85,299 research outputs found

    Generalized spin-dependent WIMP-nucleus interactions and the DAMA modulation effect

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    Guided by non-relativistic Effective Field Theory (EFT) we classify the most general spin-dependent interactions between a fermionic Weakly Interacting Massive Particle (WIMP) and nuclei, and within this class of models we discuss the viability of an interpretation of the DAMA modulation result in terms of a signal from WIMP elastic scatterings using a halo-independent approach. We find that, although several relativistic EFT's can lead to a spin-dependent cross section, in some cases with an explicit, non-negligible dependence on the WIMP incoming velocity, three main scenarios can be singled out in the non-relativistic limit which approximately encompass them all, and that only differ by their dependence on the transferred momentum. For two of them compatibility between DAMA and other constraints is possible for a WIMP mass below 30 GeV, but only for a WIMP velocity distribution in the halo of our Galaxy which departs from a Maxwellian. This is achieved by combining a suppression of the WIMP effective coupling to neutrons (to evade constraints from xenon and germanium detectors) to an explicit quadratic or quartic dependence of the cross section on the transferred momentum (that leads to a relative enhancement of the expected rate off sodium in DAMA compared to that off fluorine in droplet detectors and bubble chambers). For larger WIMP masses the same scenarios are excluded by scatterings off iodine in COUPP.Comment: 24 pages, 4 figure

    Problems with Mannheim's conformal gravity program

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    We show that Mannheim's conformal gravity program, whose potential has a term proportional to 1/r1/r and another term proportional to rr, does not reduce to Newtonian gravity at short distances, unless one assumes undesirable singularities of the mass density of the proton. Therefore, despite the claim that it successfully explains galaxy rotation curves, unless one assumes the singularities, it seems to be falsified by numerous Cavendish-type experiments performed at laboratories on Earth whose work have not found any deviations from Newton's theory. Moreover, it can be shown that as long as the total mass of the proton is positive, Mannheim's conformal gravity program leads to negative linear potential, which is problematic from the point of view of fitting galaxy rotation curves, which necessarily requires positive linear potential.Comment: 5 pages, no figures. Published versio

    D-brane width

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    Loop quantum gravity predicts that there are non-zero minimal area, and non-zero minimal volume in (3+1) dimensions. Given this, one can easily guess that one will have a non-zero minimal 9-volume in (9+1) dimensions. Therefore, in this paper, we argue that not only D9-brane but also Dp-brane for p less than 9 has a 9-volume. This idea is new, as the present view states that such a Dp-brane has p-volume but no 9 volume. To demonstrate this, first, we equate D8-brane action with D9-brane action and show that 9th direction which is perpendicular to D8-brane has non-zero width. We repeat this step for different ps; we equate Dp-brane action with Dp-1 brane action. By this iteration and induction we conclude that Dp-brane has non-zero widths for each of (9-p) directions perpendicular to the Dp-brane, and therefore, non-zero volume. When antisymmetric tensor and field strength are zero, this width is calculated to be 2 pi sqrt(alpha') for all (9-p) directions. For non-vanishing antisymmetric tensor and field strength, the width receives small corrections. In this paper, we only calculate up to the first order correction.Comment: 4 pages, no figures, argument based on loop quantum gravity adde

    Monitoring muscle fatigue following continuous load changes

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    Department of Human Factors EngineeringPrevious studies related to monitoring muscle fatigue during dynamic motion have focused on detecting the accumulation of muscle fatigue. However, it is necessary to detect both accumulation and recovery of muscle fatigue in dynamic muscle contraction while muscle load changes continuously. This study aims to investigate the development and recovery of muscle fatigue in dynamic muscle contraction conditions following continuous load changes. Twenty healthy males conducted repetitive elbow flexion and extension using 2kg and 1kg dumbbell, by turns. They performed the two tasks of different intensity (2kg intensity task, 1kg intensity task) alternately until they felt they could no longer achieve the required movement range or until they experienced unacceptable biceps muscle discomfort. Meanwhile, using EMG signal of biceps brachii muscle, fatigue detections were performed from both dynamic measurements during each dynamic muscle contraction task and isometric measurements during isometric muscle contraction right before and after each task. In each of 2kg and 1kg intensity tasks, pre, post and change value of EMG amplitude (AEMG) and center frequency were computed respectively. They were compared to check the validity of the muscle fatigue monitoring method using Wavelet transform with EMG signal from dynamic measurements. As a result, a decrease of center frequency in 2kg intensity tasks and an increase of center frequency in 1kg intensity tasks were detected. It shows that development and recovery of muscle fatigue were detected in 2kg and 1kg intensity tasks, respectively. Also, the tendency of change value of center frequency from dynamic measurements were corresponded with that from isometric measurements. It suggests that monitoring muscle fatigue in dynamic muscle contraction conditions using wavelet transform was valid to detect the development and recovery of muscle fatigue continuously. The result also shows the possibility of monitoring muscle fatigue in real-time in industry and it could propose a guideline in designing a human-robot interaction system based on monitoring user's muscle fatigue.clos

    CMB anisotropy power spectrum of 3-sphere universe for low ll

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    We calculate the CMB anisotropy power spectrum of closed universe due to scale invariant fluctuation of primordial universe by considering spherical harmonics for 3-sphere. In particular, we show that this consideration affects CMB anisotropy power spectrum, contrary to the wide belief. We show that the best-fit for Ο‡=sinβ‘βˆ’1rL\chi=\sin^{-1} r_L, where rLr_L is the radial distance of last scattering surface, is Ο‡=0.14βˆ’0.03+0.09\chi=0.14^{+0.09}_{-0.03} whereas the previous analysis from WMAP+BAO+H0H_0 gives Ο‡=0.16βˆ’0.16+0.14\chi=0.16^{+0.14}_{-0.16}.Comment: 6 pages, a typo fixe

    Anomaly-free representations of the holonomy-flux algebra

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    We work on the uniqueness, gr-qc/0504147, of representations of the holonomy-flux algebra in loop quantum gravity. We argue that for analytic diffeomorphisms, the flux operators can be only constants as functions on the configuration space in representations with no anomaly, which are zero in the standard representation.Comment: 4 page

    Quasi-Local Conservation Equations in General Relativity

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    A set of exact quasi-local conservation equations is derived from the Einstein's equations using the first-order Kaluza-Klein formalism of general relativity in the (2,2)-splitting of 4-dimensional spacetime. These equations are interpreted as quasi-local energy, momentum, and angular momentum conservation equations. In the asymptotic region of asymptotically flat spacetimes, it is shown that the quasi-local energy and energy-flux integral reduce to the Bondi energy and energy-flux, respectively. In spherically symmetric spacetimes, the quasi-local energy becomes the Misner-Sharp energy. Moreover, on the event horizon of a general dynamical black hole, the quasi-local energy conservation equation coincides with the conservation equation studied by Thorne {\it et al}. We discuss the remaining quasi-local conservation equations briefly.Comment: RevTex, 8 pages, a final version to appear in Phys. Lett.

    The Dark Energy Regulated by Emergent Conformal Symmetry

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    We have found a mechanism which regulates the dark energy in our universe. With an emergent conformal symmetry, the dark energy density is regulated to the order of a conformal anomaly parameter in the conformally coupled gravity. In the late time cosmological evolution, we have obtained a set of exact cosmological equations which deviate from the Friedmann equations significantly. Based on the recent observational cosmic expansion data, it is shown that the dark energy density is about 1/4 of the matter density at present, which is quite smaller than determined by General Relativity. The jerk parameter at present is also determined as a definite value 0.47.Comment: arXiv admin note: substantial text overlap with arXiv:0906.409

    Lagrangian formulation of the Palatini action

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    We work on the Lagrangian formulation of the Palatini action. We find that we must assume the metric compatibility condition for the Palatini action to describe General Relativity, which condition should hold in quantization. We find that we must also assume one of the torsion zero condition or the tetrad compatibility condition. Our results will hold for any action in terms of the tetrad and the internal connection which describes General Relativity.Comment: 5 pages, contents adde

    Spectrum of Projective Plane Curve Arrangements with Ordinary Singularities

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    The Hodge spectrum is an important analytic invariant of singularities encoding the Hodge filtration and the monodromy of the Milnor fiber. Explicit formulas exist for only a few cases. In this article the main result is a combinatorial formula for homogeneous polynomials in three variables whose reduced one define projective curve arrangements having only ordinary multiple points.Comment: 14 pages, add examples, correct typo
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