47 research outputs found
Dispersive Approach to Chiral Perturbation Theory
We generalise the reconstruction theorem of Stern, Sazdjian, and Fuchs based
on the dispersion relations to the case of the (2 -> 2) scattering of all the
pseudoscalar octet mesons (pi, K, eta). We formulate it in a general way and
include also a discussion of the assumptions of the theorem. It is used to
obtain the amplitudes of all such processes in the isospin limit to the
one-loop order (and can be straightforwardly extended to two loops)
independently on the particular power-counting scheme of the chiral
perturbation theory in question. The results in this general form are
presented.Comment: 25 pages, 1 figure; added one appendix and correction of typo
Dispersive construction of two-loop P->3\pi (P=K,\eta) amplitudes
The branching ratio of the \eta->3\pi decay is an important source of
information on the value of the quark mass ratio 1/R=(m_d-m_u)/(m_s-\hat m).
Furthermore, isospin breaking effects in the decays K->3\pi provide information
on the pion scattering lengths. The cusp effect in the K->3\pi decays is
presently being analyzed by the NA48 and KTeV experiments. From the theoretical
point of view, these processes have been studied by different methods. We
propose a unified and relativistic treatment relying on very general
principles, unitarity, analyticity and crossing symmetry, combined with chiral
counting, in order to construct model-independent representations of the
corresponding amplitudes that are valid at two loops. A general description of
the procedure is given and is illustrated in the case of the \eta decay
amplitude in the leading order in the isospin breaking.Comment: Talk given at "International Workshop on Effective Field Theories:
from the pion to the upsilon", February 2009, Valencia, Spain. 8 pages. PoS
styl
Knowledge support of simulation model reuse
This describes the knowledge support for engineering design based on virtual modelling and simulation. These are the results of the EC Clockwork project. A typical and important step in the development of a simulation model is the phase of reusing. Virtual modelling and simulation often use the components of previous models. The usual problem is that the only remaining part of the previous simulation models is the model itself. However, a large amount of knowledge and intermediate models have been used, developed and then lost. A special methodology and special tools have therefore been developed on support of storing, retrieving and reusing the knowledge from previous simulation models. The knowledge support includes informal knowledge, formal knowledge and intermediate engineering models. This paper describes the overall methodology and tools, using the example of developing a simulation model of Trijoint, a new machine tool
The melanoma-associated antigen 1 (MAGEA1) protein stimulates the E3 ubiquitin-ligase activity of TRIM31 within a TRIM31-MAGEA1-NSE4 complex
The MAGE (Melanoma-associated antigen) protein family members are structurally related to each other by a MAGEhomology domain comprised of 2 winged helix motifs WH/A and WH/B. This family specifically evolved in placental mammals although single homologs designated NSE3 (non-SMC element) exist in most eukaryotes. NSE3, together with its partner proteins NSE1 and NSE4 form a tight subcomplex of the structural maintenance of chromosomes SMC5–6 complex. Previously, we showed that interactions of the WH/B motif of the MAGE proteins with their NSE4/EID partners are evolutionarily conserved (including the MAGEA1-NSE4 interaction). In contrast, the interaction of the WH/A motif of NSE3 with NSE1 diverged in the MAGE paralogs. We hypothesized that the MAGE paralogs acquired new RING-finger containing partners through their evolution and form MAGE complexes reminiscent of NSE1-NSE3-NSE4 trimers. In this work, we employed the yeast 2-hybrid system to screen a human RING-finger protein library against several MAGE baits. We identified a number of potential MAGE-RING interactions and confirmed several of them (MDM4, PCGF6, RNF166, TRAF6, TRIM8, TRIM31, TRIM41) in co-immunoprecipitation experiments. Among these MAGE-RING pairs, we chose to examine MAGEA1-TRIM31 in detail and showed that both WH/A and WH/B motifs of MAGEA1 bind to the coiled-coil domain of TRIM31 and that MAGEA1 interaction stimulates TRIM31 ubiquitin-ligase activity. In addition, TRIM31 directly binds to NSE4, suggesting the existence of a TRIM31-MAGEA1-NSE4 complex reminiscent of the NSE1-NSE3-NSE4 trimer. These results suggest that MAGEA1 functions as a co-factor of TRIM31 ubiquitin-ligase and that the TRIM31-MAGEA1-NSE4 complex may have evolved from an ancestral NSE1-NSE3-NSE4 complex
Convergence properties of decays in chiral perturbation theory
Theoretical efforts to describe and explain the decays reach
far back in time. Even today, the convergence of the decay widths and some of
the Dalitz plot parameters seems problematic in low energy QCD. In the
framework of resummed CHPT, we explore the question of compatibility of
experimental data with a reasonable convergence of a carefully defined chiral
series, where NNLO remainders are assumed to be small. By treating the
uncertainties in the higher orders statistically, we numerically generate a
large set of theoretical predictions, which are then confronted with
experimental information. In the case of the decay widths, the experimental
values can be reconstructed for a reasonable range of the free parameters and
thus no tension is observed, in spite of what some of the traditional
calculations suggest. The Dalitz plot parameters and can be described
very well too. When the parameters and are concerned, we find a
mild tension for the whole range of the free parameters, at less than 2
C.L. This can be interpreted in two ways - either some of the higher order
corrections are indeed unexpectedly large or there is a specific configuration
of the remainders, which is, however, not completely improbable. Also, the
distribution of the theoretical uncertainties is found to be significantly
non-gaussian, so the consistency cannot be simply judged by the 1 error
bars.Comment: 57 pages, 5 figure
Two-loop representations of low-energy pion form factors and pi-pi scattering phases in the presence of isospin breaking
Dispersive representations of the pi-pi scattering amplitudes and pion form
factors, valid at two-loop accuracy in the low-energy expansion, are
constructed in the presence of isospin-breaking effects induced by the
difference between the charged and neutral pion masses. Analytical expressions
for the corresponding phases of the scalar and vector pion form factors are
computed. It is shown that each of these phases consists of the sum of a
"universal" part and a form-factor dependent contribution. The first one is
entirely determined in terms of the pi-pi scattering amplitudes alone, and
reduces to the phase satisfying Watson's theorem in the isospin limit. The
second one can be sizeable, although it vanishes in the same limit. The
dependence of these isospin corrections with respect to the parameters of the
subthreshold expansion of the pi-pi amplitude is studied, and an equivalent
representation in terms of the S-wave scattering lengths is also briefly
presented and discussed. In addition, partially analytical expressions for the
two-loop form factors and pi-pi scattering amplitudes in the presence of
isospin breaking are provided.Comment: 57 pages, 12 figure
The Molecular Identification of Organic Compounds in the Atmosphere: State of the Art and Challenges
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Knowledge supported conceptual control design methodology of mechatronic systems
Combining gameplay and narrative techniques to enhance the user experience of viewing galleries
Owing to high production costs, the reuse of film and television broadcast content in spin-off merchandise is often necessary. Games and DVDs are popular spin-off products, and when aimed at children in particular, they often include viewing galleries in which a user can browse scenes from the original broadcast. This is a highly economic form of literal content reuse, since it minimizes authoring additional resources. There is also the potential to improve the experience of users as they interact with content in viewing galleries. Ways to do so become apparent by examining the principles of both narrative and gameplay which underpin the original broadcasts and their spin-offs. Scene-Driver is a narrative-driven game architecture that enables the user, via a domino-like interface, to select and order content. This mechanism creates an engaging means for a user to interact with existing broadcast content. Three versions of the Scene-Driver approach to content reuse have been developed, each using content from a children’s animated television series called Tiny Planets. Four studies to evaluate the Scene-Driver game have been done, all with positive results