135 research outputs found
The Scalar Meson f0(980) in Heavy-Meson Decays
A phenomenological analysis of the scalar meson f0(980) is performed that
relies on the quasi-two body decays D and Ds -> f0(980)P, with P=pi, K. The
two-body branching ratios are deduced from experimental data on D or Ds -> pi
pi pi, K Kbar pi and from the f0(980) -> pi+ pi- and f0(980) -> K+ K- branching
fractions. Within a covariant quark model, the scalar form factors F0(q2) for
the transitions D and Ds -> f0(980) are computed. The weak D decay amplitudes,
in which these form factors enter, are obtained in the naive factorization
approach assuming a quark-antiquark state for the scalar and pseudoscalar
mesons. They allow to extract information on the f0(980) wave function in terms
of u-ubar, d-dbar and s-sbar pairs as well as on the mixing angle between the
strange and non-strange components. The weak transition form factors are
modeled by the one-loop triangular diagram using two different relativistic
approaches: covariant light-front dynamics and dispersion relations. We use the
information found on the f0(980) structure to evaluate the scalar and vector
form factors in the transitions D and Ds -> f0(980), as well as to make
predictions for B and Bs -> f0(980), for the entire kinematically allowed
momentum range of q2.Comment: 45 pages, 9 figures and 9 tables. The use of dispersion relations to
calculate the weak transition form factors is better justified. A more
extensive discussion on the strange and non-strange flavor content mixing is
introduced. Results unchanged. Version to appear in Phys. Rev.
Pion structure in the nuclear medium
Using the light-front pion wave function based on a Bethe-Salpeter amplitude
model, we study the properties of the pion in symmetric nuclear matter. The
pion model we adopt is well constrained by previous studies to explain the pion
properties in vacuum. In order to consistently incorporate the constituent up
and down quarks of the pion immersed in symmetric nuclear matter, we use the
quark-meson coupling model, which has been widely applied to various hadronic
and nuclear phenomena in a nuclear medium with success. We predict the
in-medium modifications of the pion lectromagnetic form factor, charge radius
and weak decay constant in symmetric nuclear matter.Comment: Use revtex4, 7 figures. Title change. Revised text and figures.
Accepted, Physical Review C (August, 2014
State sampling dependence of the Hopfield network inference
The fully connected Hopfield network is inferred based on observed
magnetizations and pairwise correlations. We present the system in the glassy
phase with low temperature and high memory load. We find that the inference
error is very sensitive to the form of state sampling. When a single state is
sampled to compute magnetizations and correlations, the inference error is
almost indistinguishable irrespective of the sampled state. However, the error
can be greatly reduced if the data is collected with state transitions. Our
result holds for different disorder samples and accounts for the previously
observed large fluctuations of inference error at low temperatures.Comment: 4 pages, 1 figure, further discussions added and relevant references
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Looking into the matter of light-quark hadrons
In tackling QCD, a constructive feedback between theory and extant and
forthcoming experiments is necessary in order to place constraints on the
infrared behaviour of QCD's \beta-function, a key nonperturbative quantity in
hadron physics. The Dyson-Schwinger equations provide a tool with which to work
toward this goal. They connect confinement with dynamical chiral symmetry
breaking, both with the observable properties of hadrons, and hence provide a
means of elucidating the material content of real-world QCD. This contribution
illustrates these points via comments on: in-hadron condensates; dressed-quark
anomalous chromo- and electro-magnetic moments; the spectra of mesons and
baryons, and the critical role played by hadron-hadron interactions in
producing these spectra.Comment: 11 pages, 7 figures. Contribution to the Proceedings of "Applications
of light-cone coordinates to highly relativistic systems - LIGHTCONE 2011,"
23-27 May, 2011, Dallas. The Proceedings will be published in Few Body
System
Annihilation range and final-state interaction in the antiproton-proton annihilation into pi-pi+
The large set of accurate data on differential cross section and analyzing
power from the CERN LEAR experiment on in the range
from 360 to 1550 MeV/c is well reproduced within a distorted wave approximation
approach. The initial scattering wave functions originate from a
recent model. The transition operator is obtained from a combination
of the and quark-antiquark annihilation mechanisms. A good fit
to the data, in particular the reproduction of the double dip structure
observed in the analyzing powers, requires quark wave functions for proton,
antiproton, and pions with radii slightly larger than the respective measured
charge radii. This corresponds to an increase in range of the annihilation
mechanisms and consequently the amplitudes for total angular momentum J=2 and
higher are much larger than in previous approaches. The final state
wave functions, parameterized in terms of phase shifts and
inelasticities, are also a very important ingredient for the fine tuning of the
fit to the observables.Comment: 11 pages, 11 figures (Revtex 4), revised version with one additional
figure. Accepted for publication in PR
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
Academic freedom: in justification of a universal ideal
This paper examines the justification for, and benefits of, academic freedom to academics, students, universities and the world at large. The paper surveys the development of the concept of academic freedom within Europe, more especially the impact of the reforms at the University of Berlin instigated by Wilhelm von Humboldt. Following from this, the paper examines the reasons why the various facets of academic freedom are important and why the principle should continue to be supported
Survey of nucleon electromagnetic form factors
A dressed-quark core contribution to nucleon electromagnetic form factors is
calculated. It is defined by the solution of a Poincare' covariant Faddeev
equation in which dressed-quarks provide the elementary degree of freedom and
correlations between them are expressed via diquarks. The nucleon-photon vertex
involves a single parameter; i.e., a diquark charge radius. It is argued to be
commensurate with the pion's charge radius. A comprehensive analysis and
explanation of the form factors is built upon this foundation. A particular
feature of the study is a separation of form factor contributions into those
from different diagram types and correlation sectors, and subsequently a
flavour separation for each of these. Amongst the extensive body of results
that one could highlight are: r_1^{n,u}>r_1^{n,d}, owing to the presence of
axial-vector quark-quark correlations; and for both the neutron and proton the
ratio of Sachs electric and magnetic form factors possesses a zero.Comment: 43 pages, 17 figures, 12 tables, 5 appendice
Gut microbiota trajectory in early life may predict development of celiac disease.
BACKGROUND: To investigate whether alterations in the developing intestinal microbiota and immune markers precede celiac disease (CD) onset in infants at familial risk of developing the disease. METHODS: A nested case-control study was carried out as part of a larger prospective cohort study, which included healthy full-term newborns (> 200) with at least one first relative with biopsy-verified CD. The present study includes cases of CD (n = 10) and the best-matched controls (n = 10) who did not develop the disease after 5-year follow-up. Fecal microbiota, assessed by high-throughput 16S rRNA gene amplicon sequencing, and immune parameters were profiled at 4 and 6 months of age and related to CD onset. RESULTS: The microbiota of infants who remained healthy showed an increase in bacterial diversity over time, characterized by increases in Firmicutes families, but not those who developed CD. Infants who subsequently developed CD showed a significant reduction in sIgA levels over time, while those who remained healthy showed increases in TNF-α correlated to Bifidobacterium spp. An increased relative abundance of Bifidobacterium longum was associated with control children while increased proportions of Bifidobacterium breve and Enterococcus spp. were associated with CD development. CONCLUSION: The findings suggest that alterations in the early trajectory of gut microbiota in infants at CD risk could influence the immune maturation process and predispose to CD, although larger population studies are warranted to confirm this hypothesis
Collective perspective on advances in Dyson-Schwinger Equation QCD
We survey contemporary studies of hadrons and strongly interacting quarks
using QCD's Dyson-Schwinger equations, addressing: aspects of confinement and
dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and
transition form factors, from small- to large-Q^2; parton distribution
functions; the physics of hadrons containing one or more heavy quarks; and
properties of the quark gluon plasma.Comment: 56 pages. Summary of lectures delivered by the authors at the
"Workshop on AdS/CFT and Novel Approaches to Hadron and Heavy Ion Physics,"
2010-10-11 to 2010-12-03, hosted by the Kavli Institute for Theoretical
Physics, China, at the Chinese Academy of Science
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