2,641 research outputs found
Multiple photon effects in fermion-(anti)fermion scattering at SSC energies
We use the theory of Yennie, Frautschi and Suura to realize, via Monte Carlo
methods, the process f\,\bbbarf\to f'\,\bbbarf'+n\gamma at SSC and LHC
energies, where and are quarks or leptons. QED infrared divergences
are canceled to all orders in perturbation theory. The resulting Monte Carlo
event generator, SSC-YFS2, is used to study the effects of initial-state photon
radiation on these processes in the SSC environment. Sample Monte Carlo data
are presented and discussed. We find that the respective multiple-photon
effects must be taken into account in discussing precise predictions for SSC
physics processes.Comment: 14 pages + 8 figures + 1 tabl
Summary of the Very Large Hadron Collider Physics and Detector Workshop
One of the options for an accelerator beyond the LHC is a hadron collider
with higher energy. Work is going on to explore accelerator technologies that
would make such a machine feasible. This workshop concentrated on the physics
and detector issues associated with a hadron collider with an energy in the
center of mass of the order of 100 to 200 TeV
Environmental Effects on Corrosion Properties of Alloy 22
During the regulatory life of the Yucca Mountain High Level Nuclear Waste (HLNW) repository the primary engineered barrier that is to prevent release of radioactive material into the environment is proposed to be a Corrosion-Resistant Material (CRM) outer shell covering the Waste Package (WP) container. The current selection for the CRM is Alloy 22 (UNS N06022), a Ni-Cr-Mo-W-Fe alloy. Alloy 22 forms a defective chromic oxide passive film which results in excellent corrosion resistance; the presence of molybdenum in Alloy 22 offers corrosion resistance in reducing environments as well as oxidizing environments
Evaluation of the Theoretical Uncertainties in the Z to ll Cross Sections at the LHC
We study the sources of systematic errors in the measurement of the Z to ll
cross-sections at the LHC. We consider the systematic errors in both the total
cross-section and acceptance for anticipated experimental cuts. We include the
best available analysis of QCD effects at NNLO in assessing the effect of
higher order corrections and PDF and scale uncertainties on the theoretical
acceptance. In addition, we evaluate the error due to missing NLO electroweak
corrections and propose which MC generators and computational schemes should be
implemented to best simulate the events.Comment: 23 pages, 52 eps figures, LaTeX with JHEP3.cls, epsfig. Added a
reference, acknowledgment, and a few clarifying comments. 4/29: Changes in
references, minor rewordings and misprint corrections, and one new table
(Table 4) comparing CTEQ and MRST PDFs in the NNLO calculation. Version 6
adds email addresses and corrects one referenc
Consistent Treatment of Soft and Hard Processes in Hadronic Interactions
The QCD improved parton model is a very successful concept to treat processes
in hadronic interactions, whenever large partonic transverse momenta are
involved. However, cross sections diverge in the limit p_T -> 0, and the usual
treatment is the definition of a lower cutoff p_T_min, such that processes with
a smaller p_T -- so-called soft processes -- are simply ignored, which is
certainly not correct for example at RHIC energies. A more consistent procedure
amounts to introduce a technical parameter Q_0^2, referred to as soft
virtuality scale, which is nothing but an artificial borderline between soft
and hard physics. We will discuss such a formalism, which coincides with the
improved parton model for high p_T processes and with the phenomenological
treatment of soft scattering, when only small virtualities are involved. The
most important aspect of our approach is that it allows to obtain a smooth
transition between soft and hard scattering, and therefore no artificial
dependence on a cutoff parameter should appear.Comment: 19 pages, 19 figure
Summary of the SUSY Working Group of the 1999 Les Houches Workshop
The results obtained by the Working Group on Supersymmetry at the 1999 Les
Houches Workshop on Collider Physics are summarized. Separate chapters treat
"general" supersymmetry, R-parity violation, gauge mediated supersymmetry
breaking, and anomaly mediated supersymmetry breaking.Comment: LaTeX, 110 pages with numerous .ps and .eps files. proc.tex is main
tex fil
On Convergence of the Inexact Rayleigh Quotient Iteration with the Lanczos Method Used for Solving Linear Systems
For the Hermitian inexact Rayleigh quotient iteration (RQI), the author has
established new local general convergence results, independent of iterative
solvers for inner linear systems. The theory shows that the method locally
converges quadratically under a new condition, called the uniform positiveness
condition. In this paper we first consider the local convergence of the inexact
RQI with the unpreconditioned Lanczos method for the linear systems. Some
attractive properties are derived for the residuals, whose norms are
's, of the linear systems obtained by the Lanczos method. Based on
them and the new general convergence results, we make a refined analysis and
establish new local convergence results. It is proved that the inexact RQI with
Lanczos converges quadratically provided that with a
constant . The method is guaranteed to converge linearly provided
that is bounded by a small multiple of the reciprocal of the
residual norm of the current approximate eigenpair. The results are
fundamentally different from the existing convergence results that always
require , and they have a strong impact on effective
implementations of the method. We extend the new theory to the inexact RQI with
a tuned preconditioned Lanczos for the linear systems. Based on the new theory,
we can design practical criteria to control to achieve quadratic
convergence and implement the method more effectively than ever before.
Numerical experiments confirm our theory.Comment: 20 pages, 8 figures. arXiv admin note: text overlap with
arXiv:0906.223
Optimization viewpoint on Kalman smoothing, with applications to robust and sparse estimation
In this paper, we present the optimization formulation of the Kalman
filtering and smoothing problems, and use this perspective to develop a variety
of extensions and applications. We first formulate classic Kalman smoothing as
a least squares problem, highlight special structure, and show that the classic
filtering and smoothing algorithms are equivalent to a particular algorithm for
solving this problem. Once this equivalence is established, we present
extensions of Kalman smoothing to systems with nonlinear process and
measurement models, systems with linear and nonlinear inequality constraints,
systems with outliers in the measurements or sudden changes in the state, and
systems where the sparsity of the state sequence must be accounted for. All
extensions preserve the computational efficiency of the classic algorithms, and
most of the extensions are illustrated with numerical examples, which are part
of an open source Kalman smoothing Matlab/Octave package.Comment: 46 pages, 11 figure
Bond-charge Interaction in the extended Hubbard chain
We study the effects of bond-charge interaction (or correlated hopping) on
the properties of the extended ({\it i.e.,} with both on-site () and
nearest-neighbor () repulsions) Hubbard model in one dimension at
half-filling. Energy gaps and correlation functions are calculated by Lanczos
diagonalization on finite systems. We find that, irrespective of the sign of
the bond-charge interaction, , the charge--density-wave (CDW) state is more
robust than the spin--density-wave (SDW) state. A small bond-charge interaction
term is enough to make the differences between the CDW and SDW correlation
functions much less dramatic than when . For and fixed (
is the uncorrelated hopping integral), there is an intermediate phase between a
charge ordered phase and a phase corresponding to singly-occupied sites, the
nature of which we clarify: it is characterized by a succession of critical
points, each of which corresponding to a different density of doubly-occupied
sites. We also find an unusual slowly decaying staggered spin-density
correlation function, which is suggestive of some degree of ordering. No
enhancement of pairing correlations was found for any in the range
examined.Comment: 10 pages, 7 PostScript figures, RevTeX 3; to appear in Phys Rev
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