8,675 research outputs found
On the density of the odd values of the partition function, II: An infinite conjectural framework
We continue our study of a basic but seemingly intractable problem in integer
partition theory, namely the conjecture that is odd exactly of
the time. Here, we greatly extend on our previous paper by providing a
doubly-indexed, infinite framework of conjectural identities modulo 2, and show
how to, in principle, prove each such identity. However, our conjecture remains
open in full generality.
A striking consequence is that, under suitable existence conditions, if any
-multipartition function is odd with positive density and
(mod 3), then is also odd with positive density. These are all facts
that appear virtually impossible to show unconditionally today.
Our arguments employ a combination of algebraic and analytic methods,
including certain technical tools recently developed by Radu in his study of
the parity of the Fourier coefficients of modular forms.Comment: 14 pages. To appear in the J. of Number Theor
Partition function of the Potts model on self-similar lattices as a dynamical system and multiple transitions
We present an analytic study of the Potts model partition function on two
different types of self-similar lattices of triangular shape with non integer
Hausdorff dimension. Both types of lattices analyzed here are interesting
examples of non-trivial thermodynamics in less than two dimensions. First, the
Sierpinski gasket is considered. It is shown that, by introducing suitable
geometric coefficients, it is possible to reduce the computation of the
partition function to a dynamical system, whose variables are directly
connected to (the arising of) frustration on macroscopic scales, and to
determine the possible phases of the system. The same method is then used to
analyse the Hanoi graph. Again, dynamical system theory provides a very elegant
way to determine the phase diagram of the system. Then, exploiting the analysis
of the basins of attractions of the corresponding dynamical systems, we
construct various examples of self-similar lattices with more than one critical
temperature. These multiple critical temperatures correspond to crossing phases
with different degrees of frustration.Comment: 16 pages, 12 figures, 1 table; title changed, references and
discussion on multiple transitions adde
On the density of the odd values of the partition function
The purpose of this note is to introduce a new approach to the study of one
of the most basic and seemingly intractable problems in partition theory,
namely the conjecture that the partition function is equidistributed
modulo 2.
Our main result will relate the densities, say , of the odd values
of the -multipartition functions , for several integers . In
particular, we will show that if for some , then (assuming it exists) ; that is,
itself is odd with positive density. Notice that, currently, the best
unconditional result does not even imply that is odd for
values of . In general, we conjecture that for all
odd, i.e., that similarly to the case of , all multipartition functions
are in fact equidistributed modulo 2.
Our arguments will employ a number of algebraic and analytic methods, ranging
from an investigation modulo 2 of some classical Ramanujan identities and
several other eta product results, to a unified approach that studies the
parity of the Fourier coefficients of a broad class of modular form identities
recently introduced by Radu.Comment: Several changes with respect to the 2015 version. 18 pages. To appear
in the Annals of Combinatoric
A Schwarz Method for the Magnetotelluric Approximation of Maxwell's equations
The magnetotelluric approximation of the Maxwell's equations is used to model
the propagation of low frequency electro-magnetic waves in the Earth's
subsurface, with the purpose of reconstructing the presence of mineral or oil
deposits. We propose a classical Schwarz method for solving this
magnetotelluric approximation of the Maxwell equations, and prove its
convergence using maximum principle techniques. This is not trivial, since
solutions are complex valued, and we need a new result that the magnetotelluric
approximations satisfy a maximum modulus principle for our proof. We illustrate
our analysis with numerical experiments.Comment: 9 pages, 3 figure
Possible phases of two coupled n-component fermionic chains
A two-leg ladder with -component fermionic fields in the chains has been
considered using an analytic renormalization group method. The fixed points and
possible phases have been determined for generic filling as well as for a
half-filled system and for the case when one of the subbands is half filled. A
weak-coupling Luttinger-liquid phase and several strong-coupling gapped phases
have been found. In the Luttinger liquid phase, for the most general spin
dependence of the couplings, all modes have different velocities if the
interband scattering processes are scaled out, while doubly degenerate
modes appear if the interband scattering processes remain finite. The role of
backward-scattering, charge-transfer and umklapp processes has been analysed
using their bosonic form and the possible phases are characterized by the
number of gapless modes. As a special case the SU() symmetric Hubbard ladder
has been investigated numerically. It was found that this model does not scale
to the Luttinger liquid fixed point. Even for generic filling gaps open up in
the spectrum of the spin or charge modes, and the system is always insulator in
the presence of umklapp processes
A measure of tripartite entanglement in bosonic and fermionic systems
We describe an efficient theoretical criterion suitable for the evaluation of
the tripartite entanglement of any mixed three-boson or -fermion state, based
on the notion of the entanglement of particles for bipartite systems of
identical particles. Our approach allows one to quantify the accessible amount
of quantum correlations in the systems without any violation of the local
particle number superselection rule. A generalization of the tripartite
negativity is here applied to some correlated systems including the
continuous-time quantum walks of identical particles (both for bosons and
fermions) and compared with other criteria recently proposed in the literature.
Our results show the dependence of the entanglement dynamics upon the quantum
statistics: the bosonic bunching results into a low amount of quantum
correlations while Fermi-Dirac statistics allows for higher values of the
entanglement.Comment: 19 pages, 3 figure
Learned Belief-Propagation Decoding with Simple Scaling and SNR Adaptation
We consider the weighted belief-propagation (WBP) decoder recently proposed
by Nachmani et al. where different weights are introduced for each Tanner graph
edge and optimized using machine learning techniques. Our focus is on
simple-scaling models that use the same weights across certain edges to reduce
the storage and computational burden. The main contribution is to show that
simple scaling with few parameters often achieves the same gain as the full
parameterization. Moreover, several training improvements for WBP are proposed.
For example, it is shown that minimizing average binary cross-entropy is
suboptimal in general in terms of bit error rate (BER) and a new "soft-BER"
loss is proposed which can lead to better performance. We also investigate
parameter adapter networks (PANs) that learn the relation between the
signal-to-noise ratio and the WBP parameters. As an example, for the (32,16)
Reed-Muller code with a highly redundant parity-check matrix, training a PAN
with soft-BER loss gives near-maximum-likelihood performance assuming simple
scaling with only three parameters.Comment: 5 pages, 5 figures, submitted to ISIT 201
Quieting the Sharholders\u27 Voice: Empirical Evidence of Pervasive Bundling in Proxy Solicitations
The integrity of shareholder voting is critical to the legitimacy of corporate law. One threat to this process is proxy “bundling,” or the joinder of more than one separate item into a single proxy proposal. Bundling deprives shareholders of the right to convey their views on each separate matter being put to a vote and forces them to either reject the entire proposal or approve items they might not otherwise want implemented.
In this Paper, we provide the first comprehensive evaluation of the anti-bundling rules adopted by the Securities and Exchange Commission (“SEC”) in 1992. While we find that the courts have carefully developed a framework for the proper scope and application of the rules, the SEC and proxy advisory firms have been less vigilant in defending this instrumental shareholder right. In particular, we note that the most recent SEC interpretive guidance has undercut the effectiveness of the existing rules, and that, surprisingly, proxy advisory firms do not have well-defined heuristics to discourage bundling.
Building on the theoretical framework, this Article provides the first large-scale empirical study of bundling of management proposals. We develop four possible definitions of impermissible bundling and, utilizing a data set of over 1,300 management proposals, show that the frequency of bundling in our sample ranges from 6.2 percent to 28.8 percent (depending on which of the four bundling definitions is used). It is apparent that bundling occurs far more frequently than indicated by prior studies.
We further examine our data to report the items that are most frequently bundled and to analyze the proxy advisors’ recommendations and the voting patterns associated with bundled proposals. This Article concludes with important implications for the SEC, proxy advisors, and institutional investors as to how each party can more effectively deter impermissible bundling and thus better protect the shareholder franchise
Spine-sheath layer radiative interplay in subparsec-scale jets and the TeV emission from M87
Simple one-zone homogeneous synchrotron self-Compton models have severe
difficulties in explaining the TeV emission observed in the radiogalaxy M87.
Also the site of the TeV emission region is uncertain: it could be the
unresolved jet close to the nucleus, analogously to what proposed for blazars,
or an active knot, called HST-1, tens of parsec away. We explore the
possibility that the TeV emission of M87 is produced in the misaligned subpc
scale jet. We base our modelling on a structured jet, with a fast spine
surrounded by a slower layer. In this context the main site responsible for the
emission of the TeV radiation is the layer, while the (debeamed) spine accounts
for the emission from the radio to the GeV band: therefore we expect a more
complex correlation with the TeV component than that expected in one-zone
scenarios, in which both components are produced by the same region. Observed
from small angles, the spine would dominate the emission, with an overall
Spectral Energy Distribution close to those of BL Lac objects with a
synchrotron peak located at low energy (LBLs).Comment: 5 pages, 2 figures. Accepted for publication in MNRAS Letter
Homogeneous and inhomogeneous contributions to the luminescence linewidth of point defects in amorphous solids: Quantitative assessment based on time-resolved emission spectroscopy
The article describes an experimental method that allows to estimate the
inhomogeneous and homogeneous linewidths of the photoluminescence band of a
point defect in an amorphous solid. We performed low temperature time-resolved
luminescence measurements on two defects chosen as model systems for our
analysis: extrinsic Oxygen Deficient Centers (ODC(II)) in amorphous silica and
F+ 3 centers in crystalline Lithium Fluoride. Measurements evidence that only
defects embedded in the amorphous matrix feature a dependence of the radiative
decay lifetime on the emission energy and a time dependence of the first moment
of the emission band. A theoretical model is developed to link these properties
to the structural disorder typical of amorphous solids. Specifically, the
observations on ODC(II) are interpreted by introducing a gaussian statistical
distribution of the zero phonon line energy position. Comparison with the
results obtained on F+ 3 crystalline defects strongly confirms the validity of
the model. By analyzing experimental data within this frame, we obtain separate
estimations of the homogenous and inhomogeneous contributions to the measured
total linewidth of ODC(II), which results to be mostly inhomogeneous.Comment: 8 pages, 4 figure
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