Compactness and finite forcibility of graphons

Graphons are analytic objects associated with convergent sequences of graphs. Problems from extremal combinatorics and theoretical computer science led to a study of graphons determined by finitely many subgraph densities, which are referred to as finitely forcible. Following the intuition that such graphons should have finitary structure, Lovasz and Szegedy conjectured that the topological space of typical vertices of a finitely forcible graphon is always compact. We disprove the conjecture by constructing a finitely forcible graphon such that the associated space is not compact. The construction method gives a general framework for constructing finitely forcible graphons with non-trivial properties

A heuristic description of high-pT hadron production in heavy ion collisions

Using a simplified model for in-medium dipole evolution accounting for color filtering effects we study production of hadrons at large transverse momenta $p_T$ in heavy ion collisions. In the framework of this model, several important sources of the nuclear suppression observed recently at RHIC and LHC have been analysed. A short production length of the leading hadron $l_p$ causes a strong onset of color transparency effects manifested themselves as a steep rise of the nuclear modification factor $R_{AA}(p_T)$ at large hadron $p_T$'s. A dominance of quarks with higher $l_p$ leads to a weaker suppression at RHIC than the one observed at LHC. In the RHIC kinematic region we include an additional suppression factor steeply falling with $p_T$, which is tightly related to the energy conservation constraints. The latter is irrelevant at LHC up to $p_T\lesssim 70$ GeV while it causes a rather flat $p_T$ dependence of the $R_{AA}(p_T)$ factor at RHIC c.m. energy $\sqrt{s} = 200$ GeV and even an increasing suppression with $p_T$ at $\sqrt{s} = 62$ GeV. The calculations contain only a medium density adjustment, and for an initial time scale $t_0$ = 1 fm we found the energy-dependent maximal values of the transport coefficient, $\hat{q}_0 = 0.7, 1.0$ and 1.3 GeV$^2$/fm corresponding to $\sqrt{s} = 62, 200$ GeV and 2.76 TeV, respectively. We present a broad variety of predictions for the nuclear modification factor and the azimuthal asymmetry which are in a good agreement with available data from experiments at RHIC and LHC.Comment: 14 pages, 17 figures; extra clarifications added in Sects. II and III (with additional Figs. 1-6) and in the extended Sect. V B (with additional Fig.11), references added, conclusions unchange

Monetary Policy before Euro Adoption: Challenges for EU New Members

This article analyzes the main issues for monetary policy in new EU member states before their euro adoption. These are typically rooted in the challenge of fulfilling concurrently of the Maastricht inflation and exchange rate criterion, as these countries are experiencing equilibrium real exchange rate appreciation. In this article we first distinguish between the wording, written interpretation and “revealed” interpretation of the inflation and exchange rate criteria. Then we discuss the options for monetary policy in the period of fulfilment of these criteria in terms of its transparency, its continuity with the previous monetary policy regime, the choice of central parity for the ERM II, the setting of the fluctuation bandwidth, the probability of fulfilment of both criteria and the impact on economic stability.http://deepblue.lib.umich.edu/bitstream/2027.42/57233/1/wp853 .pd

Credit cycles and macro fundamentals

We study the relation between the credit cycle and macro economic fundamentals in an intensity based framework. Using rating transition and default data of U.S. corporates from Standard and Poor’s over the period 1980–2005 we directly estimate the credit cycle from the micro rating data. We relate this cycle to the business cycle, bank lending conditions, and financial market variables. In line with earlier studies, these variables appear to explain part of the credit cycle. As our main contribution, we test for the correct dynamic specification of these models. In all cases, the hypothesis of correct dynamic specification is strongly rejected. Moreover, accounting for dynamic mis-specification, many of the variables thought to explain the credit cycle, turn out to be insignificant. The main exceptions are GDP growth, and to some extent stock returns and stock return volatilities. Their economic significance appears low, however. This raises the puzzle of what macro-economic fundamentals explain default and rating dynamics. JEL Classification: G11, G2

Monetary Policy before Euro Adoption: Challenges for EU New Members

This article analyzes the main issues for monetary policy in new EU member states before their euro adoption. These are typically rooted in the challenge of fulfilling concurrently of the Maastricht inflation and exchange rate criterion, as these countries are experiencing equilibrium real exchange rate appreciation. In this article we first distinguish between the wording, written interpretation and “revealed” interpretation of the inflation and exchange rate criteria. Then we discuss the options for monetary policy in the period of fulfilment of these criteria in terms of its transparency, its continuity with the previous monetary policy regime, the choice of central parity for the ERM II, the setting of the fluctuation bandwidth, the probability of fulfilment of both criteria and the impact on economic stability.monetary policy, euro adoption, ERM II, EU

The finite mass beamsplitter in high power interferometers

The beamplitter in high-power interferometers is subject to significant radiation-pressure fluctuations. As a consequence, the phase relations which appear in the beamsplitter coupling equations oscillate and phase modulation fields are generated which add to the reflected fields. In this paper, the transfer function of the various input fields impinging on the beamsplitter from all four ports onto the output field is presented including radiation-pressure effects. We apply the general solution of the coupling equations to evaluate the input-output relations of the dual-recycled laser-interferometer topology of the gravitational-wave detector GEO600 and the power-recycling, signal-extraction topology of advanced LIGO. We show that the input-output relation exhibits a bright-port dark-port coupling. This mechanism is responsible for bright-port contributions to the noise density of the output field and technical laser noise is expected to decrease the interferometer's sensitivity at low frequencies. It is shown quantitatively that the issue of technical laser noise is unimportant in this context if the interferometer contains arm cavities.Comment: 10 pages, 7 figure