47 research outputs found
Nucleosynthesis Predictions and High-Precision Deuterium Measurements
Two new high-precision measurements of the deuterium abundance from absorbers
along the line of sight to the quasar PKS1937--1009 were presented. The
absorbers have lower neutral hydrogen column densities (N(HI)
18\,cm) than for previous high-precision measurements, boding well for
further extensions of the sample due to the plenitude of low column density
absorbers. The total high-precision sample now consists of 12 measurements with
a weighted average deuterium abundance of D/H = . The
sample does not favour a dipole similar to the one detected for the fine
structure constant. The increased precision also calls for improved
nucleosynthesis predictions. For that purpose we have updated the public
AlterBBN code including new reactions, updated nuclear reaction rates, and the
possibility of adding new physics such as dark matter. The standard Big Bang
Nucleosynthesis prediction of D/H = is consistent
with the observed value within 1.7 standard deviations.Comment: 10 pages, 5 figures, conference proceedings from VarCosmoFun 201
Combining Planck with Large Scale Structure gives strong neutrino mass constraint
We present the strongest current cosmological upper limit on the sum of
neutrino masses of < 0.18 (95% confidence). It is obtained by adding
observations of the large-scale matter power spectrum from the WiggleZ Dark
Energy Survey to observations of the cosmic microwave background data from the
Planck surveyor, and measurements of the baryon acoustic oscillation scale. The
limit is highly sensitive to the priors and assumptions about the neutrino
scenario. We explore scenarios with neutrino masses close to the upper limit
(degenerate masses), neutrino masses close to the lower limit where the
hierarchy plays a role, and addition of massive or massless sterile species.Comment: 7 pages, 4 figures. Found bug in analysis which is fixed in v2. The
resulting constraints on M_nu remain very strong. Additional info added on
hierarch
WiggleZ Dark Energy Survey: Cosmological neutrino mass constraint from blue high-redshift galaxies
The absolute neutrino mass scale is currently unknown, but can be constrained by cosmology. The WiggleZ high redshift, star-forming, and blue galaxy sample offers a complementary data set to previous surveys for performing these measurements, with potentially different systematics from nonlinear structure formation, redshift-space distortions, and galaxy bias. We obtain a limit of ∑m_ν<0.60  eV (95% confidence) for WiggleZ+Wilkinson Microwave Anisotropy Probe. Combining with priors on the Hubble parameter and the baryon acoustic oscillation scale gives ∑m_ν<0.29  eV, which is the strongest neutrino mass constraint derived from spectroscopic galaxy redshift surveys
Cosmological neutrino mass constraint from the WiggleZ Dark Energy Survey
The absolute neutrino mass scale is currently unknown, but can be constrained from cosmology. We use the large-scale structure information from the WiggleZ Dark Energy Survey to constrain the sum of neutrino masses. The WiggleZ high redshift star-forming blue galaxy sample is less sensitive to systematic effects from non-linear structure formation, pairwise galaxy velocities, redshift-space distortions, and galaxy bias than previous surveys. Through exhaustive tests using numerical dark-matter simulations of the WiggleZ survey, we demonstrate that at small scales common modelling approaches lead to systematic errors in the recovered cosmological parameters, and we use the simulations to calibrate a new non-linear fitting formula extending to small scales (k = 0.3hMpc). We obtain an upper limit on the sum of neutrino masses of 0.60eV (95% confidence) for WiggleZ+Wilkinson Microwave Anisotropy Probe. Combining with priors on the Hubble Parameter and the baryon acoustic oscillation scale gives an upper limit of 0.29eV, which is the strongest neutrino mass constraint derived from spectroscopic galaxy redshift surveys
Sterile neutrinos in the Milky Way: Observational constraints
We consider the possibility of constraining decaying dark matter by looking
out through the Milky Way halo. Specifically we use Chandra blank sky
observations to constrain the parameter space of sterile neutrinos. We find
that a broad band in parameter space is still open, leaving the sterile
neutrino as an excellent dark matter candidate.Comment: Submitted to ApJL, 4 pages, 4 figure
Mutual information estimation for graph convolutional neural networks
Measuring model performance is a key issue for deep learning practitioners.
However, we often lack the ability to explain why a specific architecture
attains superior predictive accuracy for a given data set. Often, validation
accuracy is used as a performance heuristic quantifying how well a network
generalizes to unseen data, but it does not capture anything about the
information flow in the model. Mutual information can be used as a measure of
the quality of internal representations in deep learning models, and the
information plane may provide insights into whether the model exploits the
available information in the data. The information plane has previously been
explored for fully connected neural networks and convolutional architectures.
We present an architecture-agnostic method for tracking a network's internal
representations during training, which are then used to create the mutual
information plane. The method is exemplified for graph-based neural networks
fitted on citation data. We compare how the inductive bias introduced in
graph-based architectures changes the mutual information plane relative to a
fully connected neural network.Comment: Northern Lights Deep Learning proceedings, 8 pages, 3 figure
A gradient boosting approach for optimal selection of bidding strategies in reservoir hydro
Power producers use a wide range of decision support systems to manage and
plan for sales in the day-ahead electricity market, and they are often faced
with the challenge of choosing the most advantageous bidding strategy for any
given day. The optimal solution is not known until after spot clearing. Results
from the models and strategy used, and their impact on profitability, can
either continuously be registered, or simulated with use of historic data.
Access to an increasing amount of data opens for the application of machine
learning models to predict the best combination of models and strategy for any
given day. In this article, historical performance of two given bidding
strategies over several years have been analyzed with a combination of domain
knowledge and machine learning techniques (gradient boosting and neural
networks). A wide range of variables accessible to the models prior to bidding
have been evaluated to predict the optimal strategy for a given day. Results
indicate that a machine learning model can learn to slightly outperform a
static strategy where one bidding method is chosen based on overall historic
performance
Neural Operator Learning for Long-Time Integration in Dynamical Systems with Recurrent Neural Networks
Deep neural networks are an attractive alternative for simulating complex
dynamical systems, as in comparison to traditional scientific computing
methods, they offer reduced computational costs during inference and can be
trained directly from observational data. Existing methods, however, cannot
extrapolate accurately and are prone to error accumulation in long-time
integration. Herein, we address this issue by combining neural operators with
recurrent neural networks to construct a novel and effective architecture,
resulting in superior accuracy compared to the state-of-the-art. The new hybrid
model is based on operator learning while offering a recurrent structure to
capture temporal dependencies. The integrated framework is shown to stabilize
the solution and reduce error accumulation for both interpolation and
extrapolation of the Korteweg-de Vries equation.Comment: 12 pages, 5 figure
Pseudo-Hamiltonian neural networks with state-dependent external forces
Hybrid machine learning based on Hamiltonian formulations has recently been successfully demonstrated for simple mechanical systems, both energy conserving and not energy conserving. We introduce a pseudo-Hamiltonian formulation that is a generalization of the Hamiltonian formulation via the port-Hamiltonian formulation, and show that pseudo-Hamiltonian neural network models can be used to learn external forces acting on a system. We argue that this property is particularly useful when the external forces are state dependent, in which case it is the pseudo-Hamiltonian structure that facilitates the separation of internal and external forces. Numerical results are provided for a forced and damped mass–spring system and a tank system of higher complexity, and a symmetric fourth-order integration scheme is introduced for improved training on sparse and noisy data.publishedVersio
Port-Hamiltonian Neural Networks with State-Dependent Ports
Hybrid machine learning based on Hamiltonian formulations has recently been
successfully demonstrated for simple mechanical systems, both energy conserving
and not energy conserving. We show that port-Hamiltonian neural network models
can be used to learn external forces acting on a system. We argue that this
property is particularly useful when the external forces are state dependent,
in which case it is the port-Hamiltonian structure that facilitates the
separation of internal and external forces. Numerical results are provided for
a forced and damped mass-spring system and a tank system of higher complexity,
and a symmetric fourth-order integration scheme is introduced for improved
training on sparse and noisy data.Comment: 21 pages, 12 figures; v3: restructured the paper for more clarity,
major changes to the text, updated plot