202,592 research outputs found
Effective range expansion in various scenarios of EFT(\notpi)
Using rigorous solutions, we compare the ERE parameters obtained in three
different scenarios of EFT(\notpi) in nonperturbative regime. A scenario with
unconventional power counting (like KSW) is shown to be disfavored by the PSA
data, while the one with elaborate prescription of renormalization but keeping
conventional power counting intact seems more promising.Comment: 6 pages, 3 tables, no figure, revtex4-1, minor revisions, to appear
in EP
Stable embedded solitons
Stable embedded solitons are discovered in the generalized third-order
nonlinear Schroedinger equation. When this equation can be reduced to a
perturbed complex modified KdV equation, we developed a soliton perturbation
theory which shows that a continuous family of sech-shaped embedded solitons
exist and are nonlinearly stable. These analytical results are confirmed by our
numerical simulations. These results establish that, contrary to previous
beliefs, embedded solitons can be robust despite being in resonance with the
linear spectrum.Comment: 2 figures. To appear in Phys. Rev. Let
Imperfection Information, Optimal Monetary Policy and Informational Consistency
This paper examines the implications of imperfect information (II) for optimal monetary policy with a consistent set of informational assumptions for the modeller and the private sector an assumption we term the informational consistency. We use an estimated simple NK model from Levine et al. (2012), where the assumption of symmetric II significantly improves the fit of the model to US data to assess the welfare costs of II under commitment, discretion and simple Taylor-type rules. Our main results are: first, common to all information sets we find significant welfare gains from commitment only with a zero-lower bound constraint on the interest rate. Second, optimized rules take the form of a price level rule, or something very close across all information cases. Third, the combination of limited information and a lack of commitment can be particularly serious for welfare. At the same time we find that II with lags introduces a ‘tying ones hands’ effect on the policymaker that may improve welfare under discretion. Finally, the impulse response functions under our most extreme imperfect information assumption (output and inflation observed with a two-quarter delay) exhibit hump-shaped behaviour and the fiscal multiplier is significantly enhanced in this case
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Atomic electron tomography in three and four dimensions
Atomic electron tomography (AET) has become a powerful tool for atomic-scale structural characterization in three and four dimensions. It provides the ability to correlate structures and properties of materials at the single-atom level. With recent advances in data acquisition methods, iterative three-dimensional (3D) reconstruction algorithms, and post-processing methods, AET can now determine 3D atomic coordinates and chemical species with sub-Angstrom precision, and reveal their atomic-scale time evolution during dynamical processes. Here, we review the recent experimental and algorithmic developments of AET and highlight several groundbreaking experiments, which include pinpointing the 3D atom positions and chemical order/disorder in technologically relevant materials and capturing how atoms rearrange during early nucleation at four-dimensional atomic resolution
Localization and delocalization errors in density functional theory and implications for band-gap prediction
The band-gap problem and other systematic failures of approximate functionals
are explained from an analysis of total energy for fractional charges. The
deviation from the correct intrinsic linear behavior in finite systems leads to
delocalization and localization errors in large or bulk systems. Functionals
whose energy is convex for fractional charges such as LDA display an incorrect
apparent linearity in the bulk limit, due to the delocalization error. Concave
functionals also have an incorrect apparent linearity in the bulk calculation,
due to the localization error and imposed symmetry. This resolves an important
paradox and opens the possibility to obtain accurate band-gaps from DFT.Comment: 4 pages 4 figure
Ab Initio Approach to the Non-Perturbative Scalar Yukawa Model
We report on the first non-perturbative calculation of the scalar Yukawa
model in the single-nucleon sector up to four-body Fock sector truncation (one
"scalar nucleon" and three "scalar pions"). The light-front Hamiltonian
approach with a systematic non-perturbative renormalization is applied. We
study the -body norms and the electromagnetic form factor. We find that the
one- and two-body contributions dominate up to coupling .
As we approach the coupling , we discover that the
four-body contribution rises rapidly and overtakes the two- and three-body
contributions. By comparing with lower sector truncations, we show that the
form factor converges with respect to the Fock sector expansion.Comment: 8 pages, 12 figures, to be published in Phys. Lett.
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Information, VARs and DSGE Models
How informative is a time series representation of a given vector of observables about the structural shocks and impulse response functions in a DSGE model? In this paper we refer to this econometrician’s problem as “E-invertibility” and consider the corresponding information problem of the agents in the assumed DGP, the DSGE model, which we refer to as “A-invertibility” We consider how the general nature of the agents’ signal extraction problem under imperfect information impacts on the econometrician’s problem of attempting to infer the nature of structural shocks and associated impulse responses from the data. We also examine a weaker condition of recoverability. A general conclusion is that validating a DSGE model by comparing its impulse response functions with those of a data VAR is more problematic when we drop the common assumption in the literature that agents have perfect information as an endowment. We develop measures of approximate fundamentalness for both perfect and imperfect information cases and illustrate our results using analytical and numerical examples
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