2,705 research outputs found
Extrapolation in NLP
We argue that extrapolation to examples outside the training space will often
be easier for models that capture global structures, rather than just maximise
their local fit to the training data. We show that this is true for two popular
models: the Decomposable Attention Model and word2vec
Iso-vector and Iso-scalar Tensor Charges of the Nucleon from Lattice QCD
We present results for the iso-vector and flavor diagonal tensor charges
, , , and needed to probe novel tensor
interactions at the TeV scale in neutron and nuclear -decays and the
contribution of the quark electric dipole moment (EDM) to the neutron EDM. The
lattice QCD calculations were done using nine ensembles of gauge configurations
generated by the MILC collaboration using the HISQ action with 2+1+1 dynamical
flavors. These ensembles span three lattice spacings and
fm and three quark masses corresponding to the pion masses and MeV. Using estimates from these ensembles, we
quantify all systematic uncertainties and perform a simultaneous extrapolation
in the lattice spacing, volume and light quark masses for the connected
contributions. The final estimates of the connected nucleon (proton) tensor
charge for the iso-vector combination is in the
scheme at GeV. The additional disconnected quark loop
contributions needed for the flavor-diagonal matrix elements are calculated
using a stochastic estimator employing the truncated solver method with the
all-mode-averaging technique. We find that the size of the disconnected
contribution is smaller than the statistical error in the connected
contribution. This allows us to bound the disconnected contribution and include
it as an additional uncertainty in the flavor-diagonal charges. After a
continuum extrapolation, we find , and . The strangeness tensor charge, that can make a
significant contribution to the neutron EDM due to the large ratio
, is in the continuum limit.Comment: Final published versio
Quark number susceptibilities from HTL-resummed thermodynamics
We compute analytically the diagonal quark number susceptibilities for a
quark-gluon plasma at finite temperature and zero chemical potential, and
compare with recent lattice results. The calculation uses the approximately
self-consistent resummation of hard thermal and dense loops that we have
developed previously. For temperatures between 1.5 to 5 , our results
follow the same trend as the lattice data, but exceed them in magnitude by
about 5-10%. We also compute the lowest order contribution, of order
, to the off-diagonal susceptibility. This
contribution, which is not a part of our self-consistent calculation, is
numerically small, but not small enough to be compatible with a recent lattice
simulation.Comment: 13 pages, 5 figures, uses elsart.cls; v2: minor corrections; v3: sign
in eq.(1) correcte
Nucleon average quark momentum fraction with Wilson fermions
We report on an analysis of the average quark momentum fraction of the
nucleon and related quantities using Wilson fermions.
Computations are performed on four CLS ensembles covering three values of the
lattice spacing at pion masses down to .
Several source-sink separations ( to ) are used to assess the excited-state contamination. To gain
further insight, the generalized pencil-of-functions approach has been
implemented to reduce the excited-state contamination in the relevant two- and
three-point functions. Preliminary results are shown for the isovector nucleon
charges from vector, axial vector and tensor derivative (twist-2) operators.Comment: 8 pages, 3 figures, 2 tables. Talk presented at the 35th
International Symposium on Lattice Field Theory, 18-24 June 2017, Granada,
Spai
QCD calculations of form factors with higher-twist corrections
We update QCD calculations of form factors at large hadronic
recoil by including the subleading-power corrections from the higher-twist
-meson light-cone distribution amplitudes (LCDAs) up to the twist-six
accuracy and the strange-quark mass effects at leading-power in
from the twist-two -meson LCDA . The higher-twist
corrections from both the two-particle and three-particle -meson LCDAs are
computed from the light-cone QCD sum rules (LCSR) at tree level. In particular,
we construct the local duality model for the twist-five and -six -meson
LCDAs, in agreement with the corresponding asymptotic behaviours at small quark
and gluon momenta, employing the QCD sum rules in heavy quark effective theory
at leading order in . The strange quark mass effects in semileptonic
form factors yield the leading-power contribution in the heavy quark
expansion, consistent with the power-counting analysis in soft-collinear
effective theory, and they are also computed from the LCSR approach due to the
appearance of the rapidity singularities. We further explore the
phenomenological aspects of the semileptonic decays and
the rare exclusive processes , including the determination of
the CKM matrix element , the normalized differential
distributions and precision observables defined by the ratios of branching
fractions for the above-mentioned two channels in the same intervals of .Comment: 36 pages, 9 figure
Forgetting Exceptions is Harmful in Language Learning
We show that in language learning, contrary to received wisdom, keeping
exceptional training instances in memory can be beneficial for generalization
accuracy. We investigate this phenomenon empirically on a selection of
benchmark natural language processing tasks: grapheme-to-phoneme conversion,
part-of-speech tagging, prepositional-phrase attachment, and base noun phrase
chunking. In a first series of experiments we combine memory-based learning
with training set editing techniques, in which instances are edited based on
their typicality and class prediction strength. Results show that editing
exceptional instances (with low typicality or low class prediction strength)
tends to harm generalization accuracy. In a second series of experiments we
compare memory-based learning and decision-tree learning methods on the same
selection of tasks, and find that decision-tree learning often performs worse
than memory-based learning. Moreover, the decrease in performance can be linked
to the degree of abstraction from exceptions (i.e., pruning or eagerness). We
provide explanations for both results in terms of the properties of the natural
language processing tasks and the learning algorithms.Comment: 31 pages, 7 figures, 10 tables. uses 11pt, fullname, a4wide tex
styles. Pre-print version of article to appear in Machine Learning 11:1-3,
Special Issue on Natural Language Learning. Figures on page 22 slightly
compressed to avoid page overloa
Building Program Vector Representations for Deep Learning
Deep learning has made significant breakthroughs in various fields of
artificial intelligence. Advantages of deep learning include the ability to
capture highly complicated features, weak involvement of human engineering,
etc. However, it is still virtually impossible to use deep learning to analyze
programs since deep architectures cannot be trained effectively with pure back
propagation. In this pioneering paper, we propose the "coding criterion" to
build program vector representations, which are the premise of deep learning
for program analysis. Our representation learning approach directly makes deep
learning a reality in this new field. We evaluate the learned vector
representations both qualitatively and quantitatively. We conclude, based on
the experiments, the coding criterion is successful in building program
representations. To evaluate whether deep learning is beneficial for program
analysis, we feed the representations to deep neural networks, and achieve
higher accuracy in the program classification task than "shallow" methods, such
as logistic regression and the support vector machine. This result confirms the
feasibility of deep learning to analyze programs. It also gives primary
evidence of its success in this new field. We believe deep learning will become
an outstanding technique for program analysis in the near future.Comment: This paper was submitted to ICSE'1
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