26,314 research outputs found
Speckle noise in direct-detection lidar systems
The speckle noise is evaluated from some typical lidar systems. The governing equations are summarized. The mutual intensity function of the speckle pattern is calculated in terms of the laser radiation modes. Typical laser pulses are modeled and simplified expressions for the speckle noise power are derived. The signal-to-speckle-noise ratios for some proposed lidar systems are evaluated
Chiral dynamics and B to 3 pi decay
I discuss our knowledge of the scalar sector of QCD and how it impacts the
determination of the CKM angle \alpha from the isospin analysis of B\to \rho\pi
decay.Comment: invited talk at International Workshop on Heavy Quarks and Leptons,
Vietri sul Mare, Salerno, Italy, 27 May - 1 Jun 200
The mathematical basis for deterministic quantum mechanics
If there exists a classical, i.e. deterministic theory underlying quantum
mechanics, an explanation must be found of the fact that the Hamiltonian, which
is defined to be the operator that generates evolution in time, is bounded from
below. The mechanism that can produce exactly such a constraint is identified
in this paper. It is the fact that not all classical data are registered in the
quantum description. Large sets of values of these data are assumed to be
indistinguishable, forming equivalence classes. It is argued that this should
be attributed to information loss, such as what one might suspect to happen
during the formation and annihilation of virtual black holes.
The nature of the equivalence classes is further elucidated, as it follows
from the positivity of the Hamiltonian. Our world is assumed to consist of a
very large number of subsystems that may be regarded as approximately
independent, or weakly interacting with one another. As long as two (or more)
sectors of our world are treated as being independent, they all must be
demanded to be restricted to positive energy states only. What follows from
these considerations is a unique definition of energy in the quantum system in
terms of the periodicity of the limit cycles of the deterministic model.Comment: 17 pages, 3 figures. Minor corrections, comments and explanations
adde
Watson's theorem and electromagnetism in K -> pi pi decay
We consider what constraints unitarity and CPT invariance yield on the strong
and electromagnetic phases entering K -> pi pi decay. In particular, we show
that the relative size of the electromagnetically-induced changes in the I=0
and I=2 phase shifts in the two--pion final state do not depend on the explicit
coupling to the pi^+ pi^- gamma channel. This demonstrates that Watson's
theorem can be extended to include the presence of electromagnetism. We point
out the consequences for the general structure of the K -> pi pi decay
amplitudes in the presence of isospin violation.Comment: 7 pages, LaTeX, axodraw.st
On the reconstruction of planar lattice-convex sets from the covariogram
A finite subset of is said to be lattice-convex if is
the intersection of with a convex set. The covariogram of
is the function associating to each u \in
\integer^d the cardinality of . Daurat, G\'erard, and Nivat and
independently Gardner, Gronchi, and Zong raised the problem on the
reconstruction of lattice-convex sets from . We provide a partial
positive answer to this problem by showing that for and under mild extra
assumptions, determines up to translations and reflections. As a
complement to the theorem on reconstruction we also extend the known
counterexamples (i.e., planar lattice-convex sets which are not
reconstructible, up to translations and reflections) to an infinite family of
counterexamples.Comment: accepted in Discrete and Computational Geometr
Measurement of an Exceptionally Weak Electron-Phonon Coupling on the Surface of the Topological Insulator BiSe Using Angle-Resolved Photoemission Spectroscopy
Gapless surface states on topological insulators are protected from elastic
scattering on non-magnetic impurities which makes them promising candidates for
low-power electronic applications. However, for wide-spread applications, these
states should have to remain coherent at ambient temperatures. Here, we studied
temperature dependence of the electronic structure and the scattering rates on
the surface of a model topological insulator, BiSe, by high resolution
angle-resolved photoemission spectroscopy. We found an extremely weak
broadening of the topological surface state with temperature and no anomalies
in the state's dispersion, indicating exceptionally weak electron-phonon
coupling. Our results demonstrate that the topological surface state is
protected not only from elastic scattering on impurities, but also from
scattering on low-energy phonons, suggesting that topological insulators could
serve as a basis for room temperature electronic devices.Comment: published version, 5 pages, 4 figure
Nonresonant Contributions in B->rho pi Decay
We consider nonresonant contributions in the Dalitz plot analysis of B->rho
pi->pi^+ pi^- pi^0 decay and their potential impact on the extraction of the
CKM parameter alpha. In particular, we examine the role of the heavy mesons B^*
and B_0, via the process B->pi (B^*, B_0)->pi^+ pi^- pi^0, and their
interference with resonant contributions in the rho-mass region. We discuss the
inherent uncertainties and suggest that the effects may be substantially
smaller than previously indicated.Comment: 15 pages, 3 figures; minor changes, version to appear in Phys. Rev.
Multifractal analysis of perceptron learning with errors
Random input patterns induce a partition of the coupling space of a
perceptron into cells labeled by their output sequences. Learning some data
with a maximal error rate leads to clusters of neighboring cells. By analyzing
the internal structure of these clusters with the formalism of multifractals,
we can handle different storage and generalization tasks for lazy students and
absent-minded teachers within one unified approach. The results also allow some
conclusions on the spatial distribution of cells.Comment: 11 pages, RevTex, 3 eps figures, version to be published in Phys.
Rev. E 01Jan9
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