Diffusion and the BFKL Pomeron

We study the high energy behaviour of elastic scattering amplitudes within the leading logarithm approximation. In particular, we cast the amplitude in a form which allows us to study the internal dynamics of the BFKL Pomeron for general momentum transfer. We demonstrate that the momentum transfer acts as an effective infrared cut-off which ensures that the dominant contribution arises from short distance physics.Comment: 15 pages (LaTeX), 8 postscript figure

Constraints on gluon evolution at small x

The BFKL and the unified angular-ordered equations are solved to determine the gluon distribution at small $x$. The impact of kinematic constraints is investigated. Predictions are made for observables sensitive to the gluon at small $x$. In particular comparison is made with measurements at the HERA electron-proton collider of the proton structure function $F_2 (x, Q^2)$ as a function of $\ln Q^2$, the charm component, $F_2^c(x,Q^2)$ and diffractive $J/\psi$ photoproduction.Comment: 17 LaTeX pages and 9 postscript figure

QCD Predictions for the Transverse Energy Flow in Deep-Inelastic Scattering in the Small x HERA Regime

The distribution of transverse energy, $E_T$, which accompanies deep-inelastic electron-proton scattering at small $x$, is predicted in the central region away from the current jet and proton remnants. We use BFKL dynamics, which arises from the summation of multiple gluon emissions at small $x$, to derive an analytic expression for the $E_T$ flow. One interesting feature is an $x^{-\epsilon}$ increase of the $E_T$ distribution with decreasing $x$, where $\epsilon = (3\alpha_s/\pi)2\log 2$. We perform a numerical study to examine the possibility of using characteristics of the $E_T$ distribution as a means of identifying BFKL dynamics at HERA.Comment: 16 pages, REVTEX 3.0, no figures. (Hardcopies of figures available on request from Professor A.D. Martin, Department of Physics, University of Durham, DH1 3LE, England.) Durham preprint : DTP/94/0

Low Q2Q^2 wave-functions of pions and kaons and their parton distribution functions

We study the low $Q^2$ wave-functions of pions and kaons as an expansion in terms of hadron-like Fock state fluctuations. In this formalism, pion and kaon wave-functions are related one another. Consequently, the knowledge of the pion structure allows the determination of parton distributions in kaons. In addition, we show that the intrinsic (low $Q^2$) sea of pions and kaons are different due to their different valence quark structure. Finally, we analize the feasibility of a method to extract kaon's parton distribution functions within this approach and compare with available experimental data.Comment: 13 pages, 3 postscript figures include

Multiple Overlapping Tiles for Contextual Monte Carlo Tree Search

International audienceMonte Carlo Tree Search is a recent algorithm that achieves more and more successes in various domains. We propose an improvement of the Monte Carlo part of the algorithm by modifying the simulations depending on the context. The modification is based on a reward function learned on a tiling of the space of Monte Carlo simulations. The tiling is done by regrouping the Monte Carlo simulations where two moves have been selected by one player. We show that it is very efficient by experimenting on the game of Havannah

Properties of the BFKL equation and structure function predictions for HERA

The general properties of the Lipatov or BFKL equation are reviewed. Modifications to the infrared region are proposed. Numerical predictions for the deep-inelastic electron-proton structure functions at small $x$ are presented and confronted with recent HERA measurements.Comment: 21 pages, 11 figures, Latex file, Durham preprint DTP 92/2

Master Equation Study of Hydrogen Relaxation Using Complete Sets of State-to-state Transition Rates

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97096/1/AIAA2012-362.pd

Clinical delineation and natural history of the PIK3CA-related overgrowth spectrum.

Somatic mutations in the phosphatidylinositol/AKT/mTOR pathway cause segmental overgrowth disorders. Diagnostic descriptors associated with PIK3CA mutations include fibroadipose overgrowth (FAO), Hemihyperplasia multiple Lipomatosis (HHML), Congenital Lipomatous Overgrowth, Vascular malformations, Epidermal nevi, Scoliosis/skeletal and spinal (CLOVES) syndrome, macrodactyly, and the megalencephaly syndrome, Megalencephaly-Capillary malformation (MCAP) syndrome. We set out to refine the understanding of the clinical spectrum and natural history of these phenotypes, and now describe 35 patients with segmental overgrowth and somatic PIK3CA mutations. The phenotypic data show that these previously described disease entities have considerable overlap, and represent a spectrum. While this spectrum overlaps with Proteus syndrome (sporadic, mosaic, and progressive) it can be distinguished by the absence of cerebriform connective tissue nevi and a distinct natural history. Vascular malformations were found in 15/35 (43%) and epidermal nevi in 4/35 (11%) patients, lower than in Proteus syndrome. Unlike Proteus syndrome, 31/35 (89%) patients with PIK3CA mutations had congenital overgrowth, and in 35/35 patients this was asymmetric and disproportionate. Overgrowth was mild with little postnatal progression in most, while in others it was severe and progressive requiring multiple surgeries. Novel findings include: adipose dysregulation present in all patients, unilateral overgrowth that is predominantly left-sided, overgrowth that affects the lower extremities more than the upper extremities and progresses in a distal to proximal pattern, and in the most severely affected patients is associated with marked paucity of adipose tissue in unaffected areas. While the current data are consistent with some genotype-phenotype correlation, this cannot yet be confirmed

New Insights into White-Light Flare Emission from Radiative-Hydrodynamic Modeling of a Chromospheric Condensation

(abridged) The heating mechanism at high densities during M dwarf flares is poorly understood. Spectra of M dwarf flares in the optical and near-ultraviolet wavelength regimes have revealed three continuum components during the impulsive phase: 1) an energetically dominant blackbody component with a color temperature of T $\sim$ 10,000 K in the blue-optical, 2) a smaller amount of Balmer continuum emission in the near-ultraviolet at lambda $<$ 3646 Angstroms and 3) an apparent pseudo-continuum of blended high-order Balmer lines. These properties are not reproduced by models that employ a typical "solar-type" flare heating level in nonthermal electrons, and therefore our understanding of these spectra is limited to a phenomenological interpretation. We present a new 1D radiative-hydrodynamic model of an M dwarf flare from precipitating nonthermal electrons with a large energy flux of $10^{13}$ erg cm$^{-2}$ s$^{-1}$. The simulation produces bright continuum emission from a dense, hot chromospheric condensation. For the first time, the observed color temperature and Balmer jump ratio are produced self-consistently in a radiative-hydrodynamic flare model. We find that a T $\sim$ 10,000 K blackbody-like continuum component and a small Balmer jump ratio result from optically thick Balmer and Paschen recombination radiation, and thus the properties of the flux spectrum are caused by blue light escaping over a larger physical depth range compared to red and near-ultraviolet light. To model the near-ultraviolet pseudo-continuum previously attributed to overlapping Balmer lines, we include the extra Balmer continuum opacity from Landau-Zener transitions that result from merged, high order energy levels of hydrogen in a dense, partially ionized atmosphere. This reveals a new diagnostic of ambient charge density in the densest regions of the atmosphere that are heated during dMe and solar flares.Comment: 50 pages, 2 tables, 13 figures. Accepted for publication in the Solar Physics Topical Issue, "Solar and Stellar Flares". Version 2 (June 22, 2015): updated to include comments by Guest Editor. The final publication is available at Springer via http://dx.doi.org/10.1007/s11207-015-0708-

Search for lepton-flavor violation at HERA

A search for lepton-flavor-violating interactions $e p \to \mu X$ and $e p\to \tau X$ has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity of 130 pb^{-1}. The data were taken at center-of-mass energies, $\sqrt{s}$, of 300 and 318 GeV. No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below $\sqrt{s}$, limits were set on $\lambda_{eq_1} \sqrt{\beta_{\ell q}}$, where $\lambda_{eq_1}$ is the coupling of the LQ to an electron and a first-generation quark $q_1$, and $\beta_{\ell q}$ is the branching ratio of the LQ to the final-state lepton $\ell$ ($\mu$ or $\tau$) and a quark $q$. For LQ masses much larger than $\sqrt{s}$, limits were set on the four-fermion interaction term $\lambda_{e q_\alpha} \lambda_{\ell q_\beta} / M_{\mathrm{LQ}}^2$ for LQs that couple to an electron and a quark $q_\alpha$ and to a lepton $\ell$ and a quark $q_\beta$, where $\alpha$ and $\beta$ are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in $R$-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the process $e p\to \tau X$, the ZEUS limits are the most stringent to date.Comment: 37 pages, 10 figures, Accepted by EPJC. References and 1 figure (Fig. 6) adde