3,380 research outputs found
Universality class for bootstrap percolation with on the cubic lattice
We study the bootstrap percolation model on a cubic lattice, using
Monte Carlo simulation and finite-size scaling techniques. In bootstrap
percolation, sites on a lattice are considered occupied (present) or vacant
(absent) with probability or , respectively. Occupied sites with less
than occupied first-neighbours are then rendered unoccupied; this culling
process is repeated until a stable configuration is reached. We evaluate the
percolation critical probability, , and both scaling powers, and
, and, contrarily to previous calculations, our results indicate that the
model belongs to the same universality class as usual percolation (i.e.,
). The critical spanning probability, , is also numerically
studied, for systems with linear sizes ranging from L=32 up to L=480: the value
we found, , is the same as for usual percolation with
free boundary conditions.Comment: 11 pages; 4 figures; to appear in Int. J. Mod. Phys.
Flavour Physics and CP Violation in the Standard Model and Beyond
We present the invited lectures given at the Third IDPASC School which took
place in Santiago de Compostela in January 2013. The students attending the
school had very different backgrounds, some of them were doing their Ph.D. in
experimental particle physics, others in theory. As a result, and in order to
make the lectures useful for most of the students, we focused on basic topics
of broad interest, avoiding the more technical aspects of Flavour Physics and
CP Violation. We make a brief review of the Standard Model, paying special
attention to the generation of fermion masses and mixing, as well as to CP
violation. We describe some of the simplest extensions of the SM, emphasising
novel flavour aspects which arise in their framework.Comment: Invited talk at the Third IDPASC School 2013, January 21st - February
2nd 2013, Santiago de Compostela, Galiza, Spain; 36 pages, 8 figures, 2
tables; version with few misprints correcte
An Efficient Methodology for the Synthesis of 3-Styryl Coumarins
Regioselective and highly efficient Heck arylation of 3-vinyl-6,7-dimethoxycoumarin has been
developed to afford 3-styryl coumarins in good to very high yields. The increase in conjugation
reflects on the absorbance of the synthesized compounds revealing all pronounced bathochromic
shifts and hyperchromic effects
Minimal flavour violations and tree level FCNC
Consequences of a specific class of two Higgs doublet models in which the
Higgs induced tree level flavour changing neutral currents (FCNC) display
minimal flavour violation (MFV) are considered. These FCNC are fixed in terms
of the CKM matrix elements and the down quark masses. The minimal model in this
category with only two Higgs doublets has no extra CP violating phases but such
a phase can be induced by adding a complex singlet. Many of the theoretical
predictions are similar to other MFV scenario. The FCNC contribute
significantly to meson mixing and CP violation. Detailed numerical analysis
to determine the allowed Higgs contributions to neutral meson mixings and the
CKM parameters in their presence is presented. The
Higgs induced phase in the transition amplitude
is predicted to be equal for the and the systems.
There is a strong correlation between phases in and .
A measurable CP violating phase is predicted on the
basis of the observed phase in the system if is large
and close to its value determined from the inclusive b decays.Comment: 15 pages, two postscript figure
Mean-field calculation of critical parameters and log-periodic characterization of an aperiodic-modulated model
We employ a mean-field approximation to study the Ising model with aperiodic
modulation of its interactions in one spatial direction. Two different values
for the exchange constant, and , are present, according to the
Fibonacci sequence. We calculated the pseudo-critical temperatures for finite
systems and extrapolate them to the thermodynamic limit. We explicitly obtain
the exponents , , and and, from the usual scaling
relations for anisotropic models at the upper critical dimension (assumed to be
4 for the model we treat), we calculate , , , ,
and . Within the framework of a renormalization-group approach, the
Fibonacci sequence is a marginal one and we obtain exponents which depend on
the ratio , as expected. But the scaling relation is obeyed for all values of we studied. We characterize
some thermodynamic functions as log-periodic functions of their arguments, as
expected for aperiodic-modulated models, and obtain precise values for the
exponents from this characterization.Comment: 17 pages, including 9 figures, to appear in Phys. Rev.
Numerical simulation study of the dynamical behavior of the Niedermayer algorithm
We calculate the dynamic critical exponent for the Niedermayer algorithm
applied to the two-dimensional Ising and XY models, for various values of the
free parameter . For we regain the Metropolis algorithm and for
we regain the Wolff algorithm. For , we show that the mean
size of the clusters of (possibly) turned spins initially grows with the linear
size of the lattice, , but eventually saturates at a given lattice size
, which depends on . For , the Niedermayer
algorithm is equivalent to the Metropolis one, i.e, they have the same dynamic
exponent. For , the autocorrelation time is always greater than for
(Wolff) and, more important, it also grows faster than a power of .
Therefore, we show that the best choice of cluster algorithm is the Wolff one,
when compared to the Nierdermayer generalization. We also obtain the dynamic
behavior of the Wolff algorithm: although not conclusive, we propose a scaling
law for the dependence of the autocorrelation time on .Comment: Accepted for publication in Journal of Statistical Mechanics: Theory
and Experimen
Security Issues in a SOA-based Provenance System
Recent work has begun exploring the characterization and utilization of provenance in systems based on the Service Oriented Architecture (such as Web Services and Grid based environments). One of the salient issues related to provenance use within any given system is its security. Provenance presents some unique security requirements of its own, which are additionally dependent on the architectural and environmental context that a provenance system operates in. We discuss the security considerations pertaining to a Service Oriented Architecture based provenance system. Concurrently, we outline possible approaches to address them
Two-dimensional quantum spin-1/2 Heisenberg model with competing interactions
We study the quantum spin-1/2 Heisenberg model in two dimensions, interacting
through a nearest-neighbor antiferromagnetic exchange () and a ferromagnetic
dipolar-like interaction (), using double-time Green's function, decoupled
within the random phase approximation (RPA). We obtain the dependence of as a function of frustration parameter , where is the
ferromagnetic (F) transition temperature and is the ratio between the
strengths of the exchange and dipolar interaction (i.e., ). The
transition temperature between the F and paramagnetic phases decreases with
, as expected, but goes to zero at a finite value of this parameter,
namely . At T=0 (quantum phase transition), we
analyze the critical parameter for the general case of an
exchange interaction in the form , where ferromagnetic
and antiferromagnetic phases are present.Comment: 4 pages, 1 figur
Hierarchy plus anarchy in quark masses and mixings
We introduce a new parameterisation of the effect of unknown corrections from
new physics on quark and lepton mass matrices. This parameterisation is used in
order to study how the hierarchies of quark masses and mixing angles are
modified by random perturbations of the Yukawa matrices. We discuss several
examples of flavour relations predicted by different textures, analysing how
these relations are influenced by the random perturbations. We also comment on
the unlikely possibility that unknown corrections contribute significantly to
the hierarchy of masses and mixings.Comment: LaTeX, 18 pages, 16 PS figure
Dynamical behavior of the Niedermayer algorithm applied to Potts models
In this work we make a numerical study of the dynamic universality class of
the Niedermayer algorithm applied to the two-dimensional Potts model with 2, 3,
and 4 states. This algorithm updates clusters of spins and has a free
parameter, , which controls the size of these clusters, such that
is the Metropolis algorithm and regains the Wolff algorithm, for the
Potts model. For , only clusters of equal spins can be formed: we
show that the mean size of the clusters of (possibly) turned spins initially
grows with the linear size of the lattice, , but eventually saturates at a
given lattice size , which depends on . For , the Niedermayer algorithm is in the same dynamic universality
class of the Metropolis one, i.e, they have the same dynamic exponent. For
, spins in different states may be added to the cluster but the dynamic
behavior is less efficient than for the Wolff algorithm (). Therefore,
our results show that the Wolff algorithm is the best choice for Potts models,
when compared to the Niedermayer's generalization.Comment: 10 pages, 11 figures, to be published in Physica A. arXiv admin note:
substantial text overlap with arXiv:1003.365
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