564 research outputs found
Electroweak Symmetry Breaking in the DSSM
We study the theoretical and phenomenological consequences of modifying the
Kahler potential of the MSSM two Higgs doublet sector. Such modifications
naturally arise when the Higgs sector mixes with a quasi-hidden conformal
sector, as in some F-theory GUT models. In the Delta-deformed Supersymmetric
Standard Model (DSSM), the Higgs fields are operators with non-trivial scaling
dimension 1 < Delta < 2. The Kahler metric is singular at the origin of field
space due to the presence of quasi-hidden sector states which get their mass
from the Higgs vevs. The presence of these extra states leads to the fact that
even as Delta approaches 1, the DSSM does not reduce to the MSSM. In
particular, the Higgs can naturally be heavier than the W- and Z-bosons.
Perturbative gauge coupling unification, a large top quark Yukawa, and
consistency with precision electroweak can all be maintained for Delta close to
unity. Moreover, such values of Delta can naturally be obtained in
string-motivated constructions. The quasi-hidden sector generically contains
states charged under SU(5)_GUT as well as gauge singlets, leading to a rich,
albeit model-dependent, collider phenomenology.Comment: v3: 40 pages, 3 figures, references added, typos correcte
Area and individual differences in personal crime victimization incidence: The role of individual, lifestyle/routine activities and contextual predictors
This article examines how personal crime differences between areas and between individuals are predicted by area and population heterogeneity and their synergies. It draws on lifestyle/routine activities and social disorganization theories to model the number of personal victimization incidents over individuals including routine activities and area characteristics, respectively, as well as their (cross-cluster) interactions. The methodology employs multilevel or hierarchical negative binomial regression with extra binomial variation using data from the British Crime Survey and the UK Census. Personal crime rates differ substantially across areas, reflecting to a large degree the clustering of individuals with measured vulnerability factors in the same areas. Most factors suggested by theory and previous research are conducive to frequent personal victimization except the following new results. Pensioners living alone in densely populated areas face disproportionally high numbers of personal crimes. Frequent club and pub visits are associated with more personal crimes only for males and adults living with young children, respectively. Ethnic minority individuals experience fewer personal crimes than whites. The findings suggest integrating social disorganization and lifestyle theories and prioritizing resources to the most vulnerable, rather than all, residents of poor and densely populated areas to prevent personal crimes
Wavefunctions and the Point of E8 in F-theory
In F-theory GUTs interactions between fields are typically localised at
points of enhanced symmetry in the internal dimensions implying that the
coefficient of the associated operator can be studied using a local
wavefunctions overlap calculation. Some F-theory SU(5) GUT theories may exhibit
a maximum symmetry enhancement at a point to E8, and in this case all the
operators of the theory can be associated to the same point. We take initial
steps towards the study of operators in such theories. We calculate
wavefunctions and their overlaps around a general point of enhancement and
establish constraints on the local form of the fluxes. We then apply the
general results to a simple model at a point of E8 enhancement and calculate
some example operators such as Yukawa couplings and dimension-five couplings
that can lead to proton decay.Comment: 46 page
Building SO(10) models from F-theory
We revisit local F-theory SO(10) and SU(5) GUTs and analyze their properties
within the framework of the maximal underlying E_8 symmetry in the elliptic
fibration. We consider the symmetry enhancements along the intersections of
seven-branes with the GUT surface and study in detail the embedding of the
abelian factors undergoing monodromies in the covering gauge groups. We combine
flux data from the successive breaking of SO(10) to SU(5) gauge symmetry and
subsequently to the Standard Model one, and further constrain the parameters
determining the models' particle spectra. In order to eliminate dangerous
baryon number violating operators we propose ways to construct matter parity
like symmetries from intrinsic geometric origin. We study implementations of
the resulting constrained scenario in specific examples obtained for a variety
of monodromies.Comment: 53 page
Yukawa hierarchies at the point of in F-theory
We analyse the structure of Yukawa couplings in local SU(5) F-theory models
with enhancement. In this setting the symmetry is broken down to
SU(5) by a 7-brane configuration described by T-branes, all the Yukawa
couplings are generated in the vicinity of a point and only one family of
quarks and leptons is massive at tree-level. The other two families obtain
their masses when non-perturbative effects are taken into account, being
hierarchically lighter than the third family. However, and contrary to previous
results, we find that this hierarchy of fermion masses is not always
appropriate to reproduce measured data. We find instead that different T-brane
configurations breaking to SU(5) give rise to distinct hierarchical
patterns for the holomorphic Yukawa couplings. Only some of these patterns
allow to fit the observed fermion masses with reasonable local model parameter
values, adding further constraints to the construction of F-theory GUTs. We
consider an model where such appropriate hierarchy is realised and
compute its physical Yukawas, showing that realistic charged fermions masses
can indeed be obtained in this case.Comment: 46 pages + appendices, 5 figures. v2, added references and typos
corrected, version accepted on JHEP. v3, typos correcte
Rational F-Theory GUTs without exotics
We construct F-theory GUT models without exotic matter, leading to the MSSM
matter spectrum with potential singlet extensions. The interplay of engineering
explicit geometric setups, absence of four-dimensional anomalies, and realistic
phenomenology of the couplings places severe constraints on the allowed local
models in a given geometry. In constructions based on the spectral cover we
find no model satisfying all these requirements. We then provide a survey of
models with additional U(1) symmetries arising from rational sections of the
elliptic fibration in toric constructions and obtain phenomenologically
appealing models based on SU(5) tops. Furthermore we perform a bottom-up
exploration beyond the toric section constructions discussed in the literature
so far and identify benchmark models passing all our criteria, which can serve
as a guideline for future geometric engineering.Comment: 27 Pages, 1 Figur
Did they report it to stop it? A realist evaluation of the effect of an advertising campaign on victims’ willingness to report unwanted sexual behaviour
Tackling unwanted sexual behaviour (USB) on public transport is a concern for transit authorities across the world. However, high rates of underreporting mean a lack of reliable information about USB, presenting a key barrier to prevention. This paper presents a realist evaluation of an initiative called ‘Report It To Stop It’ (RITSI) implemented in London, UK, to tackle underreporting. RITSI aimed to encourage victims to report details of USB incidents to police and transit authorities through media campaigns. Results show that the initiative did increase reporting of USB and, that this increase was not due to a rise in the prevalence of USB. Crucially, there was no evidence of any increase in passengers’ fear of crime during the campaign activity. However, the impacts of this campaign were more pronounced in earlier waves, and on certain modes of transport. These findings demonstrate the importance of the context in motivating reporting behaviour change
The impact of food assistance on weight gain and disease progression among HIV-infected individuals accessing AIDS care and treatment services in Uganda
BACKGROUND: The evidence evaluating the benefits of programmatic nutrition interventions to HIV-infected individuals in developing countries, where there is a large overlap between HIV prevalence and malnutrition, is limited. This study evaluates the impact of food assistance (FA) on change in weight and disease progression as measured by WHO staging. METHODS: We utilize program data from The AIDS Support Organization (TASO) in Uganda to compare outcomes among FA recipients to a control group, using propensity score matching (PSM) methods among 14,481 HIV-infected TASO clients. RESULTS: FA resulted in a significant mean weight gain of 0.36 kg over one year period. This impact was conditional on anti-retroviral therapy (ART) receipt and disease stage at baseline. FA resulted in mean weight gain of 0.36 kg among individuals not receiving ART compared to their matched controls. HIV-infected individuals receiving FA with baseline WHO stage II and III had a significant weight gain (0.26 kg and 0.2 kg respectively) compared to their matched controls. Individuals with the most advanced disease at baseline (WHO stage IV) had the highest weight gain of 1.9 kg. The impact on disease progression was minimal. Individuals receiving FA were 2 percentage points less likely to progress by one or more WHO stage compared to their matched controls. There were no significant impacts on either outcome among individuals receiving ART. CONCLUSIONS: Given the widespread overlap of HIV and malnutrition in sub-Saharan Africa, FA programs have the potential to improve weight and delay disease progression, especially among HIV-infected individuals not yet on ART. Additional well designed prospective studies evaluating the impact of FA are urgently needed
Unification and Phenomenology of F-Theory GUTs with U(1)_PQ
We undertake a phenomenological study of SU(5) F-theory GUT models with an
additional U(1)_{PQ} symmetry. In such models, breaking SU(5) with hypercharge
flux leads to the presence of non-GUT multiplets in the spectrum. We study the
effect these have on the unification of gauge couplings, including two-loop
running as well as low- and high-scale threshold corrections. We use the
requirement of unification to constrain the size of thresholds from KK modes of
SU(5) gauge and matter fields. Assuming the non-GUT multiplets play the role of
messengers of gauge mediation leads to controlled non-universalities in the
sparticle spectrum while maintaining grand unification, and we study the LHC
phenomenology of this scenario. We find that the MSSM spectrum may become
compressed or stretched out {by up to a factor of three} depending on the
distribution of hypercharge flux. We present a set of benchmark points whose
production cross-sections and decays we investigate, and argue that precision
kinematic edge measurements will allow the LHC to distinguish between our model
and mGMSB.Comment: 46 pages, 15 figure
Dirac gauginos and unification in F-theory
Supersymmetric models in which the gauginos acquire Dirac masses, rather than
Majorana masses, offer an appealing alternative to the minimal supersymmetric
standard model, especially in the light of the bounds set on superpartner
masses by the 2011 LHC data. Dirac gauginos require the presence of chiral
multiplets in the adjoint representation of the gauge group, and the
realisation of such scenarios in F-theory is the subject of this paper. The
chiral adjoints drastically alter the usual picture of gauge coupling
unification, but this is disturbed anyway in F-theory models with non-trivial
hypercharge flux. The interplay between these two factors is explored, and it
is found for example that viable F-theory unification can be achieved at around
the reduced Planck scale, if there is an extra vector-like pair of singlet
leptons with TeV-scale mass. I then discuss the conditions which must be
satisfied by the geometry and hypercharge flux of an F-theory model with Dirac
gauginos. One nice possibility is for the visible sector to be localised on a
K3 surface, and this is discussed in some detail. Finally, I describe how to
achieve an unbroken discrete R-symmetry in such compactifications, which is an
important ingredient in many models with Dirac gauginos, and write down a
simple example which has adjoint chiral multiplets, an appropriate R-symmetry,
and allows for viable breaking of SU(5) by hypercharge flux.Comment: 25 pages, 4 figures. v2: Minor changes; references added. v3: Section
4 modified and expanded; other minor change
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