Study of interacting electrons in graphene under the renormalized-ring-diagram approximation

Using the tight-binding model with long-range Coulomb interactions between electrons, we study some of the electronic properties of graphene. The Coulomb interactions are treated with the renormalized-ring-diagram approximation. By self-consistently solving the integral equations for the Green function, we calculate the spectral density. The obtained result is in agreement with experimental observation. In addition, we also compute the density of states, the distribution functions, and the ground-state energy. Within the present approximation, we find that the imaginary part of the self-energy fixed at the Fermi momentum varies as quadratic in energy close to the chemical potential, regardless the system is doped or not. This result appears to indicate that the electrons in graphene always behave like a moderately correlated Fermi liquid.Comment: 11 pages, 13 figure

Transverse momentum broadening of vector boson production in high energy nuclear collisions

We calculate in perturbative QCD the transverse momentum broadening of vector boson production in high energy nuclear collisions. We evaluate the effect of initial-state parton multiple scattering for the production of the Drell-Yan virtual photon and $W/Z$ bosons. We calculate both the initial- and final-state multiple scattering effect for the production of heavy quarkonia and their transverse momentum broadening in both NRQCD and Color Evaporation model of quarkonium formation. We find that J/$\psi$ and $\Upsilon$ broadening in hadron-nucleus collision is close to $2C_A/C_F$ times the corresponding Drell-Yan broadening, which gives a good description of existing Fermilab data. Our calculations are also consistent with RHIC data on J/$\psi$ broadening in relativistic heavy ion collisions. We predict the transverse momentum broadening of vector boson (J/$\psi$, $\Upsilon$, and $W/Z$) production in relativistic heavy ion collisions at the LHC, and discuss the role of the vector boson broadening in diagnosing medium properties.Comment: 22 pages, 10 figures, revised version to appear in Phys. Rev.

Test of the Universality of Naive-time-reversal-odd Fragmentation Functions

We investigate the ''spontaneous'' hyperon transverse polarization in $e^+e^-$ annihilation and semi-inclusive deep inelastic scattering processes as a test of the universality of the naive-time-reversal-odd transverse momentum dependent fragmentation functions. We find that universality implies definite sign relations among various observables. This provides a unique opportunity to study initial/final state interaction effects in the fragmentation process and test the associated factorization.Comment: 4 pages, 3 figure

Beam energy dependence of Hanbury-Brown-Twiss radii from a blast-wave model

The beam energy dependence of correlation lengths (the Hanbury-Brown-Twiss radii) is calculated by using a blast-wave model and the results are comparable with those from RHIC-STAR beam energy scan data as well as the LHC-ALICE measurements. A set of parameter for the blast-wave model as a function of beam energy under study are obtained by fit to the HBT radii at each energy point. The transverse momentum dependence of HBT radii is presented with the extracted parameters for Au + Au collision at $\sqrt{s_{NN}} =$ 200 GeV and for Pb+Pb collisions at 2.76 TeV. From our study one can learn that particle emission duration can not be ignored while calculating the HBT radii with the same parameters. And tuning kinetic freeze-out temperature in a range will result in system lifetime changing in the reverse direction as it is found in RHIC-STAR experiment measurements.Comment: 9 pages, 9 figure

Quark fragmentation in the θ\theta-vacuum

The vacuum of Quantum Chromodynamics is a superposition of degenerate states with different topological numbers that are connected by tunneling (the $\theta$-vacuum). The tunneling events are due to topologically non-trivial configurations of gauge fields (e.g. the instantons) that induce local \p-odd domains in Minkowski space-time. We study the quark fragmentation in this topologically non-trivial QCD background. We find that even though QCD globally conserves \p and \cp symmetries, two new kinds of \p-odd fragmentation functions emerge. They generate interesting dihadron correlations: one is the azimuthal angle correlation $\sim \cos(\phi_1 + \phi_2)$ usually referred to as the Collins effect, and the other is the \p-odd correlation $\sim \sin(\phi_1 + \phi_2)$ that vanishes in the cross section summed over many events, but survives on the event-by-event basis. Using the chiral quark model we estimate the magnitude of these new fragmentation functions. We study their experimental manifestations in dihadron production in $e^+e^-$ collisions, and comment on the applicability of our approach in deep-inelastic scattering, proton-proton and heavy ion collisions.Comment: 4 pages, 2 figure

Analytical Results for Multifractal Properties of Spectra of Quasiperiodic Hamiltonians near the Periodic Chain

The multifractal properties of the electronic spectrum of a general quasiperiodic chain are studied in first order in the quasiperiodic potential strength. Analytical expressions for the generalized dimensions are found and are in good agreement with numerical simulations. These first order results do not depend on the irrational incommensurability.Comment: 10 Pages in RevTeX, 2 Postscript figure