17,008 research outputs found
Breaking Discrete Symmetries in Broken Gauge Theories
We study the spontaneous breaking of discrete symmetries in theories with
broken gauge symmetry. The intended application is to CP breaking in theories
with gauged flavor symmetries, but the analysis described here is preliminary.
We dispense with matter fields and take the gauge theory to be weakly coupled
and broken spontaneously by unspecified, short-distance forces. We develop an
effective-field-theory description of the resultant low energy theory, and ask
whether this theory by itself can describe the subsequent breaking of discrete
symmetries. We conclude that this can happen depending on the parameters of the
effective theory, and that the intrinsic violation is naturally of order unity.Comment: 9 pages, 1 figure, corrected typos, added a referenc
Central limit theorem for fluctuations of linear eigenvalue statistics of large random graphs
We consider the adjacency matrix of a large random graph and study
fluctuations of the function
with .
We prove that the moments of fluctuations normalized by in the limit
satisfy the Wick relations for the Gaussian random variables. This
allows us to prove central limit theorem for and then extend
the result on the linear eigenvalue statistics of any
function which increases, together with its
first two derivatives, at infinity not faster than an exponential.Comment: 22 page
Dual-mode mechanical resonance of individual ZnO nanobelts
©2003 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/82/4806/1DOI:10.1063/1.1587878The mechanical resonance of a single ZnO nanobelt, induced by an alternative electric field, was studied by in situ transmission electron microscopy. Due to the rectangular cross section of the nanobelt, two fundamental resonance modes have been observed corresponding to two orthogonal transverse vibration directions, showing the versatile applications of nanobelts as nanocantilevers and nanoresonators. The bending modulus of the ZnO nanobelts was measured to be ~52 GPa and the damping time constant of the resonance in a vacuum of 5×10–8 Torr was ~1.2 ms and quality factor Q = 500
Existence problem of proton semi-bubble structure in the state of Si
The fully self-consistent Hartree-Fock (HF) plus random phase approximation
(RPA) based on Skyrme-type interaction is used to study the existence problem
of proton semi-bubble structure in the state of Si. The
experimental excitation energy and the B(E2) strength of the state in
Si can be reproduced quite well. The tensor effect is also studied. It
is shown that the tensor interaction has a notable impact on the excitation
energy of the state and a small effect on the B(E2) value. Besides, its
effect on the density distributions in the ground and state of
Si is negligible. Our present results with T36 and T44 show that the
state of Si is mainly caused by proton transiton from orbit to orbit, and the existence of a proton
semi-bubble structure in this state is very unlikely.Comment: 6 pages, 3 figures, 3 table
Signal from noise retrieval from one and two-point Green's function - comparison
We compare two methods of eigen-inference from large sets of data, based on
the analysis of one-point and two-point Green's functions, respectively. Our
analysis points at the superiority of eigen-inference based on one-point
Green's function. First, the applied by us method based on Pad?e approximants
is orders of magnitude faster comparing to the eigen-inference based on
uctuations (two-point Green's functions). Second, we have identified the source
of potential instability of the two-point Green's function method, as arising
from the spurious zero and negative modes of the estimator for a variance
operator of the certain multidimensional Gaussian distribution, inherent for
the two-point Green's function eigen-inference method. Third, we have presented
the cases of eigen-inference based on negative spectral moments, for strictly
positive spectra. Finally, we have compared the cases of eigen-inference of
real-valued and complex-valued correlated Wishart distributions, reinforcing
our conclusions on an advantage of the one-point Green's function method.Comment: 14 pages, 8 figures, 3 table
Finite-Temperature Auxiliary-Field Quantum Monte Carlo for Bose-Fermi Mixtures
We present a quantum Monte Carlo (QMC) technique for calculating the exact
finite-temperature properties of Bose-Fermi mixtures. The Bose-Fermi
Auxiliary-Field Quantum Monte Carlo (BF-AFQMC) algorithm combines two methods,
a finite-temperature AFQMC algorithm for bosons and a variant of the standard
AFQMC algorithm for fermions, into one algorithm for mixtures. We demonstrate
the accuracy of our method by comparing its results for the Bose-Hubbard and
Bose-Fermi-Hubbard models against those produced using exact diagonalization
for small systems. Comparisons are also made with mean-field theory and the
worm algorithm for larger systems. As is the case with most fermion
Hamiltonians, a sign or phase problem is present in BF-AFQMC. We discuss the
nature of these problems in this framework and describe how they can be
controlled with well-studied approximations to expand BF-AFQMC's reach. The new
algorithm can serve as an essential tool for answering many unresolved
questions about many-body physics in mixed Bose-Fermi systems.Comment: 19 pages, 6 figure
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