Lowell S. Brown

Bio: Lowell S. Brown is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Electron & Quantum field theory. The author has an hindex of 36, co-authored 113 publications receiving 5931 citations. Previous affiliations of Lowell S. Brown include University of Washington & Fermilab.

Geonium theory: Physics of a single electron or ion in a Penning trap

Abstract: A single charged particle in a Penning trap is a bound system that rivals the hydrogen atom in its simplicity and provides similar opportunities to calculate and measure physical quantities at very high precision. We review the theory of this bound system, beginning with the simple first-order orbits and progressively dealing with small corrections which must be considered owing to the experimental precision that is being achieved. Much of the discussion will also be useful for experiments with more particles in the trap, and several of the mathematical techniques have a wider applicability.

Solar fusion cross sections

Abstract: We review and analyze the available information on the nuclear-fusion cross sections that are most important for solar energy generation and solar neutrino production. We provide best values for the low-energy cross-section factors and, wherever possible, estimates of the uncertainties. We also describe the most important experiments and calculations that are required in order to improve our knowledge of solar fusion rates.

Interaction of Intense Laser Beams with Electrons

Abstract: The interaction of an intense coherent photon beam with free electrons is discussed. The photon beam is treated as a classical external electromagnetic field. The discussion is exact within the approximation of neglecting radiative corrections and the restriction to the case of a plane-wave field or arbitrary spectral composition and polarization properties. The scattering of a single photon out of a monochromatic beam by an isolated free electron is considered in detail. The cross sections corresponding to the scattering of the various harmonics of the incident beam are evaluated. These cross sections display a complicated dependence upon the intensity of the incident beam, at least for very intense beams. It is found that a mass change induced in the electron by the external field shifts the wavelength of the scattered photons by an amount depending on the intensity of the incident beam. Other processes involving free electrons in the final state are also considered briefly, and a discussion of the magnitude of the effects depending upon the intensity is given. Two Appendices are concerned with the electron Green's function and the vacuum-vacuum transformation function in the presence of a plane-wave field. In the course of the discussion of the latter, the problem of the correct definition of the vacuum current is encountered, and it is shown that a very careful procedure is necessary to obtain a covariant result.

Vacuum Stress between Conducting Plates: An Image Solution

Abstract: The zero-point fluctuations of the electromagnetic field give rise to an attractive force between two perfectly conducting parallel plates, the Casimir force. We discuss the structure of the electromagnetic stress-energy tensor in the region between the plates for finite temperatures as well as for the zero-temperature limit, and we describe the relationship of its components to the thermodynamic variables of the radiation field. The stress-energy tensor is defined so that infinite quantities never appear, and it is explicitly computed with the aid of an image-source construction of the Green's function. The finite-temperature case involves both an infinite set of spatial images and an infinite sum of temperature-dependent images.

Energy Correlations in Electron-Positron Annihilation: Testing Quantum Chromodynamics

Abstract: An experimental measure is presented for a precise test of quantum chromodynamics. This measure involves the asymmetry in the energy-weighted opening angles of the jets of hadrons produced in the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{hadrons}$ at energy $W$. It is special for several reasons: It is reliably calculable in asymptotically free perturbation theory; it has rapidly vanishing (order $\frac{1}{{W}^{2}}$) corrections due to nonperturbative confinement effects; and it is straightforward to determine experimentally.

PYTHIA 6.4 Physics and Manual

Abstract: The Pythia program can be used to generate high-energy-physics ''events'', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

Reaction-rate theory: fifty years after Kramers

Abstract: The calculation of rate coefficients is a discipline of nonlinear science of importance to much of physics, chemistry, engineering, and biology. Fifty years after Kramers' seminal paper on thermally activated barrier crossing, the authors report, extend, and interpret much of our current understanding relating to theories of noise-activated escape, for which many of the notable contributions are originating from the communities both of physics and of physical chemistry. Theoretical as well as numerical approaches are discussed for single- and many-dimensional metastable systems (including fields) in gases and condensed phases. The role of many-dimensional transition-state theory is contrasted with Kramers' reaction-rate theory for moderate-to-strong friction; the authors emphasize the physical situation and the close connection between unimolecular rate theory and Kramers' work for weakly damped systems. The rate theory accounting for memory friction is presented, together with a unifying theoretical approach which covers the whole regime of weak-to-moderate-to-strong friction on the same basis (turnover theory). The peculiarities of noise-activated escape in a variety of physically different metastable potential configurations is elucidated in terms of the mean-first-passage-time technique. Moreover, the role and the complexity of escape in driven systems exhibiting possibly multiple, metastable stationary nonequilibrium states is identified. At lower temperatures, quantum tunneling effects start to dominate the rate mechanism. The early quantum approaches as well as the latest quantum versions of Kramers' theory are discussed, thereby providing a description of dissipative escape events at all temperatures. In addition, an attempt is made to discuss prominent experimental work as it relates to Kramers' reaction-rate theory and to indicate the most important areas for future research in theory and experiment.

Theory of Cosmological Perturbations

Abstract: We present in a manifestly gauge-invariant form the theory of classical linear gravitational perturbations in part I, and a quantum theory of cosmological perturbations in part II. Part I includes applications to several important examples arising in cosmology: a univese dominated by hydrodynamical matter, a universe filled with scalar-field matter, and higher-derivative theories of gravity. The growth rates of perturbations are calculated analytically in most interesting cases. The analysis is applied to study the evolution of fluctuations in inflationary universe models. Part II includes a unified description of the quantum generation and evolution of inhomogeneities about a classial Friedmann background. The method is based on standard canonical quantization of the action for cosmological perturbations which has been reduced to an expression in terms of a single gauge-invariant variable. The spectrum of density perturbations originating in quantum fluctuations is calculated in universe with hydrodynamical matter, in inflationary universe models with scalar-field matter, and in higher-derivative theories of gravity. The gauge-invariant theory of classical and quantized cosmological perturbations developed in parts I and II is applied in part III to several interesting physical problems. It allows a simple derivation of the relation between temperature anistropes in the cosmic microwave background. radiation and the gauge-invariant potential for metric perturbations. The generation and evolution of gravitational waves is studied. As another example, a simple analysis of entropy perturbations and non-scale-invariant spectra in inflationary universe models is presented. The gauge-invariant theory of cosmological perturbations also allows a consistent and gauge-invariant definition of statistical fluctuations.