69 research outputs found
Ground-state energy of pionic hydrogen to one loop
We investigate the ground-state energy of the pi- p atom (pionic hydrogen) in
the framework of QCD+QED. In particular, we evaluate the strong energy-level
shift. We perform the calculation at next-to-leading order in the low-energy
expansion in the framework of the relevant effective field theory. The result
provides a relation between the strong energy shift and the pion-nucleon S-wave
scattering lengths - evaluated in pure QCD - at next-to-leading order in
isospin breaking and in the low-energy expansion. We compare our result with
available model calculations.Comment: Version accepted for publication in Eur. Phys. J. C; Eq. (B8)
corrected, comment after Eq. (B11) changed, additional minor changes in the
text; preprint number adde
Point Spread Functions in Identification of Astronomical Objects from Poisson Noised Image
This article deals with modeling of astronomical objects, which is one of the most fundamental topics in astronomical science. Introduction part is focused on problem description and used methods. Point Spread Function Modeling part deals with description of basic models used in astronomical photometry and further on introduction of more sophisticated models such as combinations of interference, turbulence, focusing, etc. This paper also contains a~way of objective function definition based on the knowledge of Poisson distributed noise, which is included in astronomical data. The proposed methods are further applied to real astronomical data
Chiral condensate thermal evolution at finite baryon chemical potential within Chiral Perturbation Theory
We present a model independent study of the chiral condensate evolution in a
hadronic gas, in terms of temperature and baryon chemical potential. The
meson-meson interactions are described within Chiral Perturbation Theory and
the pion-nucleon interaction by means of Heavy Baryon Chiral Perturbation
Theory, both at one loop, and nucleon-nucleon interactions can be safely
neglected within our hadronic gas domain of validity. Together with the virial
expansion, this provides a systematic expansion at low temperatures and
chemical potentials, which includes the physical quark masses. This can serve
as a guideline for further studies on the lattice. We also obtain estimates of
the critical line of temperature and chemical potential where the chiral
condensate melts, which systematically lie somewhat higher than recent lattice
calculations but are consistent with several hadronic models. We have also
estimated uncertainties due to chiral parameters, heavier hadrons and higher
orders through unitarized Chiral Perturbation Theory.Comment: 15 pages, 15 figures, 3 tables, ReVTeX. Version to appear in Phys.
Rev. D. References added. More conservative estimate of applicability domain,
with new figure. More detailed explanation of final results with two more
figures. Results unchange
Unitarized pion-nucleon scattering amplitude from inverse amplitude method
In a recent work on low energy pion-nucleon scattering, instead of using
chiral perturbation theory (ChPT) amplitude, we started from a pion-nucleon
{\it soft-pion} result and used elastic unitarity directly as a dynamical
constraint to construct first-order unitarity corrected amplitudes. The
resulting amplitudes are crossing symmetric but, as the ChPT ones, satisfy only
approximate unitarity relation. In the present work, we reconsider our approach
and we apply the inverse amplitude method (IAM) in order to access the energy
resonance region. We present the resulting S- and P-wave phase shifts that are
shown to be in qualitative agreement with experimental data.Comment: 6 pages, 3 figure
U(3) chiral perturbation theory with infrared regularization
We include the eta-prime in chiral perturbation theory without employing
1/N_c counting rules. The method is illustrated by calculating the masses and
decay constants of the Goldstone boson octet (pions, kaons, eta) and the
singlet eta-prime up to one-loop order. The effective Lagrangian describing the
interactions of the eta-prime with the Goldstone boson octet is presented up to
fourth chiral order and the loop integrals are evaluated using infrared
regularization, which preserves Lorentz and chiral symmetry.Comment: 29 page
Bethe-Salpeter Approach for the Elastic Pion-Nucleon Scattering in Heavy Baryon Chiral Perturbation Theory
Heavy Baryon Chiral Perturbation Theory (HBChPT) to leading order provides a
kernel to solve the Bethe-Salpeter equation for the
(-channel) system, in the infinite nucleon mass limit.
Crossed Born terms include, when iterated within the Bethe-Salpeter equation,
both {\it all} one- and {\it some} two-pion intermediate states, hence
preserving elastic unitarity below the two-pion production threshold. This
suggests searching for a solution with the help of dispersion relations and
suitable subtraction constants, when all in-elasticities are explicitly
neglected. The solution allows for a successful description of the experimental
phase shift from threshold up to MeV in terms of four
subtraction constants. Next-to-leading order HBChPT calculations are also used
to estimate the unknown subtraction constants which appear in the solution.
Large discrepancies are encountered which can be traced to the slow convergence
rate of HBChPT.Comment: 11 pages, 3 figure
Anti-angiogenic activity of the flavonoid precursor 4-hydroxychalcone.
Angiogenesis, the growth of new blood vessels, is necessary for cancerous tumors to keep growing and spreading. Suppression of abnormal angiogenesis may provide therapeutic strategies for the treatment of angiogenesis-dependent disorders. In the present study, we describe the in vitro and in vivo anti-angiogenic activities of the flavonoid precursor 4-hydroxychalcone (Q797). This chalcone (22μg/ml) suppressed several steps of angiogenesis, including endothelial cell proliferation, migration and tube formation without showing any signs of cytotoxicity. Moreover, we found a selective effect on activated endothelial cells, in particular with resting endothelial cells and the human epithelial tumor cell lines (HeLa, MCF-7, A549). In addition, Q797 was able to modulate both vascular endothelial growth factor (VEGF)- and basic fibroblast growth factor (FGF)- induced phosphorylation of extracellular signal-regulated kinase (ERK)-1/-2 and Akt kinase. It did not influence the nuclear translocation of p65 subunit of the nuclear factor-κB (NF-κB) when human endothelial cells were stimulated with tumor necrosis factor (TNF)-α. Taken together this indicates that the Q797-mediated inhibition of in vitro angiogenic features of endothelial cells is most likely caused by suppression of growth factor pathways. The potent inhibitory effect of Q797 on bFGF-driven neovascularization was also demonstrated in vivo using the chick chorioallantoic membrane (CAM) assay. In summary, this chalcone could serve as a new leading structure in the discovery of new potent synthetic angiogenesis inhibitors
Unitarized pion-nucleon scattering within Heavy Baryon Chiral Perturbation Theory
By means of the Inverse Amplitude Method we unitarize the elastic
pion-nucleon scattering amplitudes obtained from Heavy Baryon Chiral
Perturbation Theory to O(q^3). Within this approach we can enlarge their
applicability range and generate the Delta(1232) resonance. We can find a
reasonable description of the pion nucleon phase shifts with (q^2) parameters
in agreement with the resonance saturation hypothesis. However, the
uncertainties in the analysis of the low energy data as well as the large
number of chiral parameters, which can have strong correlations, allow us to
obtain very good fits with rather different sets of chiral constants.Comment: Shortened version to appear in Phys. Rev. D. Brief Report
The (1535) and (1650) Resonances in Meson-Baryon Unitarized Coupled Channel Chiral Perturbation Theory
The wave meson-baryon scattering is analyzed for the strangeness S=0
sector in a Bethe-Salpeter coupled channel formalism incorporating Chiral
Symmetry. Four channels have been considered: , , ,
. The needed two particle irreducible matrix amplitude is taken from
lowest order Chiral Perturbation Theory in a relativistic formalism and low
energy constants are fitted to the elastic phase-shifts and the and cross section data. The position of
the complex poles in the second Riemann sheet of the scattering amplitude
determine masses and widths of the (1535) and (1650)
resonances, in reasonable agreement with experiment. A good overall description
of data, from threshold up to 2 GeV, is achieved keeping in mind that
the two pion production channel has not been included.Comment: 35 pages, LaTeX + 7 ps-figure files. Some minor mistakes have been
corrected for and a new appendix discussing the matching to HBChPT has been
also adde
Meson-Baryon Unitarized Coupled Channel Chiral Perturbation Theory and the (1405) and (1670) Resonances
The wave meson-baryon scattering is analyzed for the strangeness
and isospin I=0 sector in a Bethe-Salpeter coupled channel formalism
incorporating Chiral Symmetry. Four channels have been considered: , , and . The required input to solve
the Bethe-Salpeter equation is taken from lowest order Chiral Perturbation
Theory in a relativistic formalism. There appear undetermined low energy
constants, as a consequence of the renormalization of the amplitudes, which are
obtained from fits to the mass-spectrum, to the elastic
and --matrices and to the
cross section data. The position and residues of the
complex poles in the second Riemann Sheet of the scattering amplitude determine
masses, widths and branching ratios of the (1405) and
(1670) resonances, in reasonable agreement with experiment. A good
overall description of data, from threshold up to 1.75 GeV, is
achieved despite the fact that three-body channels have not been explicitly
included.Comment: 23 pages, Latex, 10 Figures. In this revised version a new subsection
3.6 on Heavy Baryon Expansion and new references have been adde
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