Custodial SO(4) symmetry and CP violation in N-Higgs-doublet potentials

We study the implementation of global $SO(4)\sim SU(2)_L\otimes SU(2)_R$ symmetry in general potentials with N-Higgs-doublets in order to obtain models with custodial $SO(3)_C$ symmetry. We conclude that any implementation of the custodial SO(4) symmetry is equivalent, by a basis transformation, to a canonical one if $SU(2)_L$ is the gauge factor, $U(1)_Y$ is embedded in $SU(2)_R$ and we require $N$ copies of the doublet representation of $SU(2)_R$. The invariance by SO(4) automatically leads to a CP invariant potential and the basis of the canonical implementation of SO(4) is aligned to a basis where CP-symmetry acts in the standard fashion. We show different but equivalent implementations for the 2HDM, including an implementation not previously considered.Comment: 22pp, REVTeX4. Published versio

Plasmonic Enhancement of Emission from Si-nanocrystals

Plasmonic gratings of different periodicities are fabricated on top of Silicon nanocrystals embedded in Silicon Dioxide. Purcell enhancements of up to 2 were observed, which matches the value from simulations. Plasmonic enhancements are observed for the first three orders of the plasmonic modes, with the peak enhancement wavelength varying with the periodicity. Biharmonic gratings are also fabricated to extract the enhanced emission from the first order plasmonic mode, resulting in enhancements with quality factors of up to 16.Comment: 4 pages, 5 figures added explanation of low purcell enhancement updated figure

Self-Regulation of Star Formation in Low Metallicity Clouds

We investigate the process of self-regulated star formation via photodissociation of hydrogen molecules in low metallicity clouds. We evaluate the influence region's scale of a massive star in low metallicity gas clouds whose temperatures are between 100 and 10000 Kelvin. A single O star can photodissociate hydrogen molecules in the whole of the host cloud. If metallicity is smaller than about 10^{-2.5} of the solar metallicity, the depletion of coolant of the the host cloud is very serious so that the cloud cannot cool in a free-fall time, and subsequent star formation is almost quenched. On the contrary, if metallicity is larger than about 10^{-1.5} of the solar metallicity, star formation regulation via photodissociation is not efficient. The typical metallicity when this transition occurs is about 1/100 of the solar metallicity. This indicates that stars do not form efficiently before the metallicity becomes larger than about 1/100 of the solar metallicity and we considered that this value becomes the lower limit of the metallicity of luminous objects such as galaxies.Comment: 14 pages, including 5 figures, To appear in ApJ, Vol. 53

On the Decelerating Shock Instability of Plane-Parallel Slab with Finite Thickness

Dynamical stability of the shock compressed layer with finite thickness is investigated. It is characterized by self-gravity, structure, and shock condition at the surfaces of the compressed layer. At one side of the shocked layer, its surface condition is determined via the ram pressure, while at the other side the thermal pressure supports its structure. When the ram pressure dominates the thermal pressure, we expect deceleration of the shocked layer. Especially, in this paper, we examine how the stratification of the decelerating layer has an effect on its dynamical stability. Performing the linear perturbation analysis, a {\it more general} dispersion relation than the previous one obtained by one of the authors is derived. It gives us an interesting information about the stability of the decelerating layer. Importantly, the DSI (Decelerating Shock Instability) and the gravitational instability are always incompatible. We also consider the evolution effect of the shocked layer. In the early stages of its evolution, only DSI occurs. On the contrary, in the late stages, it is possible for the shocked layer to be unstable for the DSI (in smaller scale) and the gravitational instability (in larger scale). Furthermore, we find there is a stable range of wavenumbers against both the DSI and the gravitational instability between respective unstable wavenumber ranges. These stable modes suggest the ineffectiveness of DSI for the fragmentation of the decelerating slab.Comment: 17 pages, 6 figures. The Astrophysical Journal Vol.532 in pres

Photodissociative Regulation of Star Formation in Metal-Free Pregalactic Clouds

We study the H2 photodissociation regions around OB stars in primordial gas clouds whose virial temperatures are between a few hundred and a few thousand Kelvin. In such small objects, a single O star can photodissociate a mass equal to that of the cloud itself. As a result, the clouds deplete their molecular coolant and cannot cool in a free-fall time, and subsequent star formation is totally quenched. This indicates that stars do not form efficiently in small objects and that these objects contribute little to the reionization of the universe.Comment: 9 pages. ApJ, 518, in pres

High-concentration Er:YAG single-crystal fibers grown by laser-heated pedestal growth technique

High-concentration Er:YAG single-crystal fibers have been grown using the laser-heated pedestal growth technique. Instability in the melt and concomitant opacity of fibers were observed at source concentrations higher than 15 mol.%. Spectroscopic examination shows that broadening of the linewidth of the I<sub>13/2</sub>4→I<sub>15/2</sub>4 transition is strongly dependent on Er<sup>3+</sup> concentration

Structural Insights into Differences in Drug-binding Selectivity between Two Forms of Human α1-Acid Glycoprotein Genetic Variants, the A and F1*S Forms

Human α1-acid glycoprotein (hAGP) in serum functions as a carrier of basic drugs. In most individuals, hAGP exists as a mixture of two genetic variants, the F1*S and A variants, which bind drugs with different selectivities. We prepared a mutant of the A variant, C149R, and showed that its drug-binding properties were indistinguishable from those of the wild type. In this study, we determined the crystal structures of this mutant hAGP alone and complexed with disopyramide (DSP), amitriptyline (AMT), and the nonspecific drug chlorpromazine (CPZ). The crystal structures revealed that the drug-binding pocket on the A variant is located within an eight-stranded β-barrel, similar to that found in the F1*S variant and other lipocalin family proteins. However, the binding region of the A variant is narrower than that of the F1*S variant. In the crystal structures of complexes with DSP and AMT, the two aromatic rings of each drug interact with Phe-49 and Phe-112 at the bottom of the binding pocket. Although the structure of CPZ is similar to those of DSP and AMT, its fused aromatic ring system, which is extended in length by the addition of a chlorine atom, appears to dictate an alternative mode of binding, which explains its nonselective binding to the F1*S and A variant hAGPs. Modeling experiments based on the co-crystal structures suggest that, in complexes of DSP, AMT, or CPZ with the F1*S variant, Phe-114 sterically hinders interactions with DSP and AMT, but not CPZ. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc

Explicit parametrization of more than one vector-like quark of Nelson-Barr type

Nelson-Barr models solve the strong CP problem based on spontaneous CP violation and generically requires vector-like quarks (VLQs) mixing with standard quarks to transmit the CP violation. We devise an explicit parametrization for the case of two VLQs of either down-type or up-type and quantitatively study several aspects including the hierarchy of the VLQ Yukawas and their irreducible contribution to $\bar{\theta}$. In particular, with the use of the parametrization, we show that a big portion of the parameter space for two up-type VLQs at the TeV scale is still allowed by the constraint on $\bar{\theta}$, although this case had been previously shown to be very restricted based on estimates