44,932 research outputs found
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
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
TASEP hydrodynamics using microscopic characteristics
The convergence of the totally asymmetric simple exclusion process to the
solution of the Burgers equation is a classical result. In his seminal 1981
paper, Herman Rost proved the convergence of the density fields and local
equilibrium when the limiting solution of the equation is a rarefaction fan. An
important tool of his proof is the subadditive ergodic theorem. We prove his
results by showing how second class particles transport the rarefaction-fan
solution, as characteristics do for the Burgers equation, avoiding
subadditivity. In the way we show laws of large numbers for tagged particles,
fluxes and second class particles, and simplify existing proofs in the shock
cases. The presentation is self contained.Comment: 20 pages, 13 figures. This version is accepted for publication in
Probability Surveys, February 20 201
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
Lorentz violation in the linearized gravity
We study some consequences of the introduction of a Lorentz-violating
modification term in the linearized gravity, which leads to modified dispersion
relations for gravitational waves in the vacuum. We also discuss possible
mechanisms for the induction of such a term in the Lagrangian.Comment: Presented at the Fifth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 28-July 2, 201
model in aether-superspace
In this paper we study the dynamical generation of mass in the
Lorentz-violating model defined in two and three-dimensional
aether-superspace. We show that even though the model presents a phase
structure similar to the usual, Lorentz invariant case, the dynamically
generated mass by quantum corrections has a dependence on the Lorentz violating
background properties, except for spacelike LV vector parameter. This is to be
contrasted with the behavior of the quantum electrodynamics in the
two-dimensional aether-superspace, where the dynamical generation of mass was
shown to exhibit an explicit dependence on the aether parameters in every
possible case.Comment: 18 pages, 4 figure
Learning Visual Attributes
We present a probabilistic generative model of visual attributes, together with an efficient learning algorithm. Attributes are visual qualities of objects, such as ‘red’, ‘striped’, or ‘spotted’. The model sees attributes as patterns of image segments, repeatedly sharing some characteristic properties. These can be any combination of appearance, shape, or the layout of segments within the pattern. Moreover, attributes with general appearance are taken into account, such as the pattern of alternation of any two colors which is characteristic for stripes. To enable learning from unsegmented training images, the model is learnt discriminatively, by optimizing a likelihood ratio. As demonstrated in the experimental evaluation, our model can learn in a weakly supervised setting and encompasses a broad range of attributes. We show that attributes can be learnt starting from a text query to Google image search, and can then be used to recognize the attribute and determine its spatial extent in novel real-world images.
- …