219 research outputs found
Sigma pole position and errors of a once and twice subtracted dispersive analysis of pi-pi scattering data
We show how the new precise data on kaon decays together with forward
dispersion relations, sum rules and once- and twice-subtracted
Roy's equations allow for a precise determination of the sigma meson pole
position. We present a comparison and a study of the different sources of
uncertainties when using either once- or twice-subtracted Roy's equations to
analyze the data. Finally we present a preliminary determination of the sigma
pole from the constrained dispersive data analysis.Comment: 4 pages, 6 figures. Contribution to the proceedings of the QCD08 14th
International QCD Conference. 7-12th July 2008 Montpellier (France); one
reference removed, changed errors in Eqs (4), (5) and (7
New dispersion relations in the description of scattering amplitudes
We present a set of once subtracted dispersion relations which implement
crossing symmetry conditions for the scattering amplitudes below 1
GeV. We compare and discuss the results obtained for the once and twice
subtracted dispersion relations, known as Roy's equations, for three
partial JI waves, S0, P and S2. We also show that once subtracted dispersion
relations provide a stringent test of crossing and analyticity for
partial wave amplitudes, remarkably precise in the 400 to 1.1 GeV region, where
the resulting uncertainties are significantly smaller than those coming from
standard Roy's equations, given the same input.Comment: 8 pages, 2 figures, to appear in the Proceedings of the Meson 2008
conference, June 6-10, 2008, Cracow, Polan
Histological and mutational profile of diffuse gastric cancer: current knowledge and future challenges
Gastric cancer (GC) pathogenesis is complex and heterogeneous, reflecting morphological, molecular and genetic diversity. Diffuse gastric cancer (DGC) and intestinal gastric cancer (IGC) are the major histological types. GC may be sporadic or hereditary; sporadic GC is related to environmental and genetic low-risk factors and hereditary GC is caused by inherited high-risk mutations, so far identified only for the diffuse histotype. DGC phenotypic heterogeneity challenges the current understanding of molecular mechanisms underlying carcinogenesis. The definition of a DGC-specific mutational profile remains controversial, possibly reflecting the heterogeneity of DGC-related histological subtypes [signet-ring cell carcinoma (SRCC) and poorly cohesive carcinoma not otherwise specified (PCC-NOS)]. Indeed, DGC and DGC-related subtypes may present specific mutational profiles underlying the particularly aggressive behaviour and dismal prognosis of DGC vs IGC and PCC-NOS vs SRCC. In this systematic review, we revised the histological presentations, molecular classifications and approved therapies for gastric cancer, with a focus on DGC. We then analysed results from the most relevant studies, reporting mutational analysis data specifying mutational frequencies, and their relationship with DGC and IGC histological types, and with specific DGC subtypes (SRCC and PCC-NOS). We aimed at identifying histology-associated mutational profiles with an emphasis in DGC and its subtypes (DGC vs IGC; sporadic vs hereditary DGC; and SRCC vs PCC-NOS). We further used these mutational profiles to identify the most commonly affected molecular pathways and biological functions, and explored the clinical trials directed specifically to patients with DGC. This systematic analysis is expected to expose a DGC-specific molecular profile and shed light into potential targets for therapeutic intervention, which are currently missing.The authors acknowledge the support of the National Infrastructure ‘GenomePT’ – National Laboratory for Genome Sequencing and Analysis (POCI-01-0145-FEDER-022184). J.G-P acknowledges the support of Faculty of Medicine from University of Porto, specifically by the Doctoral Programme in Biomedicine and the Solve-RD Project (H2020-SC1-2017-Single-Stage-RTD) for his PhD fellowship. R.B-M. acknowledges the support of Institute of Biomedical Sciences Abel Salazar from University of Porto, specifically by the Doctoral Programme BiotechHealth and the FCT – Fundação para a Ciência e a Tecnologia for her PhD fellowship (ref. SFRH/BD/145132/2019). This research and its authors were funded by FEDER – Fundo Europeu de Desenvolvimento Regional funds through the COMPETE 2020 – Operacional Programme for Competitiveness and Internationalization (POCI), Portugal 2020, and by Portuguese funds through FCT – Fundação para a Ciência e a Tecnologia/Ministério da Ciência, Tecnologia e Inovação in the framework of the project ‘Institute for Research and Innovation in Health Sciences’ (POCI-01-0145-FEDER-007274). This work was also financed by the projects NORTE-01-0145-FEDER-000003 (DOCnet) and NORTE-01-0145-FEDER-000029 (CANCER) – supported by Norte Portugal Regional Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF) – project POCI-01-0145-FEDER-016390 (CancelStem) and PTDC/BTM-TEC/30164/2017 (3DChroMe), funded by ERDF, POCI and FCT
Study of a possible S=+1 dynamically generated baryonic resonance
Starting from the lowest order chiral Lagrangian for the interaction of the
baryon decuplet with the octet of pseudoscalar mesons we find an attractive
interaction in the channel with L=0 and I=1, while the interaction
is repulsive for I=2. The attractive interaction leads to a pole in the second
Riemann sheet of the complex plane and manifests itself in a large strength of
the scattering amplitude close to the threshold, which is
not the case for I=2. However, we also make a study of uncertainties in the
model and conclude that the existence of this pole depends sensitively upon the
input used and can disappear within reasonable variations of the input
parameters. We take advantage to study the stability of the other poles
obtained for the dynamically generated resonances of the model and
conclude that they are stable and not contingent to reasonable changes in the
input of the theory
Casimir type effects for scalar fields interacting with material slabs
We study the field theoretical model of a scalar field in presence of spacial
inhomogeneities in form of one and two finite width mirrors (material slabs).
The interaction of the scalar field with the defect is described with
position-dependent mass term. For the single layer system we develop a rigorous
calculation method and derive explicitly the propagator of the theory, S-matrix
elements and the Casimir self-energy of the slab. Detailed investigation of
particular limits of self-energy is presented, and connection to know cases is
discussed. The calculation method is found applicable to the two mirrors case
as well. By means of it we derive the corresponding Casimir energy and analyze
it. For particular values of the parameters of the model the obtained results
recover the Lifshitz formula. We also propose a procedure to obtain
unambiguously the finite Casimir \textit{self}-energy of a single slab without
reference to any renormalizations. We hope that our approach can be applied to
calculation of Casimir self-energies in other demanded cases (such as
dielectric ball, etc.)Comment: 22 pages, 3 figures, published version, significant changes in
Section 4.
- …