32,662 research outputs found

### Renormalization of the Non-Linear Sigma Model in Four Dimensions. A two-loop example

The renormalization procedure of the non-linear SU(2) sigma model in D=4
proposed in hep-th/0504023 and hep-th/0506220 is here tested in a truly
non-trivial case where the non-linearity of the functional equation is crucial.
The simplest example, where the non-linear term contributes, is given by the
two-loop amplitude involving the insertion of two \phi_0 (the constraint of the
non-linear sigma model) and two flat connections. In this case we verify the
validity of the renormalization procedure: the recursive subtraction of the
pole parts at D=4 yields amplitudes that satisfy the defining functional
equation. As a by-product we give a formal proof that in D dimensions (without
counterterms) the Feynman rules provide a perturbative symmetric solution.Comment: Latex, 3 figures, 19 page

### Wannier functions and Fractional Quantum Hall Effect

We introduce and study the Wannier functions for an electron moving in a
plane under the influence of a perpendicular uniform and constant magnetic
field. The relevance for the Fractional Quantum Hall Effect is discussed; in
particular it shown that an interesting Hartree-Fock state can be constructed
in terms of Wannier functions.Comment: 7 pages, RevTeX 3.0, 5 tar-compressed and uu-encoded figure

### The SU(2) X U(1) Electroweak Model based on the Nonlinearly Realized Gauge Group

The electroweak model is formulated on the nonlinearly realized gauge group
SU(2) X U(1). This implies that in perturbation theory no Higgs field is
present. The paper provides the effective action at the tree level, the Slavnov
Taylor identity (necessary for the proof of unitarity), the local functional
equation (used for the control of the amplitudes involving the Goldstone
bosons) and the subtraction procedure (nonstandard, since the theory is not
power-counting renormalizable). Particular attention is devoted to the number
of independent parameters relevant for the vector mesons; in fact there is the
possibility of introducing two mass parameters. With this choice the relation
between the ratio of the intermediate vector meson masses and the Weinberg
angle depends on an extra free parameter. We briefly outline a method for
dealing with \gamma_5 in dimensional regularization. The model is formulated in
the Landau gauge for sake of simplicity and conciseness: the QED Ward identity
has a simple and intriguing form.Comment: 19 pages, final version published by Int. J. Mod. Phys. A, some typos
corrected in eqs.(1) and (41). The errors have a pure editing origin.
Therefore they do not affect the content of the pape

### Path-integral over non-linearly realized groups and Hierarchy solutions

The technical problem of deriving the full Green functions of the elementary
pion fields of the nonlinear sigma model in terms of ancestor amplitudes
involving only the flat connection and the nonlinear sigma model constraint is
a very complex task. In this paper we solve this problem by integrating, order
by order in the perturbative loop expansion, the local functional equation
derived from the invariance of the SU(2) Haar measure under local left
multiplication. This yields the perturbative definition of the path-integral
over the non-linearly realized SU(2) group.Comment: 26 page

### Numerical analysis of the master equation

Applied to the master equation, the usual numerical integration methods, such
as Runge-Kutta, become inefficient when the rates associated with various
transitions differ by several orders of magnitude. We introduce an integration
scheme that remains stable with much larger time increments than can be used in
standard methods. When only the stationary distribution is required, a direct
iteration method is even more rapid; this method may be extended to construct
the quasi-stationary distribution of a process with an absorbing state.
Applications to birth-and-death processes reveal gains in efficiency of two or
more orders of magnitude.Comment: 7 pages 3 figure

### Theoretical implications of the second time derivative of the period of the pulsar NP0532

Theoretical implications of second time derivative with existing magnetic dipole model

### Matrix Models, Argyres-Douglas singularities and double scaling limits

We construct an N=1 theory with gauge group U(nN) and degree n+1 tree level
superpotential whose matrix model spectral curve develops an A_{n+1}
Argyres-Douglas singularity. We evaluate the coupling constants of the
low-energy U(1)^n theory and show that the large N expansion is singular at the
Argyres-Douglas points. Nevertheless, it is possible to define appropriate
double scaling limits which are conjectured to yield four dimensional
non-critical string theories as proposed by Ferrari. In the Argyres-Douglas
limit the n-cut spectral curve degenerates into a solution with n/2 cuts for
even n and (n+1)/2 cuts for odd n.Comment: 31 pages, 1 figure; the expression of the superpotential has been
corrected and the calculation of the coupling constants of the low-energy
theory has been adde

### Living with stable angina: patients' pathway and needs in angina.

AIMS: There is evidence that stable angina patients may suffer from emotional disorders that further impair their quality of life. However, the emotional experience of living with stable angina from the patient's perspective still has to be explored. Thus, the main aim of this study was to explore patients' emotional experience of having stable angina and their reported needs during the pathway from the first symptoms, through the process of diagnosis, to management and related lifestyle changes. METHODS: A survey was conducted in 75 chronic ischemic heart disease patients with angina (Brazil, China, Romania, Russia, and Turkey) using a 75-min, face-to-face in-depth interview. RESULTS AND CONCLUSION: Patients' responses highlighted the need to increase individuals' awareness on the first signs and symptoms of the disease. The survey also showed that chronic stable angina patients need constant emotional support to overcome stress, anxiety, and depression. Finally, this study suggests the need to offer greater space for dialogue with healthcare professionals to get more comprehensive and 'patient-friendly' information

### The Hierarchy Principle and the Large Mass Limit of the Linear Sigma Model

In perturbation theory we study the matching in four dimensions between the
linear sigma model in the large mass limit and the renormalized nonlinear sigma
model in the recently proposed flat connection formalism. We consider both the
chiral limit and the strong coupling limit of the linear sigma model. Our
formalism extends to Green functions with an arbitrary number of pion legs,at
one loop level,on the basis of the hierarchy as an efficient unifying principle
that governs both limits. While the chiral limit is straightforward, the
matching in the strong coupling limit requires careful use of the normalization
conditions of the linear theory, in order to exploit the functional equation
and the complete set of local solutions of its linearized form.Comment: Latex, 41 pages, corrected typos, final version accepted by IJT

### Competition interfaces and second class particles

The one-dimensional nearest-neighbor totally asymmetric simple exclusion
process can be constructed in the same space as a last-passage percolation
model in Z^2. We show that the trajectory of a second class particle in the
exclusion process can be linearly mapped into the competition interface between
two growing clusters in the last-passage percolation model. Using technology
built up for geodesics in percolation, we show that the competition interface
converges almost surely to an asymptotic random direction. As a consequence we
get a new proof for the strong law of large numbers for the second class
particle in the rarefaction fan and describe the distribution of the asymptotic
angle of the competition interface.Comment: Published at http://dx.doi.org/10.1214/009117905000000080 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org

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