357 research outputs found
Baryonic masses based on the NJL model
We employ the Nambu Jona--Lasinio model to determine the vacuum pressure on
the quarks in a baryon and hence their density inside. Then we estimate the
baryonic masses by implementing the local density approximation for the mean
field quark energies obtained in a uniform and isotropic system. We obtain a
fair agreement with the experimental masses.Comment: 17 pages, 3 figures. to be published on EPJ
Vacuum Properties of Mesons in a Linear Sigma Model with Vector Mesons and Global Chiral Invariance
We present a two-flavour linear sigma model with global chiral symmetry and
vector and axial-vector mesons. We calculate pion-pion scattering lengths and
the decay widths of scalar, vector, and axial-vector mesons. It is demonstrated
that vector and axial-vector meson degrees of freedom play an important role in
these low-energy processes and that a reasonable theoretical description
requires globally chirally invariant terms other than the vector meson mass
term. An important question for meson vacuum phenomenology is the quark content
of the physical scalar f0(600) and a0(980) mesons. We investigate this question
by assigning the quark-antiquark sigma and a0 states of our model with these
physical mesons. We show via a detailed comparison with experimental data that
this scenario can describe all vacuum properties studied here except for the
decay width of the sigma, which turns out to be too small. We also study the
alternative assignment f0(1370) and a0(1450) for the scalar mesons. In this
case the decay width agrees with the experimental value, but the pion-pion
scattering length is too small. This indicates the necessity to
extend our model by additional scalar degrees of freedom.Comment: 22 pages, 6 figure
Decays of tensor mesons and the tensor glueball in an effective field approach
The strong and electromagnetic decays of the ground-state tensor mesons are
studied in an effective field approach. A fit to the well-known experimental
data is performed. The decay ratios of the tensor glueball are evaluated and
possible candidates are discussed.Comment: 12 page
Mass Uncertainties of f0(600) and f0(1370) and their Effects on Determination of the Quark and Glueball Admixtures of the I=0 Scalar Mesons
Within a nonlinear chiral Lagrangian framework the correlations between the
quark and glueball admixtures of the isosinglet scalar mesons below 2 GeV and
the current large uncertainties on the mass of the f0(600) and the f0(1370) are
studied. The framework is formulated in terms of two scalar meson nonets (a
two-quark nonet and a four-quark nonet) together with a scalar glueball. It is
shown that while some properties of these states are sensitive to the mass of
f0(600) and f0(1370), several relatively robust conclusions can be made: The
f0(600), the f0(980), and the f0(1370) are admixtures of two and four quark
components, with f0(600) being dominantly a non-strange four-quark state, and
f0(980) and f0(1370) having a dominant two-quark component. Similarly, the
f0(1500) and the f0(1710) have considerable two and four quark admixtures, but
in addition have a large glueball component. For each state, a detailed
analysis providing the numerical estimates of all components is given. It is
also shown that this framework clearly favors the experimental values:
m[f0(600)] < 700 MeV and m[f0(1370)] = 1300-1450 MeV. Moreover, an overall fit
to the available data shows a reciprocal substructure for the f0(600) and the
f0(1370), and a linear correlation between their masses of the form m
[f0(1370)] = 0.29 m[f0(600)] + 1.22 GeV. The scalar glueball mass of 1.5-1.7
GeV is found in this analysis.Comment: placement of figures inside text improved. Content unchange
Spontaneous breaking of chiral symmetry, and eventually of parity, in a -model with two Mexican hats
A sigma-model with two linked Mexican hats is discussed. This scenario could
be realized in low-energy QCD when the ground state and the first excited
(pseudo)scalar mesons are included, and where not only in the subspace of the
ground states, but also in that of the first excited states, a Mexican hat
potential is present. This possibility can change some basic features of a
low-energy hadronic theory of QCD. It is also shown that spontaneous breaking
of parity can occur in the vacuum for some parameter choice of the model.Comment: 10 pages, 1 figur
The Glueball in a Chiral Linear Sigma Model with Vector Mesons
We present a two-flavour linear sigma model with global chiral symmetry and
(axial-)vector mesons as well as an additional glueball degree of freedom. We
study the structure of the well-established scalar resonances f0(1370) and
f0(1500): by a fit to experimentally known decay widths we find that f0(1370)
is predominantly a \bar{q}q state and f0(1500) is predominantly a glueball
state. The overall phenomenology of these two resonances can be well described.
Other assignments for our mixed quarkonium-glueball states are also tested, but
turn out to be in worse agreement with the phenomenology. As a by-product of
our analysis, the gluon condensate is determined.Comment: 8 page
QCD Tests of the Puzzling Scalar Mesons
Motivated by several recent data, we test the QCD spectral sum rules (QSSR)
predictions based on different proposals (\bar qq, \bar q\bar q qq, and
gluonium) for the nature of scalar mesons. In the I=1 and 1/2 channels, the
unusual (wrong) splitting between the a_0(980) and \kappa(900) and the a_0(980)
width can be understood from QSSR within a \bar qq assignement. However, none
of the \bar qq and \bar q\bar q qq results can explain the large \kappa width,
which may suggest that it can result from a strong interference with
non-resonant backgrounds. In the I=0 channel, QSSR and some low-energy theorems
(LET) require the existence of a low mass gluonium \sigma_B(1 GeV) coupled
strongly to Goldstone boson pairs which plays in the U(1)_V channel, a similar
role than the \eta' for the value of the U(1)_A topological charge. The
observed \sigma(600) and f_0(980) mesons result from a maximal mixing between
the gluonium \sigma_B and \bar qq(1 GeV) mesons, a mixing scheme which passes
several experimental tests. OZI violating J/\psi--> \phi\pi^+\pi^-, D_s--> 3\pi
decays and J/\psi--> \gamma S glueball filter processes may indicate that most
of the I=0 mesons above 1 GeV have important gluonium in their wave functions.
We expect that the f_0(1500), f_0(1710) and f_0(1790) have significant gluonium
component in their wave functions, while the f_0(1370) is mostly \bar qq. Tests
of these results can be provided by the measurements of the pure gluonium
\eta'\eta and 4\pi specific U(1)_A decay channels.Comment: Version to appear in Phys. Rev. D (one previous figure corrupted
Non-exponential decay in quantum field theory and in quantum mechanics: the case of two (or more) decay channels
We study the deviations from the exponential decay law, both in quantum field
theory (QFT) and quantum mechanics (QM), for an unstable particle which can
decay in (at least) two decay channels. After a review of general properties of
non-exponential decay in QFT and QM, we evaluate in both cases the decay
probability that the unstable particle decays in a given channel in the time
interval between and An important quantity is the ratio of the
probability of decay into the first and the second channel: this ratio is
constant in the Breit-Wigner limit (in which the decay law is exponential) and
equals the quantity , where and
are the respective tree-level decay widths. However, in the full
treatment (both for QFT and QM) it is an oscillating function around the mean
value and the deviations from this mean value can be
sizable. Technically, we study the decay properties in QFT in the context of a
superrenormalizable Lagrangian with scalar particles and in QM in the context
of Lee Hamiltonians, which deliver formally analogous expressions to the QFT
case.Comment: 32 pages, 10 figures. To appear in "Foundations of Physics
Metabolic syndrome and the risk of breast cancer in postmenopausal women
Background: Only a few small studies investigated the association between postmenopausal breast cancer and metabolic syndrome (MetS) as a single entity. Materials and methods: We analyzed the data of two Italian and Swiss case-control studies conducted between 1983 and 2007, including 3869 postmenopausal women with incident breast cancer and 4082 postmenopausal controls admitted to the same hospitals as cases for acute conditions. MetS was defined as the presence of at least three components among diabetes, drug-treated hypertension, drug-treated hyperlipidemia, and obesity. Results: The odds ratios (ORs) of postmenopausal breast cancer were 1.33 [95% confidence interval (CI) 1.09-1.62] for diabetes, 1.19 (95% CI 1.07-1.33) for hypertension, 1.08 (95% CI 0.95-1.22) for hyperlipidemia, 1.26 (95% CI 1.11-1.44) for body mass index ≥30 kg/m2, and 1.22 (95% CI 1.09-1.36) for waist circumference ≥88 cm. The risk of postmenopausal breast cancer was significantly increased for women with MetS (OR = 1.75, 95% CI 1.37-2.22, for three or more MetS components, P for trend for increasing number of components < 0.0001) and the risk was higher at older age (OR = 3.04, 95% CI 1.75-5.29, at age ≥70 years for three or more MetS components). Conclusions: This study supports a direct association between MetS and postmenopausal breast cancer ris
Fried foods, olive oil and colorectal cancer
Background: The epidemiologic evidence for an etiologic role of fried foods and heterocyclic amines in colorectal carcinogenesis is inconsistent. Patients and methods: We have investigated the relation between fried foods and colorectal cancer risk using data from a large, multicentric case-control study conducted in Italy and Switzerland between 1992 and 2000, with 1394 cases of colon cancer, 886 cases of rectal cancer and 4765 controls. Results: After allowing for major relevant covariates, the multivariate odds ratios (ORs) for an increment of one portion per week of fried foods were 0.97 [95% confidence interval (CI) = 0.93-1.01] for colon cancer and 1.04 (95% CI = 1.00-1.09) for rectal cancer. When we analyzed the type of fats mainly used for frying, we found that olive oil, but not other types of oils, appeared to protect from colon cancer risk (OR = 0.89, 95% CI = 0.82-0.98). Conclusions: Our results do not indicate a relevant role of fried foods on colorectal cancer risk. We found a possible favorable effect of (fried) olive oil on colon cancer risk but not on rectal cancer ris
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