1,146,855 research outputs found

    Invariant Kinematics on a One-Dimensional Lattice in Noncommutative Geometry

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    In a one-dimensional lattice, the induced metric (from a noncommutative geometry calculation) breaks translation invariance. This leads to some inconsistencies among different spectator frames, in the observation of the hoppings of a test particle between lattice sites. To resolve the inconsistencies between the different spectator frames, we replace the test particle's bare mass by an effective locally dependent mass. This effective mass also depends on the lattice constant - i.e. it is a scale dependent variable (a "running" mass). We also develop an alternative approach based on a compensating potential. The induced potential between a spectator frame and the test particle is attractive on the average. We then show that the entire formalism holds for a quantum particle represented by a wave function, just as it applies to the mechanics of a classical point particle.Comment: 17 pages, latex, epsf, amssymbols, 2 figures. Final version to be published in IJMP

    Scalar transport in compressible flow

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    Transport of scalar fields in compressible flow is investigated. The effective equations governing the transport at scales large compared to those of the advecting flow are derived by using multi-scale techniques. Ballistic transport generally takes place when both the solenoidal and the potential components of the velocity do not vanish, despite of the fact that it has zero average value. The calculation of the effective ballistic velocity VbV_b is reduced to the solution of one auxiliary equation. An analytic expression for VbV_b is derived in some special instances, i.e. flows depending on a single coordinate, random with short correlation times and slightly compressible cellular flow. The effective mean velocity VbV_b vanishes for velocity fields which are either incompressible or potential and time-independent. For generic compressible flow, the most general conditions ensuring the absence of ballistic transport are isotropy and/or parity invariance. When VbV_b vanishes (or in the frame of reference moving with velocity VbV_b), standard diffusive transport takes place. It is known that diffusion is always enhanced by incompressible flow. On the contrary, we show that diffusion is depleted in the presence of time-independent potential flow. Trapping effects due to potential wells are responsible for this depletion. For time-dependent potential flow or generic compressible flow, transport rates are enhanced or depleted depending on the detailed structure of the velocity field.Comment: 27 pages, submitted to Physica

    The Luminous Convolution Model as an alternative to dark matter in spiral galaxies

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    The Luminous Convolution Model (LCM) demonstrates that it is possible to predict the rotation curves of spiral galaxies directly from estimates of the luminous matter. We consider two frame-dependent effects on the light observed from other galaxies: relative velocity and relative curvature. With one free parameter, we predict the rotation curves of twenty-three (23) galaxies represented in forty-two (42) data sets. Relative curvature effects rely upon knowledge of both the gravitational potential from luminous mass of the emitting galaxy and the receiving galaxy, and so each emitter galaxy is compared to four (4) different Milky Way luminous mass models. On average in this sample, the LCM is more successful than either dark matter or modified gravity models in fitting the observed rotation curve data. Implications of LCM constraints on populations synthesis modeling are discussed in this paper. This paper substantially expands the results in arXiv:1309.7370.Comment: Implications of LCM constraints on populations synthesis modeling are discussed in this paper. This paper substantially expands the results in arxiv:1309.737

    The Average Physical Properties and Star Formation Histories of the UV-Brightest Star-Forming Galaxies at z~3.7

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    [Abridged] We investigate the average physical properties and star formation histories of the most UV-luminous star-forming galaxies at z~3.7. Our results are derived from analyses of the average spectral energy distributions (SEDs), constructed from stacked optical to infrared photometry, of a sample of the 1,902 most UV-luminous star-forming galaxies found in 5.3 square degrees of the NOAO Deep Wide-Field Survey. We bin the sample according to UV luminosity, and find that the shape of the average SED in the rest-frame optical and infrared is fairly constant with UV luminosity: i.e., more UV luminous galaxies are, on average, also more luminous at longer wavelengths. In the rest-UV, however, the spectral slope (measured at 0.13-0.28 um) rises steeply with the median UV luminosity from -1.8 at L L* to -1.2 in the brightest bin (L~4-5L*). We use population synthesis analyses to derive the average physical properties of these galaxies and find that: (1) L_UV, and thus star formation rates (SFRs), scale closely with stellar mass such that more UV-luminous galaxies are also more massive; (2) The median ages indicate that the stellar populations are relatively young (200-400 Myr) and show little correlation with UV luminosity; and (3) More UV-luminous galaxies are dustier than their less-luminous counterparts, such that L~4-5L* galaxies are extincted up to A(1600)=2 mag while L L* galaxies have A(1600)=0.7-1.5 mag. Based on these observations, we argue that the average star formation histories of UV-luminous galaxies are better described by models in which SFR increases with time in order to simultaneously reproduce the tight correlation between the observed SFR and stellar mass, and the universally young ages of these galaxies. We demonstrate the potential of measurements of the SFR-M* relation at multiple redshifts to discriminate between simple models of star formation histories.Comment: 14 pages, 7 figures. Accepted for publication in Astrophysical Journa

    Exploratory X-ray Monitoring of Luminous Radio-Quiet Quasars at High Redshift: No Evidence for Evolution in X-ray Variability

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    We report on the second installment of an X-ray monitoring project of seven luminous radio-quiet quasars (RQQs). New {\sl Chandra} observations of four of these, at 4.10≤z≤4.354.10\leq z\leq4.35, yield a total of six X-ray epochs, per source, with temporal baselines of ∼850−1600\sim850-1600 days in the rest frame. These data provide the best X-ray light curves for RQQs at z>4z>4, to date, enabling qualitative investigations of the X-ray variability behavior of such sources for the first time. On average, these sources follow the trend of decreasing variability amplitude with increasing luminosity, and there is no evidence for X-ray variability increasing toward higher redshifts, in contrast with earlier predictions of potential evolutionary scenarios. An ensemble variability structure function reveals that their variability level remains relatively flat across ≈20−1000\approx20 - 1000 days in the rest frame and it is generally lower than that of three similarly luminous RQQs at 1.33≤z≤2.741.33\leq z\leq 2.74 over the same temporal range. We discuss possible explanations for the increased variability of the lower-redshift subsample and, in particular, whether higher accretion rates play a leading role. Near-simultaneous optical monitoring of the sources at 4.10≤z≤4.354.10\leq z\leq 4.35 indicates that none is variable on ≈1\approx1-day timescales, although flux variations of up to ∼25\sim25\% are observed on ≈100\approx100-day timescales, typical of RQQs at similar redshifts. Significant optical-X-ray spectral slope variations observed in two of these sources are consistent with the levels observed in luminous RQQs and are dominated by X-ray variations.Comment: 11 pages (emulateapj), 4 figures. Accepted for publication in Ap
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