960 research outputs found
Reconstructing the conformal mode in simplicial gravity
We verify that summing 2D DT geometries correctly reproduces the Polyakov
action for the conformal mode, including all ghost contributions, at large
volumes. The Gaussian action is reproduced even for central charges greater
than one lending strong support to the hypothesis that the space of all
possible dyamical triangulations approximates well the space of physically
distinct metrics independent of the precise nature of the matter coupling.Comment: 3 pages, 4 figures, contribution to Lattice 9
Distributed Partial Differential Equation Solving with Julia Fast Fourier Transform Library
Scientific computing relies on advanced computational and mathematical techniques to solve complex problems in scientific domains. For the numerical rendering of spectral, nonlinear, and dynamic phenomena, there is a growing need for greater availability of a broad class of Fourier-based algorithms to perform large scale operations on multidimensional data in distributed and optimized ways. To this effect, the Julia programming language is new and has significant advantages compared to other common languages used in scientific computing. The research presented here formulates a basis for further development in high-performance scientific computing of periodic partial differential equations through the application of distributed Fast Fourier Transforms in Julia with the PencilFFTs.jl library
de Sitter Vacua, Renormalization and Locality
We analyze the renormalization properties of quantum field theories in de
Sitter space and show that only two of the maximally invariant vacuum states of
free fields lead to consistent perturbation expansions. One is the Euclidean
vacuum, and the other can be viewed as an analytic continuation of Euclidean
functional integrals on . The corresponding Lorentzian manifold is the
future half of global de Sitter space with boundary conditions on fields at the
origin of time. We argue that the perturbation series in this case has
divergences at the origin, which render the future evolution of the system
indeterminate without a better understanding of high energy physics.Comment: JHEP Latex, 13 pages, v2. references adde
Condensates and quasiparticles in inflationary cosmology: mass generation and decay widths
During de Sitter inflation massless particles of minimally coupled scalar
fields acquire a mass and a decay width thereby becoming \emph{quasiparticles}.
For bare massless particles non-perturbative infrared radiative corrections
lead to a self-consistent generation of mass, for a quartic self interaction , and for a cubic self-interaction the mass is induced
by the formation of a non-perturbative \emph{condensate} leading to . These radiatively generated masses restore de Sitter
invariance and result in anomalous scaling dimensions of superhorizon
fluctuations. We introduce a generalization of the non-perturbative
Wigner-Weisskopf method to obtain the time evolution of quantum states that
include the self-consistent generation of mass and regulate the infrared
behavior. The infrared divergences are manifest as poles in
in the single particle self-energies, leading to a re-arrangement of the
perturbative series non-analytic in the couplings. A set of simple rules that
yield the leading order infrared contributions to the decay width are obtained
and implemented. The lack of kinematic thresholds entail that all particle
states acquire a decay width, dominated by the emission and absorption of
superhorizon quanta for cubic and quartic couplings respectively to
leading order in . The decay of single particle quantum states hastens as
their wavevectors cross the Hubble radius and their width is related to the
highly squeezed limit of the bi- or tri-spectrum of scalar fluctuations
respectively.Comment: 31 pages, 7 figures. Comments and references, matches published
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A Probabilistic Approach for the Optimal Sizing of Storage Devices to Increase the Penetration of Plug-in Electric Vehicles in Direct Current Networks
The growing diffusion of electric vehicles connected to distribution networks for charging purposes is an ongoing problem that utilities must deal with. Direct current networks and storage devices have emerged as a feasible means of satisfying the expected increases in the numbers of vehicles while preserving the effective operation of the network. In this paper, an innovative probabilistic methodology is proposed for the optimal sizing of electrical storage devices with the aim of maximizing the penetration of plug-in electric vehicles while preserving efficient and effective operation of the network. The proposed methodology is based on an analytical solution of the problem concerning the power losses minimization in distribution networks equipped with storage devices. The closed-form expression that was obtained is included in a Monte Carlo simulation procedure aimed at handling the uncertainties in loads and renewable generation units. The results of several numerical applications are reported and discussed to demonstrate the validity of the proposed solution. Also, different penetration levels of generation units were analyzed in order to focus on the importance of renewable generation
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