Gaussian Process Vector Autoregressions and Macroeconomic Uncertainty

We develop a non-parametric multivariate time series model that remains agnostic on the precise relationship between a (possibly) large set of macroeconomic time series and their lagged values. The main building block of our model is a Gaussian process prior on the functional relationship that determines the conditional mean of the model, hence the name of Gaussian process vector autoregression (GP-VAR). A flexible stochastic volatility specification is used to provide additional flexibility and control for heteroskedasticity. Markov chain Monte Carlo (MCMC) estimation is carried out through an efficient and scalable algorithm which can handle large models. The GP-VAR is illustrated by means of simulated data and in a forecasting exercise with US data. Moreover, we use the GP-VAR to analyze the effects of macroeconomic uncertainty, with a particular emphasis on time variation and asymmetries in the transmission mechanisms.Comment: JEL: C11, C14, C32, E32; KEYWORDS: Bayesian non-parametrics, non-linear vector autoregressions, asymmetric uncertainty shock

On the contribution of the electromagnetic dipole operator O7{\cal O}_7 to the Bˉs→μ+μ−\bar B_s \to \mu^+\mu^- decay amplitude

We construct a factorization theorem that allows to systematically include QCD corrections to the contribution of the electromagnetic dipole operator in the effective weak Hamiltonian to the $\bar B_s \to \mu^+\mu^-$ decay amplitude. We first rederive the known result for the leading-order QED box diagram, which features a double-logarithmic enhancement associated to the different rapidities of the light quark in the $\bar B_s$ meson and the energetic muons in the final state. We provide a detailed analysis of the cancellation of the related endpoint divergences appearing in individual momentum regions, and show how the rapidity logarithms can be isolated by suitable subtractions applied to the corresponding bare factorization theorem. This allows us to include in a straightforward manner the QCD corrections arising from the renormalization-group running of the hard matching coefficient of the electromagnetic dipole operator in soft-collinear effective theory, the hard-collinear scattering kernel, and the $B_s$-meson distribution amplitude. Focusing on the contribution from the double endpoint logarithms, we derive a compact formula that resums the leading-logarithmic QCD corrections.Comment: 33 pages, 3 figure

A puzzle in Bˉ(s)0→D(s)(∗)+{π−,K−}\bar{B}_{(s)}^0 \to D_{(s)}^{(*)+} \lbrace \pi^-, K^-\rbrace decays and extraction of the fs/fdf_s/f_d fragmentation fraction

We provide updated predictions for the hadronic decays $\bar{B}_s^0\to D_s^{(*)+} \pi^-$ and $\bar{B}^0\to D^{(*)+} K^-$. They are based on $\mathcal{O}(\alpha_s^2)$ results for the QCD factorization amplitudes at leading power and on recent results for the $\bar{B}_{(s)} \to D_{(s)}^{(*)}$ form factors up to order ${\cal O}(\Lambda_{\rm QCD}^2/m_c^2)$ in the heavy-quark expansion. We give quantitative estimates of the matrix elements entering the hadronic decay amplitudes at order ${\cal O}(\Lambda_{\rm QCD}/m_b)$ for the first time. Our results are very precise, and uncover a substantial discrepancy between the theory predictions and the experimental measurements. We explore two possibilities for this discrepancy: non-factorizable contributions larger than predicted by the QCD factorization power counting, and contributions beyond the Standard Model. We determine the $f_s/f_d$ fragmentation fraction for the CDF, D0 and LHCb experiments for both scenarios.Comment: 13 pages, 4 tables: v2: minor modifications, accepted for publication in EPJ

Quantum Oscillations of the Quasiparticle Lifetime in a Metal

Following nearly a century of research, it remains a puzzle that the low-lying excitations of metals are remarkably well explained by effective single-particle theories of non-interacting bands. The abundance of interactions in real materials raises the question of direct spectroscopic signatures of phenomena beyond effective single-particle, single-band behaviour. Here we report the identification of quantum oscillations (QOs) in the three-dimensional topological semimetal CoSi, which defy the standard description in two fundamental aspects. First, the oscillation frequency corresponds to the difference of semi-classical quasi-particle (QP) orbits of two bands, which are forbidden as half of the trajectory would oppose the Lorentz force. Second, the oscillations exist up to above 50K - in stark contrast to all other oscillatory components - which vanish below a few K. Our findings are in excellent agreement with generic model calculations of QOs of the QP lifetime. Since the only precondition for their existence is a non-linear coupling of at least two electronic orbits, e.g., due to QP scattering on defects or collective excitations, such QOs of the QP lifetime are generic for any metal featuring Landau quantization with multiple orbits. They are consistent with certain frequencies in topological semi-metals, unconventional superconductors, rare-earth compounds, and Rashba-systems, and permit to identify and gauge correlation phenomena, e.g., in two-dimensional materials and multiband metals

Gaussian process vector autoregressions and macroeconomic uncertainty

We develop a nonparametric multivariate time series model that remains agnostic on the precise relationship between a (possibly) large set of macroeconomic time series and their lagged values. The main building block of our model is a Gaussian process prior on the functional relationship that determines the conditional mean of the model, hence, the name of Gaussian process vector autoregression (GP-VAR). A flexible stochastic volatility specification is used to provide additional flexibility and control for heteroscedasticity. Markov chain Monte Carlo (MCMC) estimation is carried out through an efficient and scalable algorithm which can handle large models. The GP-VAR is used to analyze the effects of macroeconomic uncertainty, with a particular emphasis on time variation and asymmetries in the transmission mechanisms

Klassifizierung und Bewertung von Aggregationsstrategien für heutige und zukünftige Geschäftsmodelle

Der zunehmende Anteil dezentraler Erzeugung durch den Ausbau erneuerbarer Energien erfordert eine veränderte Organisation des Energiesystems, um auch bei sinkender installierter konventioneller Kapazität und steigender Systemkomplexität die Bereitstellung von ausreichend Flexibilität gewährleisten zu können – Flexibilität, die für zahlreiche Anwendungsfälle eingesetzt werden kann und muss. Im Energiesystem der Zukunft sollen unzählige technische Einheiten reibungsfrei aufeinander abgestimmt dafür sorgen, dass sich Erzeugung und Verbrauch zu jedem Zeitpunkt im Gleichgewicht befinden, ohne Restriktionen im Netzbetrieb auf den verschiedenen Spannungsebenen zu verletzen. Aufgrund von Markteintrittsbarrieren und begrenzten Erlöspotenzialen ist es heute technisch und wirtschaftlich nicht sinnvoll, jede technische Einheit separat zu betreiben und zu vermarkten. Die Aggregation der zahlreichen Einheiten nimmt bei der Bewältigung der Herausforderungen im Energiesystem daher eine bedeutsame Rolle ein. Diese kann auf vielfältige Art und Weise umgesetzt werden. Diese Arbeit richtet den Blick, basierend auf Steuerungskategorien und daraus ableitbaren Aggregationsstrategien, auf mögliche neue Aggregationskonzepte, die für die Bereitstellung von Flexibilität infrage kommen und diskutiert deren Eignung als potenzielle Geschäftsmodelle. Hierfür werden zunächst die heutigen Geschäftsmodelle, zugehörige Value Streams und potenzielle zukünftige Value Streams beleuchtet, die sich aus den Anwendungsfällen für Flexibilität ergeben. Dabei zeigt sich, dass sich Aggregationskonzepte etabliert haben, die durch eine zentrale Kommunikation und Steuerung eine gemeinsame Vermarktung von Anlagen ermöglichen. Es wird häufig übersehen, dass das Potenzial dieses Aggregationskonzepts dahingehend beschränkt ist, dass es sich - zumindest nach heutigem Stand - erst ab einer bestimmten Anlagengröße wirtschaftlich umsetzen lässt. Neue Aggregationskonzepte, bei denen seitens des Flexibilitätsanbieters keine Fahrkurven kommuniziert werden, sondern nur die generelle Bereitschaft, Flexibilität auf ein Signal hin (z.B. Preis) bereitzustellen, gehen zwar mit einer größeren Unsicherheit für den Flexibilitätsnutzer einher, könnten jedoch bislang ungenutzte technische Flexibilitätspotenziale heben. Ohne neue Aggregationskonzepte droht daher ein großer Teil des vorhandenen technischen Flexibilitätspotenzials unerschlossen zu bleiben. Die Grenzen der heutigen Geschäftsmodelle liefern die Grundlage für die anschließende Diskussion dieser neuen Aggregationskonzepte

Solvent content of protein crystals from diffraction intensities by Independent Component Analysis

An analysis of the protein content of several crystal forms of proteins has been performed. We apply a new numerical technique, the Independent Component Analysis (ICA), to determine the volume fraction of the asymmetric unit occupied by the protein. This technique requires only the crystallographic data of structure factors as input.Comment: 9 pages, 2 figures, 1 tabl

Network of topological nodal planes, multifold degeneracies, and Weyl points in CoSi

We report the identification of symmetry-enforced nodal planes (NPs) in CoSi providing the missing topological charges in an entire network of band-crossings comprising in addition multifold degeneracies and Weyl points, such that the fermion doubling theorem is satisfied. In our study we have combined measurements of Shubnikov-de Haas (SdH) oscillations in CoSi with material-specific calculations of the electronic structure and Berry curvature, as well as a general analysis of the band topology of space group (SG) 198. The observation of two nearly dispersionless SdH frequency branches provides unambiguous evidence of four Fermi surface sheets at the R point that reflect the symmetry-enforced orthogonality of the underlying wave functions at the intersections with the NPs. Hence, irrespective of the spin-orbit coupling strength, SG198 features always six- and fourfold degenerate crossings at R and $\Gamma$ that are intimately connected to the topological charges distributed across the network