458 research outputs found
Quantum gravitational corrected evolution equations of charged black holes
We explain how quantum gravity, treated as an effective field theory, might
modify the evaporative evolution of a four-dimensional, non-extremal,
non-rotating, charged black hole. With some approximations, we derive a set of
coupled differential equations describing the charge and mass of the black hole
as a function of time. These equations represent a generalisation of the
analogous ones already present in the literature for classical black holes.Comment: 12 pages; accepted for publication in JHA
Lyapunov exponents in supersymmetric Jackiw-Teitelboim gravity
We study supersymmetric Jackiw-Teitelboim (JT) gravity at
finite temperature coupled to matter. The matter fields are related to
superconformal primaries by AdS/CFT duality. Due to broken super
reparametrisation invariance in the SCFT dual, there are corrections to
superconformal correlators. These are generated by the exchange of
super-Schwarzian modes which is dual to the exchange of 2D supergravity modes.
We compute corrections to four-point functions for superconformal primaries and
analyse the behaviour of out-of-time-ordered correlators. In particular,
four-point functions of two pairs of primaries with mutually vanishing
two-point functions are considered. By decomposing the corresponding
supermultiplet into its components, we find different Lyapunov exponents. The
value of the Lyapunov exponents depends on whether the correction is due to
graviton, gravitini or graviphoton exchange. If mutual two-point functions do
not vanish all components grow with maximal Lyapunov exponent.Comment: 13 pages, v2: reference adde
Topological color codes on Union Jack lattices: A stable implementation of the whole Clifford group
We study the error threshold of topological color codes on Union Jack
lattices that allow for the full implementation of the whole Clifford group of
quantum gates. After mapping the error-correction process onto a statistical
mechanical random 3-body Ising model on a Union Jack lattice, we compute its
phase diagram in the temperature-disorder plane using Monte Carlo simulations.
Surprisingly, topological color codes on Union Jack lattices have similar error
stability than color codes on triangular lattices, as well as the Kitaev toric
code. The enhanced computational capabilities of the topological color codes on
Union Jack lattices with respect to triangular lattices and the toric code
demonstrate the inherent robustness of this implementation.Comment: 8 pages, 4 figures, 1 tabl
Schwarzschild-type black holes in Starobinsky-Bel-Robinson gravity
We study physical properties of a Schwarzschild-type black hole in the
framework of the recently proposed Starobinsky-Bel-Robinson (SBR) modified
theory of gravity, working perturbatively in the new coupling constant. In
particular, we compute the temperature, entropy, pressure and lifetime of a
Schwarzschild-type black hole.Comment: 10 pages; v3: one more reference added, final version accepted for
publication in Physics Letters
Mobile Keystroke Biometrics Using Transformers
Among user authentication methods, behavioural biometrics has proven to be
effective against identity theft as well as user-friendly and unobtrusive. One
of the most popular traits in the literature is keystroke dynamics due to the
large deployment of computers and mobile devices in our society. This paper
focuses on improving keystroke biometric systems on the free-text scenario.
This scenario is characterised as very challenging due to the uncontrolled text
conditions, the influence of the user's emotional and physical state, and the
in-use application. To overcome these drawbacks, methods based on deep learning
such as Convolutional Neural Networks (CNNs) and Recurrent Neural Networks
(RNNs) have been proposed in the literature, outperforming traditional machine
learning methods. However, these architectures still have aspects that need to
be reviewed and improved. To the best of our knowledge, this is the first study
that proposes keystroke biometric systems based on Transformers. The proposed
Transformer architecture has achieved Equal Error Rate (EER) values of 3.84\%
in the popular Aalto mobile keystroke database using only 5 enrolment sessions,
outperforming by a large margin other state-of-the-art approaches in the
literature.Comment: 6 pages, 6 figure
Editorial
Apresentação de trabalhos de investigação provenientes de investigadores de diversas origens e graus, resultando esta pluralidade da seleção dos trabalhos mais atuais e pertinentes no atual panorama jurÃdico
TypeFormer: Transformers for Mobile Keystroke Biometrics
The broad usage of mobile devices nowadays, the sensitiveness of the
information contained in them, and the shortcomings of current mobile user
authentication methods are calling for novel, secure, and unobtrusive solutions
to verify the users' identity. In this article, we propose TypeFormer, a novel
Transformer architecture to model free-text keystroke dynamics performed on
mobile devices for the purpose of user authentication. The proposed model
consists in Temporal and Channel Modules enclosing two Long Short-Term Memory
(LSTM) recurrent layers, Gaussian Range Encoding (GRE), a multi-head
Self-Attention mechanism, and a Block-Recurrent structure. Experimenting on one
of the largest public databases to date, the Aalto mobile keystroke database,
TypeFormer outperforms current state-of-the-art systems achieving Equal Error
Rate (EER) values of 3.25% using only 5 enrolment sessions of 50 keystrokes
each. In such way, we contribute to reducing the traditional performance gap of
the challenging mobile free-text scenario with respect to its desktop and
fixed-text counterparts. Additionally, we analyse the behaviour of the model
with different experimental configurations such as the length of the keystroke
sequences and the amount of enrolment sessions, showing margin for improvement
with more enrolment data. Finally, a cross-database evaluation is carried out,
demonstrating the robustness of the features extracted by TypeFormer in
comparison with existing approaches
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