8,167 research outputs found
Neutrino masses in quartification schemes
The idea of quark-lepton universality at high energies has recently been
explored in unified theories based upon the quartification gauge group SU(3)^4.
These schemes encompass a quark-lepton exchange symmetry that results upon the
introduction of leptonic colour. It has been demonstrated that in models in
which the quartification gauge symmetry is broken down to the standard model
gauge group, gauge coupling constant unification can be achieved, and there is
no unique scenario. The same is also true when the leptonic colour gauge group
is only partially broken, leaving a remnant SU(2)_\ell symmetry at the standard
model level. Here we perform an analysis of the neutrino mass spectrum of such
models. We show that these models do not naturally generate small Majorana
neutrino masses, thus correcting an error in our earlier quartification paper,
but with the addition of one singlet neutral fermion per family there is a
realisation of see-saw suppressed masses for the neutrinos. We also show that
these schemes are consistent with proton decay.Comment: 12 pages, minor changes. To appear in Phys. Rev.
Unification via intermediate symmetry breaking scales with the quartification gauge group
The idea of quark-lepton universality at high energies has been introduced as
a natural extension to the standard model. This is achieved by endowing leptons
with new degrees of freedom -- leptonic colour, an analogue of the familiar
quark colour. Grand and partially unified models which utilise this new gauge
symmetry SU(3)_\ell have been proposed in the context of the quartification
gauge group SU(3)^4. Phenomenologically successful gauge coupling constant
unification without supersymmetry has been demonstrated for cases where the
symmetry breaking leaves a residual SU(2)_\ell unbroken. Though attractive,
these schemes either incorporate ad hoc discrete symmetries and
non-renormalisable mass terms, or achieve only partial unification. We show
that grand unified models can be constructed where the quartification group can
be broken fully [i.e. no residual SU(2)_\ell] to the standard model gauge group
without requiring additional discrete symmetries or higher dimension operators.
These models also automatically have suppressed nonzero neutrino masses. We
perform a systematic analysis of the renormalisation-group equations for all
possible symmetry breaking routes from SU(3)^4 --> SU(3)_q x SU(2)_L x U(1)_Y.
This analysis indicates that gauge coupling unification can be achieved for
several different symmetry breaking patterns and we outline the requirements
that each gives on the unification scale. We also show that the unification
scenarios of those models which leave a residual SU(2)_\ell symmetry are not
unique. In both symmetry breaking cases, some of the scenarios require new
physics at the TeV scale, while others do not allow for new TeV phenomenology
in the fermionic sector.Comment: 25 page
Kink-induced symmetry breaking patterns in brane-world SU(3)^3 trinification models
The trinification grand unified theory (GUT) has gauge group SU(3)^3 and a
discrete symmetry permuting the SU(3) factors. In common with other GUTs, the
attractive nature of the fermionic multiplet assignments is obviated by the
complicated multi-parameter Higgs potential apparently needed for
phenomenological reasons, and also by vacuum expectation value (VEV)
hierarchies within a given multiplet. This motivates the rigorous consideration
of Higgs potentials, symmetry breaking patterns and alternative symmetry
breaking mechanisms in models with this gauge group. Specifically, we study the
recently proposed ``clash of symmetries'' brane-world mechanism to see if it
can help with the symmetry breaking conundrum. This requires a detailed
analysis of Higgs potential global minima and kink or domain wall solutions
interpolating between the disconnected global minima created through
spontaneous discrete symmetry breaking. Sufficiently long-lived metastable
kinks can also be considered. We develop what we think is an interesting,
albeit speculative, brane-world scheme whereby the hierarchical symmetry
breaking cascade, trinification to left-right symmetry to the standard model to
colour cross electromagnetism, may be induced without an initial hierarchy in
vacuum expectation values. Another motivation for this paper is simply to
continue the exploration of the rich class of kinks arising in models that are
invariant under both discrete and continuous symmetries.Comment: 12 pages, RevTex, references adde
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Refinement and preliminary evaluation of two tablet-based tests of real-world visual function
PURPOSE: To describe, refine, evaluate, and provide normative control data for two freely available tablet-based tests of real-world visual function, using a cohort of young, normally-sighted adults.
METHODS: Fifty young (18-40 years), normally-sighted adults completed tablet-based assessments of (1) face discrimination and (2) visual search. Each test was performed twice, to assess test-retest repeatability. Post-hoc analyses were performed to determine the number of trials required to obtain stable estimates of performance. Distributions were fitted to the normative data to determine the 99% population-boundary for normally sighted observers. Participants were also asked to rate their comprehension of each test.
RESULTS: Both tests provided stable estimates in around 20 trials (~1-4 min), with only a further reduction of 14%-17% in the 95% Coefficient of Repeatability (CoR95 ) when an additional 40 trials were included. When using only ~20 trials: median durations for the first run of each test were 191 s (Faces) and 51 s (Search); test-retest CoR95 were 0.27 d (Faces) and 0.84 s (Search); and normative 99% population-limits were 3.50 d (Faces) and 3.1 s (Search). No participants exhibited any difficulties completing either test (100% completion rate), and ratings of task-understanding were high (Faces: 9.6 out of 10; Search: 9.7 out of 10).
CONCLUSIONS: This preliminary assessment indicated that both tablet-based tests are able to provide simple, quick, and easy-to-administer measures of real-world visual function in normally-sighted young adults. Further work is required to assess their accuracy and utility in older people and individuals with visual impairment. Potential applications are discussed, including their use in clinic waiting rooms, and as an objective complement to Patient Reported Outcome Measures (PROMs)
High power coupled CO2 waveguide laser array
A hollow-bore ridge waveguide technique for phase locking arrays of coupled CO2 rf excited waveguide lasers was demonstrated. Stable phase-locked operation of two- and three-channel arrays has been demonstrated at the 50 W output level. Preliminary experiments with a five-element array generated an output power of 95 W but phase-locked operation was not conclusively demonstrated
Assessment of left atrial volume before and after pulmonary thromboendarterectomy in chronic thromboembolic pulmonary hypertension.
BackgroundImpaired left ventricular diastolic filling is common in chronic thromboembolic pulmonary hypertension (CTEPH), and recent studies support left ventricular underfilling as a cause. To investigate this further, we assessed left atrial volume index (LAVI) in patients with CTEPH before and after pulmonary thromboendarterectomy (PTE).MethodsForty-eight consecutive CTEPH patients had pre- & post-PTE echocardiograms and right heart catheterizations. Parameters included mean pulmonary artery pressure (mPAP), pulmonary vascular resistance (PVR), cardiac index, LAVI, & mitral E/A ratio. Echocardiograms were performed 6 ± 3 days pre-PTE and 10 ± 4 days post-PTE. Regression analyses compared pre- and post-PTE LAVI with other parameters.ResultsPre-op LAVI (mean 19.0 ± 7 mL/m2) correlated significantly with pre-op PVR (R = -0.45, p = 0.001), mPAP (R = -0.28, p = 0.05) and cardiac index (R = 0.38, p = 0.006). Post-PTE, LAVI increased by 18% to 22.4 ± 7 mL/m2 (p = 0.003). This change correlated with change in PVR (765 to 311 dyne-s/cm5, p = 0.01), cardiac index (2.6 to 3.2 L/min/m2, p = 0.02), and E/A (.95 to 1.44, p = 0.002).ConclusionIn CTEPH, smaller LAVI is associated with lower cardiac output, higher mPAP, and higher PVR. LAVI increases by ~20% after PTE, and this change correlates with changes in PVR and mitral E/A. The rapid increase in LAVI supports the concept that left ventricular diastolic impairment and low E/A pre-PTE are due to left heart underfilling rather than inherent left ventricular diastolic dysfunction
A simplified method for determining regurgitant fraction by Doppler echocardiography in patients with aortic regurtitation
AbstractObjectives. This study attempted to develop and validate a simple method for calculating aortic regurgitant fraction by use of pulsed wave Doppler echocardiography.Background. Although several investigators have been able to determine aortic regurgitant fraction by Doppler echocardiography, the methods used require accurate determination of the cross-sectional areas of intracardiac sites at which the volumetric flow is calculated.Methods. Our concept was based on a constant relation that exists between the cross-sectional area of the left ventricular outflow tract and the mitral valve annulus in normal subjects. To verify this, we used Doppler echocardiography to measure the flow velocity integral of the left ventricular outflow tract and the mitral annulus in the apical view in 50 normal subjects (32 men, 18 women, mean age 34 years).Results. Close correlation (r = 0.95) was observed between the flow velocity integral (FVI) of the outflow tract (OT) and that of the mitral annulus (MA): FVIMA/FVIOT= 0.77. Because mitral flow equals aortic flow in normal subjects, the ratio of the cross-sectional area of the mitral annulus to that of the outflow tract was 1/0.77. In patients with aortic regurgitation, the regurgitant fraction (RF) = (Aortic flow − Mitral flow)/Aortic flow = 1 − Mitral flow/Aortic flow. Substituting 0.77 for the area component of flow, RF = 1 − (1/0.77) · (FVIMA/FVIOT). To evaluate the accuracy of this method, we compared the regurgitant fraction derived by Doppler echocardiography with that from catheterization findings in 20 patients with aortic regurgitation (an isolated lesion was found in 14). The regurgitant fraction by catheterization was the difference between total (angiographic) and forward (thermodilution) stroke volumes as a percent of total flow. Good correlation was observed between catheterization and Doppler regurgitant fraction (r = 0.88, SEE 9%, p < 0.01).Conclusions. Thus, regurgitant fraction can be estimated from Doppler echocardiography in patients with aortic regurgitation by a method that requires only measurements of the flow velocity integral from the mitral annulus and left ventricular outflow tract
Pharmacological eEF2K activation promotes cell death and inhibits cancer progression.
Activation of the elongation factor 2 kinase (eEF2K) leads to the phosphorylation and inhibition of the elongation factor eEF2, reducing mRNA translation rates. Emerging evidence indicates that the regulation of factors involved in protein synthesis may be critical for controlling diverse biological processes including cancer progression. Here we show that inhibitors of the HIV aspartyl protease (HIV-PIs), nelfinavir in particular, trigger a robust activation of eEF2K leading to the phosphorylation of eEF2. Beyond its anti-viral effects, nelfinavir has antitumoral activity and promotes cell death. We show that nelfinavir-resistant cells specifically evade eEF2 inhibition. Decreased cell viability induced by nelfinavir is impaired in cells lacking eEF2K. Moreover, nelfinavir-mediated anti-tumoral activity is severely compromised in eEF2K-deficient engrafted tumors in vivo Our findings imply that exacerbated activation of eEF2K is detrimental for tumor survival and describe a mechanism explaining the anti-tumoral properties of HIV-PIs
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