7,370 research outputs found
Few-body physics in effective field theory
Effective Field Theory (EFT) provides a powerful framework that exploits a
separation of scales in physical systems to perform systematically improvable,
model-independent calculations. Particularly interesting are few-body systems
with short-range interactions and large two-body scattering length. Such
systems display remarkable universal features. In systems with more than two
particles, a three-body force with limit cycle behavior is required for
consistent renormalization already at leading order. We will review this EFT
and some of its applications in the physics of cold atoms and nuclear physics.
In particular, we will discuss the possibility of an infrared limit cycle in
QCD. Recent extensions of the EFT approach to the four-body system and N-boson
droplets in two spatial dimensions will also be addressed.Comment: 10 pages, 5 figures, Proceedings of the INT Workshop on "Nuclear
Forces and the Quantum Many-Body Problem", Oct. 200
A Semantic Framework for the Security Analysis of Ethereum smart contracts
Smart contracts are programs running on cryptocurrency (e.g., Ethereum)
blockchains, whose popularity stem from the possibility to perform financial
transactions, such as payments and auctions, in a distributed environment
without need for any trusted third party. Given their financial nature, bugs or
vulnerabilities in these programs may lead to catastrophic consequences, as
witnessed by recent attacks. Unfortunately, programming smart contracts is a
delicate task that requires strong expertise: Ethereum smart contracts are
written in Solidity, a dedicated language resembling JavaScript, and shipped
over the blockchain in the EVM bytecode format. In order to rigorously verify
the security of smart contracts, it is of paramount importance to formalize
their semantics as well as the security properties of interest, in particular
at the level of the bytecode being executed.
In this paper, we present the first complete small-step semantics of EVM
bytecode, which we formalize in the F* proof assistant, obtaining executable
code that we successfully validate against the official Ethereum test suite.
Furthermore, we formally define for the first time a number of central security
properties for smart contracts, such as call integrity, atomicity, and
independence from miner controlled parameters. This formalization relies on a
combination of hyper- and safety properties. Along this work, we identified
various mistakes and imprecisions in existing semantics and verification tools
for Ethereum smart contracts, thereby demonstrating once more the importance of
rigorous semantic foundations for the design of security verification
techniques.Comment: The EAPLS Best Paper Award at ETAP
Nonuniversal Effects in the Homogeneous Bose Gas
Effective field theory predicts that the leading nonuniversal effects in the
homogeneous Bose gas arise from the effective range for S-wave scattering and
from an effective three-body contact interaction. We calculate the leading
nonuniversal contributions to the energy density and condensate fraction and
compare the predictions with results from diffusion Monte Carlo calculations by
Giorgini, Boronat, and Casulleras. We give a crude determination of the
strength of the three-body contact interaction for various model potentials.
Accurate determinations could be obtained from diffusion Monte Carlo
calculations of the energy density with higher statistics.Comment: 24 pages, RevTex, 5 ps figures, included with epsf.te
Deformation of grain boundaries in polar ice
The ice microstructure (grain boundaries) is a key feature used to study ice
evolution and to investigate past climatic changes. We studied a deep ice core,
in Dome Concordia, Antarctica, which records past mechanical deformations. We
measured a "texture tensor" which characterizes the pattern geometry and
reveals local heterogeneities of deformation along the core. These results
question key assumptions of the current models used for dating
Fabrication of cooled radial turbine rotor
A design and fabrication program was conducted to evaluate a unique concept for constructing a cooled, high temperature radial turbine rotor. This concept, called split blade fabrication was developed as an alternative to internal ceramic coring. In this technique, the internal cooling cavity is created without flow dividers or any other detail by a solid (and therefore stronger) ceramic plate which can be more firmly anchored within the casting shell mold than can conventional detailed ceramic cores. Casting is conducted in the conventional manner, except that the finished product, instead of having finished internal cooling passages, is now a split blade. The internal details of the blade are created separately together with a carrier sheet. The inserts are superalloy. Both are produced by essentially the same software such that they are a net fit. The carrier assemblies are loaded into the split blade and the edges sealed by welding. The entire wheel is Hot Isostatic Pressed (HIPed), braze bonding the internal details to the inside of the blades. During this program, two wheels were successfully produced by the split blade fabrication technique
Generalized Swiss-cheese cosmologies: Mass scales
We generalize the Swiss-cheese cosmologies so as to include nonzero linear
momenta of the associated boundary surfaces. The evolution of mass scales in
these generalized cosmologies is studied for a variety of models for the
background without having to specify any details within the local
inhomogeneities. We find that the final effective gravitational mass and size
of the evolving inhomogeneities depends on their linear momenta but these
properties are essentially unaffected by the details of the background model.Comment: 10 pages, 14 figures, 1 table, revtex4, Published form (with minor
corrections
The Two-Dimensional S=1 Quantum Heisenberg Antiferromagnet at Finite Temperatures
The temperature dependence of the correlation length, susceptibilities and
the magnetic structure factor of the two-dimensional spin-1 square lattice
quantum Heisenberg antiferromagnet are computed by the quantum Monte Carlo loop
algorithm (QMC). In the experimentally relevant temperature regime the
theoretically predicted asymptotic low temperature behavior is found to be not
valid. The QMC results however, agree reasonably well with the experimental
measurements of La2NiO4 even without considering anisotropies in the exchange
interactions.Comment: 4 Pages, 1 table, 4 figure
Caltech Faint Galaxy Redshift Survey X: A Redshift Survey in the Region of the Hubble Deep Field North
A redshift survey has been carried out in the region of the Hubble Deep Field
North using the Low Resolution Imaging Spectrograph at the Keck Observatory.
The resulting redshift catalog, which contains 671 entries, is a compendium of
our own data together with published LRIS/Keck data. It is more than 92%
complete for objects, irrespective of morphology, to mag in the HDF
itself and to mag in the Flanking Fields within a diameter of 8 arcmin
centered on the HDF, an unusually high completion for a magnitude limited
survey performed with a large telescope. A median redshift is reached
at .
Strong peaks in the redshift distribution, which arise when a group or poor
cluster of galaxies intersect the area surveyed, can be identified to in this dataset. More than 68% of the galaxies are members of these
redshift peaks. In a few cases, closely spaced peaks in can be resolved
into separate groups of galaxies that can be distinguished in both velocity and
location on the sky.
The radial separation of these peaks in the pencil-beam survey is consistent
with a characteristic length scale for the their separation of 70 Mpc
in our adopted cosmology (, ). Strong
galaxy clustering is in evidence at all epochs back to . (abstract
abridged)Comment: Accepted to the ApJ. This version contains all the figures and
tables. 2 minor typos in table 2b correcte
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