4,243 research outputs found
SUSY and the Electroweak Phase Transition
We analyze the effective 3 dimensional theory previously constructed for the
MSSM and multi-Higgs models to determine the regions of parameter space in
which the electroweak phase transition is sufficiently strong for a
asymmetry to survive in the low temperature phase. We find that the inclusion
of all supersymmetric scalars and all 1-loop corrections has the effect of
enhancing the strength of the phase transition. Without a light stop or
extension of the MSSM the phase transition is sufficiently first order only if
the lightest Higgs mass M_{h}\lsi 70 GeV and tan\beta\lsi 1.75.Comment: 17 pages, 6 figures, uses eps
Competition of rotation and stratification in flux concentrations
In a strongly stratified turbulent layer, a uniform horizontal magnetic field
can become unstable to spontaneously form local flux concentrations due to a
negative contribution of turbulence to the large-scale (mean-field) magnetic
pressure. This mechanism, called the negative effective magnetic pressure
instability (NEMPI), is of interest in connection with dynamo scenarios where
most of the magnetic field resides in the bulk of the convection zone, and not
at the bottom. Recent work using the mean-field hydromagnetic equations has
shown that NEMPI becomes suppressed at rather low rotation rates with Coriolis
numbers as low as 0.1.}{Here we extend these earlier investigations by studying
the effects of rotation both on the development of NEMPI and on the effective
magnetic pressure. We also quantify the kinetic helicity from direct numerical
simulations (DNS) and compare with earlier work.}{To calculate the rotational
effect on the effective magnetic pressure we consider both DNS and analytical
studies using the approach. To study the effects of rotation on the
development of NEMPI we use both DNS and mean-field calculations of the 3D
hydromagnetic equations in a Cartesian domain.}{We find that the growth rates
of NEMPI from earlier mean-field calculations are well reproduced with DNS,
provided the Coriolis number is below about 0.06. In that case, kinetic and
magnetic helicities are found to be weak. For faster rotation, dynamo action
becomes possible. However, there is an intermediate range of rotation rates
where dynamo action on its own is not yet possible, but the rotational
suppression of NEMPI is being alleviated.}{Production of magnetic flux
concentrations through the suppression of turbulent pressure appears to be
possible only in the upper-most layers of the Sun, where the convective
turnover time is less than 2 hours.}Comment: 13 pages, 13 figures submitted to A&
Magnetic flux concentrations from dynamo-generated fields
The mean-field theory of magnetized stellar convection gives rise to the two
possibility of distinct instabilities: the large-scale dynamo instability,
operating in the bulk of the convection zone, and a negative effective magnetic
pressure instability (NEMPI) operating in the strongly stratified surface
layers. The latter might be important in connection with magnetic spot
formation, but the growth rate of NEMPI is suppressed with increasing rotation
rates, although recent direct numerical simulations (DNS) have shown a
subsequent increase in the growth rate. We examine quantitatively whether this
increase in the growth rate of NEMPI can be explained by an alpha squared
mean-field dynamo, and whether both NEMPI and the dynamo instability can
operate at the same time. We use both DNS and mean-field simulations (MFS) to
solve the underlying equations numerically either with or without an imposed
horizontal field. We use the test-field method to compute relevant dynamo
coefficients. DNS show that magnetic flux concentrations are still possible up
to rotation rates above which the large-scale dynamo effect produces mean
magnetic fields. The resulting DNS growth rates are quantitatively well
reproduced with MFS. As expected, for weak or vanishing rotation, the growth
rate of NEMPI increases with increasing gravity, but there is a correction term
for strong gravity and large turbulent magnetic diffusivity. Magnetic flux
concentrations are still possible for rotation rates above which dynamo action
takes over. For the solar rotation rate, the corresponding turbulent turnover
time is about 5 hours, with dynamo action commencing in the layers beneath.Comment: 10 pages, 10 figures, submitted to A&
Efficiency of Human Activity on Information Spreading on Twitter
Understanding the collective reaction to individual actions is key to
effectively spread information in social media. In this work we define
efficiency on Twitter, as the ratio between the emergent spreading process and
the activity employed by the user. We characterize this property by means of a
quantitative analysis of the structural and dynamical patterns emergent from
human interactions, and show it to be universal across several Twitter
conversations. We found that some influential users efficiently cause
remarkable collective reactions by each message sent, while the majority of
users must employ extremely larger efforts to reach similar effects. Next we
propose a model that reproduces the retweet cascades occurring on Twitter to
explain the emergent distribution of the user efficiency. The model shows that
the dynamical patterns of the conversations are strongly conditioned by the
topology of the underlying network. We conclude that the appearance of a small
fraction of extremely efficient users results from the heterogeneity of the
followers network and independently of the individual user behavior.Comment: 29 pages, 10 figure
Exploring accumulative query expansion for relevance feedback
For the participation of Dublin City University (DCU) in the Relevance Feedback (RF) track of INEX 2010, we investigated the relation between the length of relevant text passages and the number of RF terms. In our experiments, relevant passages are segmented into non-overlapping windows of xed length which are sorted by similarity with the query. In each retrieval iteration, we extend the current query with the most frequent terms extracted from these word windows. The number of feedback terms corresponds to a constant number, a number proportional to the length of relevant passages, and a number inversely proportional to the length of relevant passages, respectively. Retrieval experiments show a signicant increase in MAP for INEX 2008 training data and improved precisions at early recall levels for the 2010 topics as compared to the baseline Rocchio feedback
Neutrinos in the simplest little Higgs scenario and TeV leptogenesis
The little Higgs scenario may provide an interesting framework to accommodate
TeV scale leptogenesis because a TeV Majorana mass of the right-handed neutrino
that we employ for the latter may find a natural place near the ultraviolet
cutoff of the former. In this work we study how a light neutrino spectrum,
generated radiatively, and TeV scale leptogenesis can be embedded in the
simplest little
Higgs framework. Alternatively, we highlight how the neutrino Yukawa textures
of the latter are constrained.Comment: 10 pages, latex, v2: refs and comments added, to appear in PR
Symmetry Nonrestoration at High Temperature in Little Higgs Models
A detailed study of the high temperature dynamics of the scalar sector of
Little Higgs scenarios, proposed to stabilize the electroweak scale, shows that
the electroweak gauge symmetry remains broken even at temperatures much larger
than the electroweak scale. Although we give explicit results for a particular
modification of the Littlest Higgs model, we expect that the main features are
generic. As a spin-off, we introduce a novel way of dealing with scalar
fluctuations in nonlinear sigma models, which might be of interest for
phenomenological applications.Comment: 23 pages, LaTeX, 4 figure
Semantic Web-enabled Protocol Mediation for the Logistics Domain
Among the problems that arise when trying to make different applications interoperate with each other, protocol mediation is one of the most difficult ones and for which less relevant literature can be found. Protocol mediation is concerned with non-matching message interaction patterns in application interaction. In this paper we describe the design and implementation of a protocol mediation component that has been applied in the interoperation between two heterogeneous logistic provider systems (using two different standards: RosettaNet and EDIFACT), for a specific freight forwarding task
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