1,620 research outputs found
Quantum systems as classical systems
A characteristical property of a classical physical theory is that the
observables are real functions taking an exact outcome on every (pure) state;
in a quantum theory, at the contrary, a given observable on a given state can
take several values with only a predictable probability. However, even in the
classical case, when an observer is intrinsically unable to distinguish between
some distinct states he can convince himself that the measure of its
''observables'' can have several values in a random way with a statistical
character. What kind of statistical theory is obtainable in this way? It is
possible, for example, to obtain exactly the statistical previsions of quantum
mechanics? Or, in other words, can a physical system showing a classical
behaviour appear to be a quantum system to a confusing observer? We show that
from a mathematical viewpoint it is not difficult to produce a theory with
hidden variables having this property. We don't even try to justify in physical
terms the artificial construction we propose; what we do is to give a general
and rigorous argument showing how the interplay between the classical and
quantum mechanics we offer is interpretable as the difference between an
imaginary very expert observer and another nonexpert observer. This proves also
that besides the well known theorems concerning the impossibility of hidden
variables (cfr. Von Neumann [Neu] and Jauch-Piron [J-P]) there is also room for
a result in favor of the possibility.Comment: late
Construction of a Complete Set of States in Relativistic Scattering Theory
The space of physical states in relativistic scattering theory is
constructed, using a rigorous version of the Dirac formalism, where the Hilbert
space structure is extended to a Gel'fand triple. This extension enables the
construction of ``a complete set of states'', the basic concept of the original
Dirac formalism, also in the cases of unbounded operators and continuous
spectra. We construct explicitly the Gel'fand triple and a complete set of
``plane waves'' -- momentum eigenstates -- using the group of space-time
symmetries. This construction is used (in a separate article) to prove a
generalization of the Coleman-Mandula theorem to higher dimension.Comment: 30 pages, Late
On the controversy concerning the definition of quark and gluon angular momentum
A major controversy has arisen in QCD as to how to split the total angular
momentum into separate quark and gluon contributions, and as to whether the
gluon angular momentum can itself be split, in a gauge invariant way, into a
spin and orbital part. Several authors have proposed various answers to these
questions and offered a variety of different expressions for the relevant
operators. I argue that none of these is acceptable and suggest that the
canonical expression for the momentum and angular momentum operators is the
correct and physically meaningful one. It is then an inescapable fact that the
gluon angular momentum operator cannot, in general, be split in a gauge
invariant way into a spin and orbital part. However, the projection of the
gluon spin onto its direction of motion i.e. its helicity is gauge invariant
and is measured in deep inelastic scattering on nucleons. The Ji sum rule,
relating the quark angular momentum to generalized parton distributions, though
not based on the canonical operators, is shown to be correct, if interpreted
with due care. I also draw attention to several interesting aspects of QED and
QCD, which, to the best of my knowledge, are not commented upon in the standard
textbooks on Field Theory.Comment: 41 pages; Some incorrect statements have been rectified and a
detailed discussion has been added concerning the momentum carried by quarks
and the Ji sum rule for the angular momentu
Chromosomal in situ suppression hybridization of human gonosomes and autosomes and its use in clinical cytogenetics
DNA libraries from sorted human gonosomes were used selectively to stain the X and Y chromosomes in normal and aberrant cultured human cells by chromosomal in situ suppression (CISS-) hybridization. The entire X chromosome was stained in metaphase spreads. Interphase chromosome domains of both the active and inactive X were clearly delineated. CISS-hybridization of the Y chromosome resulted in the specific decoration of the euchromatic part (Ypter-q11), whereas the heterochromatic part (Yq12) remained unlabeled. The stained part of the Y chromosome formed a compact domain in interphase nuclei. This approach was applied to amniotic fluid cells containing a ring chromosome of unknown origin (47,XY; +r). The ring chromosome was not stained by library probes from the gonosomes, thereby suggesting its autosomal origin. The sensitivity of CISS-hybridization was demonstrated by the detection of small translocations and fragments in human lymphocyte metaphase spreads after irradiation with 60Co-gamma-rays. Lymphocyte cultures from two XX-males were investigated by CISS-hybridization with Y-library probes. In both cases, metaphase spreads demonstrated a translocation of Yp-material to the short arm of an X chromosome. The translocated Y-material could also be demonstrated directly in interphase nuclei. CISS-hybridization of autosomes 7 and 13 was used for prenatal diagnosis in a case with a known balanced translocation t(7;13) in the father. The same translocation was observed in amniotic fluid cells from the fetus. Specific staining of the chromosomes involved in such translocations will be particularly important, in the future, in cases that cannot be solved reliably by conventional chromosome banding alone
Physical qubits from charged particles: IR divergences in quantum information
We consider soft photons effects (IR structure of QED) on the construction of
physical qubits. Soft-photons appear when we build charged qubits from the
asymptotic states of QED. This construction is necessary in order to include
the effect of soft photons on entanglement measures. The nonexistence of free
charged particles (due to the long range of QED interactions) lead us to
question the sense of the very concept of free charged qubit. In this letter,
using the "dressing" formalism, we build physical charged qubits from dressed
fields which have the correct asymptotic behavior, are gauge invariant, their
propagators have a particle pole structure and are free from infrared
divergences. Finally, we discuss the impact of the soft corrections on the
entanglement measures.Comment: 4 pages, 2 figures, RevTeX. Version 2: Some references update
Radiative corrections to the Dalitz plot of K_{l3}^\pm decays
We calculate the model-independent radiative corrections to the Dalitz plot
of K_{l3}^\pm decays to order (\alpha/\pi)(q/M_1), where q is the momentum
transfer and M_1 is the mass of the kaon. The final results are presented,
first, with the triple integration over the variables of the bremsstrahlung
photon ready to be performed numerically and, second, in an analytical form.
These two forms are useful to crosscheck on one another and with other
calculations. This paper is organized to make it accessible and reliable in the
analysis of the Dalitz plot of precision experiments and is not compromised to
fixing the form factors at predetermined values. It is assumed that the real
photons are kinematically discriminated. Otherwise, our results have a general
model-independent applicability.Comment: RevTex4, 38 pages, 5 figures, 5 tables; some typos corrected;
discussion extended to compare with other result
Probabilities from envariance?
Zurek claims to have derived Born's rule noncircularly in the context of an
ontological no-collapse interpretation of quantum states, without any "deus ex
machina imposition of the symptoms of classicality." After a brief review of
Zurek's derivation it is argued that this claim is exaggerated if not wholly
unjustified. In order to demonstrate that Born's rule arises noncircularly from
deterministically evolving quantum states, it is not sufficient to assume that
quantum states are somehow associated with probabilities and then prove that
these probabilities are given by Born's rule. One has to show how irreducible
probabilities can arise in the context of an ontological no-collapse
interpretation of quantum states. It is argued that the reason why all attempts
to do this have so far failed is that quantum states are fundamentally
algorithms for computing correlations between possible measurement outcomes,
rather than evolving ontological states.Comment: To appear in IJQI; 9 pages, LaTe
Infraparticle Scattering States in Non-Relativistic QED: II. Mass Shell Properties
We study the infrared problem in the usual model of QED with non-relativistic
matter. We prove spectral and regularity properties characterizing the mass
shell of an electron and one-electron infraparticle states of this model. Our
results are crucial for the construction of infraparticle scattering states,
which are treated in a separate paper.Comment: AMS Latex, 45 pages, 2 figure
Current Oncological Treatment of Patients with Pancreatic Cancer in Germany: Results from a National Survey on behalf of the Arbeitsgemeinschaft Internistische Onkologie and the Chirurgische Arbeitsgemeinschaft Onkologie of the Germany Cancer Society
Background: No data have previously been available regarding the current treatment of patients with pancreatic cancer (PC) in German hospitals and medical practices. Methods: Between February 2007 and March 2008 we conducted a national survey {[}on behalf of the Arbeitsgemeinschaft Internistische Onkologie (AIO) and the Chirurgische Arbeitsgemeinschaft Onkologie (CAO)] regarding the current surgical and oncological treatment of PC in Germany. Standardized questionnaires were sent via mailing lists to members of the AIO and CAO (n = 1,130). The data were analyzed using SPSS software (version 16.0). Pre-defined subgroup analysis was performed by grouping the results of each question with regard to the professional site of the responding physician and to the number of patients treated in their institution by year. Results: 181 (16%) of the oncological questionnaires were sent back. For 61% of the participating centers, a histological confirmation of PC diagnosis is obligatory. 21% of physicians offer neoadjuvant therapy to patients with potentially resectable PC. In the adjuvant treatment after curative-intent surgery, gemcitabine (Gem) is regarded as standard of care by 71% after R0 resection and 62% after R1 resection. For patients with locally advanced PC, 52% of the participating centers recommend systemic chemotherapy, 17% prefer combined primary chemoradiotherapy. Most centers (59%) base their decision of combination regimens for metastatic disease on the performance status of their patients. In patients with a good status, 28% apply single-agent Gem, 3% use Gem + capecitabine, 12% Gem + erlotinib, 16% Gem + oxaliplatin, and 8% Gem + cisplatin. Only 28% of the survey doctors offer second-line treatment to the majority of their patients with advanced PC. Conclusion: Not every PC patient in Germany is treated according to the present S3 guidelines. Diagnosis and treatment of PC in Germany still need to be improved. Copyright (C) 2009 S. Karger AG, Base
Triple Compton effect: A photon splitting into three upon collision with a free electron
The process in which a photon splits into three after the collision with a
free electron (triple Compton effect) is the most basic process for the
generation of a high-energy multi-particle entangled state composed out of
elementary quanta. The cross section of the process is evaluated in two
experimentally realizable situations, one employing gamma photons and
stationary electrons, and the other using keV photons and GeV electrons of an
x-ray free electron laser. For the first case, our calculation is in agreement
with the only available measurement of the differential cross section for the
process under study. Our estimates indicate that the process should be readily
measurable also in the second case. We quantify the polarization entanglement
in the final state by a recently proposed multi-particle entanglement measure.Comment: 5 pages; RevTeX; to be published in Phys.Rev.Let
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