6,526 research outputs found
On Consistency Of Noncommutative Chern-Simons Theory
We consider the noncommutative extension of Chern-Simons theory. We show the
the theory can be fully expanded in power series of the noncommutative
parameter theta and that no non-analytical sector exists. The theory appears to
be unstable under radiative corrections, but we show that the infinite set of
instabilities, to all orders in \hbar and in theta, is confined to a BRS exact
cocycle. We show also that the theory is anomaly free. The quantum theory
cannot be written in terms of the Groenewald-Moyal star product, and hence
doubts arise on the interpretation of the noncommutative nature of the
underlying spacetime. Nonetheless, the deformed theory is well defined as a
quantum field theory, and the beta function of the Chern-Simons coupling
constant vanishes, as in the ordinary Chern-Simons theory.Comment: 17 page
Instabilities of noncommutative two dimensional BF model
The noncommutative extension of two dimensional BF model is considered. It is
shown that the realization of the noncommutative map via the Groenewold-Moyal
star product leads to instabilities of the action, hence to a non
renormalizable theory.Comment: 9 page
Gamma-Ray Constraints on Neutralino Dark Matter Clumps in the Galactic Halo
According to high resolution cold dark matter (CDM) simulations, large
virialized halos are formed through the constant merging of smaller halos
formed at earlier times. In particular, the halo of our Galaxy may have
hundreds of dark matter clumps. The annihilation of dark matter particles such
as the neutralino in these clumps generates -ray fluxes that can
potentially be detected by future experiments such as GLAST. We find that,
depending on the parameters of the clump density profile and on the
distribution of clumps in the Galactic halo, the contribution to the diffuse
-ray background from clumps can constrain the properties of neutralinos
such as the mass and annihilation cross section. We model the density profile
of clumps by three representative dark matter profiles: singular isothermal
spheres (SIS), Moore profiles, and Navarro, Frenk and White (NFW) density
profiles and calculate the spectrum and angular distribution in the sky of the
-ray flux due to neutralino annihilation in the clumpy halo of the
Galaxy. The calculations are carried out in the context of two different
scenarios for the distribution of clumps in the Galaxy and their
concentrations, which result in very different conclusions.Comment: 24 pages, 7 ps fig
The origin of the positron excess in cosmic rays
We show that the positron excess measured by the PAMELA experiment in the
region between 10 and 100 GeV may well be a natural consequence of the standard
scenario for the origin of Galactic cosmic rays. The 'excess' arises because of
positrons created as secondary products of hadronic interactions inside the
sources, but the crucial physical ingredient which leads to a natural
explanation of the positron flux is the fact that the secondary production
takes place in the same region where cosmic rays are being accelerated.
Therefore secondary positrons (and electrons) participate in the acceleration
process and turn out to have a very flat spectrum, which is responsible, after
propagation in the Galaxy, for the observed positron 'excess'. This effect
cannot be avoided though its strength depends on the values of the
environmental parameters during the late stages of evolution of supernova
remnants.Comment: 4 Pages, 2 figures. Some references and discussion adde
General Solution Of Linear Vector Supersymmetry
We give the general solution of the Ward identity for the linear vector
supersymmetry which characterizes all topological models. Such solution, whose
expression is quite compact and simple, greatly simplifies the study of
theories displaying a supersymmetric algebraic structure, reducing to a few
lines the proof of their possible finiteness. In particular, the cohomology
technology usually involved for the quantum extension of these theories, is
completely bypassed. The case of Chern-Simons theory is taken as an example.Comment: 18 pages, LaTeX, no figure
Learned Hand and the Self-Government Theory of the First Amendment: \u3cem\u3eMasses Publishing Co. v. Patten\u3c/em\u3e
Sitting as a federal district judge in the case of Masses Publishing Co. v. Patten, Learned Hand was called upon to interpret the Espionage Act of 1917 just six weeks after its passage. The Act was potentially the most speech-restrictive piece of federal legislation since the Alien and Sedition Acts of 1798. Judge Hand recognized this and ruled that the terms of the Act must be construed in light of the first amendment. He defined the limits of legally protected war criticism, and presumably of political advocacy generally, according to a test that makes the crucial consideration the content of the speaker\u27s message. He ruled that speech is not a sufficient basis for legal sanctions so long as one stops short of urging upon others that it is their duty or their interest to resist the law ....” It is clear from his correspondence that Hand took pride in this test and in the reasoning that lay behind it, and hoped his approach would serve as a benchmark for interpretation of the first amendment.
He was sorely disappointed. His judgment in the Masses case, holding that war criticism that stopped short of explicit counseling of law violation could not be banished from the mails, was quickly overruled by the Second Circuit. His eloquent and carefully reasoned opinion in Masses did not elicit much attention or admiration from academic commentators. Especially disconcerting to Hand was his failure to persuade Justice Oliver Wendell Holmes, the judge he probably admired most
Learned Hand\u27s Seven Other Ideas about the Freedom of Speech
I say “other” because, regarding the freedom of speech, Learned Hand has suffered the not uncommon fate of having his best ideas either drowned out or credited exclusively to others due to the excessive attention that has been bestowed on one of his lesser ideas. Sitting as a district judge in the case of Masses Publishing Co. v. Patten, Hand wrote the earliest judicial opinion about the freedom of speech that has attained canonical status. He ruled that under the recently passed Espionage Act of 1917, writings critical of government cannot be grounds for imposing criminal punishment or the denial of mailing privileges unless the authors tell their readers it is in their interest or is their duty to violate the law. Hostile criticism very likely to cause harm or intended to do so is not punishable under that statute, he concluded, if it stops short of direct advocacy of law violation. He derived this standard in the guise of statutory interpretation but very little in the text of the law or its history of passage suggested his reading. Rather, to support his preferred test Hand drew upon what he took to be the basic presuppositions of democratic governance, assumed to underlie the enactment of the statute. In subsequent private correspondence, he repeatedly invoked his test as not only implicit in the Espionage Act but also the best interpretation of the First Amendment
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