568 research outputs found
Dynamical breakdown of Abelian gauge chiral symmetry by strong Yukawa interactions
We consider a model with anomaly-free Abelian gauge axial-vector symmetry,
which is intended to mimic the standard electroweak gauge chiral SU(2)_L x
U(1)_Y theory. Within this model we demonstrate: (1) Strong Yukawa interactions
between massless fermion fields and a massive scalar field carrying the axial
charge generate dynamically the fermion and boson proper self-energies, which
are ultraviolet-finite and chirally noninvariant. (2) Solutions of the
underlying Schwinger-Dyson equations found numerically exhibit a huge
amplification of the fermion mass ratios as a response to mild changes of the
ratios of the Yukawa couplings. (3) The `would-be' Nambu-Goldstone boson is a
composite of both the fermion and scalar fields, and it gives rise to the mass
of the axial-vector gauge boson. (4) Spontaneous breakdown of the gauge
symmetry further manifests by mass splitting of the complex scalar and by new
symmetry-breaking vertices, generated at one loop. In particular, we work out
in detail the cubic vertex of the Abelian gauge boson.Comment: 11 pages, REVTeX4, 10 eps figures; additional remarks and references
added; version published in Phys. Rev.
Towards a case-based learning approach to support software architecture education
Software architecture education remains challenging for instructors,
students, and software industry professionals. Several initiatives have been
proposed to mitigate the inherent challenges, including games, supporting
tools, collaborative courses, and hands-on projects. Case-based learning has
been introduced in software architecture, and its benefits are recognized.
However, choosing the right cases that cover the stated learning objectives and
developing learning activities to achieve high-order learning are also
challenging. The main goal of this paper is to present a case-based learning
approach that guides the development of learning objectives, the finding and
selection of real-world software architecture cases, and the design of
instructional activities. We applied our approach in software architecture
related courses during the past few years. The results show that it can
leverage the ways to adequately explore cases for educational purposes while
also motivating instructors and students to the software architecture
education
Searching for Radio Pulsars in 3EG Sources at Urumqi Observatory
Since mid-2005, a pulsar searching system has been operating at 18 cm on the
25-m radio telescope of Urumqi Observatory. Test observations on known pulsars
show that the system can perform the intended task. The prospect of using this
system to observe 3EG sources and other target searching tasks is discussed.Comment: a training project about MSc thesi
Double photo-ionization of He near a polarizable surface
We calculate the differential cross-section of the direct double
photo-ionization of He physisorbed on a polarizable surface. By including the
influence of the surface potential in the correlated two-electron final state
wavefunction, we show that the differential cross-section carries detailed
information on the electronic correlations at the surface. In particular,
photo-emission along opposite directions, which is prohibited in the free
space, is allowed if the surface potential is long-ranged.Comment: To appear in Phys. Rev. B - Rapid Comm. - 4 pages, 2 PostScript
figures embedde
How Robust are the Estimated Effects of Nonpharmaceutical Interventions against COVID-19?
To what extent are effectiveness estimates of nonpharmaceutical interventions (NPIs) against COVID-19 influenced by the assumptions our models make? To answer this question, we investigate 2 state-of-the-art NPI effectiveness models and propose 6 variants that make different structural assumptions. In particular, we investigate how well NPI effectiveness estimates generalise to unseen countries, and their sensitivity to unobserved factors. Models which account for noise in disease transmission compare favourably. We further evaluate how robust estimates are to different choices of epidemiological parameters and data. Focusing on models that assume transmission noise, we find that previously published results are robust across these choices and across different models. Finally, we mathematically ground the interpretation of NPI effectiveness estimates when certain common assumptions do not hold
Dynamical electroweak symmetry breaking due to strong Yukawa interactions
We present a new mechanism for electroweak symmetry breaking (EWSB) based on
a strong Yukawa dynamics. We consider an SU(2)_L x U(1)_Y gauge invariant model
endowed with the usual Standard model fermion multiplets and with two massive
scalar doublets. We show that, unlike in the Standard model, EWSB is possible
even with vanishing vacuum expectation values of the scalars. Such EWSB is
achieved dynamically by means of the (presumably strong) Yukawa couplings and
manifests itself by the emergence of fermion and gauge boson masses and scalar
mass-splittings, which are expressed in a closed form in terms of the fermion
and scalar proper self-energies. The `would-be' Nambu--Goldstone bosons are
shown to be composites of both the fermions and the scalars. We demonstrate
that the simplest version of the model is compatible with basic experimental
constraints.Comment: 6 pages, REVTeX4, 3 eps figures; discussion of compatibility with EW
precision data added; version published in J. Phys.
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