141,623 research outputs found
Hamiltonian Description of Composite Fermions: Aftermath
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 , and the
observability of dipoles are clarified.Comment: Revised for publication in PRL, 4 - epsilon page
Composite Millicharged Dark Matter
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
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
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
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
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
- …