1,607 research outputs found
Finite temperature results on the 2d Ising model with mixed perturbation
A numerical study of finite temperature features of thermodynamical
observables is performed for the lattice 2d Ising model. Our results support
the conjecture that the Finite Size Scaling analysis employed in the study of
integrable perturbation of Conformal Field Theory is still valid in the present
case, where a non-integrable perturbation is considered.Comment: 9 pages, Latex, added references and improved introductio
The Coester Line in Relativistic Mean Field Nuclear Matter
The Walecka model contains essentially two parameters that are associated
with the Lorentz scalar (S) and vector (V) interactions. These parameters are
related to a two-body interaction consisting of S and V, imposing the condition
that the two-body binding energy is fixed. We have obtained a set of different
values for the nuclear matter binding energies at equilibrium densities. We
investigated the existence of a linear correlation between and ,
claimed to be universal for nonrelativistic systems and usually known as the
Coester line, and found an approximate linear correlation only if remains
constant. It is shown that the relativistic content of the model, which is
related to the strength of , is responsible for the shift of the Coester
line to the empirical region of nuclear matter saturation.Comment: 7 pages, 5 figure
Finite Nuclei in a Relativistic Mean-Field Model with Derivative Couplings
We study finite nuclei, at the mean-field level, using the Zimanyi-Moskowski
model and one of its variations (the ZM3 model). We calculate energy levels and
ground-state properties in nuclei where the mean-field approach is reliable.
The role played by the spin-orbit potential in sorting out mean-field model
descriptions is emphasized.Comment: 17 pages, 9 figures, 30 kbytes. Uses EPSF.TEX. To appear in Zeit. f.
Phys. A (Hadrons and Nuclei
Naturalistic study on the effectiveness of psycho-oncological interventions in cancer patients and their partners
Background: There is evidence for the efficacy of psycho-oncological interventions (POI) in randomized controlled trials for cancer patients. Our objective was to explore, under naturalistic conditions (using propensity score matching), whether POI are effective to decrease anxiety, depression, distress and overall psychopathological symptoms within cancer patients and their partners. Methods: This study was conducted in the Oncology and Hematology Center of a University clinic in Switzerland with a group of 186 patients and 117 partners. Outcome measures of mental health were the Hospital Anxiety and Depression Scale and the Symptom Checklist (SCL-9-K). Repeated-measures ANOVAs were used to analyze change over time and group effects between individuals with POI vs. without POI. Results: Highly distressed patients and their partners participating in POI reported better mental health over time. Among moderately distressed patients, a decrease over time emerged in depression and distress independent of POI. No effectiveness of POI could be demonstrated in moderately distressed patients and partners. Conclusion: Most of the highly distressed patients receive additional POI and therefore conclusions about the efficacy of POI are difficult. For moderately distressed individuals, POI as implemented in Switzerland does not improve mental health in such patients and their partners, which may be caused by very time limited POI treatments. Studies with more intense POI treatments are neede
Point-Coupling Models from Mesonic Hypermassive Limit and Mean-Field Approaches
In this work we show how nonlinear point-coupling models, described by a
Lagrangian density that presents only terms up to fourth order in the fermion
condensate , are derived from a modified meson-exchange
nonlinear Walecka model. The derivation can be done through two distinct
methods, namely, the hypermassive meson limit within a functional integral
approach, and the mean-field approximation in which equations of state at zero
temperature of the nonlinear point-coupling models are directly obtained.Comment: 18 pages. Accepted for publication in Braz. J. Phy
Universal Ratios in the 2-D Tricritical Ising Model
We consider the universality class of the two-dimensional Tricritical Ising
Model. The scaling form of the free-energy naturally leads to the definition of
universal ratios of critical amplitudes which may have experimental relevance.
We compute these universal ratios by a combined use of results coming from
Perturbed Conformal Field Theory, Integrable Quantum Field Theory and numerical
methods.Comment: 4 pages, LATEX fil
On three-point connectivity in two-dimensional percolation
We argue the exact universal result for the three-point connectivity of
critical percolation in two dimensions. Predictions for Potts clusters and for
the scaling limit below p_c are also given.Comment: 10 pages, 1 figur
One-point functions in integrable quantum field theory at finite temperature
We determine the form factor expansion of the one-point functions in
integrable quantum field theory at finite temperature and find that it is
simpler than previously conjectured. We show that no singularities are left in
the final expression provided that the operator is local with respect to the
particles and argue that the divergences arising in the non-local case are
related to the absence of spontaneous symmetry breaking on the cylinder. As a
specific application, we give the first terms of the low temperature expansion
of the one-point functions for the Ising model in a magnetic field.Comment: 10 pages, late
Proposal to improve the behaviour of self-energy contributions to the S-matrix
A simple modification of the definition of the S-matrix is proposed. It is
expected that the divergences related to nonzero self-energies are considerably
milder with the modified definition than with the usual one. This conjecture is
verified in a few examples using perturbation theory. The proposed formula is
written in terms of the total Hamiltonian operator and a free Hamiltonian
operator and is therefore applicable in any case when these Hamiltonian
operators are known.Comment: 24 pages, 1 figure; v2: revised version; v3: section 3 improved.
Accepted for publication in Central European Journal of Physics; v4: minor
text misprints correcte
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