58,061 research outputs found
Kramers-Moyall cumulant expansion for the probability distribution of parallel transporters in quantum gauge fields
A general equation for the probability distribution of parallel transporters
on the gauge group manifold is derived using the cumulant expansion theorem.
This equation is shown to have a general form known as the Kramers-Moyall
cumulant expansion in the theory of random walks, the coefficients of the
expansion being directly related to nonperturbative cumulants of the shifted
curvature tensor. In the limit of a gaussian-dominated QCD vacuum the obtained
equation reduces to the well-known heat kernel equation on the group manifold.Comment: 7 page
Center vortex properties in the Laplace center gauge of SU(2) Yang-Mills theory
Resorting to the the Laplace center gauge (LCG) and to the Maximal-center
gauge (MCG), respectively, confining vortices are defined by center projection
in either case. Vortex properties are investigated in the continuum limit of
SU(2) lattice gauge theory. The vortex (area) density and the density of vortex
crossing points are investigated. In the case of MCG, both densities are
physical quantities in the continuum limit. By contrast, in the LCG the
piercing as well as the crossing points lie dense in the continuum limit. In
both cases, an approximate treatment by means of a weakly interacting vortex
gas is not appropriate.Comment: reference added, submitted to Phys. Lett.
Structural matching by discrete relaxation
This paper describes a Bayesian framework for performing relational graph matching by discrete relaxation. Our basic aim is to draw on this framework to provide a comparative evaluation of a number of contrasting approaches to relational matching. Broadly speaking there are two main aspects to this study. Firstly we locus on the issue of how relational inexactness may be quantified. We illustrate that several popular relational distance measures can be recovered as specific limiting cases of the Bayesian consistency measure. The second aspect of our comparison concerns the way in which structural inexactness is controlled. We investigate three different realizations ai the matching process which draw on contrasting control models. The main conclusion of our study is that the active process of graph-editing outperforms the alternatives in terms of its ability to effectively control a large population of contaminating clutter
The BSM-AI project: SUSY-AI - Generalizing LHC limits on Supersymmetry with Machine Learning
A key research question at the Large Hadron Collider (LHC) is the test of
models of new physics. Testing if a particular parameter set of such a model is
excluded by LHC data is a challenge: It requires the time consuming generation
of scattering events, the simulation of the detector response, the event
reconstruction, cross section calculations and analysis code to test against
several hundred signal regions defined by the ATLAS and CMS experiment. In the
BSM-AI project we attack this challenge with a new approach. Machine learning
tools are thought to predict within a fraction of a millisecond if a model is
excluded or not directly from the model parameters. A first example is SUSY-AI,
trained on the phenomenological supersymmetric standard model (pMSSM). About
300,000 pMSSM model sets - each tested with 200 signal regions by ATLAS - have
been used to train and validate SUSY-AI. The code is currently able to
reproduce the ATLAS exclusion regions in 19 dimensions with an accuracy of at
least 93 percent. It has been validated further within the constrained MSSM and
a minimal natural supersymmetric model, again showing high accuracy. SUSY-AI
and its future BSM derivatives will help to solve the problem of recasting LHC
results for any model of new physics.
SUSY-AI can be downloaded at http://susyai.hepforge.org/. An on-line
interface to the program for quick testing purposes can be found at
http://www.susy-ai.org/
DEFROST: A New Code for Simulating Preheating after Inflation
At the end of inflation, dynamical instability can rapidly deposit the energy
of homogeneous cold inflaton into excitations of other fields. This process,
known as preheating, is rather violent, inhomogeneous and non-linear, and has
to be studied numerically. This paper presents a new code for simulating scalar
field dynamics in expanding universe written for that purpose. Compared to
available alternatives, it significantly improves both the speed and the
accuracy of calculations, and is fully instrumented for 3D visualization. We
reproduce previously published results on preheating in simple chaotic
inflation models, and further investigate non-linear dynamics of the inflaton
decay. Surprisingly, we find that the fields do not want to thermalize quite
the way one would think. Instead of directly reaching equilibrium, the
evolution appears to be stuck in a rather simple but quite inhomogeneous state.
In particular, one-point distribution function of total energy density appears
to be universal among various two-field preheating models, and is exceedingly
well described by a lognormal distribution. It is tempting to attribute this
state to scalar field turbulence.Comment: RevTeX 4.0; 16 pages, 9 figure
Inherent Structures in m-component Spin Glasses
We observe numerically the properties of the infinite-temperature inherent
structures of m-component vector spin glasses in three dimensions. An increase
of m implies a decrease of the amount of minima of the free energy, down to the
trivial presence of a unique minimum. For little m correlations are small and
the dynamics are quickly arrested, while for larger m low-temperature
correlations crop up and the convergence is slower, to a limit that appears to
be related with the system size.Comment: Version accepted in Phys. Rev. B, 10 pages, 11 figure
Realistic GUT Yukawa Couplings from a Random Clockwork Model
We present realistic models of flavor in SU(5) and SO(10) grand unified
theories (GUTs). The models are renormalizable and do not require any exotic
representations in order to accommodate the necessary GUT breaking effects in
the Yukawa couplings. They are based on a simple clockwork Lagrangian whose
structure is enforced with just two (one) vectorlike U(1) symmetries in the
case of SU(5) and SO(10) respectively. The inter-generational hierarchies arise
spontaneously from products of matrices with order one random entries.Comment: 18 pages, 2 figure
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