7,932 research outputs found
A Feynman graph selection tool in GRACE system
We present a Feynman graph selection tool {\tt grcsel}, which is an
interpreter written in C language. In the framework of {\tt GRACE}, it enables
us to get a subset of Feynman graphs according to given conditions.Comment: 3 pages, 2 figures, Latex, ACAT200
State Differentiation by Transient Truncation in Coupled Threshold Dynamics
Dynamics with a threshold input--output relation commonly exist in gene,
signal-transduction, and neural networks. Coupled dynamical systems of such
threshold elements are investigated, in an effort to find differentiation of
elements induced by the interaction. Through global diffusive coupling, novel
states are found to be generated that are not the original attractor of
single-element threshold dynamics, but are sustained through the interaction
with the elements located at the original attractor. This stabilization of the
novel state(s) is not related to symmetry breaking, but is explained as the
truncation of transient trajectories to the original attractor due to the
coupling. Single-element dynamics with winding transient trajectories located
at a low-dimensional manifold and having turning points are shown to be
essential to the generation of such novel state(s) in a coupled system.
Universality of this mechanism for the novel state generation and its relevance
to biological cell differentiation are briefly discussed.Comment: 8 pages. Phys. Rev. E. in pres
Symbiotic Cell Differentiation and Cooperative Growth in Multicellular Aggregates
As cells grow and divide under a given environment, they become crowded and
resources are limited, as seen in bacterial biofilms and multicellular
aggregates. These cells often show strong interactions through exchanging
chemicals, as in quorum sensing, to achieve mutualism. Here, to achieve stable
division of labor, three properties are required. First, isogenous cells
differentiate into several types. Second, this aggregate of distinct cell types
shows better growth than that of isolated cells, by achieving division of
labor. Third, this cell aggregate is robust in the number distribution of
differentiated cell types. We here address how cells acquire the ability of
cell differentiation and division of labor simultaneously, which is also
connected with the robustness of a cell society. For this purpose, we developed
a dynamical-systems model of cells consisting of chemical components with
intracellular catalytic reaction dynamics. The reactions convert external
nutrients into internal components for cellular growth, and the divided cells
interact via chemical diffusion. We found that cells sharing an identical
catalytic network spontaneously differentiate via induction from cell-cell
interactions, and then achieve division of labor, enabling a higher growth rate
than that in the unicellular case. This symbiotic differentiation emerged for a
class of reaction networks with limited resources and strong cell-cell
interactions. Then, robustness in the cell type distribution was achieved,
while instability of collective growth could emerge even among the cooperative
cells when the internal reserves of products were dominant. The present
mechanism is simple and general as a natural result of interacting cells with
resource limitation, and is consistent with the observed behaviors and forms of
several aggregates of unicellular organisms.Comment: 14 pages, 6 figure
Emergent lattices with geometrical frustration in doped extended Hubbard models
Spontaneous charge ordering occurring in correlated systems may be considered
as a possible route to generate effective lattice structures with
unconventional couplings. For this purpose we investigate the phase diagram of
doped extended Hubbard models on two lattices: (i) the honeycomb lattice with
on-site and nearest-neighbor Coulomb interactions at filling
() and (ii) the triangular lattice with on-site , nearest-neighbor
, and next-nearest-neighbor Coulomb interactions at filling
(). We consider various approaches including mean-field approximations,
perturbation theory, and variational Monte Carlo. For the honeycomb case (i),
charge order induces an effective triangular lattice at large values of
and , where is the nearest-neighbor hopping integral. The
nearest-neighbor spin exchange interactions on this effective triangular
lattice are antiferromagnetic in most of the phase diagram, while they become
ferromagnetic when is much larger than . At ,
ferromagnetic and antiferromagnetic exchange interactions nearly cancel out,
leading to a system with four-spin ring-exchange interactions. On the other
hand, for the triangular case (ii) at large and finite , we find no
charge order for small , an effective kagome lattice for intermediate ,
and one-dimensional charge order for large . These results indicate that
Coulomb interactions induce [case (i)] or enhance [case(ii)] emergent
geometrical frustration of the spin degrees of freedom in the system, by
forming charge order.Comment: 18 pages, 26 figure
Short Gamma-Ray Bursts with Extended Emission Observed with Swift/BAT and Fermi/GBM
Some short GRBs are followed by longer extended emission, lasting anywhere
from ~10 to ~100 s. These short GRBs with extended emission (EE) can possess
observational characteristics of both short and long GRBs (as represented by
GRB 060614), and the traditional classification based on the observed duration
places some of them in the long GRB class. While GRBs with EE pose a challenge
to the compact binary merger scenario, they may therefore provide an important
link between short and long duration events. To identify the population of GRBs
with EE regardless of their initial classifications, we performed a systematic
search of short GRBs with EE using all available data (up to February 2013) of
both Swift/BAT and Fermi/GBM. The search identified 16 BAT and 14 GBM detected
GRBs with EE, several of which are common events observed with both detectors.
We investigated their spectral and temporal properties for both the spikes and
the EE, and examined correlations among these parameters. Here we present the
results of the systematic search as well as the properties of the identified
events. Finally, their properties are also compared with short GRBs with EE
observed with BATSE, identified through our previous search effort. We found
several strong correlations among parameters, especially when all of the
samples were combined. Based on our results, a possible progenitor scenario of
two-component jet is discussed.Comment: Published in MNRAS; matched to the published versio
Predictive flavour symmetries of the neutrino mass matrix
Here we propose an flavour symmetry model which implies a lower bound
on the neutrinoless double beta decay rate, corresponding to an effective mass
parameter M_{ee} \gsim 0.03 eV, and a direct correlation between the expected
magnitude of CP violation in neutrino oscillations and the value of
, as well as a nearly maximal CP phase .Comment: 4 pages, 4 figure
Spontaneous symmetry breaking in correlated wave functions
We show that Jastrow-Slater wave functions, in which a density-density
Jastrow factor is applied onto an uncorrelated fermionic state, may possess
long-range order even when all symmetries are preserved in the wave function.
This fact is mainly related to the presence of a sufficiently strong Jastrow
term (also including the case of full Gutzwiller projection, suitable for
describing spin models). Selected examples are reported, including the spawning
of N\'eel order and dimerization in spin systems, and the stabilization of
charge and orbital order in itinerant electronic systems.Comment: 13 pages, 11 figure
Anomalous Quartic and Couplings in Collision With Initial Beams and Final State Polarizations
The constraints on the anomalous quartic and
gauge boson couplings are investigated through the processes
and . Considering the
longitudinal and transverse polarization states of the final W or Z boson and
incoming beam polarizations we find 95% confidence level limits on the
anomalous coupling parameters and with an integrated luminosity
of 500 and =0.5, 1 TeV energies. Assuming the
couplings are independent of the
couplings we show that the longitudinal polarization state of the final gauge
boson improves the sensitivity to anomalous couplings by a factor of 2-3
depending on energy and coupling. An extra enhancement in sensitivity by a
factor of 1.3 comes from a set of initial beam polarizations
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