22,504 research outputs found
Direct UV-written broadband directional planarwaveguide couplers
Editore: Optical Society of Americ
Ghosts of Critical Gravity
Recently proposed "critical" higher-derivative gravities in are
expected to carry logarithmic representation of the Anti de Sitter isometry
group. In this note, we quantize linear fluctuations of these critical
gravities, which are known to be either identical with linear fluctuations of
Einstein's gravity or else satisfy logarithmic boundary conditions at spacial
infinity. We identify the scalar product uniquely defined by the symplectic
structure implied by the classical action, and show that it does not posses
null vectors. Instead, we show that the scalar product between any two Einstein
modes vanishes, while the scalar product of an Einstein mode with a logarithmic
mode is generically nonzero. This is the basic property of logarithmic
representation that makes them neither unitary nor unitarizable.Comment: v2: typos corrected and slight clarifications. 11 page
The order of the Roberge-Weiss endpoint (finite size transition) in QCD
We consider the endpoint of the Roberge-Weiss (RW) first order transition
line present for imaginary baryon chemical potentials. We remark that it
coincides with the finite size transition relevant in the context of large
QCD and study its order in the theory with two degenerate flavors. The RW
endpoint is first order in the limit of large and small quark masses, while it
weakens for intermediate masses where it is likely in the Ising 3d universality
class. Phenomenological implications and further speculations about the QCD
phase diagram are discussed.Comment: 5 pages, 8 figures. Version accepted for publication in Physical
Review D (R
Curvature perturbations from dimensional decoupling
The scalar modes of the geometry induced by dimensional decoupling are
investigated. In the context of the low energy string effective action,
solutions can be found where the spatial part of the background geometry is the
direct product of two maximally symmetric Euclidean manifolds whose related
scale factors evolve at a dual rate so that the expanding dimensions first
accelerate and then decelerate while the internal dimensions always contract.
After introducing the perturbative treatment of the inhomogeneities, a class of
five-dimensional geometries is discussed in detail. Quasi-normal modes of the
system are derived and the numerical solution for the evolution of the metric
inhomogeneities shows that the fluctuations of the internal dimensions provide
a term that can be interpreted, in analogy with the well-known four-dimensional
situation, as a non-adiabatic pressure density variation. Implications of this
result are discussed with particular attention to string cosmological
scenarios.Comment: 25 pages, 3 figure
Treatment challenges in and outside a specialist network setting: Pancreatic neuroendocrine tumours
Pancreatic Neuroendocrine Neoplasms comprise a group of rare tumours with special biology, an often indolent behaviour and particular diagnostic and therapeutic requirements. The specialized biochemical tests and radiological investigations, the complexity of surgical options and the variety of medical treatments that require individual tailoring, mandate a multidisciplinary approach that can be optimally achieved through an organized network. The present study describes currents concepts in the management of these tumours as well as an insight into the challenges of delivering the pathway in and outside a Network
Quantum critical behavior and trap-size scaling of trapped bosons in a one-dimensional optical lattice
We study the quantum (zero-temperature) critical behaviors of confined
particle systems described by the one-dimensional (1D) Bose-Hubbard model in
the presence of a confining potential, at the Mott insulator to superfluid
transitions, and within the gapless superfluid phase. Specifically, we consider
the hard-core limit of the model, which allows us to study the effects of the
confining potential by exact and very accurate numerical results. We analyze
the quantum critical behaviors in the large trap-size limit within the
framework of the trap-size scaling (TSS) theory, which introduces a new trap
exponent theta to describe the dependence on the trap size. This study is
relevant for experiments of confined quasi 1D cold atom systems in optical
lattices. At the low-density Mott transition TSS can be shown analytically
within the spinless fermion representation of the hard-core limit. The
trap-size dependence turns out to be more subtle in the other critical regions,
when the corresponding homogeneous system has a nonzero filling f, showing an
infinite number of level crossings of the lowest states when increasing the
trap size. At the n=1 Mott transition this gives rise to a modulated TSS: the
TSS is still controlled by the trap-size exponent theta, but it gets modulated
by periodic functions of the trap size. Modulations of the asymptotic power-law
behavior is also found in the gapless superfluid region, with additional
multiscaling behaviors.Comment: 26 pages, 34 figure
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