47,658 research outputs found
Conformal Symmetry and Pion Form Factor: Soft and Hard Contributions
We discuss a constraint of conformal symmetry in the analysis of the pion
form factor. The usual power-law behavior of the form factor obtained in the
perturbative QCD analysis can also be attained by taking negligible quark
masses in the nonperturbative quark model analysis, confirming the recent
AdS/CFT correspondence. We analyze the transition from soft to hard
contributions in the pion form factor considering a momentum-dependent
dynamical quark mass from a nonnegligible constituent quark mass at low
momentum region to a negligible current quark mass at high momentum region. We
find a correlation between the shape of nonperturbative quark distribution
amplitude and the amount of soft and hard contributions to the pion form
factor.Comment: 7 pages, 6 figures, extensively revised, to appear in Phys. Rev.
Six-qubit permutation-based decoherence-free orthogonal basis
There is a natural orthogonal basis of the 6-qubit decoherence-free (DF)
space robust against collective noise. Interestingly, most of the basis states
can be obtained from one another just permuting qubits. This property: (a) is
useful for encoding qubits in DF subspaces, (b) allows the implementation of
the Bennett-Brassard 1984 (BB84) protocol in DF subspaces just permuting
qubits, which completes a the method for quantum key distribution using DF
states proposed by Boileau et al. [Phys. Rev. Lett. 92, 017901 (2004)], and (c)
points out that there is only one 6-qubit DF state which is essentially new
(not obtained by permutations) and therefore constitutes an interesting
experimental challenge.Comment: REVTeX4, 5 page
Effective field theory description of halo nuclei
Nuclear halos emerge as new degrees of freedom near the neutron and proton
driplines. They consist of a core and one or a few nucleons which spend most of
their time in the classically-forbidden region outside the range of the
interaction. Individual nucleons inside the core are thus unresolved in the
halo configuration, and the low-energy effective interactions are short-range
forces between the core and the valence nucleons. Similar phenomena occur in
clusters of He atoms, cold atomic gases near a Feshbach resonance, and some
exotic hadrons. In these weakly-bound quantum systems universal scaling laws
for s-wave binding emerge that are independent of the details of the
interaction. Effective field theory (EFT) exposes these correlations and
permits the calculation of non-universal corrections to them due to
short-distance effects, as well as the extension of these ideas to systems
involving the Coulomb interaction and/or binding in higher angular-momentum
channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo
nuclei, has been used to compute the properties of single-neutron, two-neutron,
and single-proton halos of s-wave and p-wave type. This review summarizes these
results for halo binding energies, radii, Coulomb dissociation, and radiative
capture, as well as the connection of these properties to scattering
parameters, thereby elucidating the universal correlations between all these
observables. We also discuss how Halo EFT's encoding of the long-distance
physics of halo nuclei can be used to check and extend ab initio calculations
that include detailed modeling of their short-distance dynamics.Comment: 104 pages, 31 figures. Topical Review for Journal of Physics G. v2
incorporates several modifications, particularly to the Introduction, in
response to referee reports. It also corrects multiple typos in the original
submission. It corresponds to the published versio
Parametric survey of longitudinal prominence oscillation simulations
It is found that both microflare-sized impulsive heating at one leg of the
loop and a suddenly imposed velocity perturbation can propel the prominence to
oscillate along the magnetic dip. An extensive parameter survey results in a
scaling law, showing that the period of the oscillation, which weakly depends
on the length and height of the prominence, and the amplitude of the
perturbations, scales with , where represents the
curvature radius of the dip, and is the gravitational acceleration of
the Sun. This is consistent with the linear theory of a pendulum, which implies
that the field-aligned component of gravity is the main restoring force for the
prominence longitudinal oscillations, as confirmed by the force analysis.
However, the gas pressure gradient becomes non-negligible for short
prominences. The oscillation damps with time in the presence of non-adiabatic
processes. Compared to heat conduction, the radiative cooling is the dominant
factor leading to the damping. A scaling law for the damping timescale is
derived, i.e., , showing
strong dependence on the prominence length , the geometry of the magnetic
dip (characterized by the depth and the width ), and the velocity
perturbation amplitude . The larger the amplitude, the faster the
oscillation damps. It is also found that mass drainage significantly reduces
the damping timescale when the perturbation is too strong.Comment: 17 PAGES, 8FIGURE
Heisenberg-picture approach to the exact quantum motion of a time-dependent forced harmonic oscillator
In the Heisenberg picture, the generalized invariant and exact quantum
motions are found for a time-dependent forced harmonic oscillator. We find the
eigenstate and the coherent state of the invariant and show that the
dispersions of these quantum states do not depend on the external force. Our
formalism is applied to several interesting cases.Comment: 15 pages, two eps files, to appear in Phys. Rev. A 53 (6) (1996
Observation of magnetocoriolis waves in a liquid metal Taylor-Couette experiment
The first observation of fast and slow magnetocoriolis (MC) waves in a
laboratory experiment is reported. Rotating nonaxisymmetric modes arising from
a magnetized turbulent Taylor-Couette flow of liquid metal are identified as
the fast and slow MC waves by the dependence of the rotation frequency on the
applied field strength. The observed slow MC wave is damped but the observation
provides a means for predicting the onset of the Magnetorotational Instability
HDIdx: High-Dimensional Indexing for Efficient Approximate Nearest Neighbor Search
Fast Nearest Neighbor (NN) search is a fundamental challenge in large-scale
data processing and analytics, particularly for analyzing multimedia contents
which are often of high dimensionality. Instead of using exact NN search,
extensive research efforts have been focusing on approximate NN search
algorithms. In this work, we present "HDIdx", an efficient high-dimensional
indexing library for fast approximate NN search, which is open-source and
written in Python. It offers a family of state-of-the-art algorithms that
convert input high-dimensional vectors into compact binary codes, making them
very efficient and scalable for NN search with very low space complexity
The General Theory of Quantum Field Mixing
We present a general theory of mixing for an arbitrary number of fields with
integer or half-integer spin. The time dynamics of the interacting fields is
solved and the Fock space for interacting fields is explicitly constructed. The
unitary inequivalence of the Fock space of base (unmixed) eigenstates and the
physical mixed eigenstates is shown by a straightforward algebraic method for
any number of flavors in boson or fermion statistics. The oscillation formulas
based on the nonperturbative vacuum are derived in a unified general
formulation and then applied to both two and three flavor cases. Especially,
the mixing of spin-1 (vector) mesons and the CKM mixing phenomena in the
Standard Model are discussed emphasizing the nonperturbative vacuum effect in
quantum field theory
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