4,446 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
Leptogenesis and Low energy CP violation, a link
How is CP violation of low energy related to CP violation required from
baryon number asymmetry ? We give an example which shows a direct link between
CP violation of neutrino oscillation and baryogenesis through leptogenesis.Comment: 3 pages and 2 figures, Talk presented at 4th Nufac02, July 1-6, 200
Non-universal behavior for aperiodic interactions within a mean-field approximation
We study the spin-1/2 Ising model on a Bethe lattice in the mean-field limit,
with the interaction constants following two deterministic aperiodic sequences:
Fibonacci or period-doubling ones. New algorithms of sequence generation were
implemented, which were fundamental in obtaining long sequences and, therefore,
precise results. We calculate the exact critical temperature for both
sequences, as well as the critical exponent , and . For
the Fibonacci sequence, the exponents are classical, while for the
period-doubling one they depend on the ratio between the two exchange
constants. The usual relations between critical exponents are satisfied, within
error bars, for the period-doubling sequence. Therefore, we show that
mean-field-like procedures may lead to nonclassical critical exponents.Comment: 6 pages, 7 figures, to be published in Phys. Rev.
CP violation in neutrino oscillation and leptogenesis
We study the correlation between CP violation in neutrino oscillations and
leptogenesis in the framework with two heavy Majorana neutrinos and three light
neutrinos. Among three unremovable CP phases, a heavy Majorana phase
contributes to leptogenesis. We show how the heavy Majorana phase contributes
to Jarlskog determinant as well as neutrinoless double decay by
identifying a low energy CP violating phase which signals the CP violating
phase for leptogenesis. For some specific cases of the Dirac mass term of
neutrinos, a direct relation between lepton number asymmetry and is
obtained. For the most general case of the framework, we study the effect on coming from the phases which are not related to leptogenesis, and also show
how the correlation can be lost in the presence of those phases.Comment: 4 pages and 3 figure
Tree FCNC and non-unitarity of CKM matrix
We discuss possible signatures of the tree level FCNC, which results from the
non-unitarity of CKM matrix. We first define the unitaity step-by-step, and
possible test of the non-unitaity through the 4-value-KM parametrization. We,
then, show how the phase angle of the unitary triangle would change in case of
the vector-like down quark model. As another example of tree FCNC, we
investigate the leptophobic model and its application to the recent
mixing measurements.Comment: Talk given at Neutrino Masses and Mixings 2006 (NMM2006), Shizuoka,
Japan (December 2006
Small violations of unitarity, the phase in Bs mixing and visible t->cZ decays at the LHC
We show that it is possible to accommodate the observed size of the phase in
--, mixing in the framework of a model with violation of
unitarity. This violation is associated to the presence of a new
isosinglet quark , which mixes both with and and has a mass
not exceeding 500 GeV. The crucial point is the fact that this framework allows
for of order , to be
contrasted with the situation in the Standard Model, where is
constrained to be of order . We point out that this scenario implies
rare top decays at a rate observable at the LHC and
significantly different from unity. In this framework, one may also account for
the observed size of -- mixing without having to invoke long
distance contributions. It is also shown that in the present scenario, the
observed size of -- mixing constrains
to be of order
, which is significantly smaller than what is allowed in generic
models with violations of unitarity.Comment: 20 pages. References added. Additional observables considered,
updated numerical examples, conclusions unchange
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