1,636 research outputs found

    Correlated Emission of Hadrons from Recombination of Correlated Partons

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    We discuss different sources of hadron correlations in relativistic heavy ion collisions. We show that correlations among partons in a quasi-thermal medium can lead to the correlated emission of hadrons by quark recombination and argue that this mechanism offers a plausible explanation for the dihadron correlations in the few GeV/c momentum range observed in Au+Au collisions at RHIC.Comment: 4 pages, 2 figures; v2: typo on p.4 correcte

    A model of semimetallic behavior in strongly correlated electron systems

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    Metals with values of the resistivity and the Hall coefficient much larger than typical ones, e.g., of sodium, are called semimetals. We suggest a model for semimetals which takes into account the strong Coulomb repulsion of the charge carriers, especially important in transition-metal and rare-earth compounds. For that purpose we extend the Hubbard model by coupling one additional orbital per site via hybridization to the Hubbard orbitals. We calculate the spectral function, resistivity and Hall coefficient of the model using dynamical mean-field theory. Starting from the Mott-insulating state, we find a transition to a metal with increasing hybridization strength (``self-doping''). In the metallic regime near the transition line to the insulator the model shows semimetallic behavior. We compare the calculated temperature dependence of the resistivity and the Hall coefficient with the one found experimentally for Yb4As3\rm Yb_4As_3. The comparison demonstrates that the anomalies in the transport properties of Yb4As3\rm Yb_4As_3 possibly can be assigned to Coulomb interaction effects of the charge carriers not captured by standard band structure calculations.Comment: 9 pages RevTeX with 7 ps figures, accepted by PR

    Photonic analog of graphene model and its extension -- Dirac cone, symmetry, and edge states --

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    This paper presents a theoretical analysis on bulk and edge states in honeycomb lattice photonic crystals with and without time-reversal and/or space-inversion symmetries. Multiple Dirac cones are found in the photonic band structure and the mass gaps are controllable via symmetry breaking. The zigzag and armchair edges of the photonic crystals can support novel edge states that reflect the symmetries of the photonic crystals. The dispersion relation and the field configuration of the edge states are analyzed in detail in comparison to electronic edge states. Leakage of the edge states to free space is inherent in photonic systems and is fully taken into account in the analysis. A topological relation between bulk and edge, which is analogous to that found in quantum Hall systems, is also verified.Comment: 9 pages, 7 figure

    Cronin Effect in Hadron Production off Nuclei

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    Recent data from RHIC for high-pTp_T hadrons in gold-gold collisions raised again the long standing problem of quantitatively understanding the Cronin effect, i.e. nuclear enhancement of high-pTp_T hadrons due to multiple interactions in nuclear matter. In nucleus-nucleus collisions this effect has to be reliably calculated as baseline for a signal of new physics in high-pTp_T hadron production. The only possibility to test models is to compare with available data for pApA collisions, however, all existing models for the Cronin effect rely on a fit to the data to be explained. We develop a phenomenological description based on the light-cone QCD-dipole approach which allows to explain available data without fitting to them and to provide predictions for pApA collisions at RHIC and LHC. We point out that the mechanism causing Cronin effect drastically changes between the energies of fixed target experiments and RHIC-LHC. High-pTp_T hadrons are produced incoherently on different nucleons at low energies, whereas the production amplitudes interfere if the energy is sufficiently high.Comment: the final version to appear in Phys. Rev. Let

    Stability of the compressible quantum Hall state around the half-filled Landau level

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    We study the compressible states in the quantum Hall system using a mean field theory on the von Neumann lattice. In the lowest Landau level, a kinetic energy is generated dynamically from Coulomb interaction. The compressibility of the state is calculated as a function of the filling factor ν\nu and the width dd of the spacer between the charge carrier layer and dopants. The compressibility becomes negative below a critical value of dd and the state becomes unstable at ν=1/2\nu=1/2. Within a finite range around ν=1/2\nu=1/2, the stable compressible state exists above the critical value of dd.Comment: 4 pages, 4 Postscript figures, RevTe

    Phenomenology of a light scalar: the dilaton

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    We make use of the language of non-linear realizations to analyze electro-weak symmetry breaking scenarios in which a light dilaton emerges from the breaking of a nearly conformal strong dynamics, and compare the phenomenology of the dilaton to that of the well motivated light composite Higgs scenario. We argue that -- in addition to departures in the decay/production rates into massless gauge bosons mediated by the conformal anomaly -- characterizing features of the light dilaton scenario (as well as other scenarios admitting a light CP-even scalar not directly related to the breaking of the electro-weak symmetry) are off-shell events at high invariant mass involving two longitudinally polarized vector bosons and a dilaton, and tree-level flavor violating processes. Accommodating both electro-weak precision measurements and flavor constraints appears especially challenging in the ambiguous scenario in which the Higgs and the dilaton fields strongly mix. We show that warped higgsless models of electro-weak symmetry breaking are explicit and tractable realizations of this limiting case. The relation between the naive radion profile often adopted in the study of holographic realizations of the light dilaton scenario and the actual dynamical dilaton field is clarified in the Appendix.Comment: 21 page

    Modular symbols in Iwasawa theory

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    This survey paper is focused on a connection between the geometry of GLd\mathrm{GL}_d and the arithmetic of GLd1\mathrm{GL}_{d-1} over global fields, for integers d2d \ge 2. For d=2d = 2 over Q\mathbb{Q}, there is an explicit conjecture of the third author relating the geometry of modular curves and the arithmetic of cyclotomic fields, and it is proven in many instances by the work of the first two authors. The paper is divided into three parts: in the first, we explain the conjecture of the third author and the main result of the first two authors on it. In the second, we explain an analogous conjecture and result for d=2d = 2 over Fq(t)\mathbb{F}_q(t). In the third, we pose questions for general dd over the rationals, imaginary quadratic fields, and global function fields.Comment: 43 page

    Reentrant charge ordering caused by polaron formation

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    Based on a two-dimensional extended Hubbard model with electron-phonon interaction, we have studied the effect of polaron formation on the charge ordering (CO) transition. It is found that for fully ferromagnetically ordered spins the CO state may go through a process of appearance, collapse and reappearance with decreasing temperature. This is entirely due to a emperature-dependent polaron bandwidth. On the other hand, when a paramagnetic spin state is considered, only a simple reentrant behavior of the CO transition is found, which is only partly due to polaron effect. This model is proposed as an explanation of the observed reentrant behavior of the CO transition in the layered manganite LaSr2_2Mn2_2O7_7.Comment: 4 pages, 2 eps figures, revised version accepted by Phys. Rev. Let

    cDNA microarray analysis of bovine embryo gene expression profiles during the pre-implantation period

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    BACKGROUND: After fertilization, embryo development involves differentiation, as well as development of the fetal body and extra-embryonic tissues until the moment of implantation. During this period various cellular and molecular changes take place with a genetic origin, e.g. the elongation of embryonic tissues, cell-cell contact between the mother and the embryo and placentation. To identify genetic profiles and search for new candidate molecules involved during this period, embryonic gene expression was analyzed with a custom designed utero-placental complementary DNA (cDNA) microarray. METHODS: Bovine embryos on days 7, 14 and 21, extra-embryonic membranes on day 28 and fetuses on days 28 were collected to represent early embryo, elongating embryo, pre-implantation embryo, post-implantation extra-embryonic membrane and fetus, respectively. Gene expression at these different time points was analyzed using our cDNA microarray. Two clustering algorithms such as k-means and hierarchical clustering methods identified the expression patterns of differentially expressed genes across pre-implantation period. Novel candidate genes were confirmed by real-time RT-PCR. RESULTS: In total, 1,773 individual genes were analyzed by complete k-means clustering. Comparison of day 7 and day 14 revealed most genes increased during this period, and a small number of genes exhibiting altered expression decreased as gestation progressed. Clustering analysis demonstrated that trophoblast-cell-specific molecules such as placental lactogens (PLs), prolactin-related proteins (PRPs), interferon-tau, and adhesion molecules apparently all play pivotal roles in the preparation needed for implantation, since their expression was remarkably enhanced during the pre-implantation period. The hierarchical clustering analysis and RT-PCR data revealed new functional roles for certain known genes (dickkopf-1, NPM, etc) as well as novel candidate genes (AW464053, AW465434, AW462349, AW485575) related to already established trophoblast-specific genes such as PLs and PRPs. CONCLUSIONS: A large number of genes in extra-embryonic membrane increased up to implantation and these profiles provide information fundamental to an understanding of extra-embryonic membrane differentiation and development. Genes in significant expression suggest novel molecules in trophoblast differentiation
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