53,333 research outputs found
The potential of the effective Polyakov line action from the underlying lattice gauge theory
I adapt a numerical method, previously applied to investigate the Yang-Mills
vacuum wavefunctional, to the problem of extracting the effective Polyakov line
action from SU(N) lattice gauge theories, with or without matter fields. The
method can be used to find the variation of the effective Polyakov line action
along any trajectory in field configuration space; this information is
sufficient to determine the potential term in the action, and strongly
constrains the possible form of the kinetic term. The technique is illustrated
for both pure and gauge-Higgs SU(2) lattice gauge theory at finite temperature.
A surprise, in the pure gauge theory, is that the potential of the
corresponding Polyakov line action contains a non-analytic (yet
center-symmetric) term proportional to |P|^3, where P is the trace of the
Polyakov line at a given point, in addition to the expected analytic terms
proportional to even powers of P.Comment: 24 pages, 12 figure
The Precision Monte Carlo Event Generator KK For Two-Fermion Final States In e+e- Collisions
We present the Monte Carlo event generator KK version 4.13 for precision
predictions of the Electroweak Standard Model for the process , at centre of mass energies from
lepton threshold to 1TeV, that is for LEP, SLC, future Linear Colliders,
-factories etc. Effects due to photon emission from initial beams and
outgoing fermions are calculated in QED up to second order, including all
interference effects, within Coherent Exclusive Exponentiation (CEEX), which is
based on Yennie-Frautschi-Suura exponentiation. Electroweak corrections are
included in first order, with higher order extensions, using the DIZET 6.x
library. Final state quarks hadronize according to the parton shower model
using JETSET. Beams can be polarized longitudinally and transversely. Decay of
the tau leptons is simulated using the TAUOLA library, taking into account spin
polarization effects as well. In particular the complete spin correlations
density matrix of the initial state beams and final state tau's is incorporated
in an exact manner. Effects due to beamstrahlung are simulated in a realistic
way. The main improvements with respect to KORALZ are: (a) inclusion of the
initial-final state QED interference, (b) inclusion of the exact matrix element
for two photons, and (c) inclusion of the transverse spin correlations in
decays (as in KORALB).Comment: Source code available from http://home.cern.ch/jadac
ratio as a tool to refine Effective Polyakov Loop models
Effective Polyakov line actions are a powerful tool to study the finite
temperature behaviour of lattice gauge theories. They are much simpler to
simulate than the original lattice model and are affected by a milder sign
problem, but it is not clear to which extent they really capture the rich
spectrum of the original theories. We propose here a simple way to address this
issue based on the so called second moment correlation length . The
ratio between the exponential correlation length and the second
moment one is equal to 1 if only a single mass is present in the spectrum, and
it becomes larger and larger as the complexity of the spectrum increases. Since
both and are easy to measure on the lattice, this is a cheap
and efficient way to keep track of the spectrum of the theory. As an example of
the information one can obtain with this tool we study the behaviour of
in the confining phase of the () gauge
theory and show that it is compatible with 1 near the deconfinement transition,
but it increases dramatically as the temperature decreases. We also show that
this increase can be well understood in the framework of an effective string
description of the Polyakov loop correlator. This non-trivial behaviour should
be reproduced by the Polyakov loop effective action; thus, it represents a
stringent and challenging test of existing proposals and it may be used to
fine-tune the couplings and to identify the range of validity of the
approximations involved in their construction.Comment: 1+17 pages, 3 pdf figures; v2: 1+17 pages, 3 pdf figures: discussion
in section 1,2 and 5 expanded, misprints corrected; matches journal versio
Echo Cancellation - A Likelihood Ratio Test for Double-talk Versus Channel Change
Echo cancellers are in wide use in both electrical (four wire to two wire mismatch) and acoustic (speaker-microphone coupling) applications. One of the main design problems is the control logic for adaptation. Basically, the algorithm weights should be frozen in the presence of double-talk and adapt quickly in the absence of double-talk. The control logic can be quite complicated since it is often not easy to discriminate between the echo signal and the near-end speaker. This paper derives a log likelihood ratio test (LRT) for deciding between double-talk (freeze weights) and a channel change (adapt quickly) using a stationary Gaussian
stochastic input signal model. The probability density function of a sufficient statistic under each hypothesis is obtained and the performance of the test is evaluated as a function of the system parameters. The receiver operating characteristics (ROCs) indicate that it is difficult to correctly decide between double-talk and a channel change based upon a single look. However, post-detection integration of approximately one hundred sufficient statistic samples yields a detection probability close to unity (0.99) with a small false alarm probability (0.01)
Unconventional machine learning of genome-wide human cancer data
Recent advances in high-throughput genomic technologies coupled with
exponential increases in computer processing and memory have allowed us to
interrogate the complex aberrant molecular underpinnings of human disease from
a genome-wide perspective. While the deluge of genomic information is expected
to increase, a bottleneck in conventional high-performance computing is rapidly
approaching. Inspired in part by recent advances in physical quantum
processors, we evaluated several unconventional machine learning (ML)
strategies on actual human tumor data. Here we show for the first time the
efficacy of multiple annealing-based ML algorithms for classification of
high-dimensional, multi-omics human cancer data from the Cancer Genome Atlas.
To assess algorithm performance, we compared these classifiers to a variety of
standard ML methods. Our results indicate the feasibility of using
annealing-based ML to provide competitive classification of human cancer types
and associated molecular subtypes and superior performance with smaller
training datasets, thus providing compelling empirical evidence for the
potential future application of unconventional computing architectures in the
biomedical sciences
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