3,332 research outputs found
Building an Argument for the Use of Science Fiction in HCI Education
Science fiction literature, comics, cartoons and, in particular, audio-visual
materials, such as science fiction movies and shows, can be a valuable addition
in Human-computer interaction (HCI) Education. In this paper, we present an
overview of research relative to future directions in HCI Education, distinct
crossings of science fiction in HCI and Computer Science teaching and the
Framework for 21st Century Learning. Next, we provide examples where science
fiction can add to the future of HCI Education. In particular, we argue herein
first that science fiction, as tangible and intangible cultural artifact, can
serve as a trigger for creativity and innovation and thus, support us in
exploring the design space. Second, science fiction, as a means to analyze
yet-to-come HCI technologies, can assist us in developing an open-minded and
reflective dialogue about technological futures, thus creating a singular base
for critical thinking and problem solving. Provided that one is cognizant of
its potential and limitations, we reason that science fiction can be a
meaningful extension of selected aspects of HCI curricula and research.Comment: 6 pages, 1 table, IHSI 2019 accepted submissio
Higher Derivative Corrections to R-charged Black Holes: Boundary Counterterms and the Mass-Charge Relation
We carry out the holographic renormalization of Einstein-Maxwell theory with
curvature-squared corrections. In particular, we demonstrate how to construct
the generalized Gibbons-Hawking surface term needed to ensure a perturbatively
well-defined variational principle. This treatment ensures the absence of ghost
degrees of freedom at the linearized perturbative order in the
higher-derivative corrections. We use the holographically renormalized action
to study the thermodynamics of R-charged black holes with higher derivatives
and to investigate their mass to charge ratio in the extremal limit. In five
dimensions, there seems to be a connection between the sign of the higher
derivative couplings required to satisfy the weak gravity conjecture and that
violating the shear viscosity to entropy bound. This is in turn related to
possible constraints on the central charges of the dual CFT, in particular to
the sign of c-a.Comment: 30 pages. v2: references added, some equations simplifie
The Weak Gravity Conjecture and the Viscosity Bound with Six-Derivative Corrections
The weak gravity conjecture and the shear viscosity to entropy density bound
place constraints on low energy effective field theories that may help to
distinguish which theories can be UV completed. Recently, there have been
suggestions of a possible correlation between the two constraints. In some
interesting cases, the behavior was precisely such that the conjectures were
mutually exclusive. Motivated by these works, we study the mass to charge and
shear viscosity to entropy density ratios for charged AdS5 black branes, which
are holographically dual to four-dimensional CFTs at finite temperature. We
study a family of four-derivative and six-derivative perturbative corrections
to these backgrounds. We identify the region in parameter space where the two
constraints are satisfied and in particular find that the inclusion of the
next-to-leading perturbative correction introduces wider possibilities for the
satisfaction of both constraints.Comment: 24 pages, 6 figures, v2: published version, refs added, minor
clarificatio
Black Holes in Quasi-topological Gravity
We construct a new gravitational action which includes cubic curvature
interactions and which provides a useful toy model for the holographic study of
a three parameter family of four- and higher-dimensional CFT's. We also
investigate the black hole solutions of this new gravity theory. Further we
examine the equations of motion of quasi-topological gravity. While the full
equations in a general background are fourth-order in derivatives, we show that
the linearized equations describing gravitons propagating in the AdS vacua
match precisely the second-order equations of Einstein gravity.Comment: 33 pages, 4 figures; two references adde
Lovelock theories, holography and the fate of the viscosity bound
We consider Lovelock theories of gravity in the context of AdS/CFT. We show
that, for these theories, causality violation on a black hole background can
occur well in the interior of the geometry, thus posing more stringent
constraints than were previously found in the literature. Also, we find that
instabilities of the geometry can appear for certain parameter values at any
point in the geometry, as well in the bulk as close to the horizon. These new
sources of causality violation and instability should be related to CFT
features that do not depend on the UV behavior. They solve a puzzle found
previously concerning unphysical negative values for the shear viscosity that
are not ruled out solely by causality restrictions. We find that, contrary to
previous expectations, causality violation is not always related to positivity
of energy. Furthermore, we compute the bound for the shear viscosity to entropy
density ratio of supersymmetric conformal field theories from d=4 till d=10 -
i.e., up to quartic Lovelock theory -, and find that it behaves smoothly as a
function of d. We propose an approximate formula that nicely fits these values
and has a nice asymptotic behavior when d goes to infinity for any Lovelock
gravity. We discuss in some detail the latter limit. We finally argue that it
is possible to obtain increasingly lower values for the shear viscosity to
entropy density ratio by the inclusion of more Lovelock terms.Comment: 42 pages, 17 figures, JHEP3.cls. v2: reference adde
Viscosity Bound and Causality in Superfluid Plasma
It was argued by Brigante et.al that the lower bound on the ratio of the
shear viscosity to the entropy density in strongly coupled plasma is translated
into microcausality violation in the dual gravitational description. Since
transport properties of the system characterize its infrared dynamics, while
the causality of the theory is determined by its ultraviolet behavior, the
viscosity bound/microcausality link should not be applicable to theories that
undergo low temperature phase transitions. We present an explicit model of
AdS/CFT correspondence that confirms this fact.Comment: 27 pages, 5 figures. References added, typos fixe
Entanglement Entropy for Singular Surfaces
We study entanglement entropy for regions with a singular boundary in higher
dimensions using the AdS/CFT correspondence and find that various singularities
make new universal contributions. When the boundary CFT has an even spacetime
dimension, we find that the entanglement entropy of a conical surface contains
a term quadratic in the logarithm of the UV cut-off. In four dimensions, the
coefficient of this contribution is proportional to the central charge 'c'. A
conical singularity in an odd number of spacetime dimensions contributes a term
proportional to the logarithm of the UV cut-off. We also study the entanglement
entropy for various boundary surfaces with extended singularities. In these
cases, similar universal terms may appear depending on the dimension and
curvature of the singular locus.Comment: 66 pages,4 figures. Some typos are removed and a reference is adde
Holographic GB gravity in arbitrary dimensions
We study the properties of the holographic CFT dual to Gauss-Bonnet gravity
in general dimensions. We establish the AdS/CFT dictionary and in
particular relate the couplings of the gravitational theory to the universal
couplings arising in correlators of the stress tensor of the dual CFT. This
allows us to examine constraints on the gravitational couplings by demanding
consistency of the CFT. In particular, one can demand positive energy fluxes in
scattering processes or the causal propagation of fluctuations. We also examine
the holographic hydrodynamics, commenting on the shear viscosity as well as the
relaxation time. The latter allows us to consider causality constraints arising
from the second-order truncated theory of hydrodynamics.Comment: 48 pages, 9 figures. v2: New discussion on free fields in subsection
3.3 and new appendix B on conformal tensor fields. Added comments on the
relation between the central charge appearing in the two-point function and
the "central charge" characterizing the entropy density in the discussion.
References adde
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