2,765 research outputs found
Fermion confinement via Quantum Walks in 2D+1 and 3D+1 spacetime
We analyze the properties of a two and three dimensional quantum walk that
are inspired by the idea of a brane-world model put forward by Rubakov and
Shaposhnikov [1]. In that model, particles are dynamically confined on the
brane due to the interaction with a scalar field. We translated this model into
an alternate quantum walk with a coin that depends on the external field, with
a dependence which mimics a domain wall solution. As in the original model,
fermions (in our case, the walker), become localized in one of the dimensions,
not from the action of a random noise on the lattice (as in the case of
Anderson localization), but from a regular dependence in space. On the other
hand, the resulting quantum walk can move freely along the "ordinary"
dimension.Comment: 5 pages, 6 figure
Hexagonal Tilings and Locally C6 Graphs
We give a complete classification of hexagonal tilings and locally C6 graphs,
by showing that each of them has a natural embedding in the torus or in the
Klein bottle. We also show that locally grid graphs are minors of hexagonal
tilings (and by duality of locally C6 graphs) by contraction of a perfect
matching and deletion of the resulting parallel edges, in a form suitable for
the study of their Tutte uniqueness.Comment: 14 figure
Transforming triangulations on non planar-surfaces
We consider whether any two triangulations of a polygon or a point set on a
non-planar surface with a given metric can be transformed into each other by a
sequence of edge flips. The answer is negative in general with some remarkable
exceptions, such as polygons on the cylinder, and on the flat torus, and
certain configurations of points on the cylinder.Comment: 19 pages, 17 figures. This version has been accepted in the SIAM
Journal on Discrete Mathematics. Keywords: Graph of triangulations,
triangulations on surfaces, triangulations of polygons, edge fli
Active galactic nuclei synapses: X-ray versus optical classifications using artificial neural networks
(Abridged) Many classes of active galactic nuclei (AGN) have been defined
entirely throughout optical wavelengths while the X-ray spectra have been very
useful to investigate their inner regions. However, optical and X-ray results
show many discrepancies that have not been fully understood yet. The aim of
this paper is to study the "synapses" between the X-ray and optical
classifications.
For the first time, the new EFLUXER task allowed us to analyse broad band
X-ray spectra of emission line nuclei (ELN) without any prior spectral fitting
using artificial neural networks (ANNs). Our sample comprises 162 XMM-Newton/pn
spectra of 90 local ELN in the Palomar sample. It includes starbursts (SB),
transition objects (T2), LINERs (L1.8 and L2), and Seyferts (S1, S1.8, and S2).
The ANNs are 90% efficient at classifying the trained classes S1, S1.8, and
SB. The S1 and S1.8 classes show a wide range of S1- and S1.8-like components.
We suggest that this is related to a large degree of obscuration at X-rays. The
S1, S1.8, S2, L1.8, L2/T2/SB-AGN (SB with indications of AGN), and SB classes
have similar average X-ray spectra within each class, but these average spectra
can be distinguished from class to class. The S2 (L1.8) class is linked to the
S1.8 (S1) class with larger SB-like component than the S1.8 (S1) class. The L2,
T2, and SB-AGN classes conform a class in the X-rays similar to the S2 class
albeit with larger fractions of SB-like component. This SB-like component is
the contribution of the star-formation in the host galaxy, which is large when
the AGN is weak. An AGN-like component seems to be present in the vast majority
of the ELN, attending to the non-negligible fraction of S1-like or S1.8-like
component. This trained ANN could be used to infer optical properties from
X-ray spectra in surveys like eRosita.Comment: 15 pages, 7 figures, accepted for publication in A&A. Appendix B only
in the full version of the paper here:
https://dl.dropboxusercontent.com/u/3484086/AGNSynapsis_OGM_online.pd
Local and Large scale Environment of Seyfert Galaxies
We present a three-dimensional study of the local (<100 h^-1} kpc) and the
large scale (<1 h^{-1} Mpc) environment of the two main types of Seyfert AGN
galaxies. For this purpose we use 48 Sy1 galaxies (with redshifts in the range
0.007<z<0.036) and 56 Sy2 galaxies (with 0.004<z<0.020), located at high
galactic latitudes, as well as two control samples of non-active galaxies
having the same morphological, redshift, and diameter size distributions as the
corresponding Seyfert samples. Using the Center for Astrophysics (CfA2) and
Southern Sky Redshift Survey (SSRS) galaxy catalogues (m_B~15.5) and our own
spectroscopic observations (m_B~18.5), we find that within a projected distance
of 100 h^-1 kpc and a radial velocity separation of dv<600 km/sec around each
of our AGNs, the fraction of Seyfert 2 galaxies with a close neighbor is
significantly higher than that of their control (especially within 75 h^{-1}
kpc) and Seyfert 1 galaxy samples, confirming a previous two-dimensional
analysis of Dultzin-Hacyan et al. We also find that the large-scale environment
around the two types of Seyfert galaxies does not vary with respect to their
control sample galaxies. However, in the Seyfert 2 and control galaxy samples
do differ significantly when compared to the corresponding Seyfert 1 samples.
Since the main difference between these samples is their morphological type
distribution, we argue that the large-scale environmental difference cannot be
attributed to differences in nuclear activity but rather to their different
type of host galaxies.Comment: accepted for publication in ApJ, Abstract size reduced (according to
new rules) and corrected reference
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