77 research outputs found
Simulation of the space-time evolution of color-flux tubes
We give the description of the computer program which simulates boost-invariant evolution of color flux tubes in high-energy processes. The program provides a graphic demonstration of space-time trajectories of created particles and can also be used as Monte Carlo generator of events
Boost-invariant motion of relativistic perfect fluid
Equations of motion of relativistic perfect fluid subject to Bjorken’s boost-invariant conditions are analysed. General relations between the gradient of temperature and the shape of stream lines are derived. The case of pure transverse motion (vanishing radial velocity) is studied in some detail. It is shown that the stable solution exists only for a very restricted class of the equations of state of the fluid
Color flux tubes and quark-gluon plasma production
We study how the plasma production in ultrarelativistic heavy-ion collisions depends on the radius of the initial color flux tubes
Characteristic form of boost-invariant and cylindrically non-symmetric hydrodynamic equations
It is shown that the boost-invariant and cylindrically non-symmetric
hydrodynamic equations for baryon-free matter may be reduced to only two
coupled differential equations. In the case where the system exhibits the
cross-over phase transition, the standard numerical methods may be applied to
solve these equations and the proposed scheme allows for a very convenient
analysis of the cylindrically non-symmetric hydrodynamic expansion.Comment: 8 pages, 3 figures, 3 sets of figure
Anisotropic Inflation from Extra Dimensions
Vacuum multidimensional cosmological models with internal spaces being
compact -dimensional Lie group manifolds are considered. Products of
3-spheres and manifold (a novelty in cosmology) are studied. It turns
out that the dynamical evolution of the internal space drives an accelerated
expansion of the external world (power law inflation). This generic solution
(attractor in a phase space) is determined by the Lie group space without any
fine tuning or arbitrary inflaton potentials. Matter in the four dimensions
appears in the form of a number of scalar fields representing anisotropic scale
factors for the internal space. Along the attractor solution the volume of the
internal space grows logarithmically in time. This simple and natural model
should be completed by mechanisms terminating the inflationary evolution and
transforming the geometric scalar fields into ordinary particles.Comment: LaTeX, 11 pages, 5 figures available via fax on request to
[email protected], submitted to Phys. Lett.
Temperature dependent sound velocity in hydrodynamic equations for relativistic heavy-ion collisions
We analyze the effects of different forms of the sound-velocity function
cs(T) on the hydrodynamic evolution of matter formed in the central region of
relativistic heavy-ion collisions. At high temperatures (above the critical
temperature Tc) the sound velocity is calculated from the recent lattice
simulations of QCD, while in the low temperature region it is obtained from the
hadron gas model. In the intermediate region we use different interpolations
characterized by the values of the sound velocity at the local maximum (at T =
0.4 Tc) and local minimum (at T = Tc). In all considered cases the temperature
dependent sound velocity functions yield the entropy density, which is
consistent with the lattice QCD simulations at high temperature. Our
calculations show that the presence of a distinct minimum of the sound velocity
leads to a very long (about 20 fm/c) evolution time of the system, which is not
compatible with the recent estimates based on the HBT interferometry. Hence, we
conclude that the hydrodynamic description is favored in the case where the
cross-over phase transition renders the smooth sound velocity function with a
possible shallow minimum at Tc.Comment: 6 pages, 3 figures, talk given at SQM'07 Levoca, Slovaki
Local equilibrium of the quark-gluon plasma
Within kinetic theory, we look for local equilibrium configurations of the
quark-gluon plasma by maximizing the local entropy. We use the well-established
transport equations in the Vlasov limit, supplemented with the Waldmann-Snider
collision terms. Two different classes of local equilibrium solutions are
found. The first one corresponds to the configurations that comply with the
so-called collisional invariants. The second one is given by the distribution
functions that cancel the collision terms, representing the most probable
binary interactions with soft gluon exchange in the t-channel. The two sets of
solutions agree with each other if we go beyond these dominant processes and
take into account subleading quark-antiquark annihilation/creation and gluon
number non-conserving processes. The local equilibrium state appears to be
colorful, as the color charges are not locally neutralized. Properties of such
an equilibrium state are analyzed. In particular, the related hydrodynamic
equations of a colorful fluid are derived. Possible neutralization processes
are also briefly discussed.Comment: 20 pages; minor changes, to be published in Phys. Rev.
In search of gravity mode signatures in main sequence solar-type stars observed by Kepler
Gravity modes (g modes), mixed gravito-acoustic modes (mixed modes), and
gravito-inertial modes (gi modes) possess unmatched properties as probes for
stars with radiative interiors. The structural and dynamical constraints that
they are able to provide cannot be accessed by other means. While they provide
precious insights into the internal dynamics of evolved stars as well as
massive and intermediate-mass stars, their non-detection in main sequence (MS)
solar-type stars make them a crucial missing piece in our understanding of
angular momentum transport in radiative zones and stellar rotational evolution.
In this work, we aim to apply certain analysis tools originally developed for
helioseismology in order to look for g-mode signatures in MS solar-type stars.
We select a sample of the 34 most promising MS solar-type stars with Kepler
four-year long photometric time series. All these stars are well-characterised
late F-type stars with thin convective envelopes, fast convective flows, and
stochastically excited acoustic modes (p modes). For each star, we compute the
background noise level of the Fourier power spectrum to identify significant
peaks at low frequency. After successfully detecting individual peaks in 12
targets, we further analyse four of them and observe distinct patterns of
surrounding peaks with a low probability of being noise artifacts. Comparisons
with the predictions from reference models suggest that these patterns are
compatible with the presence of non-asymptotic low-order pure g modes, pure p
modes, and mixed modes. Given their sensitivity to both the convective core
interface stratification and the coupling between p- and g-mode resonant
cavities, such modes are able to provide strong constraints on the structure
and evolutionary states of the related targets. [abridged]Comment: 19 pages, 19 figures, accepted for publication in A&
Consistency of data on soft photon production in hadronic interactions
The glob model of Lichard and Van Hove and the modified soft annihilation
model (MSAM) of Lichard and Thompson are used as a phenomenological tool for
relating results from various experiments on soft photon production in high
energy collisions. The total phenomenological expectation is composed of
contributions from classical bremsstrahlung, the soft annihilation model and
the glob model. The empirical excess above the background from hadronic decays
at very small longitudinal momenta of photons is well reproduced, as well as
that for transverse momenta pT >~ 10 MeV/c. Some data do not require the glob
model and MSAM components in the phenomenological mixture, but do not exclude
them. On the basis of consistency of all data with the total theoretical
expectation we argue that the results of all experiments are mutually
consistent. The models are unable to describe the excess of ultrasoft photons
(pT <~ 10 MeV/c), seen by some, but not all, experiments. This may indicate an
as yet unknown projectile-mass-dependent production mechanism. Possible
relations of soft photon production to other phenomena are discussed. A
simple-to-use, but physically equivalent version of the glob model is
developed, which enables an easy check of presented results.Comment: 25 pages, RevTeX, epsf.sty, 12 embedded figure
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