89 research outputs found
Strong Unification
We investigate the possibility that unification occurs at strong coupling. We
show that, despite the fact the couplings pass through a strong coupling
regime, accurate predictions for their low energy values are possible because
the couplings of the theory flow to infrared fixed points. We determine the
low-energy QCD coupling in a favoured class of strong coupling models and find
it is reduced from the weak coupling predictions, lying close to the
experimentally measured value. We extend the analysis to the determination of
quark and lepton masses and show that (even without Grand Unification) the
infra-red fixed point structure may lead to good predictions for the top mass,
the bottom to tau mass ratio and . Finally we discuss the
implications for the unification scale finding it to be increased from the MSSM
value and closer to the heterotic string prediction.Comment: 12 pages, LateX, no figure
Biodegradation and antimicrobial properties of zinc oxideâpolymer composite materials for urinary stent applications
Research advancements in the field of urinary stents have mainly been in the selection of materials and coatings to address commonly faced problems of encrustation and bacterial adhesion. In this study, polylactic acid (PLA) and polypropylene (PP) were evaluated with zinc oxide (ZnO) coating to assess its ability to reduce or eliminate the problems of encrustation and bacteria adhesion. PLA and PP films were prepared via twin screw extrusion. ZnO microparticles were prepared using sol-gel hydrothermal synthesis. The as-prepared ZnO microparticles were combined in the form of a functional coating and deposited on both polymer substrates using a doctor blade technique. The ZnO-coated PP and PLA samples as well as their uncoated counterparts were characterized from the physicochemical standpoints, antibacterial and biodegradation properties. The results demonstrated that both the polymers preserved their mechanical and thermal properties after coating with ZnO, which showed a better adhesion on PLA than on PP. Moreover, the ZnO coating successfully enhanced the antibacterial properties with respect to bare PP/PLA substrates. All the samples were investigated after immersion in simulated body fluid and artificial urine. The ZnO layer was completely degraded following 21 days immersion in artificial urine irrespective of the substrate, with encrustations more evident in PP and ZnO-coated PP films than PLA and ZnO-coated PLA films. Overall, the addition of ZnO coating on PLA displayed better adhesion, antibacterial activity and delayed the deposition of encrustations in comparison to PP substrates
Infra-red fixed points in supersymmetry
Model independent constraints on supersymmetric models emerge when certain
couplings are drawn towards their infra-red (quasi) fixed points in the course
of their renormalization group evolution. The general principles are first
reviewed and the conclusions for some recent studies of theories with R-parity
and baryon and lepton number violations are summarized.Comment: 5 pages Latex with 2 figures embedded as eps files Talk given at
WHEPP6, Chennai, India, January 3-15, 2000, to appear in special issue of
Praman
Infrared alignment of SUSY flavor structures
The various experimental bounds on flavor-changing interactions severely
restrict the low-energy flavor structures of soft supersymmetry breaking
parameters. In this work, we show that with a particular assumption of Yukawa
couplings, the fermion mass and sfermion soft mass matrices are simultaneously
diagonalized by common mixing matrices and we then obtain an alignment solution
for the flavor problems. The required condition is generated by renormalization
group evolutions and achieved at low-energy scale independently of high-energy
structures of couplings. In this case, the diagonal entries of the soft scalar
mass matrices are determined by gaugino and Higgs soft masses. We also discuss
possible realizations of this scenario and the characteristic sparticle
spectrum in the models.Comment: 18 pages, 1 figur
Infrared Fixed Point Structure in Minimal Supersymmetric Standard Model with Baryon and Lepton Number Violation
We study in detail the renomalization group evolution of Yukawa couplings and
soft supersymmetry breaking trilinear couplings in the minimal supersymmetric
standard model with baryon and lepton number violation. We obtain the exact
solutions of these equations in a closed form, and then depict the infrared
fixed point structure of the third generation Yukawa couplings and the highest
generation baryon and lepton number violating couplings. Approximate analytical
solutions for these Yukawa couplings and baryon and lepton number violating
couplings, and the soft supersymmetry breaking couplings are obtained in terms
of their initial values at the unification scale. We then numerically study the
infrared fixed surfaces of the model, and illustrate the approach to the fixed
points.Comment: 16 pages REVTeX, figures embedded as epsfigs, replaced with version
to appear in Physical Review D, minor typographical errors eliminated and
references reordered, figures correcte
Lifetime Bipolar Disorder comorbidity and related clinical characteristics in patients with primary Obsessive Compulsive Disorder: a report from the International College of Obsessive-Compulsive Spectrum Disorders (ICOCS)
IntroductionBipolar disorder (BD) and obsessive compulsive disorder (OCD) are prevalent, comorbid, and disabling conditions, often characterized by early onset and chronic course. When comorbid, OCD and BD can determine a more pernicious course of illness, posing therapeutic challenges for clinicians. Available reports on prevalence and clinical characteristics of comorbidity between BD and OCD showed mixed results, likely depending on the primary diagnosis of analyzed samples.MethodsWe assessed prevalence and clinical characteristics of BD comorbidity in a large international sample of patients with primary OCD (n = 401), through the International College of Obsessive-Compulsive Spectrum Disorders (ICOCS) snapshot database, by comparing OCD subjects with vs without BD comorbidity.ResultsAmong primary OCD patients, 6.2% showed comorbidity with BD. OCD patients with vs without BD comorbidity more frequently had a previous hospitalization (p < 0.001) and current augmentation therapies (p < 0.001). They also showed greater severity of OCD (p < 0.001), as measured by the Yale-Brown Obsessive Compulsive Scale (Y-BOCS).ConclusionThese findings from a large international sample indicate that approximately 1 out of 16 patients with primary OCD may additionally have BD comorbidity along with other specific clinical characteristics, including more frequent previous hospitalizations, more complex therapeutic regimens, and a greater severity of OCD. Prospective international studies are needed to confirm our findings.Peer reviewe
Fermion Mass Hierarchies and Small Mixing Angles from Extra Dimensions
In this paper we study renormalization-group evolutions of Yukawa matrices
enhanced by Kaluza-Klein excited modes and analyze their infrared fixed-point
structure. We derive necessary conditions to obtain hierarchies between
generations on the fixed point. These conditions restrict how the fields in the
models can extend to higher dimension. Several specific mechanisms to realize
the conditions are presented. We also take account of generation mixing effects
and find a scenario where the mixing angles become small at low energy even
with large initial values at high-energy scale. A toy model is shown to lead
realistic quark mass matrices.Comment: 23 pages, 7 figures, LaTeX, a supplementary explanation and
references adde
Large Neutrino Mixing from Renormalization Group Evolution
The renormalization group evolution equation for two neutrino mixing is known
to exhibit nontrivial fixed point structure corresponding to maximal mixing at
the weak scale. The presence of the fixed point provides a natural explanation
of the observed maximal mixing of if the and
are assumed to be quasi-degenerate at the seesaw scale without
constraining on the mixing angles at that scale. In particular, it allows them
to be similar to the quark mixings as in generic grand unified theories. We
discuss implementation of this program in the case of MSSM and find that the
predicted mixing remains stable and close to its maximal value, for all
energies below the (TeV) SUSY scale. We also discuss how a particular
realization of this idea can be tested in neutrinoless double beta decay
experiments.Comment: Latex file, 21 pages and 4 ps figures include
Mass predictions based on a supersymmetric SU(5) fixed point
I examine the possibility that the third generation fermion masses are
determined by an exact fixed point of the minimal supersymmetric SU(5) model.
When one-loop supersymmetric thresholds are included, this unified fixed point
successfully predicts the top quark mass, 175 +(-) 2 GeV, as well as the weak
mixing angle. The bottom quark mass prediction is sensitive to the
supersymmetric thresholds; it approaches the measured value for mu <0 and very
large unified gaugino mass. The experimental measurement of the tau lepton mass
determines tan(beta), and the strong gauge coupling and fine structure constant
fix the unification scale and the unified gauge coupling.Comment: 40 pages, 9 figures, 9 tables, Revtex
Regularisation Techniques for the Radiative Corrections of Wilson lines and Kaluza-Klein states
Within an effective field theory framework we compute the most general
structure of the one-loop corrections to the 4D gauge couplings in one- and
two-dimensional orbifold compactifications with non-vanishing constant gauge
background (Wilson lines). Although such models are non-renormalisable, we keep
the analysis general by considering the one-loop corrections in three
regularisation schemes: dimensional regularisation (DR), Zeta-function
regularisation (ZR) and proper-time cut-off regularisation (PT). The relations
among the results obtained in these schemes are carefully addressed. With
minimal re-definitions of the parameters involved, the results obtained for the
radiative corrections can be applied to most orbifold compactifications with
one or two compact dimensions. The link with string theory is discussed. We
mention a possible implication for the gauge couplings unification in such
models.Comment: 37 pages, 1 Figure, LaTeX; minor correction
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