behaviour of the central bank is important in order to understand how the other shocks affect the economy. It is here that monetary policy can contribute to a more stable and efficient economic growth. In addition to the causes of the cyclical movements, the downward trend in the volatility of the economic aggregates is being discussed. The reduction of the volatility in real growth of both the euro area and the United States, especially since the mid 1980s, is mainly related to the fact that the size of the exogenous shocks has been smaller. Changes in the economic structure or dynamics and a more efficient monetary policy in themselves do not account for the sharp reduction of real volatility. The same findings may also help to explain the synchronisation of the business cycles between the two economic blocks. Despite the globalisation of the economy, there is no clear trend towards more correlation in economic growth. The relatively small scale of the simultaneous – predominantly demand-related – shocks having occurred recently, may provide some explanation. In the absence of severe synchronised shocks, country- or sector-specific shocks remained relatively important to the pattern of economic activity. As to the future, this implies that it would be wrong to be too optimistic about the dynamic stability of the economy or the efficiency of stabilisation policies.DSGE models, Business cycle fluctuations

Probing few-particle Laughlin states of photons via correlation measurements

We propose methods to create and observe Laughlin-like states of photons in a strongly nonlinear optical cavity. Such states of strongly interacting photons can be prepared by pumping the cavity with a Laguerre-Gauss beam, which has a well-defined orbital angular momentum per photon. The Laughlin-like states appear as sharp resonances in the particle-number-resolved transmission spectrum. Power spectrum and second-order correlation function measurements yield unambiguous signatures of these few-particle strongly-correlated states.Comment: 11 pages including appendice

Synchronized and desynchronized phases of coupled non-equilibrium exciton-polariton condensates

We theoretically analyze the synchronized and desynchronized phases of coupled non-equilibrium polariton condensates within mean field theory. An analytical condition for the existence of a synchronized phase is derived for two coupled wells. The case of many wells in a 2D disordered geometry is studied numerically. The relation to recent experiments on polariton condensation in CdTe microcavities is discussed.Comment: 5 pages, 3 figure

Classical capacity of a qubit depolarizing channel with memory

The classical product state capacity of a noisy quantum channel with memory is investigated. A forgetful noise-memory channel is constructed by Markov switching between two depolarizing channels which introduces non-Markovian noise correlations between successive channel uses. The computation of the capacity is reduced to an entropy computation for a function of a Markov process. A reformulation in terms of algebraic measures then enables its calculation. The effects of the hidden-Markovian memory on the capacity are explored. An increase in noise-correlations is found to increase the capacity

Finite-temperature Wigner solid and other phases of ripplonic polarons on a helium film

Electrons on liquid helium can form different phases depending on density, and temperature. Also the electron-ripplon coupling strength influences the phase diagram, through the formation of so-called "ripplonic polarons", that change how electrons are localized, and that shifts the transition between the Wigner solid and the liquid phase. We use an all-coupling, finite-temperature variational method to study the formation of a ripplopolaron Wigner solid on a liquid helium film for different regimes of the electron-ripplon coupling strength. In addition to the three known phases of the ripplopolaron system (electron Wigner solid, polaron Wigner solid, and electron fluid), we define and identify a fourth distinct phase, the ripplopolaron liquid. We analyse the transitions between these four phases and calculate the corresponding phase diagrams. This reveals a reentrant melting of the electron solid as a function of temperature. The calculated regions of existence of the Wigner solid are in agreement with recent experimental data.Comment: 12 pages, 6 figures. arXiv admin note: text overlap with arXiv:1012.4576, arXiv:0709.4140 by other author

The vortex state in the BEC to BCS crossover: a path-integral description

We derive a path-integral description of the vortex state of a fermionic superfluid in the crossover region between the molecular condensate (BEC) regime and the Cooper pairing (BCS) regime. This path-integral formalism, supplemented by a suitable choice for the saddle point value of the pairing field in the presence of a vortex, offers a unified description that encompasses both the BEC and BCS limits. The vortex core size is studied as a function of the tunable interaction strength between the fermionic atoms. We find that in the BEC regime, the core size is determined by the molecular healing length, whereas in the BCS regime, the core size is proportional only to the Fermi wave length. The observation of such quantized vortices in dilute Fermi gases would provide an unambiguous proof of the realization of superfluidity in these gases.Comment: 10 pages, 2 figure

Nitraatuitspoeling op lössgrasland onder de loep

De resultaten van dit onderzoek geven aan dat de minerale stikstof die in de herfst in de bodem als nitraat achterblijft naar diepere lagen verdwijnt

Coherent Oscillations in an Exciton-Polariton Josephson Junction

We report on the observation of spontaneous coherent oscillations in a microcavity polariton bosonic Josephson junction. The condensation of exciton polaritons takes place under incoherent excitation in a disordered environment, where double potential wells tend to appear in the disordered landscape. Coherent oscillations set on at an excitation power well above the condensation threshold. The time resolved population and phase dynamics reveal the analogy with the AC Josephson effect. We have introduced a theoretical two-mode model to describe the observed effects, which allows us to explain how the different realizations of the pulsed experiment have a similar phase relation

Nominal wage rigidities in a new Keynesian model with frictional unemployment

In this paper, we propose a search and matching model with nominal stickiness à la Calvo in the wage bargaining. We analyze the properties of the model, first, in the context of a typical real business cycle model driven by stochastic productivity shocks and second, in a fully specified monetary DSGE model with various real and nominal rigidities and multiple shocks. The model generates realistic statistics for the important labor market variablesDSGE, Search and Matching, Nominal Wage Rigidity, Monetary Policy