13,090 research outputs found

    f(T)f(T) Theories and Varying Fine Structure Constant

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    In analogy to f(R)f(R) theory, recently a new modified gravity theory, namely the so-called f(T)f(T) theory, has been proposed to drive the current accelerated expansion without invoking dark energy. In the present work, by extending Bisabr's idea, we try to constrain f(T)f(T) theories with the varying fine structure "constant", αe2/c\alpha\equiv e^2/\hbar c. We find that the constraints on f(T)f(T) theories from the observational Δα/α\Delta\alpha/\alpha data are very severe. In fact, they make f(T)f(T) theories almost indistinguishable from Λ\LambdaCDM model.Comment: 12 pages, 4 figures, 1 table, revtex4; v2: discussions added, Phys. Lett. B in press; v3: published versio

    On Frankl and Furedi's conjecture for 3-uniform hypergraphs

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    The Lagrangian of a hypergraph has been a useful tool in hypergraph extremal problems. In most applications, we need an upper bound for the Lagrangian of a hypergraph. Frankl and Furedi in \cite{FF} conjectured that the rr-graph with mm edges formed by taking the first mm sets in the colex ordering of N(r){\mathbb N}^{(r)} has the largest Lagrangian of all rr-graphs with mm edges. In this paper, we give some partial results for this conjecture.Comment: 19 pages, 1 figure. arXiv admin note: substantial text overlap with arXiv:1211.650
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