102 research outputs found
Study of below 1 GeV using Integral Equation Approach
The scattering of is studied using the axial
anomaly, elastic unitarity, analyticity and crossing symmetry. Using the
technique to derive the Roy's equation, an integral equation for the P-wave
amplitude is obtained in terms of the strong P-wave pion pion phase shifts. Its
solution is obtained numerically by an iteration procedure using the starting
point as the solution of the integral equation of the Muskelshsvilli-Omnes
type. It is, however, ambiguous and depends sensitively on the second
derivative of the P-wave amplitude at which cannot directly be
measured.Comment: 26 pages, 10 figure
Analyticity, Crossing Symmetry and the Limits of Chiral Perturbation Theory
The chiral Lagrangian for Goldstone boson scattering is a power series
expansion in numbers of derivatives. Each successive term is suppressed by
powers of a scale, , which must be less than of order where is the Goldstone boson decay constant and is the
number of flavors. The chiral expansion therefore breaks down at or below . We argue that the breakdown of the chiral expansion is
associated with the appearance of physical states other than Goldstone bosons.
Because of crossing symmetry, some ``isospin'' channels will deviate from their
low energy behavior well before they approach the scale at which their low
energy amplitudes would violate unitarity. We argue that the estimates of
``oblique'' corrections from technicolor obtained by scaling from QCD are
untrustworthy.Comment: harvmac, 18 pages (3 figures), HUTP-92/A025, BUHEP-92-18, new version
fixes a TeX problem in little mod
Another look at scattering in the scalar channel
We set up a general framework to describe scattering below 1 GeV
based on chiral low-energy expansion with possible spin-0 and 1 resonances.
Partial wave amplitudes are obtained with the method, which satisfy
unitarity, analyticity and approximate crossing symmetry. Comparison with the
phase shift data in the J=0 channel favors a scalar resonance near the
mass.Comment: 17 pages, 5 figures, REVTe
Meson-meson scattering within one loop Chiral Perturbation Theory and its unitarization
We present the complete one-loop calculation of all the two meson scattering
amplitudes within the framework of SU(3) Chiral Perturbation Theory, which
includes pions, kaons and the eta. In addition, we have unitarized these
amplitudes with the coupled channel Inverse Amplitude Method, which ensures
simultaneously the good low energy properties of Chiral Perturbation Theory and
unitarity. We show how this method provides a remarkable description of
meson-meson scattering data up to 1.2 GeV including the scattering lengths and
the generation of seven light resonances, which is consistent with previous
determination of the chiral parameters. Particular attention is paid to discuss
the differences and similarities of this work with previous analysis in the
literature.Comment: 20 pages, 5 figures. Comments on sigma, kappa and eta', as well as
some references added. Final version to appear in Phys.Rev.
Protective Contributions against Invasive Streptococcus pneumoniae Pneumonia of Antibody and Th17-Cell Responses to Nasopharyngeal Colonisation
The nasopharyngeal commensal bacteria Streptococcus pneumoniae is also a frequent cause of serious infections. Nasopharyngeal colonisation with S. pneumoniae inhibits subsequent re-colonisation by inducing Th17-cell adaptive responses, whereas vaccination prevents invasive infections by inducing antibodies to S. pneumoniae capsular polysaccharides. In contrast, protection against invasive infection after nasopharyngeal colonisation with mutant S. pneumoniae strains was associated with antibody responses to protein antigens. The role of colonisation-induced Th17-cell responses during subsequent invasive infections is unknown. Using mouse models, we show that previous colonisation with S. pneumoniae protects against subsequent lethal pneumonia mainly by preventing bacteraemia with a more modest effect on local control of infection within the lung. Previous colonisation resulted in CD4-dependent increased levels of Th17-cell cytokines during subsequent infectious challenge. However, mice depleted of CD4 cells prior to challenge remained protected against bacteraemia, whereas no protection was seen in antibody deficient mice and similar protection could be achieved through passive transfer of serum. Serum from colonised mice but not antibody deficient mice promoted phagocytosis of S. pneumoniae, and previously colonised mice were able to rapidly clear S. pneumoniae from the blood after intravenous inoculation. Thus, despite priming for a Th17-cell response during subsequent infection, the protective effects of prior colonisation in this model was not dependent on CD4 cells but on rapid clearance of bacteria from the blood by antibody-mediated phagocytosis. These data suggest that whilst nasopharyngeal colonisation induces a range of immune responses, the effective protective responses depend upon the site of subsequent infectio
Existence of the -meson below 1 GeV and glueball
On the basis of a simultaneous description of the isoscalar s-wave channel of
the scattering (from the threshold up to 1.9 GeV) and of the
process (from the threshold to 1.4 GeV) in the
model-independent approach, a confirmation of the -meson at 665
MeV and an indication for the glueball nature of the state are
obtained. It is shown that the large -background, usually obtained,
combines, in reality, the influence of the left-hand branch-point and the
contribution of a very wide resonance at 665 MeV. The coupling constants
of the observed states with the and systems and lengths of
the and scattering are obtained.Comment: 13 pages, 3 figures, LaTex; submitted to Physics Letters
Effects of deletion of the Streptococcus pneumoniae lipoprotein diacylglyceryl transferase gene lgt on ABC transporter function and on growth in vivo
Lipoproteins are an important class of surface associated proteins that have diverse roles and frequently are involved in the virulence of bacterial pathogens. As prolipoproteins are attached to the cell membrane by a single enzyme, prolipoprotein diacylglyceryl transferase (Lgt), deletion of the corresponding gene potentially allows the characterisation of the overall importance of lipoproteins for specific bacterial functions. We have used a Δlgt mutant strain of Streptococcus pneumoniae to investigate the effects of loss of lipoprotein attachment on cation acquisition, growth in media containing specific carbon sources, and virulence in different infection models. Immunoblots of triton X-114 extracts, flow cytometry and immuno-fluorescence microscopy confirmed the Δlgt mutant had markedly reduced lipoprotein expression on the cell surface. The Δlgt mutant had reduced growth in cation depleted medium, increased sensitivity to oxidative stress, reduced zinc uptake, and reduced intracellular levels of several cations. Doubling time of the Δlgt mutant was also increased slightly when grown in medium with glucose, raffinose and maltotriose as sole carbon sources. These multiple defects in cation and sugar ABC transporter function for the Δlgt mutant were associated with only slightly delayed growth in complete medium. However the Δlgt mutant had significantly reduced growth in blood or bronchoalveolar lavage fluid and a marked impairment in virulence in mouse models of nasopharyngeal colonisation, sepsis and pneumonia. These data suggest that for S. pneumoniae loss of surface localisation of lipoproteins has widespread effects on ABC transporter functions that collectively prevent the Δlgt mutant from establishing invasive infection
Collision times in pi-pi and pi-K scattering and spectroscopy of meson resonances
Using the concept of collision time (time delay) introduced by Eisenbud and
Wigner and its connection to on-shell intermediate unstable states, we study
mesonic resonances in pi-pi and pi-K scattering. The time-delay method proves
its usefulness by revealing the spectrum of the well-known rho- and K*-mesons
and by supporting some speculations on rho-mesons in the 1200 MeV region. We
use this method further to shed some light on more speculative meson
resonances, among others the enigmatic scalars. We confirm the existence of
chiralons below 1 GeV in the unflavoured and strange meson sector.Comment: 22 pages LaTex, 8 figure
Couplings of light I=0 scalar mesons to simple operators in the complex plane
The flavour and glue structure of the light scalar mesons in QCD are probed
by studying the couplings of the I=0 mesons and to the
operators , and to two photons. The Roy dispersive
representation for the amplitude is used to determine the
pole positions as well as the residues in the complex plane. On the real axis,
is constrained to solve the Roy equation together with elastic
unitarity up to the K\Kbar threshold leading to an improved description of
the . The problem of using a two-particle threshold as a matching
point is discussed. A simple relation is established between the coupling of a
scalar meson to an operator and the value of the related pion form-factor
computed at the resonance pole. Pion scalar form-factors as well as two-photon
partial-wave amplitudes are expressed as coupled-channel Omn\`es dispersive
representations. Subtraction constants are constrained by chiral symmetry and
experimental data. Comparison of our results for the couplings with
earlier determinations of the analogous couplings of the lightest I=1 and
scalar mesons are compatible with an assignment of the ,
, , into a nonet. Concerning the gluonic operator
we find a significant coupling to both the and the
.Comment: 31 pages, 5 figure
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