5,242 research outputs found
Liberating Efimov physics from three dimensions
When two particles attract via a resonant short-range interaction, three
particles always form an infinite tower of bound states characterized by a
discrete scaling symmetry. It has been considered that this Efimov effect
exists only in three dimensions. Here we review how the Efimov physics can be
liberated from three dimensions by considering two-body and three-body
interactions in mixed dimensions and four-body interaction in one dimension. In
such new systems, intriguing phenomena appear, such as confinement-induced
Efimov effect, Bose-Fermi crossover in Efimov spectrum, and formation of
interlayer Efimov trimers. Some of them are observable in ultracold atom
experiments and we believe that this study significantly broadens our horizons
of universal Efimov physics.Comment: 17 pages, 5 figures, contribution to a special issue of Few-Body
Systems devoted to Efimov Physic
Influence of self-gravity on the runaway instability of black hole-torus systems
Results from the first fully general relativistic numerical simulations in
axisymmetry of a system formed by a black hole surrounded by a self-gravitating
torus in equilibrium are presented, aiming to assess the influence of the torus
self-gravity on the onset of the runaway instability. We consider several
models with varying torus-to-black hole mass ratio and angular momentum
distribution orbiting in equilibrium around a non-rotating black hole. The tori
are perturbed to induce the mass transfer towards the black hole. Our numerical
simulations show that all models exhibit a persistent phase of axisymmetric
oscillations around their equilibria for several dynamical timescales without
the appearance of the runaway instability, indicating that the self-gravity of
the torus does not play a critical role favoring the onset of the instability,
at least during the first few dynamical timescales.Comment: To appear on Phys.Rev.Let
Quantizing Majorana Fermions in a Superconductor
A Dirac-type matrix equation governs surface excitations in a topological
insulator in contact with an s-wave superconductor. The order parameter can be
homogenous or vortex valued. In the homogenous case a winding number can be
defined whose non-vanishing value signals topological effects. A vortex leads
to a static, isolated, zero energy solution. Its mode function is real, and has
been called "Majorana." Here we demonstrate that the reality/Majorana feature
is not confined to the zero energy mode, but characterizes the full quantum
field. In a four-component description a change of basis for the relevant
matrices renders the Hamiltonian imaginary and the full, space-time dependent
field is real, as is the case for the relativistic Majorana equation in the
Majorana matrix representation. More broadly, we show that the Majorana
quantization procedure is generic to superconductors, with or without the Dirac
structure, and follows from the constraints of fermionic statistics on the
symmetries of Bogoliubov-de Gennes Hamiltonians. The Hamiltonian can always be
brought to an imaginary form, leading to equations of motion that are real with
quantized real field solutions. Also we examine the Fock space realization of
the zero mode algebra for the Dirac-type systems. We show that a
two-dimensional representation is natural, in which fermion parity is
preserved.Comment: 26 pages, no figure
Toshisada Nishida (1941–2011): Chimpanzee Rapport
Frans de Waal pays tribute to pioneering primatologist Toshisada Nishida, who transformed our understanding of chimpanzee behavior and culture and galvanized efforts to ensure their conservation
Counting Majorana zero modes in superconductors
A counting formula for computing the number of (Majorana) zero modes bound to
topological point defects is evaluated in a gradient expansion for systems with
charge-conjugation symmetry. This semi-classical counting of zero modes is
applied to some examples that include graphene and a chiral p-wave
superconductor in two-dimensional space. In all cases, we explicitly relate the
counting of zero modes to Chern numbers.Comment: 21 pages, 3 figure
Breakdown of smoothness for the Muskat problem
In this paper we show that there exist analytic initial data in the stable
regime for the Muskat problem such that the solution turns to the unstable
regime and later breaks down i.e. no longer belongs to .Comment: 93 pages, 10 figures (6 added
Detection of arcs in Saturn's F ring during the 1995 Sun ring-plane crossing
Observations of the November 1995 Sun crossing of the Saturn's ring-plane
made with the 3.6m CFH telescope, using the UHAO adaptive optics system, are
presented here. We report the detection of four arcs located in the vicinity of
the F ring. They can be seen one day later in HST images. The combination of
both data sets gives accurate determinations of their orbits. Semi-major axes
range from 140020 km to 140080 km, with a mean of 140060 +- 60 km. This is
about 150 km smaller than previous estimates of the F ring radius from Voyager
1 and 2 data, but close to the orbit of another arc observed at the same epoch
in HST images.Comment: 8 pages, 3 figures, 1 table, To appear in A&A, for comments :
[email protected]
A general T-matrix approach applied to two-body and three-body problems in cold atomic gases
We propose a systematic T-matrix approach to solve few-body problems with
s-wave contact interactions in ultracold atomic gases. The problem is generally
reduced to a matrix equation expanded by a set of orthogonal molecular states,
describing external center-of-mass motions of pairs of interacting particles;
while each matrix element is guaranteed to be finite by a proper
renormalization for internal relative motions. This approach is able to
incorporate various scattering problems and the calculations of related
physical quantities in a single framework, and also provides a physically
transparent way to understand the mechanism of resonance scattering. For
applications, we study two-body effective scattering in 2D-3D mixed dimensions,
where the resonance position and width are determined with high precision from
only a few number of matrix elements. We also study three fermions in a
(rotating) harmonic trap, where exotic scattering properties in terms of mass
ratios and angular momenta are uniquely identified in the framework of
T-matrix.Comment: 14 pages, 4 figure
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