28,509 research outputs found

    On twisted forms and relative algebraic K-theory

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    This paper introduces a new approach to the study of certain aspects of Galois module theory by combining ideas arising from the study of the Galois structure of torsors of finite group schemes with techniques coming from relative algebraic KK-theory.Comment: Final version. To appear in the Proceedings of the London Mathematical Societ

    Tamagawa Numbers for Motives with (Non-Commutative) Coefficients

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    Let MM be a motive which is defined over a number field and admits an action of a finite dimensional semisimple \bq-algebra AA. We formulate and study a conjecture for the leading coefficient of the Taylor expansion at 00 of the AA-equivariant LL-function of MM. This conjecture simultaneously generalizes and refines the Tamagawa number conjecture of Bloch, Kato, Fontaine, Perrin-Riou et al. and also the central conjectures of classical Galois module theory as developed by Frƶhlich, Chinburg, M. Taylor et al. The precise formulation of our conjecture depends upon the choice of an order \A in AA for which there exists a `projective \A-structure' on MM. The existence of such a structure is guaranteed if \A is a maximal order, and also occurs in many natural examples where \A is non-maximal. In each such case the conjecture with respect to a non-maximal order refines the conjecture with respect to a maximal order. We develop a theory of determinant functors for all orders in AA by making use of the category of virtual objects introduced by Deligne

    Investigation into diode pumped modelocked ND based laser oscillators for the CLIC photoinjector system

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    The photo-injector system envisaged for the proposed CLIC linear e+-e- accelerator at CERN has a demanding set of specifications on output pulse structure, power and timing stability. This paper reports on results obtained with quasi-CW diode pumped laser oscillators with output stabilisation. A 300W 804nm diode array stack is used to side pump Nd:YLF (1047nm) crystals with 200Ī¼s pulses at 100Hz repetition rate. Using feedback from the laser output to control an acousto-optic loss modulator in the cavity, start-up spiking and Q-switched behaviour is suppressed. Preliminary results obtained on incorporation of a saturable absorbing mirror for passive modelocking are presented
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