11,705 research outputs found
Dynamical Mass Generation in Landau gauge QCD
We summarise results on the infrared behaviour of Landau gauge QCD from the
Green's functions approach and lattice calculations. Approximate,
nonperturbative solutions for the ghost, gluon and quark propagators as well as
first results for the quark-gluon vertex from a coupled set of Dyson-Schwinger
equations are compared to quenched and unquenched lattice results. Almost
quantitative agreement is found for all three propagators. Similar effects of
unquenching are found in both approaches. The dynamically generated quark
masses are close to `phenomenological' values. First results for the
quark-gluon vertex indicate a complex tensor structure of the non-perturbative
quark-gluon interaction.Comment: 6 pages, 6 figures, Summary of a talk given at the international
conference QCD DOWN UNDER, March 10 - 19, Adelaide, Australi
On the Absence of the Zeno Effect in Relativistic Quantum Field Theory
We study the time evolution of decaying particles in renormalizable models of
Relativistic Quantum Field Theory. Significant differences between the latter
and Non Relativistic Quantum Mechanics are found -in particular, the Zeno
effect seems to be absent in such RQFT models. Conventional renormalization
yields finite time behavior in some cases but fails to produce finite survival
probabilities in others.Comment: Revised version of the paper Time evolution and Zeno effect in
relativistic quantum field theory. To appear in Phys. Lett.
Making the Voting Rights Act Relevant to the Demographics of America: A Reponse to Farrell and Johnson
Making the Voting Rights Act Relevant to the Demographics of America: A Reponse to Farrell and Johnson
Rho and Sigma Mesons in Unitarized Thermal ChPT
We present our recent results for the rho and sigma mesons considered as
resonances in pion-pion scattering in a thermal bath. We use chiral
perturbation theory to fourth order in p for the low energy behaviour, then
extend the analysis via the unitarization method of the Inverse Amplitude into
the resonance region. The width of the rho broadens about twice the amount
required by phase space considerations alone, its mass staying practically
constant up to temperatures of order 150 MeV. The sigma meson behaves in
accordance to chiral symmetry restoration expectations.Comment: Proc. Workshop Strong and Electroweak Matter 02, Heidelberg, German
Surface Vacuum Energy in Cutoff Models: Pressure Anomaly and Distributional Gravitational Limit
Vacuum-energy calculations with ideal reflecting boundaries are plagued by
boundary divergences, which presumably correspond to real (but finite) physical
effects occurring near the boundary. Our working hypothesis is that the stress
tensor for idealized boundary conditions with some finite cutoff should be a
reasonable ad hoc model for the true situation. The theory will have a sensible
renormalized limit when the cutoff is taken away; this requires making sense of
the Einstein equation with a distributional source. Calculations with the
standard ultraviolet cutoff reveal an inconsistency between energy and pressure
similar to the one that arises in noncovariant regularizations of cosmological
vacuum energy. The problem disappears, however, if the cutoff is a spatial
point separation in a "neutral" direction parallel to the boundary. Here we
demonstrate these claims in detail, first for a single flat reflecting wall
intersected by a test boundary, then more rigorously for a region of finite
cross section surrounded by four reflecting walls. We also show how the
moment-expansion theorem can be applied to the distributional limits of the
source and the solution of the Einstein equation, resulting in a mathematically
consistent differential equation where cutoff-dependent coefficients have been
identified as renormalizations of properties of the boundary. A number of
issues surrounding the interpretation of these results are aired.Comment: 22 pages, 2 figures, 1 table; PACS 03.70.+k, 04.20.Cv, 11.10.G
On the order of summability of the Fourier inversion formula
In this article we show that the order of the point value, in the sense of Łojasiewicz, of a tempered distribution and the order of summability of the pointwise Fourier inversion formula are closely related. Assuming that the order of the point values and certain order of growth at infinity are given for a tempered distribution, we estimate the order of summability of the Fourier inversion formula. For Fourier series, and in other cases, it is shown that if the distribution has a distributional point value of order k, then its Fourier series is e.v. Cesàro summable to the distributional point value of order k+1. Conversely, we also show that if the pointwise Fourier inversion formula is e.v. Cesàro summable of order k, then the distribution is the (k+1)-th derivative of a locally integrable function, and the distribution has a distributional point value of order k+2. We also establish connections between orders of summability and local behavior for other Fourier inversion problems
Characterizing and attributing the warming trend in sea and land surface temperatures
Because of low-frequency internal variability, the observed and underlying warming trends in temperature series can be markedly different. Important differences in the observed nonlinear trends in hemispheric temperature series suggest that the northern and southern hemispheres have responded differently to the changes in the radiative forcing. Using recent econometric techniques, we can reconcile such differences and show that all sea and land temperatures share similar time series properties and a common underlying warming trend having a dominant anthropogenic origin. We also investigate the interhemispheric temperature asymmetry (ITA) and show that the differences in warming between hemispheres are in part driven by anthropogenic forcing but that most of the observed rapid changes is likely due to natural variability. The attribution of changes in ITA is relevant since increases in the temperature contrast between hemispheres could potentially produce a shift in the Intertropical Convergence Zone and alter rainfall patterns. The existence of a current slowdown in the warming and its causes are also investigated. The results suggest that the slowdown is a common feature in global and hemispheric sea and land temperatures that can, at least partly, be attributed to changes in anthropogenic forcing.info:eu-repo/semantics/publishedVersio
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