40,039 research outputs found

### Collisional-dissociative recombination of electrons with molecular ions

Recombination rate calculation of electrons in plasma having ions of molecules with both repulsive and bound neutral state

### Naive time-reversal odd phenomena in semi-inclusive deep-inelastic scattering from light-cone constituent quark models

We present results for leading-twist azimuthal asymmetries in semi-inclusive
lepton-nucleon deep-inelastic scattering due to naively time-reversal odd
transverse-momentum dependent parton distribution functions from the light-cone
constituent quark model. We carefully discuss the range of applicability of the
model, especially with regard to positivity constraints and evolution effects.
We find good agreement with available experimental data from COMPASS and
HERMES, and present predictions to be tested in forthcoming experiments at
Jefferson Lab.Comment: 10 pages, 7 figures, discussion of evolution effects extended, to
appear in Phys.Rev.

### Two-Loop Virtual Corrections to Drell-Yan Production at order alpha_s alpha^3

The Drell-Yan mechanism for the production of lepton pairs is one of the most
basic processes for physics studies at hadron colliders. It is therefore
important to have accurate theoretical predictions. In this work we compute the
two-loop virtual mixed QCD x QED corrections to Drell-Yan production. We
evaluate the Feynman diagrams by decomposing the amplitudes into a set of known
master integrals and their coefficients, which allows us to derive an
analytical result. We also perform a detailed study of the ultraviolet and
infrared structure of the two-loop amplitude and the corresponding poles in
epsilon.Comment: 20 pages, 3 figure

### The Stability of an Isotropic Cosmological Singularity in Higher-Order Gravity

We study the stability of the isotropic vacuum Friedmann universe in gravity
theories with higher-order curvature terms of the form $(R_{ab}R^{ab})^{n}$
added to the Einstein-Hilbert Lagrangian of general relativity on approach to
an initial cosmological singularity. Earlier, we had shown that, when $% n=1$,
a special isotropic vacuum solution exists which behaves like the
radiation-dominated Friedmann universe and is stable to anisotropic and small
inhomogeneous perturbations of scalar, vector and tensor type. This is
completely different to the situation that holds in general relativity, where
an isotropic initial cosmological singularity is unstable in vacuum and under a
wide range of non-vacuum conditions. We show that when $n\neq 1$, although a
special isotropic vacuum solution found by Clifton and Barrow always exists, it
is no longer stable when the initial singularity is approached. We find the
particular stability conditions under the influence of tensor, vector, and
scalar perturbations for general $n$ for both solution branches. On approach to
the initial singularity, the isotropic vacuum solution with scale factor
$a(t)=t^{P_{-}/3}$ is found to be stable to tensor perturbations for $0.5<n<
1.1309$ and stable to vector perturbations for $0.861425 < n \leq 1$, but is
unstable as $t \to 0$ otherwise. The solution with scale factor
$a(t)=t^{P_{+}/3}$ is not relevant to the case of an initial singularity for
$n>1$ and is unstable as $t \to 0$ for all $n$ for each type of perturbation.Comment: 25 page

### Renormalization of the Vector Current in QED

It is commonly asserted that the electromagnetic current is conserved and
therefore is not renormalized. Within QED we show (a) that this statement is
false, (b) how to obtain the renormalization of the current to all orders of
perturbation theory, and (c) how to correctly define an electron number
operator. The current mixes with the four-divergence of the electromagnetic
field-strength tensor. The true electron number operator is the integral of the
time component of the electron number density, but only when the current
differs from the MSbar-renormalized current by a definite finite
renormalization. This happens in such a way that Gauss's law holds: the charge
operator is the surface integral of the electric field at infinity. The theorem
extends naturally to any gauge theory.Comment: 9 pages. Corresponds to published version (Phys. Rev. D), including
appendix about Weeks's parado

### Bending vibrational data accuracy study

Computer program for predicting structural bending vibrational dat

### Relative distributions of W's and Z's at low transverse momenta

Despite large uncertainties in the $W^\pm$ and $Z^0$ transverse momentum
($q_T$) distributions for q_T\lsim 10 GeV, the ratio of the distributions
varys little. The uncertainty in the ratio of $W$ to $Z$ $q_T$ distributions is
on the order of a few percent, independent of the details of the
nonperturbative parameterization.Comment: 13 pages in revtex, 5 postscript figures available upon request,
UIOWA-94-0

### A concept for a fuel efficient flight planning aid for general aviation

A core equation for estimation of fuel burn from path profile data was developed. This equation was used as a necessary ingredient in a dynamic program to define a fuel efficient flight path. The resultant algorithm is oriented toward use by general aviation. The pilot provides a description of the desired ground track, standard aircraft parameters, and weather at selected waypoints. The algorithm then derives the fuel efficient altitudes and velocities at the waypoints

### Cosmological models with flat spatial geometry

The imposition of symmetries or special geometric properties on submanifolds
is less restrictive than to impose them in the full space-time. Starting from
this idea, in this paper we study irrotational dust cosmological models in
which the geometry of the hypersurfaces generated by the fluid velocity is
flat, which supposes a relaxation of the restrictions imposed by the
Cosmological Principle. The method of study combines covariant and tetrad
methods that exploits the geometrical and physical properties of these models.
This procedure will allow us to determine all the space-times within this class
as well as to study their properties. Some important consequences and
applications of this study are also discussed.Comment: 12 pages, LaTeX2e, IOP style. To appear in Classical and Quantum
Gravit

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