255 research outputs found
AURA_ A MEDIA DEVICE FOR NEW NARRATION SPACES IN MUSEUM CONTEXTS
The long months of social distance to which the pandemic has forced us have certainly accelerated the idea that the remediation of the concept of distance in a digital horizon can open up new spaces of negotiation for many social and cultural
practices in the future. But it has also, dramatically, highlighted the limits and risks contained in the very idea that the
experience of the meta-universe can really do without the mediation of physical reality and human direct intervention. The
reflections and design experience proposed here therefore aim to reflect on the role that the new technologies and traditional
professionals are playing in relation with the phygital cultural experience. The idea of the contemporary museum is indagated,
questioning, however, the quality of the 'relationship' between the work of art and the user and the ways in which design can
respond creatively to the demand for cultural consumption by activating new processes of attribution of meaning
Tents, Beds and Clothing: The Evocative Objects of Contemporary Art Textile
The vast collection of textiles, fabrics and fibres from Vesuvian sites, kept at the MANN (National Archaeological Museum of Naples), represents one of the most interesting and, until now, less explored bequests of a not marginal aspect of ancient culture, among whose ‘folds’ it is possible to trace important elements of an history that crosses the sphere of production, distribution, habits and society of Pompeii and, more generally, of Roman culture. The contribution intends to present the first results of a work of research and documentation on this precious textile material and the task of reinterpreting, that the research group is carrying out in order to illustrate a process of dissemination and cultural promotion of the complex knowledge that is kept in it
Instanton Counting and Wall-Crossing for Orbifold Quivers
Noncommutative Donaldson-Thomas invariants for abelian orbifold singularities can be studied via the enumeration of instanton solutions in a six-dimensional noncommutative {Mathematical expression} gauge theory; this construction is based on the generalized McKay correspondence and identifies the instanton counting with the counting of framed representations of a quiver which is naturally associated with the geometry of the singularity. We extend these constructions to compute BPS partition functions for higher-rank refined and motivic noncommutative Donaldson-Thomas invariants in the Coulomb branch in terms of gauge theory variables and orbifold data. We introduce the notion of virtual instanton quiver associated with the natural symplectic charge lattice which governs the quantum wall-crossing behaviour of BPS states in this context. The McKay correspondence naturally connects our formalism with other approaches to wall-crossing based on quantum monodromy operators and cluster algebras
Gauge-Invariant Resummation Formalism and Unitarity in Non-Commutative QED
We re-examine the perturbative properties of four-dimensional non-commutative
QED by extending the pinch techniques to the theta-deformed case. The explicit
independence of the pinched gluon self-energy from gauge-fixing parameters, and
the absence of unphysical thresholds in the resummed propagators permits a
complete check of the optical theorem for the off-shell two-point function. The
known anomalous (tachyonic) dispersion relations are recovered within this
framework, as well as their improved version in the (softly broken) SUSY case.
These applications should be considered as a first step in constructing
gauge-invariant truncations of the Schwinger-Dyson equations in the
non-commutative case. An interesting result of our formalism appears when
considering the theory in two dimensions: we observe a finite gauge-invariant
contribution to the photon mass because of a novel incarnation of IR/UV mixing,
which survives the commutative limit when matter is present.Comment: 30 pages, 2 eps figure, uses axodraw. Citations adde
Area-preserving diffeomorphisms in gauge theory on a non-commutative plane: a lattice study
We consider Yang-Mills theory with the U(1) gauge group on a non-commutative
plane. Perturbatively it was observed that the invariance of this theory under
area-preserving diffeomorphisms (APDs) breaks down to a rigid subgroup SL(2,R).
Here we present explicit results for the APD symmetry breaking at finite gauge
coupling and finite non-commutativity. They are based on lattice simulations
and measurements of Wilson loops with the same area but with a variety of
different shapes. Our results are consistent with the expected loss of
invariance under APDs. Moreover, they strongly suggest that non-perturbatively
the SL(2,R) symmetry does not persist either.Comment: 28 pages, 15 figures, published versio
Morita Duality and Noncommutative Wilson Loops in Two Dimensions
We describe a combinatorial approach to the analysis of the shape and
orientation dependence of Wilson loop observables on two-dimensional
noncommutative tori. Morita equivalence is used to map the computation of loop
correlators onto the combinatorics of non-planar graphs. Several
nonperturbative examples of symmetry breaking under area-preserving
diffeomorphisms are thereby presented. Analytic expressions for correlators of
Wilson loops with infinite winding number are also derived and shown to agree
with results from ordinary Yang-Mills theory.Comment: 32 pages, 9 figures; v2: clarifying comments added; Final version to
be published in JHE
Magnetic and transport properties of the new antiferromagnetic Kondo-lattice CeNiBi2
We report results of the first studies on the magnetic and transport
properties of a new material CeNiBi_2. The magnetic susceptibility exhibits a
sharp peak at T_N = 6K, indicating an antiferromagnetic phase transition. This
antiferromagnetic order below T_N is confirmed by magnetization measurement,
which displays a metamagnetic-like transition at H_m = 5 T. Both
low-temperature susceptibility and high-field magnetization are suggestive of
strong crystalline-electric-field effect in CeNiBi_2. The electrical
resistivity shows the presence of Kondo and crystal-field effects with a sharp
drop below TN due to the antiferromagnetic ordering. This sharp drop below T_N
in the electrical resistivity is suppressed slightly to higher temperatures by
an applied magnetic field to 18 T. With increasing magnetic field, the slope of
magnetoresistance changes from positive to negative, being indicative of the
transition to a ferromagnetic state.Comment: 11 pages, including 4 figure
An example of localized D-branes solution on PP-wave backgrounds
In this note we provide an explicit example of type IIB supersymmetric
D3-branes solution on a pp-wave like background, consisting in the product of
an eight-dimensional pp-wave times a two-dimensional flat space. An interesting
property of our solution is the fully localization of the D3-branes (i.e. the
solution depends on all the transverse coordinates). Then we show the
generalization to other Dp-branes and to the D1/D5 system.Comment: 14 pages, 1 table; v2. references adde
A non-perturbative study of 4d U(1) non-commutative gauge theory -- the fate of one-loop instability
Recent perturbative studies show that in 4d non-commutative spaces, the
trivial (classically stable) vacuum of gauge theories becomes unstable at the
quantum level, unless one introduces sufficiently many fermionic degrees of
freedom. This is due to a negative IR-singular term in the one-loop effective
potential, which appears as a result of the UV/IR mixing. We study such a
system non-perturbatively in the case of pure U(1) gauge theory in four
dimensions, where two directions are non-commutative. Monte Carlo simulations
are performed after mapping the regularized theory onto a U(N) lattice gauge
theory in d=2. At intermediate coupling strength, we find a phase in which open
Wilson lines acquire non-zero vacuum expectation values, which implies the
spontaneous breakdown of translational invariance. In this phase, various
physical quantities obey clear scaling behaviors in the continuum limit with a
fixed non-commutativity parameter , which provides evidence for a
possible continuum theory. The extent of the dynamically generated space in the
non-commutative directions becomes finite in the above limit, and its
dependence on is evaluated explicitly. We also study the dispersion
relation. In the weak coupling symmetric phase, it involves a negative
IR-singular term, which is responsible for the observed phase transition. In
the broken phase, it reveals the existence of the Nambu-Goldstone mode
associated with the spontaneous symmetry breaking.Comment: 29 pages, 23 figures, references adde
Probability distribution of the index in gauge theory on 2d non-commutative geometry
We investigate the effects of non-commutative geometry on the topological
aspects of gauge theory using a non-perturbative formulation based on the
twisted reduced model. The configuration space is decomposed into topological
sectors labeled by the index nu of the overlap Dirac operator satisfying the
Ginsparg-Wilson relation. We study the probability distribution of nu by Monte
Carlo simulation of the U(1) gauge theory on 2d non-commutative space with
periodic boundary conditions. In general the distribution is asymmetric under
nu -> -nu, reflecting the parity violation due to non-commutative geometry. In
the continuum and infinite-volume limits, however, the distribution turns out
to be dominated by the topologically trivial sector. This conclusion is
consistent with the instanton calculus in the continuum theory. However, it is
in striking contrast to the known results in the commutative case obtained from
lattice simulation, where the distribution is Gaussian in a finite volume, but
the width diverges in the infinite-volume limit. We also calculate the average
action in each topological sector, and provide deeper understanding of the
observed phenomenon.Comment: 16 pages,10 figures, version appeared in JHE
- …