1,095 research outputs found
On Representations of Conformal Field Theories and the Construction of Orbifolds
We consider representations of meromorphic bosonic chiral conformal field
theories, and demonstrate that such a representation is completely specified by
a state within the theory. The necessary and sufficient conditions upon this
state are derived, and, because of their form, we show that we may extend the
representation to a representation of a suitable larger conformal field theory.
In particular, we apply this procedure to the lattice (FKS) conformal field
theories, and deduce that Dong's proof of the uniqueness of the twisted
representation for the reflection-twisted projection of the Leech lattice
conformal field theory generalises to an arbitrary even (self-dual) lattice. As
a consequence, we see that the reflection-twisted lattice theories of Dolan et
al are truly self-dual, extending the analogies with the theories of lattices
and codes which were being pursued. Some comments are also made on the general
concept of the definition of an orbifold of a conformal field theory in
relation to this point of view.Comment: 11 pages, LaTeX. Updated references and added preprint n
Asymmetry in functional connectivity of the human habenula revealed by high-resolution cardiac-gated resting state imaging
The habenula is a hub for cognitive and emotional signals that are relayed to the aminergic centers in the midbrain and, thus, plays an important role in goal-oriented behaviors. Although it is well described in rodents and non-human primates, the habenula functional network remains relatively uncharacterized in humans, partly because of the methodological challenges associated with the functional magnetic resonance imaging of small structures in the brain. Using high-resolution cardiac-gated resting state imaging in healthy humans and precisely identifying each participants' habenula, we show that the habenula is functionally coupled with the insula, parahippocampus, thalamus, periaqueductal grey, pons, striatum and substantia nigra/ventral tegmental area complex. Furthermore, by separately examining and comparing the functional maps from the left and right habenula, we provide the first evidence of an asymmetry in the functional connectivity of the habenula in humans. Hum Brain Mapp 37:2602-2615, 2016. © 2016 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc
Demyelination and axonal preservation in a transgenic mouse model of Pelizaeus-Merzbacher disease
It is widely thought that demyelination contributes to the degeneration of axons and, in combination with acute inflammatory injury, is responsible for progressive axonal loss and persistent clinical disability in inflammatory demyelinating disease. In this study we sought to characterize the relationship between demyelination, inflammation and axonal transport changes using a Plp1-transgenic mouse model of Pelizaeus-Merzbacher disease. In the optic pathway of this non-immune mediated model of demyelination, myelin loss progresses from the optic nerve head towards the brain, over a period of months. Axonal transport is functionally perturbed at sites associated with local inflammation and 'damaged' myelin. Surprisingly, where demyelination is complete, naked axons appear well preserved despite a significant reduction of axonal transport. Our results suggest that neuroinflammation and/or oligodendrocyte dysfunction are more deleterious for axonal health than demyelination per se, at least in the short ter
Conformal Field Theories, Representations and Lattice Constructions
An account is given of the structure and representations of chiral bosonic
meromorphic conformal field theories (CFT's), and, in particular, the
conditions under which such a CFT may be extended by a representation to form a
new theory. This general approach is illustrated by considering the untwisted
and -twisted theories, and respectively,
which may be constructed from a suitable even Euclidean lattice .
Similarly, one may construct lattices and by
analogous constructions from a doubly-even binary code . In the case when
is self-dual, the corresponding lattices are also. Similarly,
and are self-dual if and only if is. We show that
has a natural ``triality'' structure, which induces an
isomorphism and also a triality
structure on . For the Golay code,
is the Leech lattice, and the triality on is the symmetry which extends the natural action of (an
extension of) Conway's group on this theory to the Monster, so setting triality
and Frenkel, Lepowsky and Meurman's construction of the natural Monster module
in a more general context. The results also serve to shed some light on the
classification of self-dual CFT's. We find that of the 48 theories
and with central charge 24 that there are 39 distinct ones,
and further that all 9 coincidences are accounted for by the isomorphism
detailed above, induced by the existence of a doubly-even self-dual binary
code.Comment: 65 page
It's Simplex! Disaggregating Measures to Improve Certified Robustness
Certified robustness circumvents the fragility of defences against
adversarial attacks, by endowing model predictions with guarantees of class
invariance for attacks up to a calculated size. While there is value in these
certifications, the techniques through which we assess their performance do not
present a proper accounting of their strengths and weaknesses, as their
analysis has eschewed consideration of performance over individual samples in
favour of aggregated measures. By considering the potential output space of
certified models, this work presents two distinct approaches to improve the
analysis of certification mechanisms, that allow for both dataset-independent
and dataset-dependent measures of certification performance. Embracing such a
perspective uncovers new certification approaches, which have the potential to
more than double the achievable radius of certification, relative to current
state-of-the-art. Empirical evaluation verifies that our new approach can
certify more samples at noise scale , with greater relative
improvements observed as the difficulty of the predictive task increases.Comment: IEEE S&P 2024, IEEE Security & Privacy 2024, 14 page
Enhancing the Antidote: Improved Pointwise Certifications against Poisoning Attacks
Poisoning attacks can disproportionately influence model behaviour by making
small changes to the training corpus. While defences against specific poisoning
attacks do exist, they in general do not provide any guarantees, leaving them
potentially countered by novel attacks. In contrast, by examining worst-case
behaviours Certified Defences make it possible to provide guarantees of the
robustness of a sample against adversarial attacks modifying a finite number of
training samples, known as pointwise certification. We achieve this by
exploiting both Differential Privacy and the Sampled Gaussian Mechanism to
ensure the invariance of prediction for each testing instance against finite
numbers of poisoned examples. In doing so, our model provides guarantees of
adversarial robustness that are more than twice as large as those provided by
prior certifications
Exploiting Certified Defences to Attack Randomised Smoothing
In guaranteeing that no adversarial examples exist within a bounded region,
certification mechanisms play an important role in neural network robustness.
Concerningly, this work demonstrates that the certification mechanisms
themselves introduce a new, heretofore undiscovered attack surface, that can be
exploited by attackers to construct smaller adversarial perturbations. While
these attacks exist outside the certification region in no way invalidate
certifications, minimising a perturbation's norm significantly increases the
level of difficulty associated with attack detection. In comparison to baseline
attacks, our new framework yields smaller perturbations more than twice as
frequently as any other approach, resulting in an up to reduction in
the median perturbation norm. That this approach also requires less
computational time than approaches like PGD. That these reductions are possible
suggests that exploiting this new attack vector would allow attackers to more
frequently construct hard to detect adversarial attacks, by exploiting the very
systems designed to defend deployed models.Comment: 15 pages, 7 figure
Categories of First-Order Quantifiers
One well known problem regarding quantifiers, in particular the 1storder
quantifiers, is connected with their syntactic categories and denotations.
The unsatisfactory efforts to establish the syntactic and ontological categories
of quantifiers in formalized first-order languages can be solved by means of the
so called principle of categorial compatibility formulated by Roman Suszko,
referring to some innovative ideas of Gottlob Frege and visible in syntactic
and semantic compatibility of language expressions. In the paper the principle
is introduced for categorial languages generated by the Ajdukiewiczâs classical
categorial grammar. The 1st-order quantifiers are typically ambiguous. Every
1st-order quantifier of the type k \u3e 0 is treated as a two-argument functorfunction
defined on the variable standing at this quantifier and its scope (the
sentential function with exactly k free variables, including the variable bound
by this quantifier); a binary function defined on denotations of its two arguments
is its denotation. Denotations of sentential functions, and hence also
quantifiers, are defined separately in Fregean and in situational semantics.
They belong to the ontological categories that correspond to the syntactic
categories of these sentential functions and the considered quantifiers. The
main result of the paper is a solution of the problem of categories of the
1st-order quantifiers based on the principle of categorial compatibility
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