1,652 research outputs found
Field theory of scaling lattice models. The Potts antiferromagnet
In contrast to what happens for ferromagnets, the lattice structure
participates in a crucial way to determine existence and type of critical
behaviour in antiferromagnetic systems. It is an interesting question to
investigate how the memory of the lattice survives in the field theory
describing a scaling antiferromagnet. We discuss this issue for the square
lattice three-state Potts model, whose scaling limit as T->0 is argued to be
described exactly by the sine-Gordon field theory at a specific value of the
coupling. The solution of the scaling ferromagnetic case is recalled for
comparison. The field theory describing the crossover from antiferromagnetic to
ferromagnetic behaviour is also introduced.Comment: 11 pages, to appear in the proceedings of the NATO Advanced Research
Workshop on Statistical Field Theories, Como 18-23 June 200
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
Critical points of coupled vector-Ising systems. Exact results
We show that scale-invariant scattering theory allows to exactly determine the critical points of two-dimensional systems with coupled O(N) and Ising order parameters. The results are obtained for N continuous and include criticality of the loop gas type. In particular, for N = 1 we exhibit three critical lines intersecting at the Berezinskii Kosterlitz Thouless transition point of the Gaussian model and related to the Z4 symmetry of the isotropic Ashkin Teller model. For N = 2 we classify the critical points that can arise in the XY-Ising model and provide exact answers about the critical exponents of the fully frustrated XY model
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
Alternative Linear Chiral Models for Nuclear Matter
The equation of state of a family of alternative linear chiral models in the
mean field approximation is discussed. We investigate the analogy between some
of these models with current models in the literature, and we show that it is
possible to reproduce very well the saturation properties of nuclear matter.Comment: 11 pages in Latex, 4 ps figures include
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
Form factors in the Bullough-Dodd related models: The Ising model in a magnetic field
We consider particular modification of the free-field representation of the
form factors in the Bullough-Dodd model. The two-particles minimal form factors
are excluded from the construction. As a consequence, we obtain convenient
representation for the multi-particle form factors, establish recurrence
relations between them and study their properties. The proposed construction is
used to obtain the free-field representation of the lightest particles form
factors in the perturbed minimal models. As a significant example
we consider the Ising model in a magnetic field. We check that the results
obtained in the framework of the proposed free-field representation are in
agreement with the corresponding results obtained by solving the bootstrap
equations.Comment: 20 pages; v2: some misprints, textual inaccuracies and references
corrected; some references and remarks adde
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
Symptoms in pediatric asthmatics and air pollution: differences in effects by symptom severity, anti-inflammatory medication use and particulate averaging time.
Experimental research in humans and animals points to the importance of adverse respiratory effects from short-term particle exposures and to the importance of proinflammatory effects of air pollutants, particularly O(subscript)3. However, particle averaging time has not been subjected to direct scientific evaluation, and there is a lack of epidemiological research examining both this issue and whether modification of air pollutant effects occurs with differences in asthma severity and anti-inflammatory medication use. The present study examined the relationship of adverse asthma symptoms (bothersome or interfered with daily activities or sleep) to O(3) and particles (less than or equal to)10 micrometer (PM10) in a Southern California community in the air inversion zone (1200-2100 ft) with high O(3) and low PM (R = 0.3). A panel of 25 asthmatics 9-17 years of age were followed daily, August through October 1995 (n = 1,759 person-days excluding one subject without symptoms). Exposures included stationary outdoor hourly PM10 (highest 24-hr mean, 54 microgram/m(3), versus median of 1-hr maximums, 56 microgram/m(3) and O(3) (mean of 1-hr maximums, 90 ppb, 5 days (greater than or equal to)120 ppb). Longitudinal regression analyses utilized the generalized estimating equations (GEE) model controlling for autocorrelation, day of week, outdoor fungi, and weather. Asthma symptoms were significantly associated with both outdoor O(3) and PM(10) in single pollutant- and co-regressions, with 1-hr and 8-hr maximum PM(10) having larger effects than the 24-hr mean. Subgroup analyses showed effects of current day PM(10) maximums were strongest in 10 more frequently symptomatic (MS) children: the odds ratios (ORs) for adverse symptoms from 90th percentile increases were 2.24 [95% confidence interval (CI), 1.46-3.46] for 1-hr PM10 (47 microgram/m(3); 1.82 (CI, 1.18-2.81) for 8-hr PM10 (36 microgram/m(3); and 1.50 (CI, 0.80-2.80) for 24-hr PM10 (25 microgram/m(3). Subgroup analyses also showed the effect of current day O(subscript)3 was strongest in 14 less frequently symptomatic (LS) children: the ORs were 2.15 (CI, 1.04-4.44) for 1-hr O(3) (58 ppb) and 1.92 (CI, 0.97-3.80) for 8-hr O(3) (46 ppb). Effects of 24-hr PM10 were seen in both groups, particularly with 5-day moving averages (ORs were 1.95 for MS and 4. 03 for LS; p(less than or equal to)0.05). The largest effects were in 7 LS children not on anti-inflammatory medications [5-day, 8-hr PM10, 9.66 (CI, 2.80-33.21); current day, 1-hr O(3), 4.14 (CI, 1.71-11.85)]. Results suggest that examination of short-term particle excursions, medication use, and symptom severity in longitudinal studies of asthma yields sensitive measures of adverse respiratory effects of air pollution
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
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