12,201 research outputs found
A semi-implicit numerical method for treating the time transient gas lubrication equation
Numerical method for treating time transient gas lubrication equatio
Twisted K-theory and K-theory of bundle gerbes
In this note we introduce the notion of bundle gerbe K-theory and investigate
the relation to twisted K-theory. We provide some examples. Possible
applications of bundle gerbe K-theory to the classification of D-brane charges
in non-trivial backgrounds are discussed.Comment: 29 pages, corrected typos, added references, included new section on
twisted Chern character in non-torsion cas
Dynamical symmetry breaking and the Nambu-Goldstone theorem in the Gaussian wave functional approximation
We analyze the group-theoretical ramifications of the Nambu-Goldstone [NG]
theorem in the self-consistent relativistic variational Gaussian wave
functional approximation to spinless field theories. In an illustrative example
we show how the Nambu-Goldstone theorem would work in the O(N) symmetric
scalar field theory, if the residual symmetry of the vacuum were
lesser than O(N-1), e.g. if the vacuum were O(N-2), or O(N-3),... symmetric.
[This does not imply that any of the "lesser" vacua is actually the absolute
energy minimum: stability analysis has not been done.] The requisite number of
NG bosons would be (2N - 3), or (3N - 6), ... respectively, which may exceed N,
the number of elementary fields in the Lagrangian. We show how the requisite
new NG bosons would appear even in channels that do not carry the same quantum
numbers as one of N "elementary particles" (scalar field quanta, or
Castillejo-Dalitz-Dyson [CDD] poles) in the Lagrangian, i.e. in those "flavour"
channels that have no CDD poles. The corresponding Nambu-Goldstone bosons are
composites (bound states) of pairs of massive elementary (CDD) scalar fields
excitations. As a nontrivial example of this method we apply it to the
physically more interesting 't Hooft model (an extended
bosonic linear model with four scalar and four pseudoscalar fields),
with spontaneously and explicitly broken chiral symmetry.Comment: 17 pages, no figure
The Non-Trivial Effective Potential of the `Trivial' lambda Phi^4 Theory: A Lattice Test
The strong evidence for the `triviality' of (lambda Phi^4)_4 theory is not
incompatible with spontaneous symmetry breaking. Indeed, for a `trivial' theory
the effective potential should be given exactly by the classical potential plus
the free-field zero-point energy of the shifted field; i.e., by the one-loop
effective potential. When this is renormalized in a simple, but nonperturbative
way, one finds, self-consistently, that the shifted field does become
non-interacting in the continuum limit. For a classically scale-invariant (CSI)
lambda Phi^4 theory one finds m_h^2 = 8 pi^2 v^2, predicting a 2.2 TeV Higgs
boson. Here we extend our earlier work in three ways: (i) we discuss the
analogy with the hard-sphere Bose gas; (ii) we extend the analysis from the CSI
case to the general case; and (iii) we propose a test of the predicted shape of
the effective potential that could be tested in a lattice simulation.Comment: 22 pages, LaTeX, DE-FG05-92ER40717-
The Spectral Energy Distribution of Fermi Bright Blazars
We have conducted a detailed investigation of the broadband spectral properties of the γ-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi γ-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/γ-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these γ-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log ν-log ν F _ν representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, α_(ro), and optical to X-ray, α_(ox), spectral slopes) and from the γ-ray spectral index. Our data show that the synchrotron peak frequency (ν^S _(peak)) is positioned between 10^(12.5) and 10^(14.5) Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10^(13) and 10^(17) Hz in featureless BL Lacertae objects. We find that the γ-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than 50% of known radio bright high energy peaked (HBL) BL Lacs are detected in the LBAS sample, only less than 13% of known bright FSRQs and LBL BL Lacs are included. This suggests that the latter sources, as a class, may be much fainter γ-ray emitters than LBAS blazars, and could in fact radiate close to the expectations of simple SSC models. We categorized all our sources according to a new physical classification scheme based on the generally accepted paradigm for Active Galactic Nuclei and on the results of this SED study. Since the LAT detector is more sensitive to flat spectrum γ-ray sources, the correlation between ν ^S _(peak) and γ-ray spectral index strongly favors the detection of high energy peaked blazars, thus explaining the Fermi overabundance of this type of sources compared to radio and EGRET samples. This selection effect is similar to that experienced in the soft X-ray band where HBL BL Lacs are the dominant type of blazars
The four-fermion interaction in D=2,3,4: a nonperturbative treatment
A new nonperturbative approach is used to investigate the Gross-Neveu model
of four fermion interaction in the space-time dimensions 2, 3 and 4, the number
of inner degrees of freedom being a fixed integer. The spontaneous symmetry
breaking is shown to exist in and the running coupling constant is
calculated. The four dimensional theory seems to be trivial.Comment: a minor correction: one more acknowledgement is added. Latex 2.09
file, 15 pages, no figures, accepted for publication to Int.J.Mod.Phys.
The gamification of cybersecurity training
Due to the rapidly and continued evolving nature of technology, there is a constant need to update police officers’ training in cyber security to ensure that the UK continues to be a secure place to live and do business. Rather than deliver traditional classroom-based training, our project assesses the effectiveness of the delivery of cyber security through the use of games based learning to simulate cybercrimes and provide training in incident response. The aim of our research is to transform the delivery of first responder training in tackling cybercrime.Through the use of a Game Jam and subsequent prototype development, we have trialed training materials that are based on serious games technology. The game poses a common incident reported to the police, for example the problem of a virtual person receiving offensive messages via Facebook and the training reflects the dialogue with that person and the technical steps to ensure that a copy of the evidence has been preserved for further investigation. Evaluation has been conducted with local police officers. Overall, this approach to the large-scale provision of training (potentially to a whole force) is shown to offer potential
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