3,649 research outputs found
On a modification method of Lefschetz thimbles
The QCD at finite density is not well understood yet, where standard Monte
Carlo simulation suffers from the sign problem. In order to overcome the sign
problem, the method of Lefschetz thimble has been explored. Basically, the
original sign problem can be less severe in a complexified theory due to the
constancy of the imaginary part of an action on each thimble. However, global
phase factors assigned on each thimble still remain. Their interference is not
negligible in a situation where a large number of thimbles contribute to the
partition function, and this could also lead to a sign problem.In this study,
we propose a method to resolve this problem by modifying the structure of
Lefschetz thimbles such that only a single thimble is relevant to the partition
function. It can be shown that observables measured in the original and
modified theories are connected by a simple identity. We exemplify that our
method works well in a toy model.Comment: 7 pages, 4 figures, talk presented at the 35th International
Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spai
The Complex Demographic History and Evolutionary Origin of the Western Honey Bee, Apis Mellifera.
The western honey bee, Apis mellifera, provides critical pollination services to agricultural crops worldwide. However, despite substantial interest and prior investigation, the early evolution and subsequent diversification of this important pollinator remain uncertain. The primary hypotheses place the origin of A. mellifera in either Asia or Africa, with subsequent radiations proceeding from one of these regions. Here, we use two publicly available whole-genome data sets plus newly sequenced genomes and apply multiple population genetic analysis methods to investigate the patterns of ancestry and admixture in native honey bee populations from Europe, Africa, and the Middle East. The combination of these data sets is critical to the analyses, as each contributes samples from geographic locations lacking in the other, thereby producing the most complete set of honey bee populations available to date. We find evidence supporting an origin of A. mellifera in the Middle East or North Eastern Africa, with the A and Y lineages representing the earliest branching lineages. This finding has similarities with multiple contradictory hypotheses and represents a disentangling of genetic relationships, geographic proximity, and secondary contact to produce a more accurate picture of the origins of A. mellifera. We also investigate how previous studies came to their various conclusions based on incomplete sampling of populations, and illustrate the importance of complete sampling in understanding evolutionary processes. These results provide fundamental knowledge about genetic diversity within Old World honey bee populations and offer insight into the complex history of an important pollinator
Dynamic view of the nuclear matrix.
The nuclear matrix is an operationally defined nuclear skeletal structure that is believed to be involved in many nuclear functions including DNA replication, transcription, repair, and prem RNA processing/transport. Until relatively recently, the nuclear matrix was thought to be a rigid and static structure, but it is now thought to be dynamic. This paradigm shift was based in part on the tracking of the intranuclear movement of proteins tagged with fluorochromes. In this review, we attempt to redefine the nuclear matrix in light of recent findings and describe some useful techniques for the dynamic analysis of nuclear function.</p
Jürgen Melzer, Wings for the Rising Sun: A Transnational History of Japanese Aviation. Cambridge, MA: Harvard University Asia Center, 2020. xxvi, 339 pp. ISBN 9780674244429
Improved estimates of rare K decay matrix-elements from Kl3 decays
The estimation of rare K decay matrix-elements from Kl3 experimental data is
extended beyond LO in Chiral Perturbation Theory. Isospin-breaking effects at
NLO (and partially NNLO) in the ChPT expansion, as well as QED radiative
corrections are now accounted for. The analysis relies mainly on the cleanness
of two specific ratios of form-factors, for which the theoretical control is
excellent. As a result, the uncertainties on the K+ --> pi+ nu nubar and KL -->
pi0 nu nubar matrix-elements are reduced by a factor of about 7 and 4,
respectively, and similarly for the direct CP-violating contribution to KL -->
pi0 l+ l-. They could be reduced even further with better experimental data for
the Kl3 slopes and the K+l3 branching ratios. As a result, the non-parametric
errors for B(K --> pi nu nubar) and for the direct CP-violating contributions
to B(KL --> pi0 l+ l-) are now completely dominated by those on the
short-distance physics.Comment: 16 pages, 1 figure. Numerical analysis updated to include the recent
Kl3 data. To appear in Phys. Rev.
Spin-torque efficiency enhanced by Rashba spin splitting in three dimensions
We examine a spin torque induced by the Rashba spin-orbit coupling in three
dimensions within the Boltzmann transport theory. We analytically calculate the
spin torque and show how its behavior is related with the spin topology in the
Fermi surfaces by studying the Fermi-energy dependence of the spin torque.
Moreover we discuss the spin-torque efficiency which is the spin torque divided
by the applied electric current in association with the current-induced
magnetization reversal. It is found that high spin-torque efficiency is
achieved when the Fermi energy lies on only the lower band and there exists an
optimal value for the Rashba parameter, where the spin-torque efficiency
becomes maximum.Comment: 7 pages, 5 figure
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