43,896 research outputs found

    Weak Gravity Conjecture for the Effective Field Theories with N Species

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    We conjecture an intrinsic UV cutoff for the validity of the effective field theory with a large number of species coupled to gravity. In four dimensions such a UV cutoff takes the form Λ=λ/NMp\Lambda=\sqrt{\lambda/ N}M_p for NN scalar fields with the same potential λϕi4\lambda \phi_i^4, i=1,...,Ni=1,...,N. This conjecture implies that the assisted chaotic inflation or N-flation might be in the swampland, not in the landscape. Similarly a UV cutoff Λ=gMp/N\Lambda=gM_p/\sqrt{N} is conjectured for the U(1) gauge theory with NN species.Comment: 12 pages; refs added and some statements clarifie

    Multiscale change-point segmentation: beyond step functions.

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    Modern multiscale type segmentation methods are known to detect multiple change-points with high statistical accuracy, while allowing for fast computation. Underpinning (minimax) estimation theory has been developed mainly for models that assume the signal as a piecewise constant function. In this paper, for a large collection of multiscale segmentation methods (including various existing procedures), such theory will be extended to certain function classes beyond step functions in a nonparametric regression setting. This extends the interpretation of such methods on the one hand and on the other hand reveals these methods as robust to deviation from piecewise constant functions. Our main finding is the adaptation over nonlinear approximation classes for a universal thresholding, which includes bounded variation functions, and (piecewise) Holder functions of smoothness order 0 < alpha <= 1 as special cases. From this we derive statistical guarantees on feature detection in terms of jumps and modes. Another key finding is that these multiscale segmentation methods perform nearly (up to a log-factor) as well as the oracle piecewise constant segmentation estimator (with known jump locations), and the best piecewise constant approximants of the (unknown) true signal. Theoretical findings are examined by various numerical simulations

    Transmission of Water Waves under Multiple Vertical Thin Plates

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    The transmission of water waves under vertical thin plates, e.g., offshore floating breakwaters, oscillating water column wave energy converters, and so on, is a crucial feature that dominates the hydrodynamic performance of marine devices. In this paper, the analytical solution to the transmission of water waves under multiple 2D vertical thin plates is firstly derived based on the linear potential theory. The influences of relevant parameters on the wave transmission are discussed, which include the number of plates, the draft of plates, the distance between plates and the water depth. The analytical results suggest that the transmission of progressive waves gradually weakens with the growth of the number and draft of plates, and under the conditions of given number and draft of plates, the distribution of plates has significant influence on the transmission of progressive waves. The results of this paper contribute to the understanding of the transmission of water waves under multiple vertical thin plates, as well as the suggestion on optimal design of complex marine devices, such as a floating breakwater with multiple plates

    Anomalous Nernst and Hall effects in magnetized platinum and palladium

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    We study the anomalous Nernst effect (ANE) and anomalous Hall effect (AHE) in proximity-induced ferromagnetic palladium and platinum which is widely used in spintronics, within the Berry phase formalism based on the relativistic band structure calculations. We find that both the anomalous Hall (σxyA\sigma_{xy}^A) and Nernst (αxyA\alpha_{xy}^A) conductivities can be related to the spin Hall conductivity (σxyS\sigma_{xy}^S) and band exchange-splitting (Δex\Delta_{ex}) by relations σxyA=ΔexeσxyS(EF)\sigma_{xy}^A =\Delta_{ex}\frac{e}{\hbar}\sigma_{xy}^S(E_F)' and αxyA=π23kB2TΔexσxys(μ)"\alpha_{xy}^A = -\frac{\pi^2}{3}\frac{k_B^2T\Delta_{ex}}{\hbar}\sigma_{xy}^s(\mu)", respectively. In particular, these relations would predict that the σxyA\sigma_{xy}^A in the magnetized Pt (Pd) would be positive (negative) since the σxyS(EF)\sigma_{xy}^S(E_F)' is positive (negative). Furthermore, both σxyA\sigma_{xy}^A and αxyA\alpha_{xy}^A are approximately proportional to the induced spin magnetic moment (msm_s) because the Δex\Delta_{ex} is a linear function of msm_s. Using the reported msm_s in the magnetized Pt and Pd, we predict that the intrinsic anomalous Nernst conductivity (ANC) in the magnetic platinum and palladium would be gigantic, being up to ten times larger than, e.g., iron, while the intrinsic anomalous Hall conductivity (AHC) would also be significant.Comment: Accepted for publication in the Physical Review

    From the Complete Yang Model to Snyder's Model, de Sitter Special Relativity and Their Duality

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    By means of Dirac procedure, we re-examine Yang's quantized space-time model, its relation to Snyder's model, the de Sitter special relativity and their UV-IR duality. Starting from a dimensionless dS_5-space in a 5+1-d Mink-space a complete Yang model at both classical and quantum level can be presented and there really exist Snyder's model, the dS special relativity and the duality.Comment: 7 papge

    Adaptive relaying method selection for multi-rate wireless networks with network coding

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