7,406 research outputs found
Beyond the unitarity bound in AdS/CFT_(A)dS
In this work we expand on the holographic description of CFTs on de Sitter
(dS) and anti-de Sitter (AdS) spacetimes and examine how violations of the
unitarity bound in the boundary theory are recovered in the bulk physics. To
this end we consider a Klein-Gordon field on AdS_(d+1) conformally compactified
such that the boundary is (A)dS_d, and choose masses and boundary conditions
such that the corresponding boundary operator violates the CFT unitarity bound.
The setup in which the boundary is AdS_d exhibits a particularly interesting
structure, since in this case the boundary itself has a boundary. The bulk
theory turns out to crucially depend on the choice of boundary conditions on
the boundary of the AdS_d slices. Our main result is that violations to the
unitarity bound in CFTs on dS_d and AdS_d are reflected in the bulk through the
presence of ghost excitations. In addition, analyzing the setup with AdS_d on
the boundary allows us to draw conclusions on multi-layered AdS/CFT-type
dualities.Comment: 30 pages, 2 figures; reference adde
A non-Abelian Black Ring
We construct a supersymmetric black ring solution of SU(2) N=1, d=5
Super-Einstein-Yang-Mills (SEYM) theory by adding a distorted BPST instanton to
an Abelian black ring solution of the same theory. The change cannot be
observed from spatial infinity: neither the mass, nor the angular momenta or
the values of the scalars at infinity differ from those of the Abelian ring.
The entropy is, however, sensitive to the presence of the non-Abelian
instanton, and it is smaller than that of the Abelian ring, in analogy to what
happens in the supersymmetric coloured black holes recently constructed in the
same theory and in N=2, d=4 SEYM. By taking the limit in which the two angular
momenta become equal we derive a non-Abelian generalization of the BMPV
rotating black-hole solution.Comment: 19 pages, no figure
Large lepton mixing and supernova 1987A
We reconsider the impact of
neutrino oscillations on the observed signal of supernova SN 1987A.
Performing a maximum-likelihood analysis using as fit parameters the released
binding energy \Eb and the average neutrino energy \Ee, we find as previous
analyses that oscillations with
large mixing angles have lower best-fit values for \Ee than small-mixing
angle (SMA) oscillations. Moreover, the inferred value of \Ee is already in
the SMA case lower than those found in simulations. This apparent conflict has
been interpreted as evidence against the large mixing oscillation solutions to
the solar neutrino problem. In order to quantify the degree to which the
experimental data favour the SMA over the large mixing solutions we use their
likelihood ratios as well as a Kolmogorov-Smirnov test. We find within the
range of SN parameters predicted by simulations regions in which the LMA-MSW
solution is either only marginally disfavoured or favoured compared to the
SMA-MSW solution. We conclude therefore that the LMA-MSW solution is not in
conflict with the current understanding of SN physics. In contrast, the vacuum
oscillation and the LOW solutions to the solar neutrino problem can be excluded
at the level for most of the SN parameter ranges found in
simulations. Only a marginal region with low values of \Ee,
and \Eb is left over, in which these oscillation
solutions can be reconciled with the neutrino signal of SN 1987A.Comment: 23 pages, 20 figures, v2: brief comments adde
Surveying the SO(10) Model Landscape: The Left-Right Symmetric Case
Grand Unified Theories (GUTs) are a very well motivated extensions of the
Standard Model (SM), but the landscape of models and possibilities is
overwhelming, and different patterns can lead to rather distinct
phenomenologies. In this work we present a way to automatise the model building
process, by considering a top to bottom approach that constructs viable and
sensible theories from a small and controllable set of inputs at the high
scale. By providing a GUT scale symmetry group and the field content, possible
symmetry breaking paths are generated and checked for consistency, ensuring
anomaly cancellation, SM embedding and gauge coupling unification. We emphasise
the usefulness of this approach for the particular case of a non-supersymmetric
SO(10) model with an intermediate left-right symmetry and we analyse how
low-energy observables such as proton decay and lepton flavour violation might
affect the generated model landscape.Comment: 36 pages, 6 figure
Compressed and Split Spectra in Minimal SUSY SO(10)
The non-observation of supersymmetric signatures in searches at the Large
Hadron Collider strongly constrains minimal supersymmetric models like the
CMSSM. We explore the consequences on the SUSY particle spectrum in a minimal
SO(10) with large D-terms and non-universal gaugino masses at the GUT scale.
This changes the sparticle spectrum in a testable way and for example can
sufficiently split the coloured and non-coloured sectors. The splitting
provided by use of the SO(10) D-terms can be exploited to obtain light first
generation sleptons or third generation squarks, the latter corresponding to a
compressed spectrum scenario.Comment: 35 pages, 10 figures, published versio
N=2 Einstein-Yang-Mills' static two-center solutions
We construct bona fide one- and two-center supersymmetric solutions to N=2,
d=4 supergravity coupled to SU(2) non-Abelian vector multiplets. The solutions
describe black holes and global monopoles alone or in equilibrium with each
other and exhibit non-Abelian hairs of different kinds.Comment: 46 pages, 1 figure; v2 references adde
Non-Abelian black holes in string theory
We study a family of 5-dimensional non-Abelian black holes that can be
obtained by adding an instanton field to the well-known D1D5W Abelian black
holes. Naively, the non-Abelian fields seem to contribute to the black-hole
entropy but not to the mass due to their rapid fall-off at spatial infinity. By
uplifting the 5-dimensional supergravity solution to 10-dimensional Heterotic
Supergravity first and then dualizing it into a Type-I Supergravity solution,
we show that the non-Abelian fields are associated to D5-branes dissolved into
the D9-branes (dual to the Heterotic "gauge 5-branes") and that their
associated RR charge does not, in fact, contribute to the entropy, which only
depends on the number16 pages of D-strings and D5 branes and the momentum along
the D-strings, as in the Abelian case. These "dissolved" or "gauge" D5-branes
do contribute to the mass in the expected form. The correct interpretation of
the 5-dimensional charges in terms of the string-theory objects solves the
non-Abelian hair puzzle, allowing for the microscopic accounting of the
entropy. We discuss the validity of the solution when alpha prime corrections
are taken into account.Comment: Latex 2e file, 21 pages. A full appendix on alpha prime corrections
and the corresponding discussions have been added. The conclusions have
suffered minor changes. Version accepted in JHE
Spatial Filtering Pipeline Evaluation of Cortically Coupled Computer Vision System for Rapid Serial Visual Presentation
Rapid Serial Visual Presentation (RSVP) is a paradigm that supports the
application of cortically coupled computer vision to rapid image search. In
RSVP, images are presented to participants in a rapid serial sequence which can
evoke Event-related Potentials (ERPs) detectable in their Electroencephalogram
(EEG). The contemporary approach to this problem involves supervised spatial
filtering techniques which are applied for the purposes of enhancing the
discriminative information in the EEG data. In this paper we make two primary
contributions to that field: 1) We propose a novel spatial filtering method
which we call the Multiple Time Window LDA Beamformer (MTWLB) method; 2) we
provide a comprehensive comparison of nine spatial filtering pipelines using
three spatial filtering schemes namely, MTWLB, xDAWN, Common Spatial Pattern
(CSP) and three linear classification methods Linear Discriminant Analysis
(LDA), Bayesian Linear Regression (BLR) and Logistic Regression (LR). Three
pipelines without spatial filtering are used as baseline comparison. The Area
Under Curve (AUC) is used as an evaluation metric in this paper. The results
reveal that MTWLB and xDAWN spatial filtering techniques enhance the
classification performance of the pipeline but CSP does not. The results also
support the conclusion that LR can be effective for RSVP based BCI if
discriminative features are available
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