40,696 research outputs found
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 GeV
The elliptic flow of thermal photons at midrapidity in Au+Au
collisions at 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 reaches a maximum
at \pt \sim 2GeV/ and the \pt-integrated reaches a maximum at
about 50% centrality. The \pt-integrated 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 = 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 () of the azimuthal angular distribution. We report on
a measurement of identified-particle as a function of (0.5-2.0
GeV/c), centrality (0-25%, 25-50%), and pseudorapidity () for
Au+Au collisions. The BRAHMS spectrometers are
used for particle identification (, 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 from redshift data indicates that
galaxies have preferred periodic redshift spacings. We fix the mass of the
scalar field as 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: (95% C.L.),
(95% C.L.) (in the range
). The best fit values of the energy density parameter of the scalar
field and the coupling constant are and ,
respectively. The value of is close to but not equal to .
Hence, in the scalar field model, the amplitude of the galaxy number count
cannot be large. However, because the best fit values of and
are not , the scalar field model has the possibility of accounting for
the periodic structure in the -- 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
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
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
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
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