Transverse Momentum in Semi-Inclusive Polarized Deep Inelastic Scattering and the Spin-Flavor Structure of the Proton

The non-valence spin-flavor structure of the nucleon extracted from semi-inclusive measurements of polarized deep inelastic scattering depends strongly on the transverse momentum of the detected hadrons which are used to determine the individual polarized sea distributions. This physics may explain the recent HERMES observation of a positively polarized strange sea through semi-inclusive scattering, in contrast to the negative strange sea polarization deduced from inclusive polarized deep inelastic scattering.Comment: 4 pages, revtex style, 2 figure

Towards an understanding of nucleon spin structure: from hard to soft scales

The workshop "The Helicity Structure of the Nucleon" (BNL June 5, 2006) was organized as part of the 2006 RHIC & AGS Users' Meeting to review the status of the spin problem and future directions. The presentations can be found at http://www.phenix.bnl.gov/WWW/publish/caidala/UsersHelicityWorkshop2006/ . Recent data suggests small polarized glue and strangeness in the proton. Here we present a personal summary of the main results and presentations. What is new and exciting in the data, and what might this tell us about the structure of the proton ?Comment: 20 pages, to appear in Int. J. Mod. Phys.

Spin constraints on Regge predictions and perturbative evolution in high energy collisions

Two key issues in the application of perturbative QCD and Regge predictions to high energy processes are whether the hard and soft pomerons should be considered as two separate distinct exchanges and whether the Regge intercepts are Q^2 independent or not. Models involving a distinct hard pomeron exchange predict much larger values for the LHC total cross-section. Here we argue that there is a polarized analogue of this issue in the isovector part of the spin structure function g_1 and that the spin data appear to favour a distinct hard exchange.Comment: 8 page

Baryon Fields with U_L(3) \times U_R(3) Chiral Symmetry: Axial Currents of Nucleons and Hyperons

We use the conventional F and D octet and decimet generator matrices to reformulate chiral properties of local (non-derivative) and one-derivative non-local fields of baryons consisting of three quarks with flavor SU(3) symmetry that were expressed in SU(3) tensor form in Ref. [12]. We show explicitly the chiral transformations of the [(6,3)\oplus(3,6)] chiral multiplet in the "SU(3) particle basis", for the first time to our knowledge, as well as those of the (3,\bar{3}) \oplus (\bar{3}, 3), (8,1) \oplus (1,8) multiplets, which have been recorded before in Refs. [4,5]. We derive the vector and axial-vector Noether currents, and show explicitly that their zeroth (charge-like) components close the SU_L(3) \times SU_R(3) chiral algebra. We use these results to study the effects of mixing of (three-quark) chiral multiplets on the axial current matrix elements of hyperons and nucleons. We show, in particular, that there is a strong correlation, indeed a definite relation between the flavor-singlet (i.e. the zeroth), the isovector (the third) and the eighth flavor component of the axial current, which is in decent agreement with the measured ones.Comment: one typo correction, and accepted by PR

Finite hadronization time and unitarity in quark recombination model

The effect of finite hadronization time is considered in the recombination model, and it is shown that the hadron multiplicity turns out to be proportional to the initial quark density and unitarity is conserved in the model. The baryon to meson ratio increases rapidly with the initial quark density due to competition among different channels.Comment: 4 pages in RevTeX, 3 eps figures, to appear in J. Phys.G as a lette

Marketing Percolation

A percolation model is presented, with computer simulations for illustrations, to show how the sales of a new product may penetrate the consumer market. We review the traditional approach in the marketing literature, which is based on differential or difference equations similar to the logistic equation (Bass 1969). This mean field approach is contrasted with the discrete percolation on a lattice, with simulations of "social percolation" (Solomon et al 2000) in two to five dimensions giving power laws instead of exponential growth, and strong fluctuations right at the percolation threshold.Comment: to appear in Physica

Hadronization in heavy ion collisions: Recombination and fragmentation of partons

We argue that the emission of hadrons with transverse momentum up to about 5 GeV/c in central relativistic heavy ion collisions is dominated by recombination, rather than fragmentation of partons. This mechanism provides a natural explanation for the observed constant baryon-to-meson ratio of about one and the apparent lack of a nuclear suppression of the baryon yield in this momentum range. Fragmentation becomes dominant at higher transverse momentum, but the transition point is delayed by the energy loss of fast partons in dense matter.Comment: 4 pages, 2 figures; v2: reference [8] added; v3: Eq.(2) corrected, two references added, version to appear in PR

Return times, recurrence densities and entropy for actions of some discrete amenable groups

Results of Wyner and Ziv and of Ornstein and Weiss show that if one observes the first k outputs of a finite-valued ergodic process, then the waiting time until this block appears again is almost surely asymptotic to $2^{hk}$, where $h$ is the entropy of the process. We examine this phenomenon when the allowed return times are restricted to some subset of times, and generalize the results to processes parameterized by other discrete amenable groups. We also obtain a uniform density version of the waiting time results: For a process on $s$ symbols, within a given realization, the density of the initial $k$-block within larger $n$-blocks approaches $2^{-hk}$, uniformly in $n>s^k$, as $k$ tends to infinity. Again, similar results hold for processes with other indexing groups.Comment: To appear in Journal d'Analyse Mathematiqu

Mid-Infrared Spectra of Classical AGN Observed with the Spitzer Space Telescope

Full low resolution (65<R<130) and high resolution (R~600) spectra between 5 microns and 37 microns obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope are presented for eight classical active galactic nuclei (AGN) which have been extensively studied previously. Spectra of these AGN are presented as comparison standards for the many objects, including sources at high redshift, which are being observed spectroscopically in the mid-infrared for the first time using the IRS. The AGN are NGC4151, Markarian 3, I Zwicky 1, NGC 1275, Centaurus A, NGC 7469, Markarian 231, and NGC 3079. These sources are used to demonstrate the range of infrared spectra encountered in objects which have widely different classification criteria at other wavelengths but which unquestionably contain AGN. Overall spectral characteristics - including continuum shape, nebular emission lines, silicate absorption and emission features, and PAH emission features - are considered to understand how spectral classifications based on mid-infrared spectra relate to those previously derived from optical spectra. The AGN are also compared to the same parameters for starburst galaxies such as NGC 7714 and the compact, low metallicity starburst SBS 0335-052 previously observed with the IRS. Results confirm the much lower strengths of PAH emission features in AGN, but there are no spectral parameters in this sample which unambiguously distinguish AGN and starbursts based only on the slopes of the continuous spectra.Comment: Accepted by Ap