2,089 research outputs found
Self-consistent approximations: application to a quasiparticle description of the thermodynamic properties of relativistic plasmas
We generalize the concept of conserving,\Phi-derivable, approximations to
relativistic field theories. Treating the interaction field as a dynamical
degree of freedom, we derive the thermodynamical potential in terms of fully
dressed propagators, an approach which allows us to resolve the entropy of a
relativistic plasma into contributions from its interacting elementary
excitations. We illustrate the derivation for a hot QED plasma of massless
particles. We also discuss how the self-consistency of the treatment manifests
itself into relationships between the contributions from interaction and matter
fields.Comment: 9 pages, 1 eps figure, to appear in "Progress in Nonequilibrium
Green's functions.", M. Bonitz (Ed.), World Scientific, Singapore 200
Minimal self-interacting dark matter models with light mediator
The light mediator scenario of self-interacting dark matter is strongly
constrained in many ways. After summarizing the various constraints, we discuss
minimal options and models which allow to nevertheless satisfy all these
constraints. One straightforward possibility arises if the dark matter and
light mediator particles have a temperature sizably smaller than the SM
particles. Another simple possibility arises if dark matter doesn't annihilate
dominantly into a pair of light mediators but into heavier particles. Both
possibilities are discussed with scalar as well as vector boson light
mediators. Further possibilities, such as with a hierarchy of quartic scalar
couplings, are also identified.Comment: 23 pages, 31 figures, accepted for publication in JCA
Microscopic spectral density in random matrix models for chiral and diquark condensation
We examine random matrix models of QCD which are capable of supporting both
chiral and diquark condensation. A numerical study of the spectral densities
near zero virtuality shows that the introduction of color in the interactions
does not alter the one-body results imposed by chiral symmetry. A model with
three colors has the spectral density predicted for the chiral ensemble with a
Dyson index beta = 2; a pseudoreal model with two colors exhibits the spectral
density of the chiral ensemble with beta = 1.Comment: 6 pages, 3 eps figures, uses revtex4 and graphicx. v2 : minor
editions, Fig. 3 shows relative deviations rather than absolute. Version to
appear in PR
Random matrix model for antiferromagnetism and superconductivity on a two-dimensional lattice
We suggest a new mean field method for studying the thermodynamic competition
between magnetic and superconducting phases in a two-dimensional square
lattice. A partition function is constructed by writing microscopic
interactions that describe the exchange of density and spin-fluctuations. A
block structure dictated by spin, time-reversal, and bipartite symmetries is
imposed on the single-particle Hamiltonian. The detailed dynamics of the
interactions are neglected and replaced by a normal distribution of random
matrix elements. The resulting partition function can be calculated exactly.
The thermodynamic potential has a structure which depends only on the spectrum
of quasiparticles propagating in fixed condensation fields, with coupling
constants that can be related directly to the variances of the microscopic
processes. The resulting phase diagram reveals a fixed number of phase
topologies whose realizations depend on a single coupling-parameter ratio,
alpha. Most phase topologies are realized for a broad range of values of alpha
and can thus be considered robust with respect to moderate variations in the
detailed description of the underlying interactions.Comment: 21 pages, 8 figures, RevTex 4. Minor grammatical errors corrected in
the last versio
Random matrix models for chiral and diquark condensation
We consider random matrix models for the thermodynamic competition between
chiral symmetry breaking and diquark condensation in QCD at finite temperature
and finite baryon density. The models produce mean field phase diagrams whose
topology depends solely on the global symmetries of the theory. We discuss the
block structure of the interactions that is imposed by chiral, spin, and color
degrees of freedom and comment on the treatment of density and temperature
effects. Extension of the coupling parameters to a larger class of theories
allows us to investigate the robustness of the phase topology with respect to
variations in the dynamics of the interactions. We briefly study the phase
structure as a function of coupling parameters and the number of colors.Comment: 6 pages, 2 figures, proceedings of the workshop "Three Days of
Hadronic Physics", Joint Meeting Heidelberg-Liege-Paris-Rostock,
16/12/2004-18/12/2004, Sol Cress, Spa, Belgium. v2: typographical errors
corrected in reference
Conservation and its Effect on Indigenous Communities
This project investigates the effects of conservation on indigenous populations
The Temporal and Directional Dependencies of Sway During 10 Seconds of Single Leg Stance in Young, Healthy College Students
Background: Single Leg Stance (SLS) testing is used in clinical assessments of balance, but little is known about the temporal structure of sway parameters during this test. SLS research is equivocal on the effects of sway over time and the direction of balance initiation. Sway data in a healthy young population may provide insight on how balance is initiated and maintained in relation to the initial step direction. This may lead to novel approaches to help healthy elderly populations decrease fall risk and fall-related mortality. Purpose: The purpose of the study was to examine the temporal and directional dependencies of sway parameters during 10 seconds of SLS in young, healthy adults. Methods: Six healthy, young college students (five male, one female) performed 10 seconds of SLS on their dominant leg, stepping from a frontward and sideward direction. Ground reaction forces measured with a force platform were used to calculate the sway parameters: sway area, sway velocity, anterior-posterior and medio-lateral sway, and sway path. Preliminary Results: Compared to the final second, the sway area, path and velocities were significantly higher in seconds one and two in the forward and sideward directions. Anterior-posterior sway was lower during seconds one and two in the forward direction. Medio-lateral sway was higher in second 2 in the forward direction, and lower at seconds one, two, and four in the sideward direction
Ordinal HyperPlane Loss
This research presents the development of a new framework for analyzing ordered class data, commonly called “ordinal class” data. The focus of the work is the development of classifiers (predictive models) that predict classes from available data. Ratings scales, medical classification scales, socio-economic scales, meaningful groupings of continuous data, facial emotional intensity and facial age estimation are examples of ordinal data for which data scientists may be asked to develop predictive classifiers. It is possible to treat ordinal classification like any other classification problem that has more than two classes. Specifying a model with this strategy does not fully utilize the ordering information of classes. Alternatively, the researcher may choose to treat the ordered classes as though they are continuous values. This strategy imposes a strong assumption that the real “distance” between two adjacent classes is equal to the distance between two other adjacent classes (e.g., a rating of ‘0’ versus ‘1,’ on an 11-point scale is the same distance as a ‘9’ versus a ‘10’). For Deep Neural Networks (DNNs), the problem of predicting k ordinal classes is typically addressed by performing k-1 binary classifications. These models may be estimated within a single DNN and require an evaluation strategy to determine the class prediction. Another common option is to treat ordinal classes as continuous values for regression and then adjust the cutoff points that represent class boundaries that differentiate one class from another. This research reviews a novel loss function called Ordinal Hyperplane Loss (OHPL) that is particularly designed for data with ordinal classes. OHPLnet has been demonstrated to be a significant advancement in predicting ordinal classes for industry standard structured datasets. The loss function also enables deep learning techniques to be applied to the ordinal classification problem of unstructured data. By minimizing OHPL, a deep neural network learns to map data to an optimal space in which the distance between points and their class centroids are minimized while a nontrivial ordering relationship among classes are maintained. The research reported in this document advances OHPL loss, from a minimally viable loss function, to a more complete deep learning methodology. New analysis strategies were developed and tested that improve model performance as well as algorithm consistency in developing classification models. In the applications chapters, a new algorithm variant is introduced that enables OHPLall to be used when large data records cause a severe limitation on batch size when developing a related Deep Neural Network
Direct Detection is testing Freeze-in
Dark Matter (DM) may belong to a hidden sector that is only feebly
interacting with the Standard Model (SM) and may have never been in thermal
equilibrium in the Early Universe. In this case, the observed abundance of dark
matter particles could have built up through a process known as Freeze-in. We
show that, for the first time, direct detection experiments are testing this DM
production mechanism. This applies to scenarios where the SM and hidden sectors
communicate through a light mediator particle of mass less than a few MeV.
Through the exchange of such light mediator, the very same FIMP candidates can
have self-interactions that are in the range required to address the small
scale structure issues of collisionless cold dark matter.Comment: 7 pages, 4 figures. References added. Discussion of further
constraints on parameters. Figures updated. Conclusions unchanged. Matches
published versio
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