3,525 research outputs found
The Schwinger Model on a circle: relation between Path Integral and Hamiltonian approaches
We solve the massless Schwinger model exactly in Hamiltonian formalism on a
circle. We construct physical states explicitly and discuss the role of the
spectral flow and nonperturbative vacua. Different thermodynamical correlation
functions are calculated and after performing the analytical continuation are
compared with the corresponding expressions obtained for the Schwinger model on
the torus in Euclidean Path Integral formalism obtained before.Comment: 40 page
The General Correlation Function in the Schwinger Model on a Torus
In the framework of the Euclidean path integral approach we derive the exact
formula for the general N-point chiral densities correlator in the Schwinger
model on a torusComment: 17 pages, misprints corrected, references adde
Angular momentum transport and large eddy simulations in magnetorotational turbulence: the small Pm limit
Angular momentum transport in accretion discs is often believed to be due to
magnetohydrodynamic turbulence mediated by the magnetorotational instability.
Despite an abundant literature on the MRI, the parameters governing the
saturation amplitude of the turbulence are poorly understood and the existence
of an asymptotic behavior in the Ohmic diffusion regime is not clearly
established. We investigate the properties of the turbulent state in the small
magnetic Prandtl number limit. Since this is extremely computationally
expensive, we also study the relevance and range of applicability of the most
common subgrid scale models for this problem. Unstratified shearing boxes
simulations are performed both in the compressible and incompressible limits,
with a resolution up to 800 cells per disc scale height. The latter constitutes
the largest resolution ever attained for a simulation of MRI turbulence. In the
presence of a mean magnetic field threading the domain, angular momentum
transport converges to a finite value in the small Pm limit. When the mean
vertical field amplitude is such that {\beta}, the ratio between the thermal
and magnetic pressure, equals 1000, we find {\alpha}~0.032 when Pm approaches
zero. In the case of a mean toroidal field for which {\beta}=100, we find
{\alpha}~0.018 in the same limit. Both implicit LES and Chollet-Lesieur closure
model reproduces these results for the {\alpha} parameter and the power
spectra. A reduction in computational cost of a factor at least 16 (and up to
256) is achieved when using such methods. MRI turbulence operates efficiently
in the small Pm limit provided there is a mean magnetic field. Implicit LES
offers a practical and efficient mean of investigation of this regime but
should be used with care, particularly in the case of a vertical field.
Chollet-Lesieur closure model is perfectly suited for simulations done with a
spectral code.Comment: Accepted for publication in A&
Mandatory IFRS Reporting and Stock Price Informativeness
In this paper, we examine whether mandatory adoption of IFRS influences the flow of firm-specific information and contributes to stock price informativeness as measured by stock return synchronicity. Using a constant sample of 1,904 mandatory IFRS adopters in 14 EU countries for the period 2003-2007, we find a V-shaped pattern in synchronicity around IFRS adoption, which is consistent with IFRS disclosures revealing new firm-specific information in the adoption period (i.e., a reduction of synchronicity) and subsequently lowering the surprise of future disclosures (i.e., an increase in synchronicity). We also find mandatory IFRS adoption increases analysts’ ability to incorporate industry-level information into stock price. However, we are unable to detect a reduction in the private information advantage enjoyed by institutional owners post-IFRS adoption. Moreover, we find the synchronicity effects to be more pronounced for firms in countries with larger differences in local GAAP relative to IFRS. Overall, our evidence yields novel insights on the consequences of mandatory IFRS adoption by investigating its effect on stock price informativeness and the distinctive roles played by a firm’s information environment.IFRS;mandatory adoption;stock return synchronicity;information environment
Mandatory Adoption of IFRS and Analysts’ Forecasts Information Properties
This study examines the properties of the information contained in analysts’ earnings forecasts for mandatory IFRS adopters in Europe for the period 2003-07. We find a significant increase in the precision of both public and private information after switching to IFRS, especially for forecasts pertaining to 2006 and later. However, we are unable to detect a change in the consensus among financial analysts after the mandatory adoption of IFRS. These results suggest that the higher percentage increase in the precision of common information is offset by a proportionate increase in the precision of private information such that consensus among analysts does not change. When exploring analyst-specific precision in more detail, we find that the analysts who are following firms in more than one European country experience the largest post-IFRS improvement in private information precision. These results hold after controlling for factors that are shown in prior research to be correlated with analysts’ information precision measures. Taken together, our results suggest that mandatory adoption of IFRS had a significant and positive effect on the information processing of financial analysts but this did not occur homogeneously across analysts.IFRS;mandatory IFRS adoption;analyst forecasts;information environment
Decoherence in QED at finite temperature
We consider a wave packet of a charged particle passing through a cavity
filled with photons at temperature T and investigate its localization and
interference properties. It is shown that the wave packet becomes localized and
the interference disappears with an exponential speed after a sufficiently long
path through the cavity.Comment: Latex, 10 page
Non-Markovianity, Loschmidt echo and criticality: a unified picture
A simple relationship between recently proposed measures of non-Markovianity
and the Loschmidt echo is established, holding for a two-level system (qubit)
undergoing pure dephasing due to a coupling with a many-body environment. We
show that the Loschmidt echo is intimately related to the information flowing
out from and occasionally back into the system. This, in turn, determines the
non-Markovianity of the reduced dynamics. In particular, we consider a central
qubit coupled to a quantum Ising ring in the transverse field. In this context,
the information flux between system and environment is strongly affected by the
environmental criticality; the qubit dynamics is shown to be Markovian exactly
and only at the critical point. Therefore non-Markovianity is an indicator of
criticality in the model considered here
On the precise connection between the GRW master-equation and master-equations for the description of decoherence
We point out that the celebrated GRW master-equation is invariant under
translations, reflecting the homogeneity of space, thus providing a particular
realization of a general class of translation-covariant Markovian
master-equations. Such master-equations are typically used for the description
of decoherence due to momentum transfers between system and environment.
Building on this analogy we show the exact relationship between the GRW
master-equation and decoherence master-equations, further providing a
collisional decoherence model formally equivalent to the GRW master-equation.
This allows for a direct comparison of order of magnitudes of relevant
parameters. This formal analogy should not lead to confusion on the utterly
different spirit of the two research fields, in particular it has to be
stressed that the decoherence approach does not lead to a solution of the
measurement problem. Building on this analogy however the feasibility of the
extension of spontaneous localization models in order to avoid the infinite
energy growth is discussed. Apart from a particular case considered in the
paper, it appears that the amplification mechanism is generally spoiled by such
modifications.Comment: 9 pages, latex, no figures, to appear on J. Phys.
IDENTIFICATION AND PLANT INTERACTION OF A PHYLLOBACTERIUM SP, A PREDOMINANT RHIZOBACTERIUM OF YOUNG SUGAR-BEET PLANTS
The second most abundant bacterium on the root surface of young sugar beet plants was identified as a Phyllobacterium sp. (Rhizobiaceae) based on a comparison of the results of 39 conventional identification tests, 167 API tests, 30 antibiotic susceptibility tests, and sodium dodecyl sulfate-polyacrylamide gel electrophoretic fingerprints of total cellular proteins with type strains of Phyllobacterium myrsinacearum and Phyllobacterium rubiacearum. It was found on 198 of 1,100 investigated plants between the 2nd and 10th leaf stage on three different fields in Belgium and one field in Spain. Densities ranged from 2 × 10(4) to 2 × 10(8) CFU/g of root. Five isolates exerted a broad-spectrum in vitro antifungal activity. DNA-DNA hybridizations showed that Phyllobacterium sp. does not contain DNA sequences that are homologous with the attachment genes chvA, chvB, the transferred-DNA (T-DNA) hormone genes iaaH and ipt from Agrobacterium tumefaciens, iaaM from A. tumefaciens and Pseudomonas savastanoi, or the nitrogenase genes nifHDK from Klebsiella pneumoniae. Phyllobacterium sp. produces indolylacetic acid in in vitro cultures and induces auxinlike effects when cocultivated with callus tissue of tobacco. When Phyllobacterium sp. was transformed with a Ti plasmid derivative, it gained the capacity to induce tumors on Kalanchoe daigremontiana. The potential role of Phyllobacterium sp. in this newly recognized niche is discussed
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