2,784 research outputs found
More About Discrete Gauge Anomalies
I discuss and extend several results concerning the cancellation of discrete
gauge anomalies. I show how heavy fermions do not decouple in the presence of
discrete gauge anomalies. As a consequence, in general, cancellation of
discrete gauge anomalies cannot be described merely in terms of low energy
operators involving only the light fermions. I also discuss cancellation of
discrete gauge anomalies through a discrete version of the Green-Schwarz (GS)
mechanism as well as the possibility of discrete gauge R-symmetries and their
anomalies.
Finally, some phenomenological applications are discussed. This includes
symmetries guaranteeing absence of FCNC in two-Higgs models and generalized
matter parities stabilizing the proton in the supersymmetric standard model. In
the presence of a discrete GS mechanism or/and gauge R-symmetries, new
possibilities for anomaly free such symmetries are found.Comment: 25 pages CERN-TH.6662/92 (replaced version contains additional
tex-macros
Conjunctive queries with negation over DL-Lite: a closer look
While conjunctive query (CQ) answering over DL-Lite has been studied extensively, there have been few attempts to analyse CQs with negated atoms. This paper deepens the study of the problem. Answering CQs with safe negation and CQs with a single inequality over DL-Lite with role inclusions is shown to be undecidable, even for a fixed TBox and query.Without role inclusions, answering CQs with one inequality is P-hard and with two inequalities CoNP-hard in data complexity
Capacity analysis of suburban rail networks
As is well known, capacity evaluation and the identification of bottlenecks on rail networks are complex issues depending upon several technical elements. This is even more perceptible in metropolitan areas where different services (freight, long distance, metro/regional, etc.) are operated using the same limited infrastructures; as a consequence, these facilities may represent bottlenecks of the rail system since they are often highly utilized and congested. This paper tries to explore the issue of capacity evaluation of complex rail networks, proposing synthetic indicators
and analyses for feasibility studies or strategic planning. The presented methodology suggests taking into account the main differences in infrastructure characteristics (e.g. single or double lines, signalling systems, terminus or passing stations, etc.) and rail services (e.g. diverse rolling stock, various frequencies, average distances and number of stops, etc.) in order to propose a general approach applicable for capacity analysis of a network as a whole, hence evaluating the utilization rate and the congestion on both lines and stations. To better explore and
validate the methodology, an application to a line of the Naples’ suburban network is presented. The results confirm the applicability and effectiveness of the proposed approach; the outcomes indicate the capacity utilization rate of the considered facilities, pointing out likely bottlenecks and possible actions to improve the system efficiency
Axions in gravity with torsion
We study a scenario allowing a solution of the strong charge parity problem
via the Peccei-Quinn mechanism, implemented in gravity with torsion. In this
framework there appears a torsion-related pseudoscalar field known as
Kalb-Ramond axion. We compare it with the so-called Barbero-Immirzi axion
recently proposed in the literature also in the context of the gravity with
torsion. We show that they are equivalent from the viewpoint of the effective
theory. The phenomenology of these torsion-descended axions is completely
determined by the Planck scale without any additional model parameters. These
axions are very light and very weakly interacting with ordinary matter. We
briefly comment on their astrophysical and cosmological implications in view of
the recent BICEP2 and Planck data.Comment: 7 pages, no figures, comments and references added, published versio
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