300 research outputs found
Probing generalized parton distributions in pi N -> l+ l- N
We study the exclusive reactions pi- p -> l+ l- n and pi+ n -> l+ l- p$ in
view of possible future experiments with high-intensity pion beams. For large
invariant mass of the lepton pair l+ l- and small squared momentum transfer to
the nucleon these are hard-scattering processes providing access to generalized
parton distributions. We estimate the cross section for these reactions,
explore their connection with the pion form factor, and discuss the role they
can play in improving our understanding of the relevant reaction mechanisms.Comment: 13 pages, 5 figure
Computational Nuclear Physics and Post Hartree-Fock Methods
We present a computational approach to infinite nuclear matter employing
Hartree-Fock theory, many-body perturbation theory and coupled cluster theory.
These lectures are closely linked with those of chapters 9, 10 and 11 and serve
as input for the correlation functions employed in Monte Carlo calculations in
chapter 9, the in-medium similarity renormalization group theory of dense
fermionic systems of chapter 10 and the Green's function approach in chapter
11. We provide extensive code examples and benchmark calculations, allowing
thereby an eventual reader to start writing her/his own codes. We start with an
object-oriented serial code and end with discussions on strategies for porting
the code to present and planned high-performance computing facilities.Comment: 82 pages, to appear in Lecture Notes in Physics (Springer), "An
advanced course in computational nuclear physics: Bridging the scales from
quarks to neutron stars", M. Hjorth-Jensen, M. P. Lombardo, U. van Kolck,
Editor
Perturbative QCD and factorization of coherent pion photoproduction on the deuteron
We analyze the predictions of perturbative QCD for pion photoproduction on
the deuteron, gamma D -> pi^0 D, at large momentum transfer using the reduced
amplitude formalism. The cluster decomposition of the deuteron wave function at
small binding only allows the nuclear coherent process to proceed if each
nucleon absorbs an equal fraction of the overall momentum transfer.
Furthermore, each nucleon must scatter while remaining close to its mass shell.
Thus the nuclear photoproduction amplitude, M_{gamma D -> pi^0 D}(u,t),
factorizes as a product of three factors: (1) the nucleon photoproduction
amplitude, M_{gamma N_1 -> pi^0 N_1}(u/4,t/4), at half of the overall momentum
transfer, (2) a nucleon form factor, F_{N_2}(t/4), at half the overall momentum
transfer, and (3) the reduced deuteron form factor, f_d(t), which according to
perturbative QCD, has the same monopole falloff as a meson form factor. A
comparison with the recent JLAB data for gamma D -> pi^0 D of Meekins et al.
[Phys. Rev. C 60, 052201 (1999)] and the available gamma p -> pi^0 p data shows
good agreement between the perturbative QCD prediction and experiment over a
large range of momentum transfers and center of mass angles. The reduced
amplitude prediction is consistent with the constituent counting rule, p^11_T
M_{gamma D -> pi^0 D} -> F(theta_cm), at large momentum transfer. This is found
to be consistent with measurements for photon lab energies E_gamma > 3 GeV at
theta_cm=90 degrees and \elab > 10 GeV at 136 degrees.Comment: RevTeX 3.1, 17 pages, 6 figures; v2: incorporates minor changes as
version accepted by Phys Rev
Low energy collective modes, Ginzburg-Landau theory, and pseudogap behavior in superconductors with long-range pairing interactions
We study the superconducting instability in systems with long but finite
ranged, attractive, pairing interactions. We show that such long-ranged
superconductors exhibit a new class of fluctuations in which the internal
structure of the Cooper pair wave function is soft, and thus lead to
"pseudogap" behavior in which the actual transition temperature is greatly
depressed from its mean field value. These fluctuations are {\it not} phase
fluctuations of the standard superconducting order parameter, and lead to a
highly unusual Ginzburg-Landau description. We suggest that the crossover
between the BCS limit of a short-ranged attraction and our problem is of
interest in the context of superconductivity in the underdoped cuprates.Comment: 20 pages with one embedded ps figure. Minor revisions to the text and
references. Final version to appear in PRB on Nov. 1st, 200
Avalanche dynamics, surface roughening and self-organized criticality - experiments on a 3 dimensional pile of rice
We present a two-dimensional system which exhibits features of self-organized
criticality. The avalanches which occur on the surface of a pile of rice are
found to exhibit finite size scaling in their probability distribution. The
critical exponents are = 1.21(2) for the avalanche size distribution and
= 1.99(2) for the cut-off size. Furthermore the geometry of the avalanches
is studied leading to a fractal dimension of the active sites of =
1.58(2). Using a set of scaling relations, we can calculate the roughness
exponent = 0.41(3) and the dynamic exponent = 1.56(8). This result is compared with that obtained from a power
spectrum analysis of the surface roughness, which yields = 0.42(3) and
= 1.5(1) in excellent agreement with those obtained from the scaling
relations.Comment: 7 pages, 8 figures, accepted for publication in PR
Method to compute the stress-energy tensor for the massless spin 1/2 field in a general static spherically symmetric spacetime
A method for computing the stress-energy tensor for the quantized, massless,
spin 1/2 field in a general static spherically symmetric spacetime is
presented. The field can be in a zero temperature state or a non-zero
temperature thermal state. An expression for the full renormalized
stress-energy tensor is derived. It consists of a sum of two tensors both of
which are conserved. One tensor is written in terms of the modes of the
quantized field and has zero trace. In most cases it must be computed
numerically. The other tensor does not explicitly depend on the modes and has a
trace equal to the trace anomaly. It can be used as an analytic approximation
for the stress-energy tensor and is equivalent to other approximations that
have been made for the stress-energy tensor of the massless spin 1/2 field in
static spherically symmetric spacetimes.Comment: 34 pages, no figure
EC85-219 1985 Nebraska Swine Report
This 1985 Nebraska Swine Report was prepared by the staff in Animal Science and cooperating departments for use in the Extension and Teaching programs at the University of Nebraska-Lincoln. Authors from the following areas contributed to this publication: Swine Nutrition, swine diseases, pathology, economics, engineering, swine breeding, meats, agronomy, and diagnostic laboratory. It covers the following areas: breeding, disease control, feeding, nutrition, economics, housing and meats
The effectiveness of green advertisements : combining ad-based and consumer-based research
Efeito de dietas contendo plasma sanguíneo desidratado sobre características microbiológicas, imunológicas e histológicas de leitões leves ao desmame
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