25 research outputs found
On the Complexity of the Bipartite Polarization Problem: from Neutral to Highly Polarized Discussions
The Bipartite Polarization Problem is an optimization problem where the goal
is to find the highest polarized bipartition on a weighted and labelled graph
that represents a debate developed through some social network, where nodes
represent user's opinions and edges agreement or disagreement between users.
This problem can be seen as a generalization of the maxcut problem, and in
previous work approximate solutions and exact solutions have been obtained for
real instances obtained from Reddit discussions, showing that such real
instances seem to be very easy to solve. In this paper, we investigate further
the complexity of this problem, by introducing an instance generation model
where a single parameter controls the polarization of the instances in such a
way that this correlates with the average complexity to solve those instances.
The average complexity results we obtain are consistent with our hypothesis:
the higher the polarization of the instance, the easier is to find the
corresponding polarized bipartition
FCNC-induced heavy-quark events at the LHC from Supersymmetry
We analyze the production and subsequent decay of the neutral Higgs bosons of
the MSSM into electrically neutral quark pairs qq'=bs,tc of different flavors
at the LHC and compare with the direct FCNC production mechanisms. The
cross-sections are computed in the unconstrained MSSM with minimal
flavor-mixing sources and taking into account the stringent bounds from
radiative B-meson decays. We extend the results previously found for these FCNC
processes, which are singularly uncommon in the SM. Specifically, we report
here on the SUSY-EW contribution of the Higgs-mediated FCNC cross-section into
bs and tc final states and the SUSY-QCD and SUSY-EW contributions to
bs-production. In this way, the complete map of MSSM predictions for the
qq'-pairs produced at the LHC becomes available. The upshot is that the most
favorable channels are: 1) the Higgs boson FCNC decays into bs, and 2) the
direct production of tc pairs, both of them at the 1 pb level and mediated by
SUSY-QCD effects. If, however, the latter are suppressed, we find a small
SUSY-EW yield for the tc-production through Higgs decays but, at the same time,
a cross-section of 0.1-1 pb for bs-production, which implies a significant
number (10^4-10^5) of bs-pairs per 100 inverse femtobarn of integrated
luminosity.Comment: LaTeX, 17 pages, 4 figures, 4 tables. Extended discussion. Accepted
in Phys. Lett.
Measuring Polarization in Online Debates
Social networks can be a very successful tool to engage users to discuss relevant topics for
society. However, there are also some dangers that are associated with them, such as the emergence
of polarization in online discussions. Recently, there has been a growing interest to try to understand
this phenomenon, as some consider that this can be harmful concerning the building of a healthy
society in which citizens get used to polite discussions and even listening to opinions that may
be different from theirs. In this work, we face the problem of defining a precise measure that can
quantify in a meaningful way the level of polarization present in an online discussion. We focus on
the Reddit social network, given that its primary focus is to foster discussions, in contrast to other
social networks that have some other uses. Our measure is based on two different characteristics
of an online discussion: the existence of a balanced bipartition of the users of the discussion, where
one partition contains mainly users in agreement (regarding the topic of the discussion) and the
other users in disagreement, and the degree of negativity of the sentiment of the interactions between
these two groups of users. We discuss how different characteristics of the discussions affect the value
of our polarization measure, and we finally perform an empirical evaluation over different sets of
Reddit discussions about diverse classes of topics. Our results seem to indicate that our measure can
capture differences in the polarization level of different discussions, which can be further understood
when analyzing the values of the different factors used to define the measure.This research was funded by Spanish Project PID2019-111544GB-C22 (MINECO/FEDER), by the European Union’s Horizon 2020 Research and Innovation Program under Grant Agreements 723596, 768824, 764025 and 814945, and by 2017 SGR 1537
Production and FCNC decay of supersymmetric Higgs bosons into heavy quarks in the LHC
We analyze the production and subsequent decay of the neutral MSSM Higgs
bosons (h = h^0, H^0, A^0) mediated by flavor changing neutral currents (FCNC)
in the LHC collider. We have computed the h-production cross-section times the
FCNC branching ratio, \sigma(pp -> h -> qq') = \sigma(pp -> h) B(h -> qq'), in
the LHC focusing on the strongly-interacting FCNC sector. Here qq' is an
electrically neutral pair of quarks of different flavors, the dominant modes
being those containing a heavy quark: tc or bs. We determine the maximum
production rates for each of these modes and identify the relevant regions of
the MSSM parameter space, after taking into account the severe restrictions
imposed by low energy FCNC processes. The analysis of \sigma(pp -> h -> qq')
singles out regions of the MSSM parameter space different from those obtained
by maximizing only the branching ratio, due to non-trivial correlations between
the parameters that maximize/minimize each isolated factor. The production
rates for the bs channel can be huge for a FCNC process (0.1-1 pb), but its
detection can be problematic. The production rates for the tc channel are more
modest (10^{-3}-10^{-2} pb), but its detection should be easier due to the
clear-cut top quark signature. A few thousand tc events could be collected in
the highest luminosity phase of the LHC, with no counterpart in the SM.Comment: 25 pages, 9 figures, 2 tables, LaTeX 2e. Typos corrected. Version to
appear in JHE
Higgs Boson Flavor-Changing Neutral Decays into Top Quark in a General Two-Higgs-Doublet Model
Higgs boson decays mediated by flavor changing neutral currents (FCNC) are
very much suppressed in the Standard Model, at the level of 10^{-15} for Higgs
boson masses of a few hundred GeV. Therefore, any experimental vestige of them
would immediately call for new physics. In this paper we consider the FCNC
decays of Higgs bosons into a top quark in a general two-Higgs-doublet model
(2HDM). The isolated top quark signature, unbalanced by any other heavy
particle, should help to identify the potential FCNC events much more than any
other final state. We compute the maximum branching ratios and the number of
FCNC Higgs boson decay events at the LHC collider at CERN. The most favorable
mode for production and subsequent FCNC decay is the lightest CP-even state in
the Type II 2HDM, followed by the other CP-even state, if it is not very heavy,
whereas the CP-odd mode can never be sufficiently enhanced. Our calculation
shows that the branching ratios of the CP-even states may reach 10^{-5}, and
that several hundred events could be collected in the highest luminosity runs
of the LHC. We also point out some strategies to use these FCNC decays as a
handle to discriminate between 2HDM and supersymmetric Higgs bosons.Comment: Minor modifications in the text. Version accepted in Nucl. Phys.
Higgs Boson Flavor-Changing Neutral Decays into Bottom Quarks in Supersymmetry
We analyze the maximum branching ratios for the Flavor Changing Neutral
Current (FCNC) decays of the neutral Higgs bosons of the Minimal Supersymmetric
Standard Model (MSSM) into bottom quarks, h -> b\bar{s} (h=h^0,H^0,A^0). We
consistently correlate these decays with the radiative B-meson decays (b->
s\gamma). A full-fledged combined numerical analysis is performed of these
high-energy and low-energy FCNC decay modes in the MSSM parameter space. Our
calculation shows that the available data on B(b->s \gamma) severely restricts
the allowed values of B(h->b\bar{s}). While the latter could reach a few
percent level in fine-tuned scenarios, the requirement of naturalness reduces
these FCNC rates into the modest range B(h->b\bar{s}) ~ 10^{-4}-10^{-3}. We
find that the bulk of the MSSM contribution to B(h->b\bar{s}) could originate
from the strong supersymmetric sector. The maximum value of the FCNC rates
obtained in this paper disagree significantly with recent (over-)estimates
existing in the literature. Our results are still encouraging because they show
that the FCNC modes h->b\bar{s} can be competitive with other Higgs boson
signatures and could play a helpful complementary role to identify the
supersymmetric Higgs bosons, particularly the lightest CP-even state in the
critical LHC mass region m_{h^0} ~= 90-130 GeV.Comment: LaTeX, 19 pages, 4 tables, 7 figures. Clarifications and discussions
added, references added. Slight changes in Figs2b,6b and 7b. Version accepted
in JHE
Loop Induced Flavor Changing Neutral Decays of the Top Quark in a General Two-Higgs-Doublet Model
Decays of the top quark induced by flavor changing neutral currents (FCNC)
are known to be extremely rare events within the Standard Model. This is so not
only for the decay modes into gauge bosons, but most notably in the case of the
Higgs channels, e.g. t-> H_{SM}+c, with a branching fraction of 10^{-13} at
most. Therefore, detection of FCNC top quark decays in a future high-energy,
and high-luminosity, machine like the LHC or the LC would be an indisputable
signal of new physics. In this paper we show that within the simplest extension
of the SM, namely the general two-Higgs-doublet model, the FCNC top quark
decays into Higgs bosons, t->(h^{0},H^{0},A^{0})+c, can be the most favored
FCNC modes -- comparable or even more efficient than the gluon channel t-> g+c.
In both cases the optimal results are obtained for Type II models. However,
only the Higgs channels can have rates reaching the detectable level (10^{-5}),
with a maximum of order 10^{-4} which is compatible with the charged Higgs
bounds from radiative B-meson decays. We compare with the previous results
obtained in the Higgs sector of the MSSM.Comment: 18 pages, LaTeX, 5 figures, 1 table. References adde