458 research outputs found
Minimal coupling method and the dissipative scalar field theory
Quantum field theory of a damped vibrating string as the simplest dissipative
scalar field investigated by its coupling with an infinit number of
Klein-Gordon fields as the environment by introducing a minimal coupling
method. Heisenberg equation containing a dissipative term proportional to
velocity obtained for a special choice of coupling function and quantum
dynamics for such a dissipative system investigated. Some kinematical relations
calculated by tracing out the environment degrees of freedom. The rate of
energy flowing between the system and it's environment obtained.Comment: 15 pages, no figur
Thermodynamic large fluctuations from uniformized dynamics
Large fluctuations have received considerable attention as they encode
information on the fine-scale dynamics. Large deviation relations known as
fluctuation theorems also capture crucial nonequilibrium thermodynamical
properties. Here we report that, using the technique of uniformization, the
thermodynamic large deviation functions of continuous-time Markov processes can
be obtained from Markov chains evolving in discrete time. This formulation
offers new theoretical and numerical approaches to explore large deviation
properties. In particular, the time evolution of autonomous and non-autonomous
processes can be expressed in terms of a single Poisson rate. In this way the
uniformization procedure leads to a simple and efficient way to simulate
stochastic trajectories that reproduce the exact fluxes statistics. We
illustrate the formalism for the current fluctuations in a stochastic pump
model
Coherence Resonance in Chaotic Systems
We show that it is possible for chaotic systems to display the main features
of coherence resonance. In particular, we show that a Chua model, operating in
a chaotic regime and in the presence of noise, can exhibit oscillations whose
regularity is optimal for some intermediate value of the noise intensity. We
find that the power spectrum of the signal develops a peak at finite frequency
at intermediate values of the noise. These are all signatures of coherence
resonance. We also experimentally study a Chua circuit and corroborate the
above simulation results. Finally, we analyze a simple model composed of two
separate limit cycles which still exhibits coherence resonance, and show that
its behavior is qualitatively similar to that of the chaotic Chua systemComment: 4 pages (including 4 figures) LaTeX fil
Quantum Horizons of the Standard Model Landscape
The long-distance effective field theory of our Universe--the Standard Model
coupled to gravity--has a unique 4D vacuum, but we show that it also has a
landscape of lower-dimensional vacua, with the potential for moduli arising
from vacuum and Casimir energies. For minimal Majorana neutrino masses, we find
a near-continuous infinity of AdS3xS1 vacua, with circumference ~20 microns and
AdS3 length 4x10^25 m. By AdS/CFT, there is a CFT2 of central charge c~10^90
which contains the Standard Model (and beyond) coupled to quantum gravity in
this vacuum. Physics in these vacua is the same as in ours for energies between
10^-1 eV and 10^48 GeV, so this CFT2 also describes all the physics of our
vacuum in this energy range. We show that it is possible to realize
quantum-stabilized AdS vacua as near-horizon regions of new kinds of quantum
extremal black objects in the higher-dimensional space--near critical black
strings in 4D, near-critical black holes in 3D. The violation of the
null-energy condition by the Casimir energy is crucial for these horizons to
exist, as has already been realized for analogous non-extremal 3D black holes
by Emparan, Fabbri and Kaloper. The new extremal 3D black holes are
particularly interesting--they are (meta)stable with an entropy independent of
hbar and G_N, so a microscopic counting of the entropy may be possible in the
G_N->0 limit. Our results suggest that it should be possible to realize the
larger landscape of AdS vacua in string theory as near-horizon geometries of
new extremal black brane solutions.Comment: 44 pages, 9 figure
Statistical post-processing of ensemble forecasts of temperature in Santiago de Chile
Indexación: Scopus.Modelling forecast uncertainty is a difficult task in any forecasting problem. In weather forecasting a possible solution is the use of forecast ensembles, which are obtained from multiple runs of numerical weather prediction models with various initial conditions and model parametrizations to provide information about the expected uncertainty. Currently all major meteorological centres issue forecasts using their operational ensemble prediction systems. However, it is a general problem that the spread of the ensemble is too small compared to observations at specific sites resulting in under-dispersive forecasts, leading to a lack of calibration. In order to correct this problem, various statistical calibration techniques have been developed in the last two decades. In the present work different post-processing techniques were tested for calibrating nine member ensemble forecasts of temperature for Santiago de Chile, obtained by the Weather Research and Forecasting model using different planetary boundary layer and land surface model parametrizations. In particular, the ensemble model output statistics and Bayesian model averaging techniques were implemented and, since the observations are characterized by large altitude differences, the estimation of model parameters was adapted to the actual conditions at hand. Compared to the raw ensemble, all tested post-processing approaches significantly improve the calibration of probabilistic forecasts and the accuracy of point forecasts. The ensemble model output statistics method using parameter estimation based on expert clustering of stations (according to their altitudes) shows the best forecast skill.https://rmets.onlinelibrary.wiley.com/doi/10.1002/met.181
On the Extra Mode and Inconsistency of Horava Gravity
We address the consistency of Horava's proposal for a theory of quantum
gravity from the low-energy perspective. We uncover the additional scalar
degree of freedom arising from the explicit breaking of the general covariance
and study its properties. The analysis is performed both in the original
formulation of the theory and in the Stueckelberg picture. A peculiarity of the
new mode is that it satisfies an equation of motion that is of first order in
time derivatives. At linear level the mode is manifest only around spatially
inhomogeneous and time-dependent backgrounds. We find two serious problems
associated with this mode. First, the mode develops very fast exponential
instabilities at short distances. Second, it becomes strongly coupled at an
extremely low cutoff scale. We also discuss the "projectable" version of
Horava's proposal and argue that this version can be understood as a certain
limit of the ghost condensate model. The theory is still problematic since the
additional field generically forms caustics and, again, has a very low strong
coupling scale. We clarify some subtleties that arise in the application of the
Stueckelberg formalism to Horava's model due to its non-relativistic nature.Comment: Discussion expanded; a figure added; accepted to JHE
Characterization of the Chilean Public Procurement Ecosystem Using Social Network Analysis
Indexación: Scopus.'Mercado Público' is a Chilean electronic platform used for purchasing processes by Chilean public organizations for the last two decades. The main aim of this study is to characterize the Chilean public procurement ecosystem by using social network analysis to detect the main communities of suppliers based on who awarded the tenders. To do this, we use a methodology that first represents the bidder-supplier relationship as a bipartite graph using purchase order information. Then we project the bipartite graph onto a monopartite graph of suppliers. We end by detecting the main supplier communities using a modularity algorithm. When we applied this methodology to the large tender segment in the Chilean public procurement market over a period of four years, we successfully detected the five largest communities and the micro and small companies which had the greatest rate of participation over time.https://ieeexplore.ieee.org/document/914958
Foraging at the Edge of Chaos: Internal Clock versus External Forcing
Activity rhythms in animal groups arise both from external changes in the environment, as well as from internal group dynamics. These cycles are reminiscent of physical and chemical systems with quasiperiodic and even chaotic behavior resulting from “autocatalytic” mechanisms. We use nonlinear differential equations to model how the coupling between the self-excitatory interactions of individuals and external forcing can produce four different types of activity rhythms: quasiperiodic, chaotic, phase locked, and displaying over or under shooting. At the transition between quasiperiodic and chaotic regimes, activity cycles are asymmetrical, with rapid activity increases and slower decreases and a phase shift between external forcing and activity. We find similar activity patterns in ant colonies in response to varying temperature during the day. Thus foraging ants operate in a region of quasiperiodicity close to a cascade of transitions leading to chaos. The model suggests that a wide range of temporal structures and irregularities seen in the activity of animal and human groups might be accounted for by the coupling between collectively generated internal clocks and external forcings
Quantum Chaos, Irreversible Classical Dynamics and Random Matrix Theory
The Bohigas--Giannoni--Schmit conjecture stating that the statistical
spectral properties of systems which are chaotic in their classical limit
coincide with random matrix theory is proved. For this purpose a new
semiclassical field theory for individual chaotic systems is constructed in the
framework of the non--linear -model. The low lying modes are shown to
be associated with the Perron--Frobenius spectrum of the underlying
irreversible classical dynamics. It is shown that the existence of a gap in the
Perron-Frobenius spectrum results in a RMT behavior. Moreover, our formalism
offers a way of calculating system specific corrections beyond RMT.Comment: 4 pages, revtex, no figure
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