51,455 research outputs found

    A Note on Commuting Diffeomorphisms on Surfaces

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    Let S be a closed surface with nonzero Euler characteristic. We prove the existence of an open neighborhood V of the identity map of S in the C^1-topology with the following property: if G is an abelian subgroup of Diff^1(S) generated by any family of elements in V then the elements of G have common fixed points. This result generalizes a similar result due to Bonatti and announced in his paper "Diffeomorphismes commutants des surfaces et stabilite des fibrations en tores".Comment: 16 page

    Kinematic Constraints to the Transition Redshift from SNe Ia Union Data

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    The kinematic approach to cosmological tests provides a direct evidence to the present accelerating stage of the universe which does not depend on the validity of general relativity, as well as on the matter-energy content of the Universe. In this context, we consider here a linear two-parameter expansion for the decelerating parameter, q(z)=q0+q1zq(z)=q_0+q_1z, where q0q_0 and q1q_1 are arbitrary constants to be constrained by the Union supernovae data. By assuming a flat Universe we find that the best fit to the pair of free parameters is (q0,q1q_0,q_1) = (−0.73,1.5)-0.73,1.5) whereas the transition redshift is zt=0.49−0.07+0.14z_t = 0.49^{+0.14}_{-0.07} (1σ1\sigma) −0.12+0.54^{+0.54}_{-0.12} (2σ2\sigma). This kinematic result is in agreement with some independent analyzes and accommodates more easily many dynamical flat models (like Λ\LambdaCDM).Comment: 10 pages, 4 figures, 1 tabl
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