4,840 research outputs found

    Color separate singlets in e+ee^+e^- annihilation

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    We use the method of color effective Hamiltonian to study the properties of states in which a gluonic subsystem forms a color singlet, and we will study the possibility that such a subsystem hadronizes as a separate unit. A parton system can normally be subdivided into singlet subsystems in many different ways, and one problem arises from the fact that the corresponding states are not orthogonal. We show that if only contributions of order 1/Nc21/N_c^2 are included, the problem is greatly simplified. Only a very limited number of states are possible, and we present an orthogonalization procedure for these states. The result is simple and intuitive and could give an estimate of the possibility to produce color separated gluonic subsystems, if no dynamical effects are important. We also study with a simple MC the possibility that configurations which correspond to "short strings" are dynamically favored. The advantage of our approach over more elaborate models is its simplicity, which makes it easier to estimate color reconnection effects in reactions which are more complicated than the relatively simple e+ee^+e^- annihilation.Comment: Revtex, 24 pages, 7 figures; Compared to the previous version, 1 new figure is added and Monte-Carlo results are re-analyzed, as suggested by the referee; To appear in Phys. Rev.

    Matrix Transfer Function Design for Flexible Structures: An Application

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    The application of matrix transfer function design techniques to the problem of disturbance rejection on a flexible space structure is demonstrated. The design approach is based on parameterizing a class of stabilizing compensators for the plant and formulating the design specifications as a constrained minimization problem in terms of these parameters. The solution yields a matrix transfer function representation of the compensator. A state space realization of the compensator is constructed to investigate performance and stability on the nominal and perturbed models. The application is made to the ACOSSA (Active Control of Space Structures) optical structure

    Electrodynamics of Media

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    Contains reports on two research projects.Joint Services Electronics Programs (U.S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E

    Electrodynamics of Media

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    Contains research objectives and reports on one research project.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E

    Asymptotic stability, concentration, and oscillation in harmonic map heat-flow, Landau-Lifshitz, and Schroedinger maps on R^2

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    We consider the Landau-Lifshitz equations of ferromagnetism (including the harmonic map heat-flow and Schroedinger flow as special cases) for degree m equivariant maps from R^2 to S^2. If m \geq 3, we prove that near-minimal energy solutions converge to a harmonic map as t goes to infinity (asymptotic stability), extending previous work down to degree m = 3. Due to slow spatial decay of the harmonic map components, a new approach is needed for m=3, involving (among other tools) a "normal form" for the parameter dynamics, and the 2D radial double-endpoint Strichartz estimate for Schroedinger operators with sufficiently repulsive potentials (which may be of some independent interest). When m=2 this asymptotic stability may fail: in the case of heat-flow with a further symmetry restriction, we show that more exotic asymptotics are possible, including infinite-time concentration (blow-up), and even "eternal oscillation".Comment: 34 page

    Quantum Zeno subspaces

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    The quantum Zeno effect is recast in terms of an adiabatic theorem when the measurement is described as the dynamical coupling to another quantum system that plays the role of apparatus. A few significant examples are proposed and their practical relevance discussed. We also focus on decoherence-free subspaces.Comment: 5 pages, 1 figure, to be published in Phys. Rev. Let

    Thermal noise in half infinite mirrors with non-uniform loss: a slab of excess loss in a half infinite mirror

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    We calculate the thermal noise in half-infinite mirrors containing a layer of arbitrary thickness and depth made of excessively lossy material but with the same elastic material properties as the substrate. For the special case of a thin lossy layer on the surface of the mirror, the excess noise scales as the ratio of the coating loss to the substrate loss and as the ratio of the coating thickness to the laser beam spot size. Assuming a silica substrate with a loss function of 3x10-8 the coating loss must be less than 3x10-5 for a 6 cm spot size and a 7 micrometers thick coating to avoid increasing the spectral density of displacement noise by more than 10%. A similar number is obtained for sapphire test masses.Comment: Passed LSC (internal) review. Submitted to Phys. Rev. D. (5/2001) Replacement: Minor typo in Eq. 17 correcte

    Relative CC"-Numerical Ranges for Applications in Quantum Control and Quantum Information

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    Motivated by applications in quantum information and quantum control, a new type of CC"-numerical range, the relative CC"-numerical range denoted WK(C,A)W_K(C,A), is introduced. It arises upon replacing the unitary group U(N) in the definition of the classical CC"-numerical range by any of its compact and connected subgroups KU(N)K \subset U(N). The geometric properties of the relative CC"-numerical range are analysed in detail. Counterexamples prove its geometry is more intricate than in the classical case: e.g. WK(C,A)W_K(C,A) is neither star-shaped nor simply-connected. Yet, a well-known result on the rotational symmetry of the classical CC"-numerical range extends to WK(C,A)W_K(C,A), as shown by a new approach based on Lie theory. Furthermore, we concentrate on the subgroup SUloc(2n):=SU(2)...SU(2)SU_{\rm loc}(2^n) := SU(2)\otimes ... \otimes SU(2), i.e. the nn-fold tensor product of SU(2), which is of particular interest in applications. In this case, sufficient conditions are derived for WK(C,A)W_{K}(C,A) being a circular disc centered at origin of the complex plane. Finally, the previous results are illustrated in detail for SU(2)SU(2)SU(2) \otimes SU(2).Comment: accompanying paper to math-ph/070103
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