78,069 research outputs found

    A possible correspondence between Ricci identities and Dirac equations in the Newman-Penrose formalism: towards an understanding of gravity induced collapse of the wave-function?

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    It is well-known that in the Newman-Penrose formalism the Riemann tensor can be expressed as a set of eighteen complex first-order equations, in terms of the twelve spin coefficients, known as Ricci identities. The Ricci tensor herein is determined via the Einstein equations. It is also known that the Dirac equation in a curved spacetime can be written in the Newman-Penrose formalism as a set of four first-order coupled equations for the spinor components of the wave-function. In the present article we suggest that it might be possible to think of the Dirac equations in the N-P formalism as a special case of the Ricci identities, after an appropriate identification of the four Dirac spinor components with four of the spin coefficients, provided torsion is included in the connection, and after a suitable generalization of the energy-momentum tensor. We briefly comment on similarities with the Einstein-Cartan-Sciama-Kibble theory. The motivation for this study is to take some very preliminary steps towards developing a rigorous description of the hypothesis that dynamical collapse of the wave-function during a quantum measurement is caused by gravity.Comment: v2. 30 pages. Additional discussion in Sections IV and V. References added. To appear in Gen. Rel. Gra

    Study of non-equilibrium transport phenomena

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    Nonequilibrium phenomena due to real gas effects are very important features of low density hypersonic flows. The shock shape and emitted nonequilibrium radiation are identified as the bulk flow behavior parameters which are very sensitive to the nonequilibrium phenomena. These parameters can be measured in shock tubes, shock tunnels, and ballistic ranges and used to test the accuracy of computational fluid dynamic (CFD) codes. Since the CDF codes, by necessity, are based on multi-temperature models, it is also desirable to measure various temperatures, most importantly, the vibrational temperature. The CFD codes would require high temperature rate constants, which are not available at present. Experiments conducted at the NASA Electric Arc-driven Shock Tube (EAST) facility reveal that radiation from steel contaminants overwhelm the radiation from the test gas. For the measurement of radiation and the chemical parameters, further investigation and then appropriate modifications of the EAST facility are required

    Finite Blocklength Rates over a Fading Channel with CSIT and CSIR

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    In this work, we obtain lower and upper bounds on the maximal transmission rate at a given codeword length nn, average probability of error ϵ\epsilon and power constraint Pˉ\bar{P}, over a finite valued, block fading additive white Gaussian noise (AWGN) channel with channel state information (CSI) at the transmitter and the receiver. These bounds characterize deviation of the finite blocklength coding rates from the channel capacity which is in turn achieved by the water filling power allocation across time. The bounds obtained also characterize the rate enhancement possible due to the CSI at the transmitter in the finite blocklength regime. The results are further elucidated via numerical examples.Comment: 10 pages, 2 figures, results for finite valued fading states, typos corrected, proofs elaborated, lower bound under short term power constraint improve

    Radiative neutralino production in low energy supersymmetric Models. II. The case of beam polarization

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    We study the production of the lightest neutralinos in the radiative process e+eχ~10χ~10γe^+e^- \to \tilde\chi^0_1 \tilde\chi^0_1\gamma in low energy supersymmetric models for the International Linear Collider energies with longitudinally polarized electron and positron beams. For this purpose we consider the case of nonminimal supersymmetric standard model as well as the case of minimal supersymmetric standard model. At the first stage of a linear collider, with s=500\sqrt{s} =500 GeV, the radiative production of the lightest neutralinos may be a viable channel to study supersymmetric partners of the Standard Model particles, especially if the other supersymmetric particles are too heavy to to be pair-produced. We consider in detail the effect of beam polarization on the production cross section. We compare and contrast the dependence of the signal cross section on the parameters of the neutralino sector of the nonminimal and minimal supersymmetric standard model when the electron and positron beams are longitudinally polarized. In order to assess the feasibility of experimentally observing the radiative neutralino production process, we consider the background to this process coming from the Standard Model process e+eννˉγe^+e^- \to \nu \bar\nu \gamma with longitudinally polarized electron and positron beams. We also consider the supersymmetric background to the radiative neutralino production process coming from the radiative production of the scalar partners of the neutrinos (sneutrinos) e+eν~ν~γe^+e^- \to \tilde\nu \tilde\nu^\ast \gamma, with longitudinally polarized beams. This process can be a a background to the radiative neutralino production when the sneutrinos decay invisibly.Comment: 20 pages, 16 figures, 13 tables; latex problem fixe