What can we learn from hydrodynamic analysis at RHIC?

We can establish a new picture, the perfect fluid sQGP core and the dissipative hadronic corona, of the space-time evolution of produced matter in relativistic heavy ion collisions at RHIC. It is also shown that the picture works well also in the forward rapidity region through an analysis based on a new class of the hydro-kinetic model and that this is a manifestation of rapid increase of entropy density in the vicinity of QCD critical temperature, namely deconfinement.Comment: 8 pages, 4 figures, talk given at Workshop on Quark-Gluon-Plasma Thermalization, Vienna, Austria, 10-12 Aug 200

Elliptic flow of thermal photons at midrapidity in Au+Au collisions at sNN=200\sqrt{s_{NN}}=200 GeV

The elliptic flow $v_{2}$ of thermal photons at midrapidity in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV is predicted, based on three-dimensional ideal hydrodynamics. Because of the interplay between the asymmetry and the strength of the transverse flow, the thermal photon $v_{2}$ reaches a maximum at \pt \sim 2GeV/$c$ and the \pt-integrated $v_{2}$ reaches a maximum at about 50% centrality. The \pt-integrated $v_{2}$ is very sensitive to the lower limit of the integral but not sensitive to the upper limit due to the rapid decrease in the spectrum of the transverse momentum.Comment: 4 pages, 2 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

Forward-rapidity azimuthal and radial flow of identified particles for sNN\sqrt{s_{NN}} = 200 GeV Au+Au collisions

A strong azimuthal flow signature at RHIC suggests rapid system equilibration leading to an almost perfect fluid state. The longitudinal extent of the flow behavior depends on how this state is formed and can be studied by measuring the pseudorapidity and transverse momentum dependence of the second Fourier component ($v_{2}(p_{T})$) of the azimuthal angular distribution. We report on a measurement of identified-particle $v_{2}$ as a function of $p_{T}$ (0.5-2.0 GeV/c), centrality (0-25%, 25-50%), and pseudorapidity ($0\leq\eta<3.2$) for $\sqrt{s_{NN}} = 200 \rm GeV$ Au+Au collisions. The BRAHMS spectrometers are used for particle identification ($\pi$, K, p) and momentum determination and the BRAHMS global detectors are used to determine the corresponding reaction-plane angles. The results are discussed in terms of the rapidity dependence of constituent quark scaling and in terms of models that develop the complete (azimuthal and radial) hydrodynamic aspects of the forward dynamics at RHIC.Comment: 4 pages, 4 figures - To appear in the conference proceedings for Quark Matter 2009, March 30-April 4, Knoxville, Tennesse

Observational tests for oscillating expansion rate of the Universe

We investigate the observational constraints on the oscillating scalar field model using data from type Ia supernovae, cosmic microwave background anisotropies, and baryon acoustic oscillations. According to a Fourier analysis, the galaxy number count $N$ from redshift $z$ data indicates that galaxies have preferred periodic redshift spacings. We fix the mass of the scalar field as $m_\phi=3.2\times 10^{-31}h$ ${\rm eV}$ such that the scalar field model can account for the redshift spacings, and we constrain the other basic parameters by comparing the model with accurate observational data. We obtain the following constraints: $\Omega_{m,0}=0.28\pm 0.03$ (95% C.L.), $\Omega_{\phi,0} -158$ (95% C.L.) (in the range $\xi \le 0$). The best fit values of the energy density parameter of the scalar field and the coupling constant are $\Omega_{\phi,0}= 0.01$ and $\xi= -25$, respectively. The value of $\Omega_{\phi,0}$ is close to but not equal to $0$. Hence, in the scalar field model, the amplitude of the galaxy number count cannot be large. However, because the best fit values of $\Omega_{\phi,0}$ and $\xi$ are not $0$, the scalar field model has the possibility of accounting for the periodic structure in the $N$--$z$ relation of galaxies. The variation of the effective gravitational constant in the scalar field model is not inconsistent with the bound from observation.Comment: 9 pages, 11 figures, 1 table, Accepted for publication in Physical Review

Modified Linear Projection for Large Spatial Data Sets

Recent developments in engineering techniques for spatial data collection such as geographic information systems have resulted in an increasing need for methods to analyze large spatial data sets. These sorts of data sets can be found in various fields of the natural and social sciences. However, model fitting and spatial prediction using these large spatial data sets are impractically time-consuming, because of the necessary matrix inversions. Various methods have been developed to deal with this problem, including a reduced rank approach and a sparse matrix approximation. In this paper, we propose a modification to an existing reduced rank approach to capture both the large- and small-scale spatial variations effectively. We have used simulated examples and an empirical data analysis to demonstrate that our proposed approach consistently performs well when compared with other methods. In particular, the performance of our new method does not depend on the dependence properties of the spatial covariance functions.Comment: 29 pages, 5 figures, 4 table

Fat Magnon

We consider a D-brane type state which shares the characteristic of the recently found giant magnon of Hofman and Maldacena. More specifically we find a bound state of giant graviton (D3-brane) and giant magnon (F-string), which has exactly the same anomalous dimension as that of the giant magnon. It is described by the D3-brane with electric flux which is topologically a $S^3$ elongated by the electric flux. The angular momentum and energy are infinite, but split sensibly into two parts -- the infinite part precisely the same as that of the giant magnon and the finite part which can be identified as the contribution from the giant graviton. We discuss that the corresponding dual gauge theory operator is not a simple chain type but rather admixture of the (sub-)determinant and chain types.Comment: 18 pages, 5 figures; v2 references added; v3 a reference added; v4 added a reference and discussions on the physical CFT operator. The version to appear in JHE

Relativistic Hydrodynamics at RHIC and LHC

Recent development of a hydrodynamic model is discussed by putting an emphasis on realistic treatment of the early and late stages in relativistic heavy ion collisions. The model, which incorporates a hydrodynamic description of the quark-gluon plasma with a kinetic approach of hadron cascades, is applied to analysis of elliptic flow data at the Relativistic Heavy Ion Collider energy. It is predicted that the elliptic flow parameter based on the hybrid model increases with the collision energy up to the Large Hadron Collider energy.Comment: 8 pages, 7 figures, talk given at YKIS Seminar on New Frontiers in QC