256 research outputs found

### Dissipative processes in superfluid quark matter

We present some results about dissipative processes in fermionic superfluids
that are relevant for compact stars. At sufficiently low temperatures the
transport properties of a superfluid are dominated by phonons. We report the
values of the bulk viscosity, shear viscosity and thermal conductivity of
phonons in quark matter at extremely high density and low temperature. Then, we
present a new dissipative mechanism that can operate in compact stars and that
is named "rocket term". The effect of this dissipative mechanism on superfluid
r-mode oscillations is sketched.Comment: 6 pages, 1 figure. Prepared for QCD@work 2010 - International
Workshop on QCD - Theory and Experiment, 20-23 June 2010, Martina Franca -
Valle d'Itria - Ital

### Effective degrees of freedom of the Quark-Gluon Plasma

The effective degrees of freedom of the Quark-Gluon Plasma are studied in the
temperature range $\sim 1-2$ $T_c$. Employing lattice results for the pressure
and the energy density, we constrain the quasiparticle chiral invariant mass to
be of order 200 MeV and the effective number of bosonic resonant states to be
at most of order $\sim 10$. The chiral mass and the effective number of bosonic
degrees of freedom decrease with increasing temperature and at $T \sim 2$ $T_c$
only quark and gluon quasiparticles survive. Some remarks regarding the role of
the gluon condensation and the baryon number-strangeness correlation are also
presented.Comment: 4 pages, 1 figur

### Effective degrees of freedom and gluon condensation in the high temperature deconfined phase

The Equation of State and the properties of matter in the high temperature
deconfined phase are analyzed by a quasiparticle approach for $T> 1.2~T_c$. In
order to fix the parameters of our model we employ the lattice QCD data of
energy density and pressure. First we consider the pure SU(3) gluon plasma and
it turns out that such a system can be described in terms of a gluon condensate
and of gluonic quasiparticles whose effective number of degrees of freedom and
mass decrease with increasing temperature. Then we analyze QCD with finite
quark masses. In this case the numerical lattice data for energy density and
pressure can be fitted assuming that the system consists of a mixture of gluon
quasiparticles, fermion quasiparticles, boson correlated pairs (corresponding
to in-medium mesonic states) and gluon condensate. We find that the effective
number of boson degrees of freedom and the in-medium fermion masses decrease
with increasing temperature. At $T \simeq 1.5 ~T_c$ only the correlated pairs
corresponding to the mesonic nonet survive and they completely disappear at $T
\simeq 2 ~T_c$. The temperature dependence of the velocity of sound of the
various quasiparticles, the effects of the breaking of conformal invariance and
the thermodynamic consistency are discussed in detail.Comment: 18 pages, 9 figure

### Meissner masses in the gCFL phase of QCD

We calculate the Meissner masses of gluons in neutral three-flavor color
superconducting matter for finite strange quark mass. In the CFL phase the
eissner masses are slowly varying function of the strange quark mass. For large
strange quark mass, in the so called gCFL phase, the Meissner masses of gluons
with colors $a=1,2,3$ and 8 become imaginary, indicating an instability.Comment: New Fig. 1 shows that also the masses of the gluons 3 and 8 are
imaginar

### Jet energy loss in the quark-gluon plasma by stream instabilities

We study the evolution of the plasma instabilities induced by two jets of
particles propagating in opposite directions and crossing a thermally
equilibrated non-Abelian plasma. In order to simplify the analysis we assume
that the two jets of partons can be described with uniform distribution
functions in coordinate space and by Gaussian distribution functions in
momentum space. We find that while crossing the quark-gluon plasma, the jets of
particles excite unstable chromomagnetic and chromoelectric modes. These fields
interact with the particles (or hard modes) of the plasma inducing the
production of currents; thus, the energy lost by the jets is absorbed by both
the gauge fields and the hard modes of the plasma. We compare the outcome of
the numerical simulations with the analytical calculation performed assuming
that the jets of particles can be described by a tsunami-like distribution
function. We find qualitative and semi-quantitative agreement between the
results obtained with the two methods.Comment: 10 pages, 3 figure

### Jet-induced gauge field instabilities in the quark-gluon plasma: A kinetic theory approach

We discuss the properties of the collective modes of a system composed by a
thermalized quark-gluon plasma traversed by a relativistic jet of partons. The
transport equations obeyed by the components of the plasma and of the jet are
studied in the Vlasov approximation. Assuming that the partons in the jet can
be described with a tsunami-like distribution function we derive the
expressions of the dispersion law of the collective modes. Then the behavior of
the unstable gauge modes of the system is analyzed for various values of the
velocity of the jet, of the momentum of the collective modes and of the angle
between these two quantities. We find that the most unstable modes are those
with momentum orthogonal to the velocity of the jet and that these
instabilities appear when the velocity of the jet is higher than a threshold
value, which depends on the plasma and jet frequencies. The results obtained
within the Vlasov approximation are compared with the corresponding results
obtained using a chromohydrodynamical approach.The effect we discuss here
suggests a possible collective mechanism for the description of the jet
quenching phenomena in heavy ion collisions.Comment: 13 pages, 6 figure

### T-matrix approach to heavy quark diffusion in the QGP

We assess transport properties of heavy quarks in the Quark-Gluon Plasma
(QGP) using static heavy-quark (HQ) potentials from lattice-QCD calculations in
a Brueckner many-body T-matrix approach to evaluate elastic
heavy-quark-light-quark scattering amplitudes. In the attractive meson and
diquark channels resonance states are formed for temperatures up to ~1.5 T_c,
increasing pertinent drag and diffusion coefficients for heavy-quark
rescattering in the QGP beyond the expectations from perturbative-QCD
calculations. We use these transport coefficients, complemented with
perturbative elastic HQ gluon scattering, in a relativistic Langevin simulation
to obtain HQ p_t distributions and elliptic flow (v_2) under conditions
relevant for the hot and dense medium created in ultrarelativistic heavy-ion
collisions. The heavy quarks are hadronized to open-charm and -bottom mesons
within a combined quark-coalescence fragmentation scheme. The resulting
single-electron spectra from their semileptonic decays are confronted with
recent data on "non-photonic electrons" in 100 AGeV Au-Au collisions at the
Relativistic Heavy-Ion Collider (RHIC).Comment: 8 pages, 7 figures, contribution to the proceedings of the 3rd
International Conference on Hard and Electro-Magnetic Probes of High-Energy
Nuclear Collisions (Hard Probes 2008), 8-14 June 2008, Illa da Toxa
(Galicia-Spain

### Inhomogeneous phase of a Gluon Plasma at finite temperature and density

By considering the non-perturbative effects associated with the fundamental
modular region, a new phase of a Gluon Plasma at finite density is proposed. It
corresponds to the transition from glueballs to non-perturbative gluons which
condense at a non vanishing momentum. In this respect the proposed phase is
analogous to the color superconducting LOFF phase for fermionic systems.Comment: 5 pages, 2 figure

- â€¦