6,951 research outputs found
Heavy Quark Dynamics in the QGP
We assess transport properties of heavy quarks in the Quark-Gluon Plasma
(QGP) that show a strong non-perturbative behavior. A T-matrix approach based
on a potential taken from lattice QCD hints at the presence of heavy-quark (HQ)
resonant scattering with an increasing strength as the temperature, ,
reaches the critical temperature, T_c \simeq 170 \; \MeV for deconfinement
from above. The implementation of HQ resonance scattering along with a
hadronization via quark coalescence under the conditions of the plasma created
in heavy-ion collisions has been shown to correctly describe both the nuclear
modification factor, , and the elliptic flow, , of single
electrons at RHIC and have correctly predicted the of D mesons at LHC
energy.Comment: 10 pages, 4 figures, Proceedings of EPIC@LHC Workshop, 6-8 July, Bar
Test-particle acceleration in a hierarchical three-dimensional turbulence model
The acceleration of charged particles is relevant to the solar corona over a
broad range of scales and energies. High-energy particles are usually detected
in concomitance with large energy release events like solar eruptions and
flares, nevertheless acceleration can occur at smaller scales, characterized by
dynamical activity near current sheets. To gain insight into the complex
scenario of coronal charged particle acceleration, we investigate the
properties of acceleration with a test-particle approach using
three-dimensional magnetohydrodynamic (MHD) models. These are obtained from
direct solutions of the reduced MHD equations, well suited for a plasma
embedded in a strong axial magnetic field, relevant to the inner heliosphere. A
multi-box, multi-scale technique is used to solve the equations of motion for
protons. This method allows us to resolve an extended range of scales present
in the system, namely from the ion inertial scale of the order of a meter up to
macroscopic scales of the order of km (th of the outer scale of
the system). This new technique is useful to identify the mechanisms that,
acting at different scales, are responsible for acceleration to high energies
of a small fraction of the particles in the coronal plasma. We report results
that describe acceleration at different stages over a broad range of time,
length and energy scales.Comment: 12 pages, 8 figures, ApJ (in press
Collective Flows in a Transport Approach
We introduce a transport approach at fixed shear viscosity to entropy ratio
\etas to study the generation of collective flows in ultra-relativistic
heavy-ion collisions. Transport theory supplies a covariant approach valid also
at large \etas and at intermediate transverse momentum , where
deviations from equilibrium is no longer negligible. Such an approach shows
that at RHIC energies a temperature dependent \etas enhances significantly
the respect to the case of constant \etas. Furthermore if NJL
chiral dynamics is self-consistently implemented we show that it does not
modify the relation between and \etas.Comment: 4 pages, 4 figures, Proceedings of Hot Quarks 2010, 21-26 June 2010
Las Londe Les Maures; to appear in Journal of Physics: Conference Serie
Magnetic Reconnection and Intermittent Turbulence in the Solar Wind
A statistical relationship between magnetic reconnection, current sheets and
intermittent turbulence in the solar wind is reported for the first time using
in-situ measurements from the Wind spacecraft at 1 AU. We identify
intermittency as non-Gaussian fluctuations in increments of the magnetic field
vector, , that are spatially and temporally non-uniform. The
reconnection events and current sheets are found to be concentrated in
intervals of intermittent turbulence, identified using the partial variance of
increments method: within the most non-Gaussian 1% of fluctuations in
, we find 87%-92% of reconnection exhausts and 9% of current
sheets. Also, the likelihood that an identified current sheet will also
correspond to a reconnection exhaust increases dramatically as the least
intermittent fluctuations are removed from the dataset. Hence, the turbulent
solar wind contains a hierarchy of intermittent magnetic field structures that
are increasingly linked to current sheets, which in turn are progressively more
likely to correspond to sites of magnetic reconnection. These results could
have far reaching implications for laboratory and astrophysical plasmas where
turbulence and magnetic reconnection are ubiquitous.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Relativistic Mean-Field Theory Equation of State of Neutron Star Matter and a Maxwellian Phase Transition to Strange Quark Matter
The equation of state of neutron star matter is examined in terms of the
relativistic mean-field theory, including a scalar-isovector -meson
effective field. The constants of the theory are determined numerically so that
the empirically known characteristics of symmetric nuclear matter are
reproduced at the saturation density. The thermodynamic characteristics of both
asymmetric nucleonic matter and -equilibrium hadron-electron
-plasmas are studied. Assuming that the transition to strange quark matter
is an ordinary first-order phase transition described by Maxwell's rule, a
detailed study is made of the variations in the parameters of the phase
transition owing to the presence of a -meson field. The quark phase is
described using an improved version of the bag model, in which interactions
between quarks are accounted for in a one-gluon exchange approximation. The
characteristics of the phase transition are determined for various values of
the bag parameter within the range and it is shown
that including a -meson field leads to a reduction in the phase
transition pressure and in the concentrations and at
the phase transition point.Comment: 17 pages, 8 figure
Strangeness and heavy flavor at RHIC: Recent results from PHENIX
We report recent results of strangeness and heavy flavor measurements from
PHENIX.
The topics are: Elliptic flow of strangeness and heavy flavor electron
production comparing to the other hadrons, meson production, and an
exotic particle search.Comment: 8 pages, 6 figures, 1 table. Submitted to J. Phys. G (Proceedings of
the 8th International Conference on Strangeness in Quark Matter, Cape Town,
South Africa, September 15-20, 2004
Logics for Rough Concept Analysis
Taking an algebraic perspective on the basic structures of Rough Concept
Analysis as the starting point, in this paper we introduce some varieties of
lattices expanded with normal modal operators which can be regarded as the
natural rough algebra counterparts of certain subclasses of rough formal
contexts, and introduce proper display calculi for the logics associated with
these varieties which are sound, complete, conservative and with uniform cut
elimination and subformula property. These calculi modularly extend the
multi-type calculi for rough algebras to a `nondistributive' (i.e. general
lattice-based) setting
Isospin Dynamics in Heavy Ion Collisions: from Coulomb Barrier to Quark Gluon Plasma
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium
nuclear interaction in regions away from saturation. In this report we present
a selection of new reaction observables in dissipative collisions particularly
sensitive to the symmetry term of the nuclear Equation of State (Iso-EoS). We
will first discuss the Isospin Equilibration Dynamics. At low energies this
manifests via the recently observed Dynamical Dipole Radiation, due to a
collective neutron-proton oscillation with the symmetry term acting as a
restoring force. At higher beam energies Iso-EoS effects will be seen in
Imbalance Ratio Measurements, in particular from the correlations with the
total kinetic energy loss. For fragmentation reactions in central events we
suggest to look at the coupling between isospin distillation and radial flow.
In Neck Fragmentation reactions important information can be obtained
from the correlation between isospin content and alignement. The high density
symmetry term can be probed from isospin effects on heavy ion reactions at
relativistic energies (few AGeV range). Rather isospin sensitive observables
are proposed from nucleon/cluster emissions, collective flows and meson
production. The possibility to shed light on the controversial neutron/proton
effective mass splitting in asymmetric matter is also suggested. A large
symmetry repulsion at high baryon density will also lead to an "earlier"
hadron-deconfinement transition in n-rich matter. A suitable treatment of the
isovector interaction in the partonic EoS appears very relevant.Comment: 18 pages, 12 figures, lecture at the 2008 Erice School on Nuclear
Physics, to appear in Progress in Particle and Nuclear Physic
Magnetic moment non-conservation in magnetohydrodynamic turbulence models
The fundamental assumptions of the adiabatic theory do not apply in presence
of sharp field gradients as well as in presence of well developed
magnetohydrodynamic turbulence. For this reason in such conditions the magnetic
moment is no longer expected to be constant. This can influence particle
acceleration and have considerable implications in many astrophysical problems.
Starting with the resonant interaction between ions and a single parallel
propagating electromagnetic wave, we derive expressions for the magnetic moment
trapping width (defined as the half peak-to-peak difference in the
particle magnetic moment) and the bounce frequency . We perform
test-particle simulations to investigate magnetic moment behavior when
resonances overlapping occurs and during the interaction of a ring-beam
particle distribution with a broad-band slab spectrum.
We find that magnetic moment dynamics is strictly related to pitch angle
for a low level of magnetic fluctuation, , where is the constant and uniform background magnetic field.
Stochasticity arises for intermediate fluctuation values and its effect on
pitch angle is the isotropization of the distribution function .
This is a transient regime during which magnetic moment distribution
exhibits a characteristic one-sided long tail and starts to be influenced by
the onset of spatial parallel diffusion, i.e., the variance
grows linearly in time as in normal diffusion. With strong fluctuations
isotropizes completely, spatial diffusion sets in and
behavior is closely related to the sampling of the varying magnetic field
associated with that spatial diffusion.Comment: 13 pages, 10 figures, submitted to PR
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