8,639 research outputs found
Implications of symmetries in the scalar sector
Symmetries play a very important r\^ole in Particle Physics. In extended
scalar sectors, the existence of symmetries may permit the models to comply
with the experimental constraints in a natural way, and at the same time reduce
the number of free parameters. There is a strong interplay among internal
symmetries of the scalar potential, its CP properties and mass degeneracies of
the physical scalars. Some of these aspects were discussed in this talk.Comment: 8 pages, to be published in the Proceedings of DISCRETE2018: 6th
Symposium on Prospects in the Physics of Discrete Symmetries, 26-30 Nov 2018.
Vienna, Austri
Symmetries and Mass Degeneracies in the Scalar Sector
We explore some aspects of models with two and three SU(2) scalar doublets
that lead to mass degeneracies among some of the physical scalars. In Higgs
sectors with two scalar doublets, the exact degeneracy of scalar masses,
without an artificial fine-tuning of the scalar potential parameters, is
possible only in the case of the inert doublet model (IDM), where the scalar
potential respects a global U(1) symmetry that is not broken by the vacuum. In
the case of three doublets, we introduce and analyze the replicated inert
doublet model, which possesses two inert doublets of scalars. We then
generalize this model to obtain a scalar potential, first proposed by Ivanov
and Silva, with a CP4 symmetry that guarantees the existence of pairwise
degenerate scalar states among two pairs of neutral scalars and two pairs of
charged scalars. Here, CP4 is a generalized CP symmetry with the property that
is the identity operator only for integer values that are
multiples of 4. The form of the CP4-symmetric scalar potential is simplest when
expressed in the Higgs basis, where the neutral scalar field vacuum expectation
value resides entirely in one of the scalar doublet fields. The symmetries of
the model permit a term in the scalar potential with a complex coefficient that
cannot be removed by any redefinition of the scalar fields within the class of
Higgs bases (in which case, we say that no real Higgs basis exists). A striking
feature of the CP4-symmetric model is that it preserves CP even in the absence
of a real Higgs basis, as illustrated by the cancellation of the contributions
to the CP violating form factors of the effective ZZZ and ZWW vertices.Comment: 52 pages, 2 figures, second revised version with new material, as
published by JHE
Dysfunctional HDL and progression of atherosclerosis in HIV-1-infected and -uninfected adults
Background: HDL function rather than absolute level may be a more accurate indicator for risk of developing atherosclerosis. Dysfunctional HDL has increased redox activity and reduced antioxidant properties, but it is unknown whether abnormal HDL function is associated with progression of atherosclerosis in HIV-1-infected subjects. Findings: We retrospectively measured serum HDL function in 91 subjects from a prospective 3-year study of carotid artery intima-media thickness (CIMT), which enrolled triads of risk factor-matched persons that were HIV-1-uninfected (n=36) or HIV-1+ with (n=29) or without (n=26) protease inhibitor (PI)-based therapy for ≥ 2 years. HDL function was assessed using a biochemical assay that measures the oxidation of dihydrorhodamine 123 (DHR oxidation rate, DOR), in which higher DOR readout corresponds to dysfunctional HDL phenotype. There were no significant associations between DOR and HIV-1 infection. In univariate analysis of 55 HIV-1-infected subjects, greater waist circumference and lower serum HDL were significantly associated with higher baseline levels of DOR (p=0.01). These subjects had significant increases in levels of DOR over time (3 years) that were associated with white race (p=0.03), higher nadir CD4 count (p0.1) (DOR), were significantly associated (p=0.02) with progression of CIMT. Conclusion: In a small matched cohort study of HIV-1-infected subjects who had a low cardiovascular risk profile, HDL function changed over time and was independently associated with anthropometric parameters of obesity but not with progression of CIMT
Steady-state hydrodynamic instabilities of active liquid crystals: Hybrid lattice Boltzmann simulations
We report hybrid lattice Boltzmann (HLB) simulations of the hydrodynamics of
an active nematic liquid crystal sandwiched between confining walls with
various anchoring conditions. We confirm the existence of a transition between
a passive phase and an active phase, in which there is spontaneous flow in the
steady state. This transition is attained for sufficiently ``extensile'' rods,
in the case of flow-aligning liquid crystals, and for sufficiently
``contractile'' ones for flow-tumbling materials. In a quasi-1D geometry, deep
in the active phase of flow-aligning materials, our simulations give evidence
of hysteresis and history-dependent steady states, as well as of spontaneous
banded flow. Flow-tumbling materials, in contrast, re-arrange themselves so
that only the two boundary layers flow in steady state. Two-dimensional
simulations, with periodic boundary conditions, show additional instabilities,
with the spontaneous flow appearing as patterns made up of ``convection
rolls''. These results demonstrate a remarkable richness (including dependence
on anchoring conditions) in the steady-state phase behaviour of active
materials, even in the absence of external forcing; they have no counterpart
for passive nematics. Our HLB methodology, which combines lattice Boltzmann for
momentum transport with a finite difference scheme for the order parameter
dynamics, offers a robust and efficient method for probing the complex
hydrodynamic behaviour of active nematics.Comment: 18 eps figures, accepted for publication in Phys. Rev.
Effect of plasma elongation on current dynamics during tokamak disruptions
Plasma terminating disruptions in tokamaks may result in relativistic runaway
electron beams with potentially serious consequences for future devices with
large plasma currents. In this paper we investigate the effect of plasma
elongation on the coupled dynamics of runaway generation and resistive
diffusion of the electric field. We find that elongated plasmas are less likely
to produce large runaway currents, partly due to the lower induced electric
fields associated with larger plasmas, and partly due to direct shaping
effects, which mainly lead to a reduction in the runaway avalanche gain.Comment: 11 pages, 3 figure
Neuregulin-3 Regulates Epithelial Progenitor Cell Positioning and Specifies Mammary Phenotype
Mutation of Neuregulin-3 (Nrg3) results in defective embryonic mammary gland development. Here, we investigate functions of Nrg3 signaling in embryonic mammary morphogenesis. Nrg3 regulates the distribution of epithelial progenitor cells within the presumptive mammary-forming region during early mammary morphogenesis. Basal and suprabasal epithelial cells are significantly smaller within the hypoplastic mammary primordium (MP) that forms in Nrg3 mutants, indicative of failure to acquire mammary epithelial cell (MEC) morphological phenotype. Activation of Erbb4 JM-a CYT-1, an Erbb4 isoform expressed in the developing MP, leads to MEC spreading and migration. Nrg3 promotes the accumulation of epithelial progenitor cells at the MP site in embryo explant cultures. Our results implicate Nrg3 signaling in mediating key events of mammary mesenchyme specification, including mesenchymal condensation, mitosis, and induction of mammary marker expression. Taken together, our results show Nrg3 has a major role in conferring specification of the mammary phenotype to both epithelial and mesenchymal progenitor cells
Associations between acute conflict and maternal care usage in Egypt: An uncontrolled before-and-after study using demographic and health survey data
Background: United Nations’ (UN) data indicate that conflict-affected low-and middle-income countries (LMICs) contribute considerably to global maternal deaths. Maternal care usage patterns during conflict have not been rigorously quantitatively examined for policy insights. This study analysed associations between acute conflict and maternal services usage and quality in Egypt using reliable secondary data (as conflict-affected settings generally lack reliable primary data). Methods: An uncontrolled before-and-after study used data from the 2014 Egypt Demographic and Health Survey (EDHS). The ‘pre-conflict sample’ included births occurring from January 2009 to January 2011. The ‘peri-conflict sample’ included births from February 2011 to December 2012. The hierarchical nature of demographic and household survey (DHS) data was addressed using multi-level modelling (MLM). Results: In total, 2569 pre-conflict and 4641 peri-conflict births were reported. After adjusting for socioeconomic variables, conflict did not significantly affect antenatal service usage. Compared to the pre-conflict period, peri-conflict births had slightly lower odds of delivery in public institutions (odds ratio [OR]: 0.987; 95% CI: 0.975-0.998; P < .05), institutional postnatal care (OR: 0.995; 95% CI: 0.98-1.00; P = .05), and at least 24 hours post-delivery stay (OR: 0.921; 95% CI: 0.906-0.935; P < .01). Peri-conflict births had relatively higher odds of doctor-assisted deliveries (OR: 1.021; 95% CI: 1.004-1.035; P < .05), institutional deliveries (OR: 1.022; 95% CI: 1.00-1.04; P < .05), private institutional deliveries (OR: 1.035; 95% CI: 1.017-1.05; P < .001), and doctor-assisted postnatal care (OR: 1.015; 95% CI: 1.003-1.027; P < .05). Sensitivity analysis did not change results significantly. Conclusion: Maternal care showed limited associations with the acute conflict, generally reflecting pre-conflict usage patterns. Further qualitative and quantitative research could identify the effects of larger conflicts on maternal care-seeking and usage, and inform approaches to building health system resilience
Stochastic Energetics of Quantum Transport
We examine the stochastic energetics of directed quantum transport due to
rectification of non-equilibrium thermal fluctuations. We calculate the quantum
efficiency of a ratchet device both in presence and absence of an external load
to characterize two quantifiers of efficiency. It has been shown that the
quantum current as well as efficiency in absence of load (Stokes efficiency) is
higher as compared to classical current and efficiency, respectively, at low
temperature. The conventional efficiency of the device in presence of load on
the other hand is higher for a classical system in contrast to its classical
counterpart. The maximum conventional efficiency being independent of the
nature of the bath and the potential remains the same for classical and quantum
systems.Comment: To be published in Phys. Rev.
Persistence with Partial Survival
We introduce a parameter , called partial survival, in the persistence of
stochastic processes and show that for smooth processes the persistence
exponent changes continuously with , being the usual
persistence exponent. We compute exactly for a one-dimensional
deterministic coarsening model, and approximately for the diffusion equation.
Finally we develop an exact, systematic series expansion for , in
powers of , for a general Gaussian process with finite density of
zero crossings.Comment: 5 pages, 2 figures, references added, to appear in Phys.Rev.Let
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