1,091 research outputs found
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
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
Evolution of Genes Neighborhood Within Reconciled Phylogenies: An Ensemble Approach
Context
The reconstruction of evolutionary scenarios for whole genomes in terms of genome rearrangements is a fundamental problem in evolutionary and comparative genomics. The DeCo algorithm, recently introduced by BĂ©rard et al., computes parsimonious evolutionary scenarios for gene adjacencies, from pairs of reconciled gene trees. However, as for many combinatorial optimization algorithms, there can exist many co-optimal, or slightly sub-optimal, evolutionary scenarios that deserve to be considered.
Contribution
We extend the DeCo algorithm to sample evolutionary scenarios from the whole solution space under the Boltzmann distribution, and also to compute Boltzmann probabilities for specific ancestral adjacencies.
Results
We apply our algorithms to a dataset of mammalian gene trees and adjacencies, and observe a significant reduction of the number of syntenic conflicts observed in the resulting ancestral gene adjacencies
Finite Temperature Dynamical Correlations in Massive Integrable Quantum Field Theories
We consider the finite-temperature frequency and momentum dependent two-point
functions of local operators in integrable quantum field theories. We focus on
the case where the zero temperature correlation function is dominated by a
delta-function line arising from the coherent propagation of single particle
modes. Our specific examples are the two-point function of spin fields in the
disordered phase of the quantum Ising and the O(3) nonlinear sigma models. We
employ a Lehmann representation in terms of the known exact zero-temperature
form factors to carry out a low-temperature expansion of two-point functions.
We present two different but equivalent methods of regularizing the divergences
present in the Lehmann expansion: one directly regulates the integral
expressions of the squares of matrix elements in the infinite volume whereas
the other operates through subtracting divergences in a large, finite volume.
Our central results are that the temperature broadening of the line shape
exhibits a pronounced asymmetry and a shift of the maximum upwards in energy
("temperature dependent gap"). The field theory results presented here describe
the scaling limits of the dynamical structure factor in the quantum Ising and
integer spin Heisenberg chains. We discuss the relevance of our results for the
analysis of inelastic neutron scattering experiments on gapped spin chain
systems such as CsNiCl3 and YBaNiO5.Comment: 54 pages, 10 figure
Calogero-Sutherland eigenfunctions with mixed boundary conditions and conformal field theory correlators
We construct certain eigenfunctions of the Calogero-Sutherland hamiltonian
for particles on a circle, with mixed boundary conditions. That is, the
behavior of the eigenfunction, as neighbouring particles collide, depend on the
pair of colliding particles. This behavior is generically a linear combination
of two types of power laws, depending on the statistics of the particles
involved. For fixed ratio of each type at each pair of neighboring particles,
there is an eigenfunction, the ground state, with lowest energy, and there is a
discrete set of eigenstates and eigenvalues, the excited states and the
energies above this ground state. We find the ground state and special excited
states along with their energies in a certain class of mixed boundary
conditions, interpreted as having pairs of neighboring bosons and other
particles being fermions. These particular eigenfunctions are characterised by
the fact that they are in direct correspondence with correlation functions in
boundary conformal field theory. We expect that they have applications to
measures on certain configurations of curves in the statistical O(n) loop
model. The derivation, although completely independent from results of
conformal field theory, uses ideas from the "Coulomb gas" formulation.Comment: 35 pages, 9 figure
Calculus on manifolds of conformal maps and CFT
In conformal field theory (CFT) on simply connected domains of the Riemann
sphere, the natural conformal symmetries under self-maps are extended, in a
certain way, to local symmetries under general conformal maps, and this is at
the basis of the powerful techniques of CFT. Conformal maps of simply connected
domains naturally have the structure of an infinite-dimensional groupoid, which
generalizes the finite-dimensional group of self-maps. We put a topological
structure on the space of conformal maps on simply connected domains, which
makes it into a topological groupoid. Further, we (almost) extend this to a
local manifold structure based on the infinite-dimensional Frechet topological
vector space of holomorphic functions on a given domain A. From this, we
develop the notion of conformal A-differentiability at the identity. Our main
conclusion is that quadratic differentials characterizing cotangent elements on
the local manifold enjoy properties similar to those of the holomorphic
stress-energy tensor of CFT; these properties underpin the local symmetries of
CFT. Applying the general formalism to CFT correlation functions, we show that
the stress-energy tensor is exactly such a quadratic differential. This is at
the basis of constructing the stress-energy tensor in conformal loop ensembles.
It also clarifies the relation between Cardy's boundary conditions for CFT on
simply connected domains, and the expression of the stress-energy tensor in
terms of metric variations.Comment: v1: 51 pages, 5 figures. v2: 56 pages, corrections and
clarifications. v3: 53 pages, one substantial addition (groupoid structure),
discussion further clarified and simplified. v4: 59 pages, introduction
improved, with a discussion on the relations with previous works. Published
versio
The VAST Survey - III. The multiplicity of A-type stars within 75 pc
With a combination of adaptive optics imaging and a multi-epoch common proper
motion search, we have conducted a large volume-limited (D 75 pc)
multiplicity survey of A-type stars, sensitive to companions beyond 30 au. The
sample for the Volume-limited A-STar (VAST) survey consists of 435 A-type
stars: 363 stars were observed with adaptive optics, 228 stars were searched
for wide common proper motion companions and 156 stars were measured with both
techniques. The projected separation coverage of the VAST survey extends from
30 to 45,000 au. A total of 137 stellar companions were resolved, including 64
new detections from the VAST survey, and the companion star fraction, projected
separation distribution and mass ratio distribution were measured. The
separation distribution forms a log-normal distribution similar to the
solar-type binary distribution, but with a peak shifted to a significantly
wider value of 387 (+132,-98) au. Integrating the fit to the distribution over
the 30 to 10,000 au observed range, the companion star fraction for A-type
stars is estimated as 33.8%+-2.6%. The mass ratio distribution of closer (<125
au) binaries is distinct from that of wider systems, with a flat distribution
for close systems and a distribution that tends towards smaller mass ratios for
wider binaries. Combining this result with previous spectroscopic surveys of
A-type stars gives an estimate of the total companion star fraction of
68.9%+-7.0%. The most complete assessment of higher order multiples was
estimated from the 156-star subset of the VAST sample with both adaptive optics
and common proper motion measurements, combined with a literature search for
companions, yielding a lower limit on the frequency of single, binary, triple,
quadruple and quintuple A-type star systems of 56.4 (-4.0,+3.8), 32.1
(-3.5,+3.9), 9.0 (-1.8,+2.8), 1.9 (-0.6,+1.8) and 0.6 (-0.2,+1.4) per cent,
respectively.Comment: 46 pages, 24 figures. Accepted for publication in the Monthly Notices
of the Royal Astronomical Society, 7th October 201
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