1,641 research outputs found
Entanglement entropy of highly degenerate states and fractal dimensions
We consider the bipartite entanglement entropy of ground states of extended
quantum systems with a large degeneracy. Often, as when there is a
spontaneously broken global Lie group symmetry, basis elements of the
lowest-energy space form a natural geometrical structure. For instance, the
spins of a spin-1/2 representation, pointing in various directions, form a
sphere. We show that for subsystems with a large number m of local degrees of
freedom, the entanglement entropy diverges as (d/2) log m, where d is the
fractal dimension of the subset of basis elements with nonzero coefficients. We
interpret this result by seeing d as the (not necessarily integer) number of
zero-energy Goldstone bosons describing the ground state. We suggest that this
result holds quite generally for largely degenerate ground states, with
potential applications to spin glasses and quenched disorder.Comment: 5 pages. v2: Small changes, published versio
Ising Field Theory on a Pseudosphere
We show how the symmetries of the Ising field theory on a pseudosphere can be
exploited to derive the form factors of the spin fields as well as the
non-linear differential equations satisfied by the corresponding two-point
correlation functions. The latter are studied in detail and, in particular, we
present a solution to the so-called connection problem relating two of the
singular points of the associated Painleve VI equation. A brief discussion of
the thermodynamic properties is also presented.Comment: 39 pages, 6 eps figures, uses harvma
More General Correlation Functions of Twist Fields From Ward Identities in the Massive Dirac Theory
Following on from previous work we derive the non-linear differential
equations of more general correlators of U(1) twist fields in two-dimensional
massive Dirac theory. Using the conserved charges of the double copy model
equations parametrising the correlators of twist fields with arbitrary twist
parameter are found. This method also gives a parametrisation of the
correlation functions of general, fermionic, descendent twist fields. The
equations parametrising correlators of primary twist fields are compared to
those of the literature and evidence is presented to confirm that these
equations represent the correct parametrisation.Comment: 18 pages, 1 figur
Alien Registration- Doyon, Mary A. (Lewiston, Androscoggin County)
https://digitalmaine.com/alien_docs/29222/thumbnail.jp
The Stellar Content Near the Galactic Center
High angular resolution J, H, K, and L' images are used to investigate the
stellar content within 6 arcsec of SgrA*. The data, which are complete to K ~
16, are the deepest multicolor observations of the region published to date.Comment: 34 pages, including 12 figure
Effects of Quasi-Static Aberrations in Faint Companion Searches
We present the first results obtained at CFHT with the TRIDENT infrared
camera, dedicated to the detection of faint companions close to bright nearby
stars. The camera's main feature is the acquisition of three simultaneous
images in three wavelengths (simultaneous differential imaging) across the
methane absorption bandhead at 1.6 micron, that enables a precise subtraction
of the primary star PSF while keeping the companion signal. The main limitation
is non-common path aberrations between the three optical paths that slightly
decorrelate the PSFs. Two types of PSF calibrations are combined with the
differential simultaneous imaging technique to further attenuate the PSF:
reference star subtraction and instrument rotation to smooth aberrations. It is
shown that a faint companion with a DeltaH of 10 magnitudes would be detected
at 0.5 arcsec from the primary.Comment: 12 pages, 10 figures, to appear in Astronomy with High Contrast
Imaging, EAS Publications Serie
Tricritical point of J1-J2 Ising model on hyperbolic lattice
A ferromagnetic-paramagnetic phase transition of the two-dimensional
frustrated Ising model on a hyperbolic lattice is investigated by use of the
corner transfer matrix renormalization group method. The model contains
ferromagnetic nearest-neighbor interaction J_1 and the competing
antiferromagnetic interaction J_2. A mean-field like second-order phase
transition is observed when the ratio \kappa = J_2 / J_1 is less than 0.203. In
the region 0.203 < \kappa < 1/4, the spontaneous magnetization is discontinuous
at the transition temperature. Such tricritical behavior suggests that the
phase transitions on hyperbolic lattices need not always be mean-field like.Comment: 7 pages, 13 figures, submitted to Phys. Rev.
Phase transition of clock models on hyperbolic lattice studied by corner transfer matrix renormalization group method
Two-dimensional ferromagnetic N-state clock models are studied on a
hyperbolic lattice represented by tessellation of pentagons. The lattice lies
on the hyperbolic plane with a constant negative scalar curvature. We observe
the spontaneous magnetization, the internal energy, and the specific heat at
the center of sufficiently large systems, where the fixed boundary conditions
are imposed, for the cases N>=3 up to N=30. The model with N=3, which is
equivalent to the 3-state Potts model on the hyperbolic lattice, exhibits the
first order phase transition. A mean-field like phase transition of the second
order is observed for the cases N>=4. When N>=5 we observe the Schottky type
specific heat below the transition temperature, where its peak hight at low
temperatures scales as N^{-2}. From these facts we conclude that the phase
transition of classical XY-model deep inside the hyperbolic lattices is not of
the Berezinskii-Kosterlitz-Thouless type.Comment: REVTeX style, 4 pages, 6 figures, submitted to Phys. Rev.
Molecular Hydrogen Kinematics in Cepheus A
We present the radial velocity structure of the molecular hydrogen outflows
associated to the star forming region Cepheus A. This structure is derived from
doppler shift of the H_2 v=1-0 S(1) emission line obtained by Fabry-Perot
spectroscopy. The East and West regions of emission, called Cep A(E) and Cep
A(W), show radial velocities in the range -20 to 0 km/s with respect to the
molecular cloud. Cep A(W) shows an increasing velocity with position offset
from the core indicating the existence of a possible accelarating machanism.
Cep A(E) has an almost constant mean radial velocity of -18 km/s along the
region although with a large dispersion in velocity, indicating the possibility
of a turbulent outflow. A detailed analysis of the Cep A(E) region shows
evidence for the presence of a Mach disk on that outflow. Also, we argue that
the presence of a velocity gradient in Cep A(W) is indicative of a C-shock in
this region. Following Riera et al. (2003), we analyzed the data using wavelet
analysis to study the line width and the central radial velocity distributions.
We found that both outflows have complex spatial and velocity structures
characteristic of a turbulent flow.Comment: 24 pages, 15 figure
Infrared images of merging galaxies
Infrared imaging of interacting galaxies is especially interesting because their optical appearance is often so chaotic due to extinction by dust and emission from star formation regions, that it is impossible to locate the nuclei or determine the true stellar distribution. However, at near-infrared wavelengths extinction is considerably reduced, and most of the flux from galaxies originates from red giant stars that comprise the dominant stellar component by mass. Thus near infrared images offer the opportunity to study directly components of galactic structure which are otherwise inaccessible. Such images may ultimately provide the framework in which to understand the activity taking place in many of the mergers with high Infrared Astronomy Satellite (IRAS) luminosities. Infrared images have been useful in identifying double structures in the nuclei of interacting galaxies which have not even been hinted at by optical observations. A striking example of this is given by the K images of Arp 220. Graham et al. (1990) have used high resolution imaging to show that it has a double nucleus coincident with the radio sources in the middle of the dust lane. The results suggest that caution should be applied in the identification of optical bright spots as multiple nuclei in the absence of other evidence. They also illustrate the advantages of using infrared imaging to study the underlying structure in merging galaxies. The authors have begun a program to take near infrared images of galaxies which are believed to be mergers of disk galaxies because they have tidal tails and filaments. In many of these the merger is thought to have induced exceptionally luminous infrared emission (cf. Joseph and Wright 1985, Sanders et al. 1988). Although the optical images of the galaxies show spectacular dust lanes and filaments, the K images all have a very smooth distribution of light with an apparently single nucleus
- …