Burkhardt-Cottingham sum rule and forward spin polarizabilities in Heavy Baryon Chiral Perturbation Theory

We study spin-dependent sum rules for forward virtual Compton scattering(VVCS) off the nucleon in heavy baryon chiral perturbation theory at order $O(p^4)$. We show how these sum rules can be evaluated from low energy expansions (in the virtual photon energy) of the forward VVCS amplitudes. We study in particular the Burkhardt -Cottingham sum rule in HBChPT and higher terms in the low energy expansion, which can be related to the generalized forward spin polarizabilities of the nucleon. The dependence of these observables on the photon virtuality $Q^2$ can be accessed, at small and intermediate $Q^2$ values, from existing and forthcoming data at Jefferson Lab.Comment: 16 pages,4 fig

The Spectrum of the Dirac Operator in the Linear Sigma Model with Quarks

We derive the spectrum of the Dirac operator for the linear sigma-model with quarks in the large N_c approximation using renormalization group flow equations. For small eigenvalues, the Banks-Casher relation and the vanishing linear term are recovered. We calculate the coefficient of the next to leading term and investigate the spectrum beyond the low energy regime.Comment: 15 pages, 6 figures, to appear in Phys. Rev.

Gas6 in chronic liver disease—a novel blood-based biomarker for liver fibrosis

Abstract The expression of the receptor tyrosine kinase Axl and its cleavage product soluble Axl (sAxl) is increased in liver fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). In this multicenter study, we evaluated the diagnostic value of Gas6, the high-affinity ligand of Axl, in patients with chronic liver disease. Levels of sAxl and Gas6, and their albumin (alb) ratios were analyzed in serum samples of patients with biopsy-proven liver fibrosis, end-stage liver disease, HCC, and healthy controls, and were compared to Fibrosis-4 (FIB-4), enhanced liver fibrosis (ELF™) test, Child-Pugh score (CPS), model of end-stage liver disease (MELD) score, hepatic venous pressure gradient, and α-fetoprotein, respectively. A total of 1111 patients (median age 57.8 y, 67.3% male) was analyzed. Gas6/alb showed high diagnostic accuracy for the detection of significant (≥F2: AUC 0.805) to advanced fibrosis (≥F3: AUC 0.818), and was superior to Fib-4 for the detection of cirrhosis (F4: AUC 0.897 vs. 0.878). In addition, Gas6/alb was highly predictive of liver disease severity (Odds ratios for CPS B/C, MELD ≥ 15, and clinically significant portal hypertension (CSPH) were 16.534, 10.258, and 12.115), and was associated with transplant-free survival (Hazard ratio 1.031). Although Gas6 and Gas6/alb showed high diagnostic accuracy for the detection of HCC in comparison to chronic liver disease patients without cirrhosis (AUC 0.852, 0.868), they failed to discriminate between HCC in cirrhosis versus cirrhosis only. In conclusion, Gas6/alb shows a high accuracy to detect significant to advanced fibrosis and cirrhosis, and predicts severity of liver disease including CSPH

Deeply virtual Compton scattering in a relativistic quark model

This thesis is mainly concerned with a model calculation for generalized parton distributions (GPDs). We calculate vectorial- and axial GPDs for the N N and N Delta transition in the framework of a light front quark model. This requires the elaboration of a connection between transition amplitudes and GPDs. We provide the first quark model calculations for N Delta GPDs. The examination of transition amplitudes leads to various model independent consistency relations. These relations are not exactly obeyed by our model calculation since the use of the impulse approximation in the light front quark model leads to a violation of Poincare covariance. We explore the impact of this covariance breaking on the GPDs and form factors which we determine in our model calculation and find large effects. The reference frame dependence of our results which originates from the breaking of Poincare covariance can be eliminated by introducing spurious covariants. We extend this formalism in order to obtain frame independent results from our transition amplitudes.Das Thema dieser Arbeit ist eine Modellrechnung für verallgemeinerte Partonverteilungen (GPDs). Es werden vektorielle- und axiale GPDs für die N N und N Delta Übergänge im Rahmen eines Quarkmodells im Lichtkegelformalismus berechnet. Hierzu muss zunächst ein Zusammenhang zwischen Übergangsamplituden und den GPDs hergestellt werden. Die Untersuchung der Übergangsamplituden führt zu einer Vielzahl modellunabhängiger Konsistenzrelationen. Diese Relationen werden von den im Modell berechneten Übergangsamplituden nicht exakt erfüllt, da die Verwendung der Impulsnäherung im Quarkmodell auf dem Lichtkegel zu einer Verletzung der Poincare Kovarianz führt. Der Einfluss, dieser Brechung der Kovarianz auf die Berechnung von GPDs und Formfaktoren wird untersucht. Es ergeben sich große Effekte, unter anderem die Abhängigkeit der Ergebnisse von der Wahl des Bezugssystems. Letztere kann durch die Einführung zusätzlicher unphysikalischer Kovarianten eliminiert werden. In dieser Arbeit wird der entsprechende Formalismus erweitert um für alle hier betrachteten Observablen Ergebnisse aus den Übergangsamplituden zu erhalten welche unabhängig von der Wahl des Bezugssystems sind

Short-time work and precautionary savings

SHORT-TIME WORK AND PRECAUTIONARY SAVINGS Short-time work and precautionary savings / Dengler, Thomas (Rights reserved) (-

Short-Time Work and Precautionary Savings

During the Covid-19 crisis, most OECD countries used short-time work (subsidised reductions in working hours) to preserve employment. This paper documents that short-time work affects the behaviour of firms (supply) and households (demand). First, using household survey data from Germany, we show that the consumption risk of short-time work is lower than that of unemployment. Second, we construct a New Keynesian model with heterogeneous workers and firms, incomplete asset markets, and labour market frictions. Short-time work weakens workers’ precautionary savings motive and lowers labour costs. This reduces the level and volatility of both the separation and unemployment rate at the cost of tying workers to less productive firms. Quantitatively, the positive employment effects dominate the productivity losses

Short-Time Work and Precautionary Savings

During the Covid-19 crisis, most OECD countries used short-time work (subsidized reductions in working hours) to preserve employment. This paper documents that short-time work affects the behavior of firms (supply) and households (demand). First, using household survey data from Germany, we show that the consumption risk of short-time work is lower than that of unemployment. Second, we construct a New Keynesian model with heterogeneous workers and firms, incomplete asset markets, and labor market frictions. Short-time work weakens workers' precautionary savings motive and lowers labor costs. This reduces the level and volatility of both the separation and unemployment rate at the cost of tying workers to less productive firms. Quantitatively, the positive employment effects dominate the productivity losses