Rare top decay t-> c l+l- as a probe of new physics

The rare top decay t-> c l+l-, which involves flavor violation, is studied as a possible probe of new physics. This decay is analyzed with the simplest Standard Model extensions with additional gauge symmetry formalism. The considered extension is the Left-Right Symmetric Model, including a new neutral gauge boson Z' that allows to obtain the decay at tree level through Flavor Changing Neutral Currents (FCNC) couplings. The neutral gauge boson couplings are considered diagonal but family non-universal in order to induce these FCNC. We find the $BR(t-> c l+l-)~10^{-13} for a range 1 TeV < M_{Z'} < 3 TeV.Comment: 9 pages, 6 figure

The Generational Seesaw Mechanism in [SU(6)]3×^{3}\timesZ3_{3}}

In the context of the left-right symmetric gauge group [SU(6)]$^3\times$ Z$_3$ which unifies nongravitational forces with flavors, we analyze the generational seesaw mechanism. At tree level we get m$_{\nu_\tau}\sim$m$_{\nu_\mu}\sim$M$^2_L$/M$_H$, m$_{\nu_e}=0$, where M$_L\sim10^2$ GeVs and M$_H\ge 100$ TeVs is the mass scale at which the horizontal interactions get spontaneously broken. The right handed neutrinos get a Majorana mass M$_R\gg$M$_H$ of the order of the scale where SU(2)$_R$ is broken. An exotic neutral lepton with a mass of the order of M$^2_H$/M$_R$ is predicted. First order radiative corrections will produce m$_{\nu_e}\neq0$ which is at least two orders of magnitude smaller than the other two neutrino masses

On the dust environment of comet C/2012 S1 (ISON) from 12 AU pre-perihelion to the end of its activity around perihelion

A Monte Carlo dust tail model has been applied to extract the dust environment parameters of the comet C/2012 S1 (ISON) from both Earth-based and SOHO LASCO C3 observations, performed from about six astronomical units (AU) inbound, to just after perihelion passage, when only a small portion of the original comet nucleus has survived in the form of a cloud of tiny particles. The early Afρ and image data are consistent with particle ejection from an extended active area located at latitudes 35°N to 90°N (for a prograde rotating nucleus), with the spin axis having a large obliquity (I 70°). This configuration nicely fits the early images and Afρ data until 3.9 AU inbound, when the emission should become isotropic in order to fit the data. The analysis of LASCO images reveals that, assuming an original nucleus of R N = 500 m with ρ = 1000 kg m-3, at least half of its mass was vaporized when the comet was at about 17 R ⊙ inbound. We conclude that at that time the nucleus suffered a cataclysmic fragmentation releasing a huge amount of material of 2.3 ×1011 kg, equivalent to a sphere of 380 m in radius with density 1000 kg m-3. The surviving material after perihelion passage consists of very small dust particles of 0.1-50 μm in radius with a total mass of just 6.7×10 8 kg. © 2014. The American Astronomical Society. All rights reserved

Measurement of the Mass of the Z-Boson and the Energy Calibration of Lep

Contains fulltext : 26847___.PDF (publisher's version ) (Open Access

Electroweak parameters of the z0 resonance and the standard model

Contains fulltext : 124399.pdf (publisher's version ) (Open Access

The Magpie Trial: A randomised trial comparing magnesium sulphate with placebo for pre-eclampsia. Outcome for children at 18 months

Objective: To assess the long-term effects of in utero exposure to magnesium sulphate for children whose mothers had pre-eclampsia. Design: Assessment at 18 months of age for children whose mothers were recruited to the Magpie Trial (recruitment 1998-2001 ISRCTN 86938761), which compared magnesium sulphate with placebo. Setting: Follow-up of children born at 125 centres in 19 countries across five continents. Population: A total of 6922 children were born to women randomised before delivery at follow-up centres. Of these, 2271 were not included for logistic reasons and 168 were excluded (101 at a centre where <20% were contacted, 40 whose death or disability was due to a problem at conception or embryogenesis and 27 whose parent/s opted out). Therefore, 4483 children were included in follow-up, of whom 3283 (73%) were contacted. Methods: Assessment by questionnaire, with interview and neurodevelopmental testing of selected children. Main outcome measures: Death or neurosensory disability at age of 18 months. Results: Of those allocated magnesium sulphate, 245/1635 (15.0%) were dead or had neurosensory disability at 18 months compared with 233/1648 (14.1%) allocated placebo (relative risk [RR] 1.06, 95% CI 0.90-1.25), and of survivors, 19/1409 (1.3%) had neurosensory disability at 18 months compared with 27/1442 (1.9%) (RR 0.72, 95% CI 0.40-1.29). There were no substantial differences in causes of death or in the risk of individual impairments or disabilities. Conclusions: The lower risk of eclampsia following prophylaxis with magnesium sulphate was not associated with a clear difference in the risk of death or disability for children at 18 months. © RCOG 2006 BJOG An International Journal of Obstetrics and Gynaecology.Articl