75 research outputs found
Gluon mass generation in the PT-BFM scheme
In this article we study the general structure and special properties of the
Schwinger-Dyson equation for the gluon propagator constructed with the pinch
technique, together with the question of how to obtain infrared finite
solutions, associated with the generation of an effective gluon mass.
Exploiting the known all-order correspondence between the pinch technique and
the background field method, we demonstrate that, contrary to the standard
formulation, the non-perturbative gluon self-energy is transverse
order-by-order in the dressed loop expansion, and separately for gluonic and
ghost contributions. We next present a comprehensive review of several subtle
issues relevant to the search of infrared finite solutions, paying particular
attention to the role of the seagull graph in enforcing transversality, the
necessity of introducing massless poles in the three-gluon vertex, and the
incorporation of the correct renormalization group properties. In addition, we
present a method for regulating the seagull-type contributions based on
dimensional regularization; its applicability depends crucially on the
asymptotic behavior of the solutions in the deep ultraviolet, and in particular
on the anomalous dimension of the dynamically generated gluon mass. A
linearized version of the truncated Schwinger-Dyson equation is derived, using
a vertex that satisfies the required Ward identity and contains massless poles
belonging to different Lorentz structures. The resulting integral equation is
then solved numerically, the infrared and ultraviolet properties of the
obtained solutions are examined in detail, and the allowed range for the
effective gluon mass is determined. Various open questions and possible
connections with different approaches in the literature are discussed.Comment: 54 pages, 24 figure
The annealing mechanism of AuGe/Ni/Au ohmic contacts to a two-dimensional electron gas in GaAs/AlGaAs heterostructures
Ohmic contacts to a two-dimensional electron gas (2DEG) in GaAs/AlGaAs
heterostructures are often realized by annealing of AuGe/Ni/Au that is
deposited on its surface. We studied how the quality of this type of ohmic
contact depends on the annealing time and temperature, and how optimal
parameters depend on the depth of the 2DEG below the surface. Combined with
transmission electron microscopy and energy-dispersive X-ray spectrometry
studies of the annealed contacts, our results allow for identifying the
annealing mechanism and proposing a model that can predict optimal annealing
parameters for a certain heterostructure.Comment: 9 pages, 4 figure
No Weight for “Due Weight”? A Children’s Autonomy Principle in Best Interest Proceedings
Article 12 of the un Convention on the Rights of the Child (crc) stipulates that children should have their views accorded due weight in accordance with age and maturity, including in proceedings affecting them. Yet there is no accepted understanding as to how to weigh children’s views, and it is associated strongly with the indeterminate notion of “competence”. In this article, case law and empirical research is drawn upon to argue that the concept of weighing their views has been an obstacle to children’s rights, preventing influence on outcomes for children in proceedings in which their best interests are determined. Younger children and those whose wishes incline against the prevailing orthodoxy (they may resist contact with a parent, for example) particularly lose out. Children’s views appear only to be given “significant weight” if the judge agrees with them anyway. As it is the notion of autonomy which is prioritised in areas such as medical and disability law and parents’ rights, it is proposed in this article that a children’s autonomy principle is adopted in proceedings – in legal decisions in which the best interest of the child is the primary consideration, children should get to choose, if they wish, how they are involved and the outcome, unless it is likely that significant harm will arise from their wishes. They should also have “autonomy support” to assist them in proceedings. This would likely ensure greater influence for children and require more transparent decision-making by adults.</jats:p
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