746 research outputs found
Higgs--mediated K -> pi nu nu-bar in the MSSM at large tan(beta)
We analyze the impact of Higgs-mediated amplitudes on the rare decays KL ->
pi0 nu nu-bar and K+ -> pi+ nu nu-bar in the MSSM with large tan(beta) and
general flavour mixing. We point out that, going beyond the minimal flavour
violation hypothesis, Z-penguin amplitudes generated by charged-Higgs exchange
can induce sizable modifications of K -> pi nu nu-bar rates. Interestingly,
these effects scale as tan^4(beta) at the amplitude level. For large values of
tan(beta), this mechanism allows deviations from the SM expectations even for
tiny (CKM-type) off-diagonal mixing terms in the right-handed squark sector.Comment: 9 pages, 2 figure
Anomalous diffusion originated by two Markovian hopping-trap mechanisms
We show through intensive simulations that the paradigmatic
features of anomalous diffusion are indeed the features of
a (continuous-time) random walk driven by two different Markovian hopping-trap mechanisms.
If and are the probabilities
of occurrence of each Markovian mechanism,
then the anomalousness parameter results to be
.
Ensemble and single-particle observables of this model have been studied
and they match the main characteristics of anomalous diffusion
as they are typically measured in living systems.
In particular, the celebrated transition of the walker's distribution
from exponential to stretched-exponential and finally
to Gaussian distribution is displayed by including also
the Brownian yet non-Gaussian interval.BERC 2018â2021
BERC 2022â2025
MOSAIC project DIT.AD004.14
Higgs-Mediated tau --> mu and tau --> e transitions in II Higgs doublet Model and Supersymmetry
We study the phenomenology of the mu-tau and e-tau lepton flavour violation
(LFV) in a general two Higgs Doublet Model (2HDM) including the supersymmetric
case. We consider several LFV decay modes of the charged fermion tau, namely
tau-> l_jgamma, tau->l_j l_k l_k and tau-> l_jeta. The predictions and the
correlations among the rates of the above processes are computed. In
particular, it is shown that tau->l_jgamma processes are the most sensitive
channels to Higgs-mediated LFV specially if the splitting among the neutral
Higgs bosons masses is not below the 10% level.Comment: v2=published version: 13 pages, 4 figures, text improved and
reference added. Two loop effects (relevant for tau->l_jgamma) added.
Conclusions unchange
Fractional Diffusion and Medium Heterogeneity: The Case of the Continuos Time Random Walk
In this contribution we show that fractional diffusion emerges from a simple Markovian Gaussian random walk when the medium displays a power-law heterogeneity. Within the framework of the continuous time random walk, the heterogeneity of the medium is represented by the selection, at any jump, of a different time-scale for an exponential survival probability. The resulting process is a non-Markovian non-Gaussian random walk. In particular, for a power-law distribution of the time-scales, the resulting random walk corresponds to a time-fractional diffusion process. We relates the power-law of the medium heterogeneity to the fractional order of the diffusion. This relation provides an interpretation and an estimation of the fractional order of derivation in terms of environment heterogeneity. The results are supported by simulations
Radiative lepton flavor violating decays in the Randall Sundrum background with localized leptons
We study the radiative lepton flavor violating l_i -> l_j\gamma decays in the
two Higgs doublet model, respecting the Randall Sundrum scenario and estimate
the contributions of the KK modes of left (right) handed charged lepton
doublets (singlets) on the branching ratios. We observe that the branching
ratios are sensitive to the contributions of the charged lepton KK modes.Comment: 23 pages, 10 figures, 2 table
Gaussian processes in complex media: new vistas on anomalous diffusion
Normal or Brownian diffusion is historically identified by the linear growth in time of the variance and by a Gaussian shape of the displacement distribution. Processes departing from the at least one of the above conditions defines anomalous diffusion, thus a nonlinear growth in time of the variance and/or a non-Gaussian displacement distribution. Motivated by the idea that anomalous diffusion emerges from standard diffusion when it occurs in a complex medium, we discuss a number of anomalous diffusion models for strongly heterogeneous systems. These models are based on Gaussian processes and characterized by a population of scales, population that takes into account the medium heterogeneity. In particular, we discuss diffusion processes whose probability density function solves space- and time-fractional diffusion equations through a proper population of time-scales or a proper population of length-scales. The considered modeling approaches are: the continuous time random walk, the generalized gray Brownian motion, and the time-subordinated process. The results show that the same fractional diffusion follows from different populations when different Gaussian processes are considered. The different populations have the common feature of a large spreading in the scale values, related to power-law decay in the distribution of population itself. This suggests the key role of medium properties, embodied in the population of scales, in the determination of the proper stochastic process underlying the given heterogeneous medium.This research was supported by the Basque Government through the BERC 2014â2017 and BERC 2018â2021 programs, and by the Spanish Ministry of Economy and Competitiveness MINECO through BCAM Severo Ochoa excellence accreditations SEV- 2013-0323 and SEV-2017-0718 and through project MTM2016- 76016-R MI
Langevin equation in complex media and anomalous diffusion
The problem of biological motion is a very intriguing and topical issue.
Many efforts are being focused on the development of novel modelling
approaches for the description of anomalous diffusion in biological systems,
such as the very complex and heterogeneous cell environment. Nevertheless,
many questions are still open, such as the joint manifestation of statistical
features in agreement with different models that can also be somewhat alternative to each other, e.g. continuous time random walk and fractional Brownian
motion. To overcome these limitations, we propose a stochastic diffusion
model with additive noise and linear friction force (linear Langevin equation),
thus involving the explicit modelling of velocity dynamics. The complexity of
the medium is parametrized via a population of intensity parameters (relaxation time and diffusivity of velocity), thus introducing an additional
randomness, in addition to white noise, in the particleâs dynamics. We
prove that, for proper distributions of these parameters, we can get both
Gaussian anomalous diffusion, fractional diffusion and its generalizations.V.S. acknowledges BCAM Internship Program, Bilbao, for the financial support to her internship research period during which she developed her masterâs thesis research
useful for her masterâs degree in Physics at University of Bologna.
S.V. acknowledges the University of Bologna for the financial support
through the âMarco Polo Programmeâ for her PhD research period
abroad spent at BCAM, Bilbao, useful for her PhD degree in Physics
at University of Bologna.
P.P. acknowledges financial support from Bizkaia Talent and European Commission
through COFUND scheme, 2015 Financial Aid Program for Researchers, project number
AYDâ000â252 hosted at BCAM, Bilbao
Microwave-assisted vacuum synthesis of tio2 nanocrystalline powders in one-pot, one-step procedure
A new method for fast and simple synthesis of crystalline TiO2 nanoparticles with photocat-alytic activity was developed by carrying out a classic solâgel reaction directly under vacuum. The use of microwaves for fast heating of the reaction medium further reduces synthesis times. When the solvent is completely removed by vacuum, the product is obtained in the form of a powder that can be easily redispersed in water to yield a stable nanoparticle suspension, exhibiting a comparable photocatalytic activity with respect to a commercial product. The present methodology can, therefore, be considered a process intensification procedure for the production of nanotitania
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