Credit cycles revisited

Credit and business cycles play an important role in economic research, especially for central banks and supervisors. We reexamine a very useful dynamic model proposed by Kiyotaki and Moore (1997) of an economy with an endogenous credit limit. They claim that a small temporary shock generates large and persistent deviations from the steady state due to a positive feedback loop and the endogenous credit constraint. We mathematically show that contrary to common belief the model does not show amplification and persistence is visible only for a few parameter settings. Kiyotaki and Moore have linearized the model despite higher order terms being more important, rendering the Taylor expansion invalid. Further, we show that spillover effects in an economy with two distinct sectors are small. The strong amplification present in the original results, which supposedly is due to the large inter-temporal or dynamic multiplier effect, is spurious. The dynamic multiplier effect is of similar size than the static effect and in all cases numerically small

QCD corrections to FCNC decays mediated by Z-penguins and W-boxes

QCD corrections are evaluated to FCNC processes like $B \to X_s \nu \bar{\nu}$, $K \to \pi \nu \bar{\nu}$, $B \to l^+ l^-$ or $K_L \to \mu^+ \mu^-$, i.e. to processes mediated by effective operators containing neutrino currents or axial leptonic currents. Such operators originate from $W$-box and $Z$-penguin diagrams in the Standard Model. QCD corrections to them are given by two-loop diagrams. We confirm results for those diagrams which are already present in the literature. However, our analytical expressions for the Wilson coefficients disagree, due to a subtlety in regulating spurious IR divergences. The numerical effect of the disagreement is rather small. The size of the perturbative QCD corrections compared to the leading terms depends on the renormalization scheme used at the leading order. It varies from 0 to around 15% for a reasonable class of schemes. The uncertainty originating from uncalculated higher-order (three-loop) QCD corrections is expected to be around 1% .Comment: 12 pages, latex, 7 ps figure

Effectiveness of policy and regulation in European sovereign credit risk markets - A network analysis

We study the impact of changes in regulations and policy interventions on systemic risk among European sovereigns measured as volatility spillovers in respective credit risk markets. Our unique intraday CDS dataset allows for precise measurement of the effectiveness of these events in a network setting. In particular, it allows discerning interventions which entail significant changes in network cross-effects with appropriate bootstrap confidence intervals. We show that it was mainly regulatory changes with the ban of trading naked sovereign CDS in 2012 as well as the new ISDA regulations in 2014 which were most effective in reducing systemic risk. In comparison, we find that the effect of policy interventions was minor and generally not sustainable. In particular, they only had a significant impact when implemented for the first time and when targeting more than one country. For the volatility spillover channels, we generally find balanced networks with no fragmentation over time

Test des Standardmodells im B-Mesonen-Sektor durch Mischungsphänomene und seltene Zerfälle

In dieser Arbeit werden die seltenen Zerfälle b -> s gamma und b -> s g, sowie die BB¯-Oszillation einschließlich QCD-Korrekturen in Next-to-Leading-Log-Approximation untersucht. Es handelt sich hierbei um Flavor Changing Neutral Current (FCNC) Prozesse, welche auf dem Born-Niveau innerhalb des Standardmodells verboten sind. Diese Prozesse sind besonders geeignet zum Testen des Standardmodells, da mögliche Erweiterungen potentiell denselben Beitrag liefern können. Als Erweiterungen werden das 2-Higgs-Dublett-Modell, Links-Rechts-Modelle und insbesondere das Minimale Supersymmetrische Standardmodell diskutiert. Am Beispiel der BB¯-Oszillation wird gezeigt, daß die Bestimmung der Wilson-Koeffizienten inabhängig von der Behandlung der leichten Felder ist. Dazu wird zum einen die dimensionale Regularisierung der IR-Divergenzen und zum anderen die Einführung von IR-Regulatoren benutzt. Für das BB¯-Mixing werden mit Hilfe der sehr genau gemessenen Massenaufspaltung "Delta m B" Aussagen zu (V td V* tb)² getroffen. Weiterhin wird das Verzweigungsverhältnis BR[B -> "X s gamma"] im Standardmodell und im Minimalen Supersymmetrischen Standardmodell bestimmt.Calculations for the rare decays b -> s gamma and b -> s g, as well as the BB¯-mixing inclusive QCD-corrections in Next-to-Leading-Log-Approximation are presented throughout this work. The decays and the mixing are caused by Flavor Changing Neutral Current (FCNC) processes, which are absent on the tree-level within the framework of the Standard-Model. Hence these processes are qualified to test the validity of the Standard-Model, because possible extensions may provide similar contributions. Considered extensions are the 2-Higgs-Doublet-Model, Left-Right-Models and the Minimal Supersymmetric Standard-Model. It is shown that the determination of the Wilson-coefficients is independent of the treatmentof the light fields for the case of the BB¯-mixing. For this proof the dimensional regularisation of the IR-divergences on one side and a regulator mass for the light fields on the other side isutilized. The well-known value for the mass splitting "Delta m B" available from the BB¯-oscillation is applied to deduce (V td V* tb)². Furthermore the branching ratio BR[B -> "X s gamma"] is calculated within the Standard-Model and the Supersymmetric Standard-Model

Data4City – A Hyperlocal Citizen App

Exploring upon the phenomena of smart cities, this paper elaborates the potential of crowdsourced data collection in small scale urban quarters. The development of the Data4City (D4C) hyperlocal app – PinCity – is based on the idea of increasing the density of real-time information in urban areas (urban neighborhoods) in order to optimize or create innovative urban services (such as public transportation, garbage collection) or urban planning, thus improving the quality of life of quarter inhabitants as a long-term goal. The main principle of the app is the small-scale implementation, as opposed to top-down smart city approaches worldwide, preferably in a city quarter, or a community, which can be subsequently scaled and interlaced to other parts of the city

Two-Loop QCD Anomalous Dimensions of Flavour-Changing Four-Quark Operators Within and Beyond the Standard Model

We calculate the two-loop QCD anomalous dimension matrix (ADM) gamma^(1)_NDR in the NDR-MSbar scheme for all the flavour-changing four-quark dimension-six operators that are relevant in both the Standard Model and its extensions. Both current-current and penguin diagrams are included. Some of our NDR-MSbar results for Delta F=1 operators overlap with the previous calculations, but several others have never been published before. In the case of Delta F=2 operators, our results are compatible with the ones obtained by Ciuchini et al. in the Regularization-Independent renormalization scheme, but differ from their NDR-MSbar results. In order to explain the difference, we calculate the ADM of Delta F=2 operators again, extracting it from the ADM of Delta F=1 operators.Comment: 37 pages, 1 figur

Master Formulae for Delta F=2 NLO-QCD Factors in the Standard Model and Beyond

We present analytic formulae for the QCD renormalization group factors relating the Wilson coefficients C_i(mu_t) and C_i(mu), with mu_t = O(m_t) and mu < mu_t, of the Delta F=2 dimension six four-quark operators Q_i in the Standard Model and in all of its extensions. Analogous analytic formulae for the QCD factors relating the matrix elements and with mu_K < 2GeV are also presented. The formulae are given in the NDR scheme. The strongest renormalization-group effects are found for the operators with the Dirac structures (1 - gamma_5)*(1 + gamma_5) and (1 - gamma_5)*(1 - gamma_5). We calculate the matrix elements in the NDR scheme using the lattice results in the LRI scheme. We give expressions for the mass differences Delta M_K and Delta M_B and the CP-violating parameter epsilon_K in terms of the non-perturbative parameters B_i and the Wilson coefficients C_i(mu_t). The latter summarize the dependence on new physics contributions.Comment: latex-file and 2 figures, 31 page

Photonic penguins at two loops and m_t-dependence of BR[ B -> X_s l^+ l^-]

We calculate two-loop matching conditions for all the operators that are relevant to B -> X_s l^+ l^- decay in the Standard Model. In effect, we are able to remove the +_16% uncertainty in the decay spectrum, which was mainly due to the renormalization-scale dependence of the top-quark mass. We find 1.46 * 10^-6 for the branching ratio integrated in the domain 0.05 < m_{l^+l^-}^2/m_b^2 < 0.25, for l= e or mu. There remains around 13% perturbative uncertainty in this quantity, while the non-perturbative effects are expected to be smaller.Comment: 38 pages, including 8 figures, uses graphic

Completing the NLO QCD calculation of B -> Xs gamma

We evaluate two-loop b -> s gamma matrix elements of all the four-quark operators containing no derivatives. Contrary to previous calculations, no expansion in the mass ratio mc/mb is performed, and all the possible Dirac and flavor structures are included. Consequently, we are able to provide the last item in the NLO analysis of B -> Xs gamma that has been missing so far, namely the two-loop matrix elements of the QCD-penguin operators. Due to smallness of the Wilson coefficients of those operators in the Standard Model, their effect on the branching ratio is small: a reduction by roughly 1%. We find BR[ B -> Xs gamma]_{E_gamma > 1.6 GeV} = (3.57 +_ 0.30)*10^{-4}.Comment: 18 pages, 2 figures, uses graphic