141,623 research outputs found

    Hamiltonian Description of Composite Fermions: Aftermath

    Full text link
    The Lowest Landau Level (LLL), long distance theory of Composite Fermions (CF) developed by Murthy and myself is minimally extended to all distances, guided by very general principles. The resulting theory is mathematically consistent, and physically appealing: we clearly see the electron and the vortices binding to form the CF. The meaning of the constraints, their role in ensuring compressibility of dipolar objects at ν=1/2\nu =1/2, and the observability of dipoles are clarified.Comment: Revised for publication in PRL, 4 - epsilon page

    Composite Millicharged Dark Matter

    Full text link
    We study a composite millicharged dark matter model. The dark matter is in the form of pion-like objects emerging from a higher scale QCD-like theory. We present two distinct possibilities with interesting phenomenological consequences based on the choice of the parameters. In the first one, the dark matter is produced non-thermally and it could potentially account for the 130 GeV Fermi photon line via decays of the "dark pions". We estimate the self-interaction cross section which might play an important role both in changing the dark matter halo profile at the center of the galaxy and in making the dark matter warmer. In the second version the dark matter is produced via the freeze-in mechanism. Finally we impose all possible astrophysical, cosmological and experimental constraints. We study in detail generic constraints on millicharged dark matter that can arise from anomalous isotope searches of different elements and we show why constraints based on direct searches from underground detectors are not generally valid.Comment: 10 pages, published versio

    Composites and Categories of Euclidean Jordan Algebras

    Get PDF
    We consider possible non-signaling composites of probabilistic models based on euclidean Jordan algebras (EJAs), satisfying some reasonable additional constraints motivated by the desire to construct dagger-compact categories of such models. We show that no such composite has the exceptional Jordan algebra as a direct summand, nor does any such composite exist if one factor has an exceptional summand, unless the other factor is a direct sum of one-dimensional Jordan algebras (representing essentially a classical system). Moreover, we show that any composite of simple, non-exceptional EJAs is a direct summand of their universal tensor product, sharply limiting the possibilities. These results warrant our focussing on concrete Jordan algebras of hermitian matrices, i.e., euclidean Jordan algebras with a preferred embedding in a complex matrix algebra}. We show that these can be organized in a natural way as a symmetric monoidal category, albeit one that is not compact closed. We then construct a related category InvQM of embedded euclidean Jordan algebras, having fewer objects but more morphisms, that is not only compact closed but dagger-compact. This category unifies finite-dimensional real, complex and quaternionic mixed-state quantum mechanics, except that the composite of two complex quantum systems comes with an extra classical bit. Our notion of composite requires neither tomographic locality, nor preservation of purity under tensor product. The categories we construct include examples in which both of these conditions fail. In such cases, the information capacity (the maximum number of mutually distinguishable states) of a composite is greater than the product of the capacities of its constituents.Comment: 60 pages, 3 tables. Substantially revised, with some new result

    Nebular Attenuation in H\alpha-selected Star-forming Galaxies at z=0.8 from the NewH\alpha\ Survey

    Full text link
    We present measurements of the dust attenuation of H\alpha-selected emission-line galaxies at z=0.8 from the NewH\alpha\ narrowband survey. The analysis is based on deep follow-up spectroscopy with Magellan/IMACS, which captures the strong rest-frame optical emission lines from [OII] \lambda 3727 to [OIII] \lambda 5007. The spectroscopic sample used in this analysis consists of 341 confirmed H\alpha\ emitters. We place constraints on the AGN fraction using diagnostics which can be applied at intermediate redshift. We find that at least 5% of the objects in our spectroscopic sample can be classified as AGN and 2% are composite, i.e. powered by a combination of star-formation and AGN activity. We measure the dust attenuation for individual objects from the ratios of the higher order Balmer lines. The H\beta\ and H\gamma\ pair of lines is detected with S/N>5 in 55 individual objects and the H\beta\ and H\delta\ pair is detected in 50 individual objects. We also create stacked spectra to probe the attenuation in objects without individual detections. The median attenuation at H\alpha\ based on the objects with individually detected lines is A(H\alpha)=0.9+-1.0 magnitudes, in good agreement with the attenuation found in local samples of star-forming galaxies. We find that the z=0.8 galaxies occupy a similar locus of attenuation as a function of magnitude, mass and SFR as a comparison sample drawn from the SDSS DR4. Both the results from the individual z=0.8 galaxies and from the stacked spectra show consistency with the mass -- attenuation and SFR -- attenuation relations found in the local Universe, indicating that these relations are also applicable at intermediate redshift.Comment: Submitted to AJ. Revised per referee's comment

    Enriched categories as a free cocompletion

    Full text link
    This paper has two objectives. The first is to develop the theory of bicategories enriched in a monoidal bicategory -- categorifying the classical theory of categories enriched in a monoidal category -- up to a description of the free cocompletion of an enriched bicategory under a class of weighted bicolimits. The second objective is to describe a universal property of the process assigning to a monoidal category V the equipment of V-enriched categories, functors, transformations, and modules; we do so by considering, more generally, the assignation sending an equipment C to the equipment of C-enriched categories, functors, transformations, and modules, and exhibiting this as the free cocompletion of a certain kind of enriched bicategory under a certain class of weighted bicolimits.Comment: 80 pages; final journal versio

    Emergence of Object Segmentation in Perturbed Generative Models

    Get PDF
    We introduce a novel framework to build a model that can learn how to segment objects from a collection of images without any human annotation. Our method builds on the observation that the location of object segments can be perturbed locally relative to a given background without affecting the realism of a scene. Our approach is to first train a generative model of a layered scene. The layered representation consists of a background image, a foreground image and the mask of the foreground. A composite image is then obtained by overlaying the masked foreground image onto the background. The generative model is trained in an adversarial fashion against a discriminator, which forces the generative model to produce realistic composite images. To force the generator to learn a representation where the foreground layer corresponds to an object, we perturb the output of the generative model by introducing a random shift of both the foreground image and mask relative to the background. Because the generator is unaware of the shift before computing its output, it must produce layered representations that are realistic for any such random perturbation. Finally, we learn to segment an image by defining an autoencoder consisting of an encoder, which we train, and the pre-trained generator as the decoder, which we freeze. The encoder maps an image to a feature vector, which is fed as input to the generator to give a composite image matching the original input image. Because the generator outputs an explicit layered representation of the scene, the encoder learns to detect and segment objects. We demonstrate this framework on real images of several object categories.Comment: 33rd Conference on Neural Information Processing Systems (NeurIPS 2019), Spotlight presentatio
    • …
    corecore