28,172 research outputs found

    On Consistency Of Noncommutative Chern-Simons Theory

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    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

    Opening the ultra high energy cosmic ray window from the top

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    While several arguments can be proposed against the existence of particles with energy in excess of (3−5)×1019(3-5)\times 10^{19} eV in the cosmic ray spectrum, these particles are actually observed and their origin seeks for an explanation. After a description of the problems encountered in explaining these ultra-high energy cosmic rays (UHECRs) in the context of astrophysical sources, we will review the so-called {\it Top-Down} (TD) Models, in which UHECRs are the result of the decay of very massive unstable particles, possibly created in the Early Universe. Particular emphasis will be given to the signatures of the TD models, likely to be accessible to upcoming experiments like Auger.Comment: 13 pages, 3 figures. Invited Talk at the Vulcano Workshop `Frontier Objects in Astrophysics and Particle Physics', May 22-27, 200

    Origin of very high and ultra high energy cosmic rays

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    While there is some level of consensus on a Galactic origin of cosmic rays up to the knee (Ek∼3×1015E_{k}\sim 3\times 10^{15} eV) and on an extragalactic origin of cosmic rays with energy above ∼1019\sim 10^{19} eV, the debate on the genesis of cosmic rays in the intermediate energy region has received much less attention, mainly because of the ambiguity intrinsic in defining such a region. The energy range between 101710^{17} eV and ∼1019\sim 10^{19} eV is likely to be the place where the transition from Galactic to extragalactic cosmic rays takes place. Hence the origin of these particles, though being of the highest importance from the physics point of view, it is also one of the most difficult aspects to investigate. Here I will illustrate some ideas concerning the sites of acceleration of these particles and the questions that their investigation may help answer, including the origin of \underline{ultra} high energy cosmic rays.Comment: Solicited Review Paper to appear in 'Comptes Rendus Physique

    Role of Strategic Reasoning in Constitutional Interpretation: In Defense of the Pathological Perspective

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    A Wiener model consists of a linear dynamic block followed by with a nonlinear static block. When identifying the parameters of such a system, the Prediction Error Method (PEM) can be used. Depending on how noise enters the system, the predictor can be difficult to express, and an approximate predictor may be interesting. The estimate obtained from using this approximate predictor is however not always consistent. In this report we investigate this inconsistency

    Dark matter distribution in the universe and ultra-high energy cosmic rays

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    Two of the greatest mysteries of modern physics are the origin of the dark matter in the universe and the nature of the highest energy particles in the cosmic ray spectrum. We discuss here possible direct and indirect connections between these two problems, with particular attention to two cases: in the first we study the local clustering of possible sources of ultra-high energy cosmic rays (UHECRs) driven by the local dark matter overdensity. In the second case we study the possibility that UHECRs are directly generated by the decay of weakly unstable super heavy dark matter.Comment: 15 pages, 7 figures. Invited Talk at the "International Workshop on observing UHECRs from space and earth", August 9-12, 2000, Metepec, Puebla (Mexico

    Origin of Galactic Cosmic Rays

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    The origin of the bulk of cosmic rays (CRs) observed at Earth is the topic of a century long investigation, paved with successes and failures. From the energetic point of view, supernova remnants (SNRs) remain the most plausible sources of CRs up to rigidity ? 10^6-10^7 GV. This confidence somehow resulted in the construction of a paradigm, the so-called SNR paradigm: CRs are accelerated through diffusive shock acceleration in SNRs and propagate diffusively in the Galaxy in an energy dependent way. Qualitative confirmation of the SNR acceleration scenario has recently been provided by gamma ray and X-ray observations. Diffusive propagation in the Galaxy is probed observationally through measurement of the secondary to primary nuclei flux ratios (such as B/C). There are however some weak points in the paradigm, which suggest that we are probably missing some physical ingredients in our models. The theory of diffusive shock acceleration at SNR shocks predicts spectra of accelerated particles which are systematically too hard compared with the ones inferred from gamma ray observations. Moreover, hard injection spectra indirectly imply a steep energy dependence of the diffusion coefficient in the Galaxy, which in turn leads to anisotropy larger than the observed one. Moreover recent measurements of the flux of nuclei suggest that the spectra have a break at rigidity ? 200 GV, which does not sit well with the common wisdom in acceleration and propagation. In this paper I will review these new developments and suggest some possible implications.Comment: Invited Review Talk in SciNeGHE 2012, 20-22 June 2012, Lecce (Italy
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