13,419 research outputs found
Nonconvex Generalization of ADMM for Nonlinear Equality Constrained Problems
The ever-increasing demand for efficient and distributed optimization
algorithms for large-scale data has led to the growing popularity of the
Alternating Direction Method of Multipliers (ADMM). However, although the use
of ADMM to solve linear equality constrained problems is well understood, we
lacks a generic framework for solving problems with nonlinear equality
constraints, which are common in practical applications (e.g., spherical
constraints). To address this problem, we are proposing a new generic ADMM
framework for handling nonlinear equality constraints, neADMM. After
introducing the generalized problem formulation and the neADMM algorithm, the
convergence properties of neADMM are discussed, along with its sublinear
convergence rate , where is the number of iterations. Next, two
important applications of neADMM are considered and the paper concludes by
describing extensive experiments on several synthetic and real-world datasets
to demonstrate the convergence and effectiveness of neADMM compared to existing
state-of-the-art methods
Di-photon excess illuminates Dark Matter
We propose a simplified model of dark matter with a scalar mediator to
accommodate the di-photon excess recently observed by the ATLAS and CMS
collaborations. Decays of the resonance into dark matter can easily account for
a relatively large width of the scalar resonance, while the magnitude of the
total width combined with the constraint on dark matter relic density lead to
sharp predictions on the parameters of the Dark Sector. Under the assumption of
a rather large width, the model predicts a signal consistent with ~300 GeV dark
matter particle in channels with large missing energy. This prediction is not
yet severely bounded by LHC Run I searches and will be accessible at the LHC
Run II in the jet plus missing energy channel with more luminosity. Our
analysis also considers astrophysical constraints, pointing out that future
direct detection experiments will be sensitive to this scenario.Comment: 23 pages, 8 figures. Added 2 figures and more discussion
New physics searches at near detectors of neutrino oscillation experiments
We systematically investigate the prospects of testing new physics with tau
sensitive near detectors at neutrino oscillation facilities. For neutrino beams
from pion decay, from the decay of radiative ions, as well as from the decays
of muons in a storage ring at a neutrino factory, we discuss which effective
operators can lead to new physics effects. Furthermore, we discuss the present
bounds on such operators set by other experimental data currently available.
For operators with two leptons and two quarks we present the first complete
analysis including all relevant operators simultaneously and performing a
Markov Chain Monte Carlo fit to the data. We find that these effects can induce
tau neutrino appearance probabilities as large as O(10^{-4}), which are within
reach of forthcoming experiments. We highlight to which kind of new physics a
tau sensitive near detector would be most sensitive.Comment: 20 pages, 2 figures, REVTeX
Precision Tests of Parity Violation Over Cosmological Distances
Recent measurements of the Cosmic Microwave Background -mode polarization
power spectrum by the BICEP2 and POLARBEAR experiments have demonstrated new
precision tools for probing fundamental physics. Regardless of origin, the fact
that we can detect sub-K CMB polarization represents a tremendous
technological breakthrough. Yet more information may be latent in the CMB's
polarization pattern. Because of its tensorial nature, CMB polarization may
also reveal parity-violating physics via a detection of cosmic polarization
rotation. Although current CMB polarimeters are sensitive enough to measure one
degree-level polarization rotation with statistical significance,
they lack the ability to differentiate this effect from a systematic
instrumental polarization rotation. Here, we motivate the search for cosmic
polarization rotation from current CMB data as well as independent radio galaxy
and quasar polarization measurements. We argue that an improvement in
calibration accuracy would allow the precise measurement of parity- and
Lorentz-violating effects. We describe the CalSat space-based polarization
calibrator that will provide stringent control of systematic polarization angle
calibration uncertainties to -- an order of magnitude improvement
over current CMB polarization calibrators. CalSat-based calibration could be
used with current CMB polarimeters searching for -mode polarization,
effectively turning them into probes of cosmic parity violation, i.e. without
the need to build dedicated instruments.Comment: 11 pages, 3 figure
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