Light colored scalars from grand unification and the forward-backward asymmetry in top quark pair production

The experimental results on the t bar t production cross section at the Tevatron are well described by the QCD contributions within the standard model, while the recent measurement of the forward-backward asymmetry cannot be accounted for within this framework. We consider light colored scalars appearing in a particular SU(5) GUT model within the 45-dimensional Higgs representation. A virtue of the model is that it connects the presence of a light colored SU(2) singlet (Delta_6) and a color octet weak doublet (Delta_1) with bounds on the proton lifetime, which constrain the parameter space of both scalars. We find that both the t bar t production cross section and the forward-backward asymmetry can be accommodated simultaneously within this model. The experimental results prefer a region for the mass of Delta_6 around 400 GeV, while Delta_1 is then constrained to have a mass around the TeV scale as well. We analyze possible experimental signatures and find that Delta_6 associated top production could be probed in the t bar t + jets final states at Tevatron and the LHC.Comment: 12 pages, 13 figures, version as publishe

Light Colored Scalar as Messenger of Up-Quark Flavor Dynamics in Grand Unified Theories

The measured forward-backward asymmetry in the t tbar production at the Tevatron might be explained by the additional exchange of a colored weak singlet scalar. Such state appears in some of the grand unified theories and its interactions with the up-quarks are purely antisymmetric in flavor space. We systematically investigate the resulting impact on charm and top quark physics. The constraints on the relevant Yukawa couplings come from the experimentally measured observables related to D0--D0bar oscillations, as well as di-jet and single top production measurements at the Tevatron. After fully constraining the relevant Yukawa couplings, we predict possible signatures of this model in rare top quark decays. In a class of grand unified models we demonstrate how the obtained information enables to constrain the Yukawa couplings of the up-quarks at very high energy scale.Comment: 13 pages, 11 figures, version as published in PR

On the alignment of velocity and magnetic fields within magnetosheath jets

Jets in the subsolar magnetosheath are localized enhancements in dynamic pressure that are able to propagate all the way from the bow shock to the magnetopause. Due to their excess velocity with respect to their environment, they push slower ambient plasma out of their way, creating a vortical plasma motion in and around them. Simulations and case study results suggest that jets also modify the magnetic field in the magnetosheath on their passage, aligning it more with their velocity. Based on Magnetospheric Multi-scale (MMS) jet observations and corresponding superposed epoch analyses of the angles phi between the velocity and magnetic fields, we can confirm that this suggestion is correct. However, while the alignment is more significant for faster than for slower jets, and for jets observed close to the bow shock, the overall effect is small: typically, reductions in phi of around 10 degrees are observed at jet core regions, where the jets' velocities are largest. Furthermore, time series of phi pertaining to individual jets significantly deviate from the superposed epoch analysis results. They usually exhibit large variations over the entire range of phi: 0 to 90 degrees. This variability is commonly somewhat larger within jets than outside them, masking the systematic decrease in phi at core regions of individual jets

Motor Unit-Driven Identification of Pathological Tremor in Electroencephalograms.

Background: Traditional studies on the neural mechanisms of tremor use coherence analysis to investigate the relationship between cortical and muscle activity, measured by electroencephalograms (EEG) and electromyograms (EMG). This methodology is limited by the need of relatively long signal recordings, and it is sensitive to EEG artifacts. Here, we analytically derive and experimentally validate a new method for automatic extraction of the tremor-related EEG component in pathological tremor patients that aims to overcome these limitations. Methods: We exploit the coupling between the tremor-related cortical activity andmotor unit population firings to build a linearminimummean square error estimator of the tremor component in EEG. We estimated the motor unit population activity by decomposing surface EMG signals into constituent motor unit spike trains, which we summed up into a cumulative spike train (CST). We used this CST to initialize our tremor-related EEG component estimate, which we optimized using a novel approach proposed here. Results: Tests on simulated signals demonstrate that our new method is robust to both noise and motor unit firing variability, and that it performs well across a wide range of spectral characteristics of the tremor. Results on 9 essential (ET) and 9 Parkinson’s disease (PD) patients show a ∼2-fold increase in amplitude of the coherence between the estimated EEG component and the CST, compared to the classical EEG-EMG coherence analysis. Conclusions: We have developed a novel method that allows for more precise and robust estimation of the tremor-related EEG component. This method does not require artifact removal, provides reliable results in relatively short datasets, and tracks changes in the tremor-related cortical activity over time.post-print2672 K

An ERK1/2-driven RNA-binding switch in nucleolin drives ribosome biogenesis and pancreatic tumorigenesis downstream of RAS oncogene

Oncogenic RAS signaling reprograms gene expression through both transcriptional and post-transcriptional mechanisms. While transcriptional regulation downstream of RAS is relatively well characterized, how RAS post-transcriptionally modulates gene expression to promote malignancy remains largely unclear. Using quantitative RNA interactome capture analysis, we here reveal that oncogenic RAS signaling reshapes the RNA-bound proteomic landscape of pancreatic cancer cells, with a network of nuclear proteins centered around nucleolin displaying enhanced RNA-binding activity. We show that nucleolin is phosphorylated downstream of RAS, which increases its binding to pre-ribosomal RNA (rRNA), boosts rRNA production, and promotes ribosome biogenesis. This nucleolin-dependent enhancement of ribosome biogenesis is crucial for RAS-induced pancreatic cancer cell proliferation and can be targeted therapeutically to inhibit tumor growth. Our results reveal that oncogenic RAS signaling drives ribosome biogenesis by regulating the RNA-binding activity of nucleolin and highlight a crucial role for this mechanism in RAS-mediated tumorigenesis