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Roberto da Silva

Publications and source records attributed to Roberto da Silva.

72 records · Page 4Linked to original sources
arXiv2014

Maximum Entropy Principle and the Higgs Boson Mass

A successful connection between Higgs boson decays and the Maximum Entropy Principle is presented. Based on the information theory inference approach we determine the Higgs boson mass as $M_H= 125.04\pm 0.25$ GeV, a value fully compatible to the LHC measurement. This is straightforwardly obtained by taking the Higgs boson branching ratios as the target probability distributions of the inference, without any extra assumptions beyond the Standard Model. Yet, the principle can be a powerful tool in the construction of any model affecting the Higgs sector. We give, as an example, the case where the Higgs boson has an extra invisible decay channel. Our findings suggest that a system of Higgs bosons undergoing a collective decay to Standard Model particles is among the most fundamental ones where the Maximum Entropy Principle applies.

hep-ph↗
arXiv2014

Nonequilibrium scaling explorations on a 2D Z(5)-symmetric model

We have investigated the dynamic critical behavior of the two-dimensional Z(5)-symmetric spin model by using short-time Monte Carlo (MC) simulations. We have obtained estimates of some critical points in its rich phase diagram and included, among the usual critical lines the study of first-order (weak) transition by looking into the order-disorder phase transition. Besides, we also investigated the soft-disorder phase transition by considering empiric methods. A study of the behavior of $β/νz$ along the self-dual critical line has been performed and special attention has been devoted to the critical bifurcation point, or FZ (Fateev-Zamolodchikov) point. Firstly, by using a refinement method and taking into account simulations out-of-equilibrium, we were able to localize parameters of this point. In a second part of our study, we turned our attention to the behavior of the model at the early stage of its time evolution in order to find the dynamic critical exponent z as well as the static critical exponents $β$ and $% ν$ of the FZ-point on square lattices. The values of the static critical exponents and parameters are in good agreement with the exact results, and the dynamic critical exponent $z\approx 2.28$ very close of the 4-state Potts model ($z\approx 2.29$).

cond-mat.stat-mech↗
arXiv2014

Stochastic model of self-driven two-species objects in the context of the pedestrian dynamics

In this work we propose a model to describe the statistical fluctuations of the self-driven objects (species A) walking against an opposite crowd (species B) in order to simulate the regime characterized by stop-and-go waves in the context of pedestrian dynamics. By using the concept of single-biased random walks (SBRW), this setup is modeled both via partial differential equations and by Monte-Carlo simulations. The problem is non-interacting until the opposite particles visit the same cell of the considered particle. In this situation, delays on the residence time of the particles per cell depends on the concentration of particles of opposite species. We analyzed the fluctuations on the position of particles and our results show a non-regular diffusion characterized by long-tailed and asymmetric distributions which is better fitted by some chromatograph distributions found in the literature. We also show that effects of the reverse crowd particles is able to enlarge the dispersion of target particles in relation to the non-biased case ($α=0$) after observing a small decrease of this dispersion

cond-mat.stat-mech↗
arXiv2012

A Simple Non-Markovian Computational Model of the Statistics of Soccer Leagues: Emergence and Scaling effects

We propose a novel algorithm that outputs the final standings of a soccer league, based on a simple dynamics that mimics a soccer tournament. In our model, a team is created with a defined potential(ability) which is updated during the tournament according to the results of previous games. The updated potential modifies a teams' future winning/losing probabilities. We show that this evolutionary game is able to reproduce the statistical properties of final standings of actual editions of the Brazilian tournament (Brasileirão). However, other leagues such as the Italian and the Spanish tournaments have notoriously non-Gaussian traces and cannot be straightforwardly reproduced by this evolutionary non-Markovian model. A complete understanding of these phenomena deserves much more attention, but we suggest a simple explanation based on data collected in Brazil: Here several teams were crowned champion in previous editions corroborating that the champion typically emerges from random fluctuations that partly preserves the gaussian traces during the tournament. On the other hand, in the Italian and Spanish leagues only a few teams in recent history have won their league tournaments. These leagues are based on more robust and hierarchical structures established even before the beginning of the tournament. For the sake of completeness, we also elaborate a totally Gaussian model (which equalizes the winning, drawing, and losing probabilities) and we show that the scores of the "Brasileirão" cannot be reproduced. Such aspects stress that evolutionary aspects are not superfluous in our modeling. Finally, we analyse the distortions of our model in situations where a large number of teams is considered, showing the existence of a transition from a single to a double peaked histogram of the final classification scores. An interesting scaling is presented for different sized tournaments.

physics.data-an↗
arXiv2012

Generalized Metropolis dynamics with a generalized master equation: An approach for time-independent and time-dependent Monte Carlo simulations of generalized spin systems

The extension of Boltzmann-Gibbs thermostatistics, proposed by Tsallis, introduces an additional parameter $q$ to the inverse temperature $β$. Here, we show that a previously introduced generalized Metropolis dynamics to evolve spin models is not local and does not obey the detailed energy balance. In this dynamics, locality is only retrieved for $q=1$, which corresponds to the standard Metropolis algorithm. Non-locality implies in very time consuming computer calculations, since the energy of the whole system must be reevaluated, when a single spin is flipped. To circumvent this costly calculation, we propose a generalized master equation, which gives rise to a local generalized Metropolis dynamics that obeys the detailed energy balance. To compare the different critical values obtained with other generalized dynamics, we perform Monte Carlo simulations in equilibrium for Ising model. By using the short time non-equilibrium numerical simulations, we also calculate for this model: the critical temperature, the static and dynamical critical exponents as function of $q$. Even for $q\neq 1$, we show that suitable time evolving power laws can be found for each initial condition. Our numerical experiments corroborate the literature results, when we use non-local dynamics, showing that short time parameter determination works also in this case. However, the dynamics governed by the new master equation leads to different results for critical temperatures and also the critical exponents affecting universality classes. We further propose a simple algorithm to optimize modeling the time evolution with a power law considering in a log-log plot two successive refinements.

cond-mat.stat-mech↗
arXiv2011

Universality in Bibliometrics

Many discussions have enlarged the literature in Bibliometrics since the Hirsh proposal, the so called $h$-index. Ranking papers according to their citations, this index quantifies a researcher only by its greatest possible number of papers that are cited at least $h$ times. A closed formula for $h$-index distribution that can be applied for distinct databases is not yet known. In fact, to obtain such distribution, the knowledge of citation distribution of the authors and its specificities are required. Instead of dealing with researchers randomly chosen, here we address different groups based on distinct databases. The first group is composed by physicists and biologists, with data extracted from Institute of Scientific Information (ISI). The second group composed by computer scientists, which data were extracted from Google-Scholar system. In this paper, we obtain a general formula for the $h$-index probability density function (pdf) for groups of authors by using generalized exponentials in the context of escort probability. Our analysis includes the use of several statistical methods to estimate the necessary parameters. Also an exhaustive comparison among the possible candidate distributions are used to describe the way the citations are distributed among authors. The $h$-index pdf should be used to classify groups of researchers from a quantitative point of view, which is meaningfully interesting to eliminate obscure qualitative methods.

physics.soc-ph↗
arXiv2010

Logarithmic behavior of degradation dynamics in metal--oxide semiconductor devices

In this paper the authors describe a theoretical simple statistical modelling of relaxation process in metal-oxide semiconductor devices that governs its degradation. Basically, starting from an initial state where a given number of traps are occupied, the dynamics of the relaxation process is measured calculating the density of occupied traps and its fluctuations (second moment) as function of time. Our theoretical results show a universal logarithmic law for the density of occupied traps $\bar{ } \sim ϕ(T,E_{F}) (A+B \ln t)$, i.e., the degradation is logarithmic and its amplitude depends on the temperature and Fermi Level of device. Our approach reduces the work to the averages determined by simple binomial sums that are corroborated by our Monte Carlo simulations and by experimental results from literature, which bear in mind enlightening elucidations about the physics of degradation of semiconductor devices of our modern life.

cond-mat.mtrl-sci↗
arXiv2010

A novel and precise time domain description of MOSFET low frequency noise due to random telegraph signals

Nowadays, random telegraph signals play an important role in integrated circuit performance variability, leading for instance to failures in memory circuits. This problem is related to the successive captures and emissions of electrons at the many traps stochastically distributed at the silicon-oxide (Si-SiO2) interface of MOS transistors. In this paper we propose a novel analytical and numerical approach to statistically describe the fluctuations of current due to random telegraph signal in time domain. Our results include two distinct situations: when the density of interface trap density is uniform in energy, and when it is an u-shape curve as prescribed in literature, here described as simple quadratic function. We establish formulas for relative error as function of the parameters related to capture and emission probabilities. For a complete analysis experimental u-shape curves are used and compared with the theoretical aproach.

cond-mat.stat-mech↗
arXiv2005

Modelling investment in artificial stock markets: Analytical and Numerical Results

In this article we study the behavior of a group of economic agents in the context of cooperative game theory, interacting according to rules based on the Potts Model with suitable modifications. Each agent can be thought of as belonging to a chain, where agents can only interact with their nearest neighbors (periodic boundary conditions are imposed). Each agent can invest an amount σ_{i}=0,...,q-1. Using the transfer matrix method we study analytically, among other things, the behavior of the investment as a function of a control parameter (denoted β) for the cases q=2 and 3. For q>3 numerical evaluation of eigenvalues and high precision numerical derivatives are used in order to assess this information.

cs.CE↗
arXiv2004

Critical dynamics and global persistence in a probabilistic three-states cellular automaton

In this work a three-states cellular automaton proposed to describe part of a biological immune system is revisited. We obtain the dynamic critical exponent $z$ of the model by means of a recent technique that mixes different initial conditions. Moreover, by using two distinct approaches, we have also calculated the global persistence exponent $θ_{g}$, related to the probability that the order parameter of the model does not change its sign up to time $t$ [$P(t)\propto t^{-θ_{g}}$].

cond-mat.stat-mech↗
arXiv2004

Modelling of Statistical Low-Frequency Noise of Deep-Submicron MOSFETs

The low-frequency noise (LF-noise) of deep submicron MOSFETs is experimentally studied with special emphasis on yield relevant parameter scattering. A novel modeling approach is developed which includes detailed consideration of statistical effects. The model is based on device physics-based parameters which cause statistical fluctuations in LF-noise behavior of individual devices. It can easily be implemented in a compact model for use in circuit simulation tools.

cond-mat.other↗
arXiv2004

Brownian Motion Limit of Random Walks in Symetric Non-Homogeneous Media

The phenomenon of macroscopic homogenization is illustrated with a simple example of diffusion. We examine the conditions under which a $d$--dimensional simple random walk in a symmetric random media converges to a Brownian motion. For $d=1$, both the macroscopic homogeneity condition and the diffusion coefficient can be read from an explicit expression for the Green's function. Except for this case, the two available formulas for the effective diffusion matrix $κ$ do not explicit show how macroscopic homogenization takes place. Using an electrostatic analogy due to Anshelevich, Khanin and Sinai \cite{AKS}, we discuss upper and lower bounds on the diffusion coefficient $κ$ for $d>1$.

math-ph↗
arXiv2004

Local persistense and blocking in the two dimensional Blume-Capel Model

In this letter we study the local persistence of the two--dimensional Blume-- Capel Model by extension of the concept of Glauber dynamics. We verify that for any value of the ratio $α=D/J$ between anisotropy $D$ and exchange $J$ the persistence shows a power law behavior. In particular for $α<0$ we find a persistence exponent $θ_{l}=0.2096(13)$, \textit{i.e.} in the Ising universality class. For $α>0$ ($α\neq 1$) we observe the occurrence of blocking.

cond-mat.stat-mech↗
arXiv2004

Critical dynamics of the Potts model: short-time Monte Carlo simulations

We calculate the new dinamic exponent $θ$ of the 4-state Potts model, using short-time simulations. Our estimates $θ_{1}=-0.0471(33)$ and $% θ_{2}=$ $-0.0429(11)$ obtained by following the behavior of the magnetization or measuring the evolution of the time correlation function of the magnetization corroborate the conjecture by Okano et. al. In addition, these values agree with previous estimate of the same dynamic exponent for the two-dimensional Ising model with three-spin interactions in one direction, that is known to belong to the same universality class as the 4-state Potts model. The anomalous dimension of initial magnetization $% x_{0}=zθ+β/ν$ is calculated by an alternative way that mixes two different initial conditions. We have also estimated the values of the static exponents $β$ and $ν$. They are in complete agreement with the pertinent results of the literature.

cond-mat.stat-mech↗
arXiv2004

Revisiting the critical behavior of nonequilibrium models in Short-time Monte Carlo Simulations

We analyze two alternative methods for determining the exponent $z$ of the contact process (CP) and Domany-Kinzel (DK) cellular automaton in Monte Carlo Simulations. One method employs mixed initial conditions, as proposed for magnetic models [Phys. Lett. A. \textbf{298}, 325 (2002)]; the other is based on the growth of the moment ratio $m(t)=< ρ^{2}(t)> /< ρ(t)> ^{2}$ starting with all sites occupied. The methods provide reliable estimates for $z$ using the short time dynamics of the process. Estimates of $ν_{||}$ are obtained using a method suggested by Grassberger.

cond-mat.stat-mech↗
arXiv2003

Global persistence exponent of the two-dimensional Blume-Capel model

The global persistence exponent $θ_g$ is calculated for the two-dimensional Blume-Capel model following a quench to the critical point from both disordered states and such with small initial magnetizations. Estimates are obtained for the nonequilibrium critical dynamics on the critical line and at the tricritical point. Ising-like universality is observed along the critical line and a different value $θ_g =1.080(4)$ is found at the tricritical point.

cond-mat.stat-mech↗
arXiv2002

Universality and scaling study of the critical behavior of the two-dimensional Blume-Capel model in short-time dynamics

In this paper we study the short-time behavior of the Blume-Capel model at the tricritical point as well as along the second order critical line. Dynamic and static exponents are estimated by exploring scaling relations for the magnetization and its moments at early stage of the dynamic evolution. Our estimates for the dynamic exponents, at the tricritical point, are $z= 2.215(2)$ and $θ= -0.53(2)$.

cond-mat.stat-mech↗