407 research outputs found
Four Dimensional Graphene
Mimicking pristine 2D graphene, we revisit the BBTW model for 4D lattice QCD
given in ref.[5] by using the hidden SU(5) symmetry of the 4D hyperdiamond
lattice H_4. We first study the link between the H_4 and SU(5); then we refine
the BBTW 4D lattice action by using the weight vectors \lambda_1, \lambda_2,
\lambda_3, \lambda_4, \lambda_5 of the 5-dimensional representation of SU(5)
satisfying {\Sigma}_i\lambda_i=0. After that we study explicitly the solutions
of the zeros of the Dirac operator D in terms of the SU(5) simple roots
\alpha_1, \alpha_2, \alpha_3, \alpha_4 generating H_4; and its fundamental
weights \omega_1, \omega_2, \omega_3, \omega_4 which generate the reciprocal
lattice H_4^\ast. It is shown, amongst others, that these zeros live at the
sites of H_4^\ast; and the continuous limit D is given by ((id\surd5)/2)
\gamma^\muk_\mu with d, \gamma^\mu and k_\mu standing respectively for the
lattice parameter of H_4, the usual 4 Dirac matrices and the 4D wave vector.
Other features such as differences with BBTW model as well as the link between
the Dirac operator following from our construction and the one suggested by
Creutz using quaternions, are also given.
Keywords: Graphene, Lattice QCD, 4D hyperdiamond, BBTW model, SU(5) Symmetry.Comment: LaTex, 26 pages, 1 figure, To appear in Phys Rev
Extremal Black Attractors in 8D Maximal Supergravity
Motivated by the new higher D-supergravity solutions on intersecting
attractors obtained by Ferrara et al. in [Phys.Rev.D79:065031-2009], we focus
in this paper on 8D maximal supergravity with moduli space
[SL(3,R)/SO(3)]x[SL(2,R)/SO(2)] and study explicitly the attractor mechanism
for various configurations of extremal black p- branes (anti-branes) with the
typical near horizon geometries AdS_{p+2}xS^{m}xT^{6-p-m} and p=0,1,2,3,4;
2<=m<=6. Interpretations in terms of wrapped M2 and M5 branes of the 11D
M-theory on 3-torus are also given.
Keywords: 8D supergravity, black p-branes, attractor mechanism, M-theory.Comment: 37 page
Second-order optimisation strategies for neural network quantum states
The Variational Monte Carlo method has recently seen important advances
through the use of neural network quantum states. While more and more
sophisticated ans\"atze have been designed to tackle a wide variety of quantum
many-body problems, modest progress has been made on the associated
optimisation algorithms. In this work, we revisit the Kronecker Factored
Approximate Curvature, an optimiser that has been used extensively in a variety
of simulations. We suggest improvements on the scaling and the direction of
this optimiser, and find that they substantially increase its performance at a
negligible additional cost. We also reformulate the Variational Monte Carlo
approach in a game theory framework, to propose a novel optimiser based on
decision geometry. We find that, on a practical test case for continuous
systems, this new optimiser consistently outperforms any of the KFAC
improvements in terms of stability, accuracy and speed of convergence. Beyond
Variational Monte Carlo, the versatility of this approach suggests that
decision geometry could provide a solid foundation for accelerating a broad
class of machine learning algorithms.Comment: 32 pages, 9 figures, 4 tables. Submitted to PRS
Reduction of Conducted Perturbations in DC-DC Voltage Converters by a Dual Randomized PWM Scheme
Randomized Pulse Width Modulation (RPWM) deals better than Deterministic PWM (DPWM) with Electro-Magnetic Compatibility (EMC) standards for conducted Electro-Magnetic Interferences (EMI). In this paper, we propose a dual RPWM scheme for DC-DC voltage converters: the buck converter and the full bridge converter. This scheme is based on the comparison of deterministic reference signals (one signal for the buck converter and two signals for the full bridge converter) to a single triangular carrier having two randomized parameters. By using directly the randomized parameters of the carrier, a mathematical model of the Power Spectral Density (PSD) of output voltage is developed for each converter. The EMC advantage of the proposed dual randomization scheme compared to the classical simple randomization schemes is clearly highlighted by the PSD analysis and confirmed by FFT (Fast Fourier Transform) analysis of the output voltage
Transient Analysis of Grounding Systems Associated to Substation Structures under Lightning Strokes
In this paper we propose a new formalism for analyzing the transient behavior of grounding systems associated to substation structures (Faraday-cage) under lightning strokes in unsettled regime. The protective device to study is formed of a guard filet connected to a grounding grid by simple conductors called down conductors. Our formalism is based on the resolution of the propagation equation in potential on 3D. The purpose of our proposition is the direct analyzing in time domain and simple implementation. We compare the results obtained by this new approach to results published in literature
Machine learning one-dimensional spinless trapped fermionic systems with neural-network quantum states
We compute the ground-state properties of fully polarized, trapped,
one-dimensional fermionic systems interacting through a gaussian potential. We
use an antisymmetric artificial neural network, or neural quantum state, as an
ansatz for the wavefunction and use machine learning techniques to
variationally minimize the energy of systems from 2 to 6 particles. We provide
extensive benchmarks with other many-body methods, including exact
diagonalisation and the Hartree-Fock approximation. The neural quantum state
provides the best energies across a wide range of interaction strengths. We
find very different ground states depending on the sign of the interaction. In
the non-perturbative repulsive regime, the system asymptotically reaches
crystalline order. In contrast, the strongly attractive regime shows signs of
bosonization. The neural quantum state continuously learns these different
phases with an almost constant number of parameters and a very modest increase
in computational time with the number of particles
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