294,052 research outputs found

    Charged Higgs Production at Linear Colliders in Large Extra Dimensions

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    In the Two-Higgs-Doublet Model(2HDM) with large extra dimensions(LED), we study the contributions of virtual Kaluza-Klein(KK) gravitons to 2HDM charged Higgs production, especially in the two important production processes e+eH+He^+e^-\to H^+H^- and e+eHtbˉe^+e^-\to H^-t\bar{b}, at future linear colliders (LC). We find that KK graviton effects can significantly modify these total cross sections and also their differential cross sections compared to their respective 2HDM values and, therefore, can be used to probe the effective scale ΛT\Lambda_T up to several TeV. For example, at s=2\sqrt{s}=2 TeV, the cross sections for e+eH+He^+e^-\to H^+H^- and e+eHtbˉe^+e^-\to H^-t\bar{b} in the 2HDM are 7.4fb for mH=150m_{H^-}=150 GeV and 0.003fb for mH=1.1m_{H^-}=1.1 TeV and tanβ=40\tan\beta=40, while in LED they are 12.1fb and 0.01fb, respectively, for ΛT=4\Lambda_T=4 Tev.Comment: 18 pages, 11 figures; a version to appear in PR

    A propeller scenario for the gamma-ray emission of low-mass X-ray binaries: The case of XSS J12270-4859

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    XSS J12270-4859 is the only low mass X-ray binary (LMXB) with a proposed persistent gamma-ray counterpart in the Fermi-LAT domain, 2FGL 1227.7-4853. Here, we present the results of the analysis of recent INTEGRAL observations, aimed at assessing the long-term variability of the hard X-ray emission, and thus the stability of the accretion state. We confirm that the source behaves as a persistent hard X-ray emitter between 2003 and 2012. We propose that XSS J12270-4859 hosts a neutron star in a propeller state, a state we investigate in detail, developing a theoretical model to reproduce the associated X-ray and gamma-ray properties. This model can be understood as being of a more general nature, representing a viable alternative by which LMXBs can appear as gamma-ray sources. In particular, this may apply to the case of millisecond pulsars performing a transition from a state powered by the rotation of their magnetic field, to a state powered by matter in-fall, such as that recently observed from the transitional pulsar PSR J1023+0038. While the surface magnetic field of a typical NS in a LMXB is lower by more than four orders of magnitude than the much more intense fields of neutron stars accompanying high-mass binaries, the radius at which the matter in-flow is truncated in a NS-LMXB system is much lower. The magnetic field at the magnetospheric interface is then orders of magnitude larger at this interface, and as consequence, so is the power to accelerate electrons. We demonstrate that the cooling of the accelerated electron population takes place mainly through synchrotron interaction with the magnetic field permeating the interface, and through inverse Compton losses due to the interaction between the electrons and the synchrotron photons they emit. We found that self-synchrotron Compton processes can explain the high energy phenomenology of XSS J12270-4859.Comment: 12 pages, 3 figures, accepted for publication in MNRAS. References update

    Darwinian Data Structure Selection

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    Data structure selection and tuning is laborious but can vastly improve an application's performance and memory footprint. Some data structures share a common interface and enjoy multiple implementations. We call them Darwinian Data Structures (DDS), since we can subject their implementations to survival of the fittest. We introduce ARTEMIS a multi-objective, cloud-based search-based optimisation framework that automatically finds optimal, tuned DDS modulo a test suite, then changes an application to use that DDS. ARTEMIS achieves substantial performance improvements for \emph{every} project in 55 Java projects from DaCapo benchmark, 88 popular projects and 3030 uniformly sampled projects from GitHub. For execution time, CPU usage, and memory consumption, ARTEMIS finds at least one solution that improves \emph{all} measures for 86%86\% (37/4337/43) of the projects. The median improvement across the best solutions is 4.8%4.8\%, 10.1%10.1\%, 5.1%5.1\% for runtime, memory and CPU usage. These aggregate results understate ARTEMIS's potential impact. Some of the benchmarks it improves are libraries or utility functions. Two examples are gson, a ubiquitous Java serialization framework, and xalan, Apache's XML transformation tool. ARTEMIS improves gson by 16.516.5\%, 1%1\% and 2.2%2.2\% for memory, runtime, and CPU; ARTEMIS improves xalan's memory consumption by 23.523.5\%. \emph{Every} client of these projects will benefit from these performance improvements.Comment: 11 page

    Further observations on the mean velocity distribution in fully developed pipe flow

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    The measurements by Zagarola & Smits (1998) of mean velocity profiles in fully developed turbulent pipe flow are repeated using a smaller Pitot probe to reduce the uncertainties due to velocity gradient corrections. A new static pressure correction (McKeon & Smits 2002) is used in analysing all data and leads to significant differences from the Zagarola & Smits conclusions. The results confirm the presence of a power-law region near the wall and, for Reynolds numbers greater than 230×10^3 (R+ >5×10^3), a logarithmic region further out, but the limits of these regions and some of the constants differ from those reported by Zagarola & Smits. In particular, the log law is found for 600<y+ <0.12R+ (instead of 600<y+ <0.07R+), and the von Kármán constant κ, the additive constant B for the log law using inner flow scaling, and the additive constant B∗ for the log law using outer scaling are found to be 0.421 ± 0.002, 5.60 ± 0.08 and 1.20 ± 0.10, respectively, with 95% confidence level (compared with 0.436±0.002, 6.15±0.08, and 1.51±0.03 found by Zagarola & Smits). The data also confirm that the pipe flow data for ReD ≤ 13.6×10^6 (as a minimum) are not affected by surface roughness
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