4,472 research outputs found
Kaluza-Klein Gluons as a Diagnostic of Warped Models
We study the properties of , the first excited state of the gluon in
representative variants of the Randall Sundrum model with the Standard Model
fields in the bulk. We find that measurements of the coupling to light quarks
(from the inclusive cross-section for ), the coupling
to bottom quarks (from the rate of ), as well as the overall
width, can provide powerful discriminants between the models. In models with
large brane kinetic terms, the resonance can even potentially be
discovered decaying into dijets against the large QCD background. We also
derive bounds based on existing Tevatron searches for resonant
production and find that they require GeV. In addition
we explore the pattern of interference between the signal and the
non-resonant SM background, defining an asymmetry parameter for the invariant
mass distribution. The interference probes the relative signs of the couplings
of the to light quark pairs and to , and thus provides an
indication that the top is localized on the other side of the extra dimension
from the light quarks, as is typical in the RS framework.Comment: 25 pages, 10 figure
quantum corrections and the inflationary observables
We study a model of inflation with terms quadratic and logarithmic in the
Ricci scalar, where the gravitational action is . These terms are expected to arise from one loop corrections involving
matter fields in curved space-time. The spectral index and the tensor to
scalar ratio yield and . i.e. is an order of magnitude bigger or smaller than the
original Starobinsky model which predicted . Further enhancement
of gives a scale invariant or higher. Other inflationary
observables are . Despite the enhancement in
, if the recent BICEP2 measurement stands, this model is disfavoured.Comment: LaTeX, 9+1 pages, 5 figure
Constrained Deep Networks: Lagrangian Optimization via Log-Barrier Extensions
This study investigates the optimization aspects of imposing hard inequality
constraints on the outputs of CNNs. In the context of deep networks,
constraints are commonly handled with penalties for their simplicity, and
despite their well-known limitations. Lagrangian-dual optimization has been
largely avoided, except for a few recent works, mainly due to the computational
complexity and stability/convergence issues caused by alternating explicit dual
updates/projections and stochastic optimization. Several studies showed that,
surprisingly for deep CNNs, the theoretical and practical advantages of
Lagrangian optimization over penalties do not materialize in practice. We
propose log-barrier extensions, which approximate Lagrangian optimization of
constrained-CNN problems with a sequence of unconstrained losses. Unlike
standard interior-point and log-barrier methods, our formulation does not need
an initial feasible solution. Furthermore, we provide a new technical result,
which shows that the proposed extensions yield an upper bound on the duality
gap. This generalizes the duality-gap result of standard log-barriers, yielding
sub-optimality certificates for feasible solutions. While sub-optimality is not
guaranteed for non-convex problems, our result shows that log-barrier
extensions are a principled way to approximate Lagrangian optimization for
constrained CNNs via implicit dual variables. We report comprehensive weakly
supervised segmentation experiments, with various constraints, showing that our
formulation outperforms substantially the existing constrained-CNN methods,
both in terms of accuracy, constraint satisfaction and training stability, more
so when dealing with a large number of constraints
HyperDense-Net: A hyper-densely connected CNN for multi-modal image segmentation
Recently, dense connections have attracted substantial attention in computer
vision because they facilitate gradient flow and implicit deep supervision
during training. Particularly, DenseNet, which connects each layer to every
other layer in a feed-forward fashion, has shown impressive performances in
natural image classification tasks. We propose HyperDenseNet, a 3D fully
convolutional neural network that extends the definition of dense connectivity
to multi-modal segmentation problems. Each imaging modality has a path, and
dense connections occur not only between the pairs of layers within the same
path, but also between those across different paths. This contrasts with the
existing multi-modal CNN approaches, in which modeling several modalities
relies entirely on a single joint layer (or level of abstraction) for fusion,
typically either at the input or at the output of the network. Therefore, the
proposed network has total freedom to learn more complex combinations between
the modalities, within and in-between all the levels of abstraction, which
increases significantly the learning representation. We report extensive
evaluations over two different and highly competitive multi-modal brain tissue
segmentation challenges, iSEG 2017 and MRBrainS 2013, with the former focusing
on 6-month infant data and the latter on adult images. HyperDenseNet yielded
significant improvements over many state-of-the-art segmentation networks,
ranking at the top on both benchmarks. We further provide a comprehensive
experimental analysis of features re-use, which confirms the importance of
hyper-dense connections in multi-modal representation learning. Our code is
publicly available at https://www.github.com/josedolz/HyperDenseNet.Comment: Paper accepted at IEEE TMI in October 2018. Last version of this
paper updates the reference to the IEEE TMI paper which compares the
submissions to the iSEG 2017 MICCAI Challeng
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