130,420 research outputs found
Comparing Beliefs, Surveys and Random Walks
Survey propagation is a powerful technique from statistical physics that has
been applied to solve the 3-SAT problem both in principle and in practice. We
give, using only probability arguments, a common derivation of survey
propagation, belief propagation and several interesting hybrid methods. We then
present numerical experiments which use WSAT (a widely used random-walk based
SAT solver) to quantify the complexity of the 3-SAT formulae as a function of
their parameters, both as randomly generated and after simplification, guided
by survey propagation. Some properties of WSAT which have not previously been
reported make it an ideal tool for this purpose -- its mean cost is
proportional to the number of variables in the formula (at a fixed ratio of
clauses to variables) in the easy-SAT regime and slightly beyond, and its
behavior in the hard-SAT regime appears to reflect the underlying structure of
the solution space that has been predicted by replica symmetry-breaking
arguments. An analysis of the tradeoffs between the various methods of search
for satisfying assignments shows WSAT to be far more powerful that has been
appreciated, and suggests some interesting new directions for practical
algorithm development.Comment: 8 pages, 5 figure
Minimally Allowed Neutrinoless Double Beta Decay Rates From Approximate Flavor Symmetries
Neutrinoless double beta decay () is among the only realistic
probes of Majorana neutrinos. In the standard scenario, dominated by light
neutrino exchange, the process amplitude is proportional to , the
element of the Majorana mass matrix. Naively, current data allows for vanishing
, but this should be protected by an appropriate flavor symmetry. All
such symmetries lead to mass matrices inconsistent with oscillation
phenomenology. I perform a spurion analysis to break all possible Abelian
symmetries that guarantee vanishing rates and search for
minimally allowed values. I survey 230 broken structures to yield
values and current phenomenological constraints under a variety of scenarios.
This analysis also extracts predictions for both neutrino oscillation
parameters and kinematic quantities. Assuming reasonable tuning levels, I find
that eV at 99% confidence. Bounds below this value
might indicate the Dirac neutrino nature or the existence of new light (eV-MeV
scale) degrees of freedom that can potentially be probed elsewhere.Comment: 19 Pages, 4 .eps Figures, 3 Table
Non-detection of a statistically anisotropic power spectrum in large-scale structure
We search a sample of photometric luminous red galaxies (LRGs) measured by
the Sloan Digital Sky Survey (SDSS) for a quadrupolar anisotropy in the
primordial power spectrum, in which P(\vec{k}) is an isotropic power spectrum
P(k) multiplied by a quadrupolar modulation pattern. We first place limits on
the 5 coefficients of a general quadrupole anisotropy. We also consider
axisymmetric quadrupoles of the form P(\vec{k}) = P(k){1 +
g_*[(\hat{k}\cdot\hat{n})^2-1/3]} where \hat{n} is the axis of the anisotropy.
When we force the symmetry axis \hat{n} to be in the direction (l,b)=(94
degrees,26 degrees) identified in the recent Groeneboom et al. analysis of the
cosmic microwave background, we find g_*=0.006+/-0.036 (1 sigma). With uniform
priors on \hat{n} and g_* we find that -0.41<g_*<+0.38 with 95% probability,
with the wide range due mainly to the large uncertainty of asymmetries aligned
with the Galactic Plane. In none of these three analyses do we detect evidence
for quadrupolar power anisotropy in large scale structure.Comment: 23 pages; 10 figures; 3 tables; replaced with version published in
JCAP (added discussion of scale-varying quadrupolar anisotropy
Symmetry Breaking Constraints: Recent Results
Symmetry is an important problem in many combinatorial problems. One way of
dealing with symmetry is to add constraints that eliminate symmetric solutions.
We survey recent results in this area, focusing especially on two common and
useful cases: symmetry breaking constraints for row and column symmetry, and
symmetry breaking constraints for eliminating value symmetryComment: To appear in Proceedings of Twenty-Sixth Conference on Artificial
Intelligence (AAAI-12
Integration of first-principles methods and crystallographic database searches for new ferroelectrics: Strategies and explorations
In this concept paper, the development of strategies for the integration of
first-principles methods with crystallographic database mining for the
discovery and design of novel ferroelectric materials is discussed, drawing on
the results and experience derived from exploratory investigations on three
different systems: (1) the double perovskite Sr(SbMn)O as a
candidate semiconducting ferroelectric; (2) polar derivatives of schafarzikite
SbO; and (3) ferroelectric semiconductors with formula
P(S,Se). A variety of avenues for further research and
investigation are suggested, including automated structure type classification,
low-symmetry improper ferroelectrics, and high-throughput first-principles
searches for additional representatives of structural families with desirable
functional properties.Comment: 13 pages, 5 figures, 4 table
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