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Description: The density oscillations of warm particle bunches is investigated theoretically. Two different mathematical approaches are employed to derive the basic equation describing density oscillations; one is a fluid approach and the second is a more general Green1s function formulation. The motion is analyzed in first order perturbation theory where it is shown, under the assumption of no degeneracy, that there are only stable oscillations. Second order perturbation theory gives damping of the motion. The perturbation theory is examined and a criterion is exhibited for its proper use. Thus, when the resistivity is small enough (but nonzero) then the motion is stable, but when the resistivity is large then the motion is essentially unstable with a growth rate which is that of an unbunched beam. The criterion is approximately evaluated using a model for a bunched beam.
Date: November 1, 1982
Creator: Channell, P.J.; Sessler, A.M. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Substructure of High-pT Jets at the LHC

Description: We study high-p{sub T} jets from QCD and from highly-boosted massive particles such as tops, W,Z and Higgs, and argue that infrared-safe observables can help reduce QCD backgrounds. Jets from QCD are characterized by different patterns of energy flow compared to the products of highly-boosted heavy particle decays, and we employ a variety of jet shapes, observables restricted to energy flow within a jet, to explore this difference. Results from Monte Carlo generators and arguments based on perturbation theory support the discriminating power of the shapes we refer to as planar flow and angularities. We emphasize that for massive jets, these and other observables can be analyzed perturbatively.
Date: July 2, 2008
Creator: Almeida, L.G.; Lee, S.J.; Perez, G.; Sterman, G.; Sung, I. & Virzi, J.
Partner: UNT Libraries Government Documents Department


Description: Recently a number of authors have suggested modifications of the Brueckner theory of nuclear matter so as to include hole-hole interactions, as well as particle-particle interactions. Iwamoto has demonstrated that in a perturbation theory calculation the inclusion of hole-hole interaction makes no change in the ground-state energy through second order. The singular two-body potential between nucleons makes it difficult, however, to conclude anything about the contribution of these terms in nuclear matter. The formal similarity between the equation of Iwamoto and the equation for the energy gap in nuclear matter, coupled with the fact that the energy gap is very small at normal density, indicates that the effect of hole-hole interactions is probably only a very small change in the ground-state energy of nuclear matter. It is the point of this note to show that this conclusion is in fact correct, the demonstration proceeding by use of the separation method for evaluating the energy of nuclear matter.
Date: April 4, 1960
Creator: Moszkowski, S.A. & Sessler, A.M.
Partner: UNT Libraries Government Documents Department


Description: Highly convenient rules are given for the general term in the time-independent perturbation-theory expansion for the self-energy operator of quantum statistical mechanics. The rules are derived by starting from the usual formalism involving time-dependent Green's functions. The well-known formulas for thermodynamic quantities in terms of the self-energy operator are included for completeness.
Date: December 17, 1962
Creator: Baym, Gordon & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department


Description: The ground-state wave function and energy of a finite system of interacting fermions are expanded in terms of multiple-particle excitations on an uncorrelated zero-order state. The resulting set of coupled equations constitutes a systematic variational generalization of Hartree-Fock theory. Comparison is made with many-body perturbation theory and it is shown that to any order the theory incorporates an infinite number of perturbation theory terms. Solutions of the equations for ground-state atomic systems are discussed and related to previous work using many-body perturbation theory. It is shown that the sums of perturbation terms necessary for convergence are automatically included in the equations for two-particle excitations. Application of the equations to open-shell atoms is described.
Date: July 1, 1963
Creator: Kelly, Hugh P. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Effect of salt identity on the phase diagram for a globularprotein in aqueous electrolyte solution

Description: Monte Carlo simulations are used to establish the potential of mean force between two globular proteins in an aqueous electrolyte solution. This potential includes nonelectrostatic contributions arising from dispersion forces first, between the globular proteins, and second, between ions in solution and between each ion and the globular protein. These latter contributions are missing from standard models. The potential of mean force, obtained from simulation, is fitted to an analytic equation. Using our analytic potential of mean force and Barker-Henderson perturbation theory, we obtain phase diagrams for lysozyme solutions that include stable and metastable fluid-fluid and solid-fluid phases when the electrolyte is 0.2 M NaSCN or NaI or NaCl. The nature of the electrolyte has a significant effect on the phase diagram.
Date: February 22, 2006
Creator: Bostrom, Mathias; Tavares, Frederico W.; Ninham, Barry W. & Prausnitz, John M.
Partner: UNT Libraries Government Documents Department

A general formula for Rayleigh-Schroedinger perturbation energy utilizing a power series expansion of the quantum mechanical Hamiltonian

Description: Perturbation theory has long been utilized by quantum chemists as a method for approximating solutions to the Schroedinger equation. Perturbation treatments represent a system`s energy as a power series in which each additional term further corrects the total energy; it is therefore convenient to have an explicit formula for the nth-order energy correction term. If all perturbations are collected into a single Hamiltonian operator, such a closed-form expression for the nth-order energy correction is well known; however, use of a single perturbed Hamiltonian often leads to divergent energy series, while superior convergence behavior is obtained by expanding the perturbed Hamiltonian in a power series. This report presents a closed-form expression for the nth-order energy correction obtained using Rayleigh-Schroedinger perturbation theory and a power series expansion of the Hamiltonian.
Date: February 1, 1997
Creator: Herbert, J.M.
Partner: UNT Libraries Government Documents Department

Unitarity-based techniques for one-loop calculations in QCD

Description: Perturbative QCD, and jet physics in particular, have matured sufficiently that rather than being merely subjects of experimental studies, they are now tools in the search for new physics. This role can be seen in the search for the top quark, as well as in recent speculations about the implications of supposed high-E{sub T} deviations of the inclusive-jet differential cross section at the Tevatron. One of the important challenges to both theorists and experimenters in coming years will be to hone jet physics as a tool in the quest for physics underlying the standard model. As such, it will be important to measurements of parameters of the theory or of non-perturbative quantities such as the parton distribution functions, as well as to searches for new physics at the LHC. Jet production, or jet production in association with identified photons or electroweak vector bosons, appears likely to provide the best information on the gluon distribution in the proton, and may also provide useful information on the strong coupling {alpha}{sub s}. In order to make use of these final states, the authors need a wider variety of higher-order calculations of matrix elements. Indeed, as the authors shall review, next-to-leading order calculations are in a certain sense the minimal useful ones. On the other hand, these calculations are quite difficult with conventional Feynman rules. In the following sections, the authors will discuss some of the techniques developed in recent years to simplify such calculations.
Date: June 1, 1996
Creator: Bern, Z.; Dixon, L. & Kosower, D.A.
Partner: UNT Libraries Government Documents Department

Perturbation of the periodic dispersion under beam crossing optics in LHC

Description: Beam crossing and separation schemes in the LHC interaction regions impose non-zero closed orbit in the low-{beta} triplets. The related perturbative dispersion is derived ; propagation, multi-crossing interference, perturbative effects around the ring are investigated and quantified. Horizontal and vertical compensation schemes are presented.
Date: May 1, 1997
Creator: Meot, F.
Partner: UNT Libraries Government Documents Department

Strings and supersymmetry as tools for perturbative QCD

Description: We review techniques simplifying the analytic calculation of one-loop QCD amplitudes with many external legs, for use in next-to-leading-order corrections to multi-jet processes. We explain how a supersymmetry-inspired organization works well in conjunction with other tools, namely the color and helicity decompositions of amplitudes, and the constraints imposed by perturbative unitarity and collinear singularities. String theory seems most useful as a heuristic guide. Using these techniques, the complete set of one-loop five-parton QCD amplitudes, as well as certain sequences of special helicity amplitudes with an arbitrary number of external gluons, have been obtained.
Date: July 1, 1995
Creator: Dixon, L.
Partner: UNT Libraries Government Documents Department


Description: The region of validity of our previously derived series expansion for the pressure of an electron-ion system in powers of the electron charge is investigated. For the case of Hydrogen, we both assess the radius of convergence of the series, as a function of the de Broglie density, and cross-compare the results with those from the spherical cellular model. These methods more or less agree in an understandable way, and indicate that the region of validity lies well inside the one-phase region. We are then in a position to combine the series results with our experiential knowledge and thus extend our assessment to general values of Z. Also, as is well known, there is a region of high density and low temperature where the pressure and the internal energy are almost independent of temperature. For this region we may, for each density, use the highest temperature for which that independence holds (to the desired accuracy) and thus extend the series results.
Date: September 1, 2000
Creator: BAKER, G. & JOHNSON, J.
Partner: UNT Libraries Government Documents Department

Time-Independent One-Speed Neutron Transport Equation with Anisotropic Scattering in Absorbing Media

Description: This report treats the time-independent, one-speed neutron transport equation with anisotropic scattering in absorbing media. For nuclear gain operators existence and uniqueness of solutions to the half-space and finite-slab problems are proved in L₂-space. The formulas needed for explicit calculations are derived by the use of perturbation theory techniques.
Date: June 1980
Creator: Hangelbroek, Rutger Jan
Partner: UNT Libraries Government Documents Department

Chiral perturbation theory for the Wilson lattice action

Description: The authors extend chiral perturbation theory to include linear dependence on the lattice spacing a for the Wilson action. The perturbation theory is written as a double expansion in the small quark mass m{sub q} and lattice spacing a. They present formulae for the mass and decay constant of a flavor-non-singlet meson in this scheme to order a and m{sub q}{sup 2}. The extension to the partially quenched theory is also described.
Date: January 25, 2002
Creator: Rupak, Gautam & Shoresh, Noam
Partner: UNT Libraries Government Documents Department

Gaugino mass without singlets

Description: In models with dynamical supersymmetry breaking in the hidden sector, the gaugino masses in the observable sector have been believed to be extremely suppressed (below 1 keV), unless there is a gauge singlet in the hidden sector with specific couplings to the observable sector gauge multiplets. We point out that there is a pure supergravity contribution to gaugino masses at the quantum level arising from the superconformal anomaly. Our results are valid to all orders in perturbation theory and are related to the ''exact'' beta functions for soft terms. There is also an anomaly contribution to the A terms proportional to the beta function of the corresponding Yukawa coupling. The gaugino masses are proportional to the corresponding gauge beta functions, and so do not satisfy the usual GUT relations.
Date: December 21, 1998
Creator: Giudice, Gian F.; Luty, Markus A.; Murayama, Hitoshi & Rattazzi, Riccardo
Partner: UNT Libraries Government Documents Department

Effective theory approach to unstable particles

Description: The authors present a novel treatment of resonant massive particles appearing as intermediate states in high energy collisions. The approach uses effective field theory methods to treat consistently the instability of the intermediate resonant state. As a result gauge invariance is respected in every step and calculations can in principle be extended to all orders in perturbation theory, the only practical limitation in going to higher orders being the standard difficulties related to multi-loop integrals. The authors believe that the longstanding problem related to the treatment of instability of particles is now solved.
Date: May 19, 2003
Creator: Zanderighi, Giulia
Partner: UNT Libraries Government Documents Department


Description: The dynamic behavior of boiling-water reactors for small perturbations was investigated in a systematic way. General expressions for the transfer functions associated with the individual feedback mechanisms were obtained for an arbitrary flux distribution, weighting function, and steam velocity distribution. Specific forms were derived in the case of a first power flux weighting, a uniform steam velocity distribution, and a sinusoidal flux distribution with an adjustable wave length. These forms were simplified and single time-constant transfer functions were obtained. The error involved in the lumped time-constant approximation was shown to be as large as 4 db in amplitude in certain feedback mechanisms. Theoretical results were applied to the experimental power-void transfer function obtained at Ramo-Wooldridge Research Laboratory, and to the EBWR transfer function. In the former case, the agreement was found to be reasonably good, but yet more systematic experimental data were needed to reach a definite conclusion as to the validity of the proposed model, which assumes a time lag associated with steam formation and a steam perturbation speed greater than the steady-state steam velocity. In the second application, the agreement between the experimental and calculated reactor responses was proved to be better than 5 db in amplitude and 10 deg in phase, in the entire frequency range from 0.01 to 100 rad/sec. (auth)
Date: October 1, 1960
Creator: Akcasu, A.Z.
Partner: UNT Libraries Government Documents Department


Description: The analysis of a reactor model that is thermally nonlinear is presented. The significant sources of feadback in the closed-loop model ane dilatational changes of the fuel due to axial expansion caused by temperature and metallurgical phase changes. Ths dynamics of this phenomenon has been represented on the Pace electronic analog com puter. The model was subjected to unusually large inputs of sinusoidal power and did not show any drastic tendencies toward being unstable. (auth)
Date: January 1, 1961
Creator: Bryant, L.T.; Carter, J.C. & Janicke, M.J.
Partner: UNT Libraries Government Documents Department


Description: The perturbation metheds used to obtain a relative plot of the electric field and the value of R/Q are described. A method involving radial pulling of dielectric and metallic beads is proposed for the R/Q measurement. The experimental data are shown to agree with the previously presented theoretical predictions. (D.C.W.)
Date: August 22, 1963
Creator: Hahn, H. & Halama, H.J.
Partner: UNT Libraries Government Documents Department

Quantum Monte Carlo study of the reaction: C1 + CH3OH -->CH2OH+ HCl

Description: A theoretical study is reported of the Cl + CH{sub 3}OH {yields} CH{sub 2}OH + HCl reaction based on the diffusion Monte Carlo (DMC) variant of the quantum Monte Carlo method. Using a DMC trial function constructed as a product of Hartree-Fock and correlation functions, we have computed the barrier height, heat of reaction, atomization energies and heats of formation of reagents and products. The DMC heat of reaction, atomization energies, and heats of formation are found to agree with experiment to within the error bounds of computation and experiment. Moller-Plesset second order perturbation theory (MP2) and density functional theory, the latter in the B3LYP generalized gradient approximation, are found to overestimate the experimental heat of reaction. Intrinsic reaction coordinate calculations at the MP2 level of theory demonstrate that the reaction is predominantly direct, i.e., proceeds without formation of intermediates, which is consistent with a recent molecular beam experiment. The reaction barrier as determined from MP2 calculations is found to be 2.24 kcal/mol and by DMC it is computed to be 2.39(49) kcal/mol.
Date: December 1, 2003
Creator: Kollias, A.C.; Couronne, O. & Lester Jr., W.A.
Partner: UNT Libraries Government Documents Department

Chromatic analysis and possible local chromatic correction in RHIC

Description: In this article we will answer the following questions for the RHIC polarized proton (p-p) and Au-Au run lattices: (1) what are the sources of second order chromaticities? (2) what is the dependence of second order chromaticity on the on-momentum {beta}-beat? (3) what is the dependence of second order chromaticity on {beta}* at IP6 and IP8? To answer these questions, we use the perturbation theory to numerically calculate the contributions of each quadrupole and sextupole to the first, second, and third order chromaticities. Possible local methods to reduce chromatic effects in RHIC ring are shortly discussed.
Date: March 28, 2011
Creator: Luo, Y.; Fischer, W.; Gu, X. & Trbojevic, D.
Partner: UNT Libraries Government Documents Department