478 research outputs found
Complete next-to-leading order calculation for pion production in nucleon-nucleon collisions at threshold
Based on a counting scheme that explicitly takes into account the large
momentum sqrt(M m_pi) characteristic for pion production in nucleon-nucleon
collisions we calculate all diagrams for the reaction NN --> NN pi at threshold
up to next-to-leading order. At this order there are no free parameters and the
size of the next-to-leading order contributions is in line with the expectation
from power counting. The sum of loop corrections at that order vanishes for the
process pp --> pp pi^0 at threshold. The total contribution at next-to-leading
order from loop diagrams that include the delta degree of freedom vanishes at
threshold in both reaction channels pp --> pp pi^0, pn pi^+.Comment: 9 pages, 4 figure
Die Schweizer Fälle von Splenohepatomegalie (Niemann-Pick) Ein Beitrag zur genetischen Abgrenzung der Phospatid-Lipoidosen
In this paper a counterpart is given to the data of our investigation about the incidence of infantile amaurotic idiocy (Tay-Sachs) in Switzerland, published here in 1954. The term > is rather unclear and had to be critisised by Letterer. The diagnose of all lipidosis is more difficult than of any other genetic character, as neither a thorough clinical and histological examination nor the chemical analysis of the brain and the big abdominal organs (spleen, liver etc.) is sufficient; it ought always to be completed by the modern histochemical method at least if we want to separate the M. Niemann-Pick from the M. Tay-Sachs. The quarrel between the > and the > concerning the independence of these two phosphatid-lipidosis does not seem to be ended definitely by chemical analysis of the affected organs. Undoubtfully these two very similar diseases must have many common traits in their pathogenesis. This does not mean, however, that they do not depend on 2 different genes, may be working at the same pheno-genetical chain (Klenk), perhaps there is a pseudo-allely, which as a matter of fact can hardly ever become proved in men. This author showed that the M. Niemann-Pick is regularly characterised by a high percentage of sphingomyelin whilst in the M. Tay-Sachs the gangliosids prevail. But recently this difference is regarded to hold only quantitatively. Therefore we have to look for genetical proofs of the independence of these two lipidosis. An observation of van Bogaert in his famous pedigree of the family Mi. and another less convincing of Driessen show that among the children of the same parents cases of both these lipidosis can appear. Since both these families are of Russian respectively Polish-Jewish origin, coming from a not very big area in which these lipidosis were found relatively very often, these two instances also could be explained by mere coincidence. Our Swiss cases which all happened in families of non Jewish origin do not show sibs the one of whom had M. Tay-Sachs and the other M. Niemann-Pick, nor were combinations of both lipidosis observed. Unfortunately excepted one, namely that of Baumann, Scheidegger & Klenk, none of our cases has been examined with all the modern methods. These 3 specialists established the theory that we deal in the M. Niemann-Pick and M. Tay-Sachs with specific cellular dystrophies and not an overloading of the blood with certain lipids, as was supposed by Pick: For, all values of blood-chemistry, principally of the total amount of fatty acids as well as of cholesterol and of anorganical phospor used to be normal in the serum of those patients. The data published by U. Pfändler could become disguised as rare exceptions or consequences of alterations in a no more fresh serum. His conclusions with regard to the pathogenesis and the way of hereditary transmission cannot become adopted neither for the adult, nor for the infantile forms of Niemann-Pick. The facts found by us and others clearly speak in favour of a simple-recessive transmission, at least for the infantile forms of M. Niemann-Pick, the same has been proved by us for M. Tay-Sachs. Videbaeks pedigree with parents of the 2 children with M. Niemann-Pic being first cousins, is not to be interpreted otherwise. Of our Swiss families with M. Niemann-Pick 3 contain each 2 fraternal and 3 isolated cases; parental consanguinity was found 4 times but not very close though 5 of these families come from isolates. The gene concerned therefore cannot be too rare. Like the other authors we did not observe secondary cases in collateral lines. The oldest of our patients reached the age of 3½ years. There is no higher incidence of other hereditary diseases, especially with regard to metabolism, in our 6 Swiss families. From the clinical standpoint there is to mention that 4 of our 5 cases studied in detail showed the typical red spot in the region of the macula retinae; one case showed a complete atrophia nervi optici and another an atrophy of the temporal parts of the papilla nervi optici. In most cases a demencia or > was noted, a fact which suggests the participation of the brain in the processus of the specific thesaurismosis. Unfortunately, however, the brain has but once been examined with the modern histochemical method
Über 27 Sippen mit infantiler amaurotischer Idiotie (Tay-Sachs)
This paper is based on 45 cases in 27 families, all of which have been studied in Children Hospitals. In Switzerland almost all cases of infantile amaurotic idiocy (Tay-Sachs) have probably been collected, so that the stated 13 primary and 14 secondary cases may allow an estimation of the frequency of this character, which seems to oscillate temporarily. In the last 10 years no new cases have been observed. All 24 autochthonus Swiss cases are from non-Jewish, mostly rural origin, in which Eastern Jews are not to be supposed as ascendants. Our in all 27 families with TS make Slome's statistic of Jewish and non-Jewish cases in literature much more significant; the incidence of parental consanguinity is, as a matter of fact, nearly twice as high in families with non-Jewish origin. There is no evidence of a milder and longer course of TS in non-Jewish families. The mode of inheritance is, according to Slome, monohybrid autosomal recessive, though in remarkably many sibships there is an accumulation of cases. The reduction method, however, gives a percentage of 28,3 ± 6,2, coming quite near to the expectation of the Mendelian quarter. The penetrance of the character is total, the expressivity generally very equal, with only a few deviations from the well—known clinical picture of TS. The interfamiliar and intrafamiliar variability therefore is small. In not even one of the families studied have there been found other forms of lipoidosis, principally no cases of splenohepatomegalia Niemann-Pick. All available respective cases in Switzerland have been collected by the present author and will soon be published in these Acta. In none of these families with M. Niemann-Pick have cases of M. Tay-Sachs been seen. This fact is liable to prove that these clinically and anatomically very similar conditions derive from independent i. e. different mutations. Modifying genes may account for the incidence of sibships in which all or almost all children died from M. TS. Environmental influences do not seem to favour its manifestations. If in the newer literature from the U.S.A. the Jewish cases of M. TS are still prevalent and if, as we heard, the concomitant manifestations occur fairly often in Israel, the origin may be sought in one at least 200 years old respective mutation in the Jewish population of a relatively restricted White-Russian er
Towards a field theoretic understanding of NN->NNpi
We study the production amplitude for the reaction NN->NNpi up to
next--to--leading order in chiral perturbation theory using a counting scheme
that takes into account the large scale introduced by the initial momentum. In
particular we investigate a subtlety that arises once the leading loop
contributions are convoluted with the NN wavefunctions as demanded by the
non--perturbative nature of the NN interaction. We show how to properly
identify the irreducible contribution of loop diagrams in such type of
reaction. The net effect of the inclusion of all next-to-leading order loops is
to enhance the leading rescattering amplitude by a factor of 4/3, bringing its
contribution to the cross section for pp->dpi+ close to the experimental value.Comment: 15 Pages, 5 Figure
Toy Model for Pion Production II: The role of three-particle singularities
The influence of three-particle breakup singularities on s-wave meson
production in nucleon-nucleon collisions is studied within the distorted wave
Born approximation. This study is based on a simple scalar model for the
two-nucleon interaction and the production mechanism. An algorithm for the
exact numerical treatment of the inherent three-body cuts, together with its
straightforward implementation is presented. It is also shown that two
often-used approximations to avoid the calculation of the three-body breakup
are not justified. The possible impact on pion production observables is
discussed.Comment: 14 pages, 6 figure
Spin partners of the and revisited
We study the implications of the heavy-quark spin symmetry for the possible
spin partners of the exotic states and in the
spectrum of bottomonium. We formulate and solve numerically the coupled-channel
equations for the states that allow for a dynamical generation of these
states as hadronic molecules. The force includes short-range contact terms and
the one-pion exchange potential, both treated fully nonperturbatively. The
strength of the potential at leading order is fixed completely by the pole
positions of the states such that the mass and the most prominent
contributions to the width of the isovector heavy-quark spin partner states
with the quantum numbers () come out as predictions.
Since the accuracy of the present experimental data does not allow one to fix
the pole positions of the 's reliably enough, we also study the pole
trajectories of their spin partner states as functions of the binding
energies. It is shown that, once the heavy-quark spin symmetry is broken by
means of the physical and masses, especially the pion tensor force
has a significant impact on the location of the partner states clearly
demonstrating the need of a coupled-channel treatment of pion dynamics to
understand the spin multiplet pattern of hadronic molecules.Comment: 21 pages, 5 figures, 1 tabl
Gauge invariance in the presence of a cutoff
We use the method of gauging equations to construct the electromagnetic
current operator for the two-nucleon system in a theory with a finite cutoff.
The employed formulation ensures that the two-nucleon T-matrix and
corresponding five-point function, in the cutoff theory, are identical to the
ones formally defined by a reference theory without a cutoff. A feature of our
approach is that it effectively introduces a cutoff into the reference theory
in a way that maintains the long-range part of the exchange current operator;
for applications to effective field theory (EFT), this property is usually
sufficient to guarantee the predictive power of the resulting cutoff theory. In
addition, our approach leads to Ward-Takahashi (WT) identities that are linear
in the interactions.
From the point of view of EFT's where such a WT identity is satisfied in the
reference theory, this ensures that gauge invariance in the cutoff theory is
maintained order by order in the expansion.Comment: 15 pages, 2 figure
Toy Model for Pion Production in Nucleon-Nucleon Collisions
We develop a toy model of pion production in nucleon-nucleon collisions that
reproduces some of the features of the chiral Lagrangian calculations. We
calculate the production amplitude and examine some common approximations.Comment: 9 pages, 3 figure
Plasmon-graviton conversion in a magnetic field in TeV-scale gravity
Kaluza-Klein (KK) gravitons emission rates due to plasmon-graviton conversion
in magnetic field are computed within the ADD model of TeV-scale gravity.
Plasma is described in the kinetic approach as the system of charged particles
and Maxwell field both confined on the brane. Interaction with multidimensional
gravity living in the bulk with compact extra dimensions is introduced
within the linearized theory. Plasma collective effects enter through the
two-point correlation function of the fluctuations of the energy-momentum
tensor. The estimate for magnetic stars is presented leading to the lower limit
of the D-dimensional Plank mass.Comment: Submitted to Proceedings of "RusGrav-14" International Conference,
27.06-02.07 2011, Ulyanovks, Russi
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