14,908 research outputs found

    Supersymmetric Higgs Triplets and Bilinear R-Parity Nonconservation

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    The supersymmetric standard model of particle interactions is extended to include two Higgs triplet superfields at the TeV scale, carrying two units of lepton number. Realistic tree-level Majorana neutrino masses are obtained in the presence of soft, i.e. bilinear, R-parity nonconservation.Comment: 5 pages, no figur

    Neutral SU(2) Gauge Extension of the Standard Model and a Vector-Boson Dark-Matter Candidate

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    If the standard model of particle interactions is extended to include a neutral SU(2)_N gauge factor, with SU(3)_C x SU(2)_L x U(1)_Y x SU(2)_N embedded in E_6 or [SU(3)]^3, a conserved generalized R parity may appear. As a result, we have the first example of a possible dark-matter candidate X_1 which is a non-Abelain vector boson. Using current data, its mass is predicted to be less than about 1 TeV. The associated Z' of this model, as well as some signatures of the Higgs sector, should then be observable at the LHC (Large Hadron Collider).Comment: 10 pages, 1 figure; version accepted in PL

    The accretion disk in the post period-minimum cataclysmic variable SDSS J080434.20+510349.2

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    This study of SDSS0804 is primarily concerned with the double-hump shape in the light curve and its connection with the accretion disk in this bounce-back system. Time-resolved photometric and spectroscopic observations were obtained to analyze the behavior of the system between superoutbursts. A geometric model of a binary system containing a disk with two outer annuli spiral density waves was applied to explain the light curve and the Doppler tomography. Observations were carried out during 2008-2009, after the object's magnitude decreased to V~17.7(0.1) from the March 2006 eruption. The light curve clearly shows a sinusoid-like variability with a 0.07 mag amplitude and a 42.48 min periodicity, which is half of the orbital period of the system. In Sept. 2010, the system underwent yet another superoutburst and returned to its quiescent level by the beginning of 2012. This light curve once again showed a double-humps, but with a significantly smaller ~0.01mag amplitude. Other types of variability like a "mini-outburst" or SDSS1238-like features were not detected. Doppler tomograms, obtained from spectroscopic data during the same period of time, show a large accretion disk with uneven brightness, implying the presence of spiral waves. We constructed a geometric model of a bounce-back system containing two spiral density waves in the outer annuli of the disk to reproduce the observed light curves. The Doppler tomograms and the double-hump-shape light curves in quiescence can be explained by a model system containing a massive >0.7Msun white dwarf with a surface temperature of ~12000K, a late-type brown dwarf, and an accretion disk with two outer annuli spirals. According to this model, the accretion disk should be large, extending to the 2:1 resonance radius, and cool (~2500K). The inner parts of the disk should be optically thin in the continuum or totally void.Comment: 12 pages, 15 figures, accepted for publication in A&

    The Nature and Frequency of Outflows from Stars in the Central Orion Nebula Cluster

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    Recent Hubble Space Telescope images have allowed the determination with unprecedented accuracy of motions and changes of shocks within the inner Orion Nebula. These originate from collimated outflows from very young stars, some within the ionized portion of the nebula and others within the host molecular cloud. We have doubled the number of Herbig-Haro objects known within the inner Orion Nebula. We find that the best-known Herbig-Haro shocks originate from a relatively few stars, with the optically visible X-ray source COUP 666 driving many of them. While some isolated shocks are driven by single collimated outflows, many groups of shocks are the result of a single stellar source having jets oriented in multiple directions at similar times. This explains the feature that shocks aligned in opposite directions in the plane of the sky are usually blue shifted because the redshifted outflows pass into the optically thick Photon Dominated Region behind the nebula. There are two regions from which optical outflows originate for which there are no candidate sources in the SIMBAD data base.Comment: 152 pages, 46 figures, 7 tables. Accepted by A

    Microbial biofilms: biosurfactants as antibiofilm agents.

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    Current microbial inhibition strategies based on planktonic bacterial physiology have been known to have limited efficacy on the growth of biofilm communities. This problem can be exacerbated by the emergence of increasingly resistant clinical strains. All aspects of biofilm measurement, monitoring, dispersal, control, and inhibition are becoming issues of increasing importance. Biosurfactants have merited renewed interest in both clinical and hygienic sectors due to their potential to disperse microbial biofilms in addition to many other advantages. The dispersal properties of biosurfactants have been shown to rival those of conventional inhibitory agents against bacterial and yeast biofilms. This makes them suitable candidates for use in new generations of microbial dispersal agents and for use as adjuvants for existing microbial suppression or eradication strategies. In this review, we explore aspects of biofilm characteristics and examine the contribution of biologically derived surface-active agents (biosurfactants) to the disruption or inhibition of microbial biofilms

    A Renormalization Group Analysis of the Higgs Boson with Heavy Fermions and Compositeness

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    We study the properties of heavy fermions in the vector-like representation of the electro-weak gauge group SU(2)W√óU(1)YSU(2)_W\times U(1)_Y with Yukawa couplings to the standard model (SM) Higgs boson. Using the renormalization group analysis, we discuss their effects on the vacuum stability and the triviality bound on the Higgs self-coupling, within the context of the standard model (i.e., the Higgs particle is elementary). Contrary to the low energy case where the decoupling theorem dictates their behavior, the inclusion of heavy fermions drastically change the SM structure at high scale. We also discuss the interesting possibility of compositeness, i.e., the Higgs particle is composed of the heavy fermions using the method of Bardeen, Hill and Lindner~\cite{BHL91}. Finally we briefly comment on their possible role in explaining RbR_b and RcR_c.Comment: Some typographic errors are corrected and title is changed. Version to appear in Physics Letter B. 9 pages 6 Postscript figures, use epsf.st

    Pseudomonas aeruginosa biofilm disruption using microbial surfactants.

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    AIMS: To establish the ability of the rhamnolipids biosurfactants from Pseudomonas aeruginosa, in the presence and absence of caprylic acid and ascorbic acid, to disrupt bacterial biofilms, compared with the anionic alkyl sulphate surfactant Sodium dodecyl sulphate (SDS). METHODS AND RESULTS: Pseudomonas aeruginosa ATCC 15442 biofilms were disrupted by rhamnolipids at concentrations between 0·5 and 0·4 g l(-1) and with SDS at 0·8 g l(-1) . The combination of rhamnolipids 0·4 g l(-1) and caprylic acid at 0·1 g l(-1) showed a remarkable effect on biofilm disruption and cell killing. After 30 min of treatment most of the biofilm was disrupted and cell viability was significantly reduced. Neither caprylic acid nor ascorbic acid has any effect on biofilm disruption at 0·1 g l(-1) . SDS is an effective antimicrobial agent; however, in the presence of caprylic acid its effect was neutralized. CONCLUSIONS: The results show that rhamnolipids at low concentration in the presence of caprylic acid are promising molecules for inhibition/disruption of biofilms formed by Ps. aeruginosa ATCC 15442. SIGNIFICANCE AND IMPACT OF THE STUDY: The disruption of biofilms has major significance in many industrial and domestic cleaning applications and in medical situations
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