1,141 research outputs found
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Bi-partite Entanglement Entropy in Massive QFT with a Boundary: the Ising Model
In this paper we give an exact infinite-series expression for the bi-partite entanglement entropy of the quantum Ising model in the ordered regime, both with a boundary magnetic field and in infinite volume. This generalizes and extends previous results involving the present authors for the bi-partite entanglement entropy of integrable quantum field theories, which exploited the generalization of the form factor program to branch-point twist fields. In the boundary case, we isolate in a universal way the part of the entanglement entropy which is related to the boundary entropy introduced by Affleck and Ludwig, and explain how this relation should hold in more general QFT models. We provide several consistency checks for the validity of our form factor results, notably, the identification of the leading ultraviolet behaviour both of the entanglement entropy and of the two-point function of twist fields in the bulk theory, to a great degree of precision by including up to 500 form factor contributions
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
On Painleve VI transcendents related to the Dirac operator on the hyperbolic disk
Dirac hamiltonian on the Poincare disk in the presence of an Aharonov-Bohm
flux and a uniform magnetic field admits a one-parameter family of self-adjoint
extensions. We determine the spectrum and calculate the resolvent for each
element of this family. Explicit expressions for Green functions are then used
to find Fredholm determinant representations for the tau function of the Dirac
operator with two branch points on the Poincare disk. Isomonodromic deformation
theory for the Dirac equation relates this tau function to a one-parameter
class of solutions of the Painleve VI equation with . We analyze long
distance behaviour of the tau function, as well as the asymptotics of the
corresponding Painleve VI transcendents as . Considering the limit of
flat space, we also obtain a class of solutions of the Painleve V equation with
.Comment: 38 pages, 5 figure
Form factors of twist fields in the lattice Dirac theory
We study U(1) twist fields in a two-dimensional lattice theory of massive
Dirac fermions. Factorized formulas for finite-lattice form factors of these
fields are derived using elliptic parametrization of the spectral curve of the
model, elliptic determinant identities and theta functional interpolation. We
also investigate the thermodynamic and the infinite-volume scaling limit, where
the corresponding expressions reduce to form factors of the exponential fields
of the sine-Gordon model at the free-fermion point.Comment: 20 pages, 2 figure
Angular Differential Imaging: a Powerful High-Contrast Imaging Technique
Angular differential imaging is a high-contrast imaging technique that
reduces quasi-static speckle noise and facilitates the detection of nearby
companions. A sequence of images is acquired with an altitude/azimuth telescope
while the instrument field derotator is switched off. This keeps the instrument
and telescope optics aligned and allows the field of view to rotate with
respect to the instrument. For each image, a reference PSF is constructed from
other appropriately-selected images of the same sequence and subtracted to
remove quasi-static PSF structure. All residual images are then rotated to
align the field and are combined. Observed performances are reported for Gemini
North data. It is shown that quasi-static PSF noise can be reduced by a factor
\~5 for each image subtraction. The combination of all residuals then provides
an additional gain of the order of the square root of the total number of
acquired images. A total speckle noise attenuation of 20-50 is obtained for
one-hour long observing sequences compared to a single 30s exposure. A PSF
noise attenuation of 100 was achieved for two-hour long sequences of images of
Vega, reaching a 5-sigma contrast of 20 magnitudes for separations greater than
8". For a 30-minute long sequence, ADI achieves 30 times better signal-to-noise
than a classical observation technique. The ADI technique can be used with
currently available instruments to search for ~1MJup exoplanets with orbits of
radii between 50 and 300 AU around nearby young stars. The possibility of
combining the technique with other high-contrast imaging methods is briefly
discussed.Comment: 27 pages, 7 figures, accepted for publication in Ap
Entanglement Content of Quantum Particle Excitations II. Disconnected Regions and Logarithmic Negativity
In this paper we study the increment of the entanglement entropy and of the (replica) logarithmic negativity in a zero-density excited state of a free massive bosonic theory, compared to the ground state. This extends the work of two previous publications by the same authors. We consider the case of two disconnected regions and find that the change in the entanglement entropy depends only on the combined size of the regions and is independent of their connectivity. We subsequently generalize this result to any number of disconnected regions. For the replica negativity we find that its increment is a polynomial with integer coefficients depending only on the sizes of the two regions. The logarithmic negativity turns out to have a more complicated functional structure than its replica version, typically involving roots of polynomials on the sizes of the regions. We obtain our results by two methods already employed in previous work: from a qubit picture and by computing four-point functions of branch point twist fields in finite volume. We test our results against numerical simulations on a harmonic chain and find excellent agreement
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Entanglement in permutation symmetric states, fractal dimensions, and geometric quantum mechanics
We study the von Neumann and Rényi bipartite entanglement entropies in the thermodynamic limit of many-body quantum states with spin-s sites that possess full symmetry under exchange of sites. It turns out that there is essentially a one-to-one correspondence between such thermodynamic states and probability measures on CP2s. Let a measure be supported on a set of possibly fractal real dimension d with respect to the Study–Fubini metric of CP2s. Let m be the number of sites in a subsystem of the bipartition. We give evidence that in the limit m → ∞, the entanglement entropy diverges like (d/2)logm. Further, if the measure is supported on a submanifold of CP2s and can be described by a density f with respect to the metric induced by the Study–Fubini metric, we give evidence that the correction term is simply related to the entropy associated with f: the geometric entropy of geometric quantum mechanics. This extends results obtained by the authors in a recent letter where the spin- case was considered. Here we provide more examples as well as detailed accounts of the ideas and computations leading to these general results. For special choices of the state in the spin-s situation, we recover the scaling behaviour previously observed by Popkov et al, showing that their result is but a special case of a more general scaling law
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.
Direct Imaging of Multiple Planets Orbiting the Star HR 8799
Direct imaging of exoplanetary systems is a powerful technique that can
reveal Jupiter-like planets in wide orbits, can enable detailed
characterization of planetary atmospheres, and is a key step towards imaging
Earth-like planets. Imaging detections are challenging due to the combined
effect of small angular separation and large luminosity contrast between a
planet and its host star. High-contrast observations with the Keck and Gemini
telescopes have revealed three planets orbiting the star HR 8799, with
projected separations of 24, 38, and 68 astronomical units. Multi-epoch data
show counter-clockwise orbital motion for all three imaged planets. The low
luminosity of the companions and the estimated age of the system imply
planetary masses between 5 and 13 times that of Jupiter. This system resembles
a scaled-up version of the outer portion of our Solar System.Comment: 30 pages, 5 figures, Research Article published online in Science
Express Nov 13th, 200
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