237 research outputs found
The minimal B-L model naturally realized at TeV scale
In a previous paper, we have proposed the minimal B-L extended standard model
as a phenomenologically viable model that realizes the Coleman-Weinberg-type
breaking of the electroweak symmetry. Assuming the classical conformal
invariance and stability up to the Planck scale, we will show in this paper
that the model naturally predicts TeV scale B-L breaking as well as a light
standard-model singlet Higgs boson and light right-handed neutrinos around the
same energy scale. We also study phenomenology and detectability of the model
at the Large Hadron Collider (LHC) and the International Linear Collider (ILC).Comment: 24pages, 8figure
Design of sample holder for in operando XAS of oxidation state changes in La<sub>1−x</sub>Sr<sub>x</sub>MnO<sub>3±δ</sub> electrodes
Dark matter in the classically conformal B-L model
When the classically conformal invariance is imposed on the minimal gauged
B-L extended Standard Model (SM), the B-L gauge symmetry is broken by the
Coleman-Weinberg mechanism naturally at the TeV scale. Introducing a new Z_2
parity in the model, we investigate phenomenology of a right-handed neutrino
dark matter whose stability is ensured by the parity. We find that the relic
abundance of the dark matter particle can be consistent with the observations
through annihilation processes enhanced by resonances of either the SM Higgs
boson, the B-L Higgs boson or the B-L gauge boson (Z' boson). Therefore, the
dark matter mass is close to half of one of these boson masses. Due to the
classically conformal invariance and the B-L gauge symmetry breaking via the
Coleman-Weinberg mechanism, Higgs boson masses, Z' boson mass and the dark
matter mass are all related, and we identify the mass region to be consistent
with experimental results. We also calculate the spin-independent cross section
of the dark matter particle off with nucleon and discuss implications for
future direct dark matter search experiments.Comment: 13 pages, 4 figure
Minimal Flavor Violation in the Minimal U(1)_{B-L} Model and Resonant Leptogenesis
We investigate the resonant leptogenesis scenario in the minimally
extended standard model with minimal flavor violation. In our
model, the gauge symmetry is broken at the TeV scale and standard
model singlet neutrinos gain Majorana masses of order TeV. In addition, we
introduce a flavor symmetry on the singlet neutrinos at a scale higher than
TeV. The flavor symmetry is explicitly broken by the neutrino Dirac Yukawa
coupling, which induces splittings in the singlet neutrino Majorana masses at
lower scales through renormalization group evolutions. We call this setup
"minimal flavor violation". The mass-splittings are proportional to the tiny
Dirac Yukawa coupling, and hence they automatically enhance the CP asymmetry
parameter necessary for the resonant leptogenesis mechanism. In this paper, we
calculate the baryon number yield by solving the Boltzmann equations, including
the effects of gauge boson that also has TeV scale mass and causes
washing-out of the singlet neutrinos in the course of thermal leptogenesis. The
Dirac Yukawa coupling for neutrinos is fixed in terms of neutrino oscillation
data and an arbitrary complex-valued orthogonal matrix. We show
that the right amount of baryon number asymmetry can be achieved through
thermal leptogenesis in the context of the minimal flavor violation with
singlet neutrinos and gauge boson at the TeV scale. These
particles can be discovered at the LHC in the near future
Resonant Leptogenesis in the Minimal B-L Extended Standard Model at TeV
We investigate the resonant leptogenesis scenario in the minimal B-L extended
standard model(SM) with the B-L symmetry breaking at the TeV scale. Through
detailed analysis of the Boltzmann equations, we show how much the resultant
baryon asymmetry via leptogenesis is enhanced or suppressed, depending on the
model parameters, in particular, the neutrino Dirac Yukawa couplings and the
TeV-scale Majorana masses of heavy degenerate neutrinos. In order to consider a
realistic case, we impose a simple ansatz for the model parameters and analyze
the neutrino oscillation parameters and the baryon asymmetry via leptogenesis
as a function of only a single CP-phase. We find that for a fixed CP-phase all
neutrino oscillation data and the observed baryon asymmetry of the present
universe can be simultaneously reproduced.Comment: 25 pages, 15 figures, version to be published in Phys. Rev.
Extracting the Redox Orbitals in Li Battery Materials with High-Resolution X-Ray Compton Scattering Spectroscopy
We present an incisive spectroscopic technique for directly probing redox
orbitals based on bulk electron momentum density measurements via
high-resolution x-ray Compton scattering. Application of our method to spinel
LixMn2O4, a lithium ion battery cathode material, is discussed. The orbital
involved in the lithium insertion and extraction process is shown to mainly be
the oxygen 2p orbital. Moreover, the manganese 3d states are shown to
experience spatial delocalization involving 0.16 electrons per Mn site during
the battery operation. Our analysis provides a clear understanding of the
fundamental redox process involved in the working of a lithium ion battery.Comment: 24 pages, 3 figure
Direct observation of active material concentration gradients and crystallinity breakdown in LiFePO4 electrodes during charge/discharge cycling of lithium batteries
The phase changes that occur during discharge of an electrode comprised of LiFePO4, carbon, and PTFE binder have been studied in lithium half cells by using X-ray diffraction measurements in reflection geometry. Differences in the state of charge between the front and the back of LiFePO4 electrodes have been visualized. By modifying the X-ray incident angle the depth of penetration of the X-ray beam into the electrode was altered, allowing for the examination of any concentration gradients that were present within the electrode. At high rates of discharge the electrode side facing the current collector underwent limited lithium insertion while the electrode as a whole underwent greater than 50% of discharge. This behavior is consistent with depletion at high rate of the lithium content of the electrolyte contained in the electrode pores. Increases in the diffraction peak widths indicated a breakdown of crystallinity within the active material during cycling even during the relatively short duration of these experiments, which can also be linked to cycling at high rate
Reactivity with Water and Bulk Ruthenium Redox of Lithium Ruthenate in Basic Solutions
The reactivity of water with Li rich layered Li2RuO3 and partial exchange of Li2O with H2O within the structure has been studied under aqueous electro chemical conditions. Upon slow delithiation in water over long time periods, micron size Li2RuO3 particles structurally transform from an O3 structure to an O1 structure with a corresponding loss of 1.25 Li ions per formula unit. The O1 stacking of the honeycomb Ru layers is imaged using high resolution HAADF STEM, and the resulting structure is solved from X ray powder diffraction and electron diffraction. In situ X ray absorption spectroscopy suggests that reversible oxidation reduction of bulk Ru sites is realized on potential cycling between 0.4 VRHE and 1.25 VRHE in basic solutions. In addition to surface redox pseudocapacitance, the partially delithiated phase of Li2RuO3 shows high capacity which can be attributed to bulk Ru redox in the structure. This work demonstrates that the interaction of aqueous electrolytes with Li rich layered oxides, can result in the formation of new phases with electro chemical properties that are distinct from the parent material. This understanding is important for the design of aqueous batteries, electrochemical capacitors and chemically stable cathode materials for Li ion batterie
Egg Formation in Lepidoptera
Reproductive biology in the Twentieth Century produced comprehensive descriptions of the mechanisms of egg formation in most of the major orders of insects. While many general principles of ovarian development and physiology emerged, every order turned out to have a set of its own special motifs. Discovery of the lepidopteran motifs is summarized in this essay. The emphasis is on developmental mechanisms, beginning with the early growth and differentiation of female germ cells and ending, after many turns in morphogenesis, physiology and biosynthesis, with eggs that are filled with yolk and encased in chorions. Examples of uniquely lepidopteran traits include the cellular composition of ovarian follicles, the number of tubular ovarioles in which they mature, the functions of cell-to-cell junctional complexes in their maturation, their use of glycosaminoglycans to maintain intercellular patency during vitellogenesis, the role of proton and calcium pumps in their ion physiology, a separate postvitellogenic period of water and inorganic ion uptake, and the fine structure and protein composition of their chorions. Discovery of this combination of idiosyncracies was based on advances in the general concepts and techniques of cell and molecular biology and on insights borrowed from studies on other insects. The lepidopteran ovary in turn has contributed much to the understanding of egg formation in insects generally
fabH deletion increases DHA productionin Escherichia coli expressing Pfa genes
Background: Some marine bacteria, such as Moritella marina, produce the nutraceutical docosahexaenoic acid (DHA) thanks to a specific enzymatic complex called Pfa synthase. Escherichia coli heterologously expressing the pfa gene cluster from M. marina also produces DHA. The aim of this study was to find genetic or metabolic conditions to increase DHA production in E. coli. Results: First, we analysed the effect of the antibiotic cerulenin, showing that DHA production increased twofold. Then, we tested a series of single gene knockout mutations affecting fatty acid biosynthesis, in order to optimize the synthesis of DHA. The most effective mutant, fabH, showed a threefold increase compared to wild type strain. The combination of cerulenin inhibition and fabH deletion rendered a 6.5-fold improvement compared to control strain. Both strategies seem to have the same mechanism of action, in which fatty acid synthesis via the canonical pathway (fab pathway) is affected in its first catalytic step, which allows the substrates to be used by the heterologous pathway to synthesize DHA. Conclusions: DHA-producing E. coli strain that carries a fabH gene deletion boosts DHA production by tuning down the competing canonical biosynthesis pathway. Our approach can be used for optimization of DHA production in different organisms.Funding: The work in the FdlC and GM laboratories was financed by the Spanish Ministry of Economy, Industry and Competitiveness Grant BFU2014-55534-C2
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