Eccentricity fluctuations from the Color Glass Condensate at RHIC and LHC

In this brief note, we determine the fluctuations of the initial eccentricity in heavy-ion collisions caused by fluctuations of the nucleon configurations. This is done via a Monte-Carlo implementation of a Color Glass Condensate $k_t$-factorization approach. The eccentricity fluctuations are found to nearly saturate elliptic flow fluctuations measured recently at RHIC. Extrapolations to LHC energies are shown.Comment: 2 pages, 2 figure

Forward particle productions at RHIC and the LHC from CGC within local rcBK evolution

In order to describe forward hadron productions in high-energy nuclear collisions, we propose a Monte-Carlo implementation of Dumitru-Hayashigaki-Jalilian-Marian formula with the unintegrated gluon distribution obtained numerically from the running-coupling BK equation. We discuss influence of initial conditions for the BK equation by comparing a model constrained by global fit of small-x HERA data and a newly proposed one from the running coupling MV model.Comment: Talk given at conference Quark Matter 2011, 4 page

Exchange between deep donors in semiconductors: a quantum defect approach

Exchange interactions among defects in semiconductors are commonly treated within effective-mass theory using a scaled hydrogenic wave-function. However such a wave-function is only applicable to shallow impurities; here we present a simple but robust generalization to treat deep donors, in which we treat the long-range part of the wavefunction using the well established quantum defect theory, and include a model central-cell correction to fix the bound-state eigenvalue at the experimentally observed value. This allows us to compute the effect of binding energy on exchange interactions as a function of donor distance; this is a significant quantity given recent proposals to carry out quantum information processing using deep donors. As expected, exchange interactions are suppressed (or increased), compared to the hydrogenic case, by the greater localization (or delocalization) of the wavefunctions of deep donors (or `super-shallow' donors with binding energy less then the hydrogenic value). The calculated results are compared with a simple scaling of the Heitler-London hydrogenic exchange; the scaled hydrogenic results give the correct order of magnitude but fail to reproduce quantitatively our calculations. We calculate the donor exchange in silicon including inter-valley interference terms for donor pairs along the $\{100\}$ direction, and also show the influence of the donor type on the distribution of nearest-neighbour exchange constants at different concentrations. Our methods can be used to compute the exchange interactions between two donor electrons with arbitrary binding energy.Comment: 11 pages, 10 figures, RevTeX

Search for a Ridge Structure Origin with Shower Broadening and Jet Quenching

We investigate the role of jet and shower parton broadening by the strong colour field in the $\Delta\eta$-$\Delta\phi$ correlation of high $p_T$ particles. When anisotropic momentum broadening ($\Delta p_z > \Delta p_T$) is given to jet and shower partons in the initial stage, a ridge-like structure is found to appear in the two hadron correlation. The ratio of the peak to the pedestal yield is overestimated.Comment: Talk given at 20th Int. Conf. on Ultra-Relativistic Nucleus-Nucleus Collisions, Jaipur, India, Feb.4-10, 200

QGP collective effects and jet transport

We present numerical simulations of the SU(2) Boltzmann-Vlasov equation including both hard elastic particle collisions and soft interactions mediated by classical Yang-Mills fields. We provide an estimate of the coupling of jets to a hot isotropic plasma, which is independent of infrared cutoffs. In addition, we investigate jet propagation in anisotropic plasmas, as created in heavy-ion collisions. The broadening of jets is found to be stronger along the beam line than in azimuth due to the creation of field configurations with B_t>E_t and E_z>B_z via plasma instabilities.Comment: 4 pages, 5 figures. Presented at the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, 4-10 Feb 200

Pumilio binds para mRNA and requires nanos and brat to regulate sodium current in drosophila motoneurons

Homeostatic regulation of ionic currents is of paramount importance during periods of synaptic growth or remodeling. Our previous work has identified the translational repressor Pumilio (Pum) as a regulator of sodium current (INa) and excitability in Drosophila motoneurons. In this current study, we show that Pum is able to bind directly the mRNA encoding the Drosophila voltage-gated sodium channel paralytic (para). We identify a putative binding site for Pum in the 3' end of the para open reading frame (ORF). Characterization of the mechanism of action of Pum, using whole-cell patch clamp and real-time reverse transcription-PCR, reveals that the full-length protein is required for translational repression of para mRNA. Additionally, the cofactor Nanos is essential for Pum-dependent para repression, whereas the requirement for Brain Tumor (Brat) is cell type specific. Thus, Pum-dependent regulation of INa in motoneurons requires both Nanos and Brat, whereas regulation in other neuronal types seemingly requires only Nanos but not Brat. We also show that Pum is able to reduce the level of nanos mRNA and as such identify a potential negative-feedback mechanism to protect neurons from overactivity of Pum. Finally, we show coupling between INa (para) and IK (Shal) such that Pum-mediated change in para results in a compensatory change in Shal. The identification of para as a direct target of Pum represents the first ion channel to be translationally regulated by this repressor and the location of the binding motif is the first example in an ORF rather than in the canonical 3'-untranslated region of target transcripts

Pseudorapidity dependence of parton energy loss in relativistic heavy ion collisions

We analyze the recent data from the BRAHMS Collaboration on the pseudorapidity dependence of nuclear modification factors in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV by using the full three dimensional hydrodynamic simulations for the density effects on parton energy loss. We first compute the transverse spectra at $\eta=0$ and 2.2, and next take a ratio $R_{\eta}=R_{AA}(\eta=2.2)/R_{AA}(\eta=0)$, where $R_{AA}$ is a nuclear modification factor. It is shown that hydrodynamic components account for $R_{\eta}\simeq 1$ at low $p_\mathrm{T}$ and that quenched pQCD components lead $R_{\eta} < 1$ at high $p_\mathrm{T}$ which are consistent with the data. Strong suppression at $\eta=2.2$ is compatible with the parton energy loss in the final state.Comment: 5 pages, 4 figures; one figure adde