2,695 research outputs found
Comment on "Light-front Schwinger model at finite temperature"
In a recent paper by A. Das and X. Zhou [Phys. Rev. D 68, 065017 (2003)] it
is claimed that explicit evaluation of the thermal photon self-energy in the
Schwinger model gives off-shell thermal Green functions that are different in
light-front and conventional quantizations. We show that the claimed difference
originates from an erroneous simplification of the fermion propagator used in
the light-front calculation.Comment: 8 pages, revtex4, added section refuting the massless limit proposed
in hep-th/031102
Thermal Field Theory and Generalized Light Front Coordinates
The dependence of thermal field theory on the surface of quantization and on
the velocity of the heat bath is investigated by working in general coordinates
that are arbitrary linear combinations of the Minkowski coordinates. In the
general coordinates the metric tensor is non-diagonal. The
Kubo, Martin, Schwinger condition requires periodicity in thermal correlation
functions when the temporal variable changes by an amount
. Light front quantization fails since
, however various related quantizations are possible.Comment: 10 page
Revisiting the -Meson Production at the Hadronic Colliders
The production of heavy-flavored hadron at the hadronic colliders provides a
challenging opportunity to test the validity of pQCD predictions. There are two
mechanisms for the hadroproduction, i.e. the gluon-gluon fusion
mechanism via the subprocess and the
extrinsic heavy quark mechanism via the subprocesses and , both of which shall have sizable
contributions in proper kinematic region. Different from the
fixed-flavor-number scheme (FFNS) previously adopted in the literature, we
study the hadroproduction under the general-mass
variable-flavor-number scheme (GM-VFNS), in which we can consistently deal with
the double counting problem from the above two mechanisms. Properties for the
hadroproduction are discussed. To be useful reference, a
comparative study of FFNS and GM-VFNS is presented. Both of which can provide
reasonable estimations for the hadroproduction. At the Tevatron,
the difference between these two schemes is small, however such difference is
obvious at the LHC. The forthcoming more precise data on LHC shall provide a
good chance to check which scheme is more appropriate to deal with the
-meson production and to further study the heavy quark components in
hadrons.Comment: 18 pages, 8 figures, 4 tables. To match the published version. To be
published in Eur.Phys.J.
Climate Policy Under FatâTailed Risk: An Application of Dice. ESRI WP403. August 2011
Uncertainty plays a significant role in evaluating climate policy, and fatâtailed uncertainty may dominate policy advice. Should we make our utmost effort to prevent the
arbitrarily large impacts of climate change under deep uncertainty? In order to answer to this question we propose an new way of investigating the impact of (fatâtailed) uncertainty on optimal climate policy: the curvature of carbon tax against the uncertainty. We find that the optimal carbon tax increases as the uncertainty about climate sensitivity increases, but it does not accelerate as implied by Weitzmanâs Dismal Theorem. We find the same result in a wide variety of sensitivity analyses. These results emphasize the importance of balancing of the costs and the benefits of climate policy, also under deep uncertainty
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Impact induced response spectrum for the safety evaluation of the high flux isotope reactor
The dynamic impact to the nearby HFIR reactor vessel caused by heavy load drop is analyzed. The impact calculation is carried out by applying the ABAQUS computer code. An impact-induced response spectrum is constructed in order to evaluate whether the HFIR vessel and the shutdown mechanism may be disabled. For the frequency range less than 10 Hz, the maximum spectral velocity of impact is approximately equal to that of the HFIR seismic design-basis spectrum. For the frequency range greater than 10 Hz, the impact-induced response spectrum is shown to cause no effect to the control rod and the shutdown mechanism. An earlier seismic safety assessment for the HFIR control and shutdown mechanism was made by EQE. Based on EQE modal solution that is combined with the impact-induced spectrum, it is concluded that the impact will not cause any damage to the shutdown mechanism, even while the reactor is in operation. The present method suggests a general approach for evaluating the impact induced damage to the reactor by applying the existing finite element modal solution that has been carried out for the seismic evaluation of the reactor
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Seismic analysis of submerged spent fuel storage structure
The purpose of this calculation is to provide structural integrity analysis for the loaded new spent fuel rack arrays against possible seismic excitation. The seismic design calculation is based on the UCRL-15910 spectrum with peak ground acceleration of 0.32g and 5% damping. This spectrum may be considered as an upper bound of the newly developed Oak Ridge site-specific spectrum with 0.29g peak ground acceleration and 5% damping. Both are more conservative than the current design basis seismic acceleration of 0.15g for HFIR. The calculation is carried out by using ABAQUS version 5.2 and the response spectrum option. Since the new racks are to be submerged in HFIR pool, the pool water induced virtual mass has been conservatively taken into consideration. The result shows that if the silo buckling is regarded as failure than, with 95% confidence, the 5% probability of failure ground acceleration is as much as 2.334g. As compared with the design basis of 0.32g, the structure is very safe against earthquake
Coulomb Effects on Electromagnetic Pair Production in Ultrarelativistic Heavy-Ion Collisions
We discuss the implications of the eikonal amplitude on the pair production
probability in ultrarelativistic heavy-ion transits. In this context the
Weizs\"acker-Williams method is shown to be exact in the ultrarelativistic
limit, irrespective of the produced particles' mass. A new equivalent
single-photon distribution is derived which correctly accounts for the Coulomb
distortions. As an immediate application, consequences for unitarity violation
in photo-dissociation processes in peripheral heavy-ion encounters are
discussed.Comment: 13 pages, 4 .eps figure
Connected Green function approach to ground state symmetry breaking in -theory
Using the cluster expansions for n-point Green functions we derive a closed
set of dynamical equations of motion for connected equal-time Green functions
by neglecting all connected functions higher than order for the
-theory in dimensions. We apply the equations to the
investigation of spontaneous ground state symmetry breaking, i.e. to the
evaluation of the effective potential at temperature . Within our momentum
space discretization we obtain a second order phase transition (in agreement
with the Simon-Griffith theorem) and a critical coupling of
as compared to a first order phase transition and
from the Gaussian effective potential approach.Comment: 25 Revtex pages, 5 figures available via fpt from the directory
ugi-94-11 of [email protected] as one postscript file (there
was a bug in our calculations, all numerical results and figures have changed
significantly), ugi-94-1
Looking into the matter of light-quark hadrons
In tackling QCD, a constructive feedback between theory and extant and
forthcoming experiments is necessary in order to place constraints on the
infrared behaviour of QCD's \beta-function, a key nonperturbative quantity in
hadron physics. The Dyson-Schwinger equations provide a tool with which to work
toward this goal. They connect confinement with dynamical chiral symmetry
breaking, both with the observable properties of hadrons, and hence provide a
means of elucidating the material content of real-world QCD. This contribution
illustrates these points via comments on: in-hadron condensates; dressed-quark
anomalous chromo- and electro-magnetic moments; the spectra of mesons and
baryons, and the critical role played by hadron-hadron interactions in
producing these spectra.Comment: 11 pages, 7 figures. Contribution to the Proceedings of "Applications
of light-cone coordinates to highly relativistic systems - LIGHTCONE 2011,"
23-27 May, 2011, Dallas. The Proceedings will be published in Few Body
System
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