Flavor Gauge Models Below the Fermi Scale

The mass and weak interaction eigenstates for the quarks of the third generation are very well aligned, an empirical fact for which the Standard Model offers no explanation. We explore the possibility that this alignment is due to an additional gauge symmetry in the third generation. Specifically, we construct and analyze an explicit, renormalizable model with a gauge boson, $X$, corresponding to the $B-L$ symmetry of the third family. Having a relatively light (in the MeV to multi-GeV range), flavor-nonuniversal gauge boson results in a variety of constraints from different sources. By systematically analyzing 20 different constraints, we identify the most sensitive probes: kaon, $B^+$, $D^+$ and Upsilon decays, $D-\bar{D}^0$ mixing, atomic parity violation, and neutrino scattering and oscillations. For the new gauge coupling $g_X$ in the range $(10^{-2} - 10^{-4})$ the model is shown to be consistent with the data. Possible ways of testing the model in $b$ physics, top and $Z$ decays, direct collider production and neutrino oscillation experiments, where one can observe nonstandard matter effects, are outlined. The choice of leptons to carry the new force is ambiguous, resulting in additional phenomenological implications, such as non-universality in semileptonic bottom decays. The proposed framework provides interesting connections between neutrino oscillations, flavor and collider physics.Comment: 44 pages, 7 figures, 3 tables; B physics constraints and references added, conclusions unchange

Actin assembly ruptures the nuclear envelope by prying the lamina away from nuclear pores and nuclear membranes in starfish oocytes.

The nucleus of oocytes (germinal vesicle) is unusually large and its nuclear envelope (NE) is densely packed with nuclear pore complexes (NPCs) stockpiled for embryonic development. We showed that breakdown of this specialized NE is mediated by an Arp2/3-nucleated F-actin 'shell' in starfish oocytes, in contrast to microtubule-driven tearing in mammalian fibroblasts. Here, we address the mechanism of F-actin-driven NE rupture by correlated live-cell, super-resolution and electron microscopy. We show that actin is nucleated within the lamina sprouting filopodia-like spikes towards the nuclear membranes. These F-actin spikes protrude pore-free nuclear membranes, whereas the adjoining membrane stretches accumulate NPCs associated with the still-intact lamina. Packed NPCs sort into a distinct membrane network, while breaks appear in ER-like, pore-free regions. Thereby, we reveal a new function for actin-mediated membrane shaping in nuclear rupture that is likely to have implications in other contexts such as nuclear rupture observed in cancer cells

Fractional Hamiltonian analysis of higher order derivatives systems

The fractional Hamiltonian analysis of 1+1 dimensional field theory is investigated and the fractional Ostrogradski's formulation is obtained. The fractional path integral of both simple harmonic oscillator with an acceleration-squares part and a damped oscillator are analyzed. The classical results are obtained when fractional derivatives are replaced with the integer order derivatives.Comment: 13 page

Unconventional superconductivity and an ambient-pressure magnetic quantum critical point in single-crystal LaNiC2_2

Superconductivity in noncentrosymmetric LaNiC$_2$ is expected to be induced by electron--phonon interactions due to its lack of magnetic instabilities. The non-Bardeen-Cooper-Schrieffer (BCS) behaviors found in this material call into question the long-standing idea that relates unconventional superconductivity with magnetic interactions. Here we report magnetic penetration-depth measurements in a high-purity single crystal of LaNiC$_2$ at pressures up to 2.5 GPa and temperatures down to 0.04 K. At ambient pressure and below 0.5$T_c$ the penetration depth goes as $T^4$ for the in-plane and $T^2$ for the out-of-plane component, firmly implying the existence of point nodes in the energy gap and the unconventional character of this superconductor. The present study also provides first evidence of magnetism in LaNiC$_2$ by unraveling a pressure-induced antiferromagnetic phase inside the superconducting state at temperatures below 0.5 K, with a quantum critical point around ambient pressure. The results presented here maintain a solid base for the notion that unconventional superconductivity only arises near magnetic order or fluctuations.Comment: 12 pages, 4 figure

Type O pure radiation metrics with a cosmological constant

In this paper we complete the integration of the conformally flat pure radiation spacetimes with a non-zero cosmological constant $\Lambda$, and $\tau \ne 0$, by considering the case $\Lambda +\tau\bar\tau \ne 0$. This is a further demonstration of the power and suitability of the generalised invariant formalism (GIF) for spacetimes where only one null direction is picked out by the Riemann tensor. For these spacetimes, the GIF picks out a second null direction, (from the second derivative of the Riemann tensor) and once this spinor has been identified the calculations are transferred to the simpler GHP formalism, where the tetrad and metric are determined. The whole class of conformally flat pure radiation spacetimes with a non-zero cosmological constant (those found in this paper, together with those found earlier for the case $\Lambda +\tau\bar\tau = 0$) have a rich variety of subclasses with zero, one, two, three, four or five Killing vectors

CGE: da divulgação à investigação

A divulgação da ciência e da tecnologia aparece como uma área fundamental na sociedade actual. Isto não será de estranhar pois os tremendos desafios que se colocam ao futuro de um planeta que a cada 12 a 13 anos tem mais mil milhões de habitantes e onde o consumo aumenta de uma forma exponencial, levanta problemas que eventualmente só o conhecimento científico poderá resolver; é importante que as opções que venham a ser tomadas possam ser compreendidas pela generalidade das pessoas, pois são justamente elas que irão ser mais afectadas por essas decisões. Ciente das responsabilidades sociais que lhe cabe enquanto instituição produtora de saber, desde sempre tem sido estratégia do CGE um forte empenhamento nas actividades de divulgação científica e tecnológica. A par do compromisso com a investigação e sua apresentação à comunidade científica, sem dúvida o primeiro factor de prestígio para qualquer grupo de investigação, acresce a responsabilidade de zelar pela qualidade com que a ciência chega ao grande público. Nesse âmbito o CGE mantém, desde a sua formação, uma dinâmica de incentivo, apoio e valorização a todas as iniciativas de divulgação científica, em particular na área das Ciências da Terra. Este trabalho continuado levou a que o CGE se destaque no panorama nacional, tendo o seu nome ligado a algumas das actividades mais importantes de divulgação que têm sido realizadas em Portugal nos últimos dez anos

Development of fluorescent nanocomposites based on CdTe quantum dots

Cadmium telluride (CdTe) quantum dots (QDs) are efficient fluorescence semiconductor nanoparticles with unique optical and physicochemical properties. Their incorporation into polymer matrices allows the development of materials with several applications such as in opto-eletronic devices. Nevertheless, one of the most important prerequisite of these high-efficiency nanocomposites is the fluorescence efficiency of the QDs– polymer, which is mainly related with the QDs dispersion. Even though many attempts have been made, there are little work reporting the effect of different polymer matrices on QDs dispersion and therefore, the charge transport in the final materials (Rakovich and Donegan 2013) 1 . In this work, a strategy to develop QDs/polymer nanocomposites is presented. Highly fluorescent CdTe QDs are embedded in different optically transparent commercial polymers, via solvent cast method. To investigate the influence of each polymeric matrix on the final properties, optical, morphological and electrical measurements were carried out. Furthermore, the results demonstrate that the addition of a surfactant produce better dispersion of the CdTe QDs in the polymeric matrices and improve the electrical properties of the resulting materials (Fig.1)

Modeling the contribution of allosteric regulation for flux control in the central carbon metabolism of E. coli

Redesign of microbial metabolism is a critical step in biotechnology for the production of industrially relevant compounds. Central carbon metabolism provides the energy and building blocks required for cellular growth and synthesis of the desired byproducts and, consequently, it is the main target for intervention in most rational strain design approaches. However, the complexity of central carbon metabolism is still not completely understood. Recent studies in different organisms show that flux control in central carbon metabolism is predominantly regulated by non-transcriptional mechanisms, leaving post-translational modifications, allosteric regulation, and thermodynamics as main candidates. In this work, we extend a model of central carbon metabolism of E.coli with allosteric interactions in order to reveal a hidden topology in metabolic networks. We use this model to integrate a multi-omic dataset containing transcript, protein, flux and metabolite levels to further dissect and analyze the contribution of allosteric regulation for metabolic flux control

Phenomenology on the QCD dipole picture revisited

We perform an adjust to the most recent structure function data, considering the QCD dipole picture applied to ep scattering. The structure function F2 at small x and intermediate Q2 can be described by the model containing an economical number of free-parameters, which encodes the hard Pomeron physics. The longitudinal structure function and the gluon distribution are predicted without further adjustments. The data description is effective, whereas a resummed next-to-leading level analysis is deserved.Comment: 18 pages, 6 figures. Version to be published in Eur. Phys. J.