251 research outputs found
Next-to-leading order static gluon self-energy for anisotropic plasmas
In this paper the structure of the next-to-leading (NLO) static gluon self
energy for an anisotropic plasma is investigated in the limit of a small
momentum space anisotropy. Using the Ward identities for the static hard-loop
(HL) gluon polarization tensor and the (nontrivial) static HL vertices, we
derive a comparatively compact form for the complete NLO correction to the
structure function containing the space-like pole associated with magnetic
instabilities. On the basis of a calculation without HL vertices, it has been
conjectured that the imaginary part of this structure function is nonzero,
rendering the space-like poles integrable. We show that there are both positive
and negative contributions when HL vertices are included, highlighting the
necessity of a complete numerical evaluation, for which the present work
provides the basis.Comment: 9 pages, 2 figure
Equation of state of the hot dense matter in a multi-phase transport model
Within the framework of a multi-phase transport model, we study the equation
of state and pressure anisotropy of the hot dense matter produced in central
relativistic heavy ion collisions. Both are found to depend on the
hadronization scheme and scattering cross sections used in the model.
Furthermore, only partial thermalization is achieved in the produced matter as
a result of its fast expansion
The 3-graviton vertex function in thermal quantum gravity
The high temperature limit of the 3-graviton vertex function is studied in
thermal quantum gravity, to one loop order. The leading () contributions
arising from internal gravitons are calculated and shown to be twice the ones
associated with internal scalar particles, in correspondence with the two
helicity states of the graviton. The gauge invariance of this result follows in
consequence of the Ward and Weyl identities obeyed by the thermal loops, which
are verified explicitly.Comment: 19 pages, plain TeX, IFUSP/P-100
Instabilities of an anisotropically expanding non-Abelian plasma: 1D+3V discretized hard-loop simulations
Non-Abelian plasma instabilities play a crucial role in the nonequilibrium
dynamics of a weakly coupled quark-gluon plasma and they importantly modify the
standard perturbative bottom-up thermalization scenario in heavy-ion
collisions. Using the auxiliary-field formulation of the hard-loop effective
theory, we study numerically the real time evolution of instabilities in an
anisotropic collisionless Yang-Mills plasma expanding longitudinally in free
streaming. In this first real-time lattice simulation we consider the most
unstable modes, long-wavelength coherent color fields that are constant in
transverse directions and which therefore are effectively 1+1-dimensional in
spacetime, except for the auxiliary fields which also depend on discretized
momentum rapidity and transverse velocity components. We reproduce the
semi-analytical results obtained previously for the Abelian regime and we
determine the nonlinear effects which occur when the instabilities have grown
such that non-Abelian interactions become important.Comment: 28 pages, 10 figures; v2 minor updates to figures and text; v3
streamlined notation, minor additions to tex
Thermalization and the chromo-Weibel instability
Despite the apparent success of ideal hydrodynamics in describing the
elliptic flow data which have been produced at Brookhaven National Lab's
Relativistic Heavy Ion Collider, one lingering question remains: is the use of
ideal hydrodynamics at times t < 1 fm/c justified? In order to justify its use
a method for rapidly producing isotropic thermal matter at RHIC energies is
required. One of the chief obstacles to early isotropization/thermalization is
the rapid longitudinal expansion of the matter during the earliest times after
the initial nuclear impact. As a result of this expansion the parton
distribution functions become locally anisotropic in momentum space. In
contrast to locally isotropic plasmas anisotropic plasmas have a spectrum of
soft unstable modes which are characterized by exponential growth of transverse
chromo-magnetic/-electric fields at short times. This instability is the QCD
analogue of the Weibel instability of QED. Parametrically the chromo-Weibel
instability provides the fastest method for generation of soft background
fields and dominates the short-time dynamics of the system.Comment: 8 pages, 4 figures, Invited plenary talk given at the 19th
International Conference on Ultrarelativistic Nucleus-Nucleus Collisions:
Quark Matter 2006 (QM 2006), Shanghai, China, 14-20 Nov 200
Non-Abelian plasma instabilities: SU(3) vs. SU(2)
We present the first 3+1 dimensional simulations of non-Abelian plasma
instabilities in gauge-covariant Boltzmann-Vlasov equations for the QCD gauge
group SU(3) as well as for SU(4) and SU(5). The real-time evolution of
instabilities for a plasma with stationary momentum-space anisotropy is studied
using a hard-loop effective theory that is discretized in the velocities of
hard particles. We find that the numerically less expensive calculations using
the group SU(2) essentially reproduce the nonperturbative dynamics of
non-Abelian plasma instabilities with higher rank gauge groups provided the
mass parameters of the corresponding hard-loop effective theories are the same.
In particular we find very similar spectra for the turbulent cascade that forms
in the strong-field regime, which is associated with an approximately linear
growth of energy in collective fields. The magnitude of the linear growth
however turns out to increase with the number of colors.Comment: 8 pages, 7 figures; v2: minor changes; accepted for publication in
Phys. Rev.
The graviton self-energy in thermal quantum gravity
We show generally that in thermal gravity, the one-particle irreducible
2-point function depends on the choice of the basic graviton fields. We derive
the relevant properties of a physical graviton self-energy, which is
independent of the parametrization of the graviton field. An explicit
expression for the graviton self-energy at high-temperature is given to
one-loop order.Comment: 13 pages, 2 figure
Electric fields in plasmas under pulsed currents
Electric fields in a plasma that conducts a high-current pulse are measured
as a function of time and space. The experiment is performed using a coaxial
configuration, in which a current rising to 160 kA in 100 ns is conducted
through a plasma that prefills the region between two coaxial electrodes. The
electric field is determined using laser spectroscopy and line-shape analysis.
Plasma doping allows for 3D spatially resolved measurements. The measured peak
magnitude and propagation velocity of the electric field is found to match
those of the Hall electric field, inferred from the magnetic-field front
propagation measured previously.Comment: 13 pages, 13 figures, submitted to PR
Energy loss in a strongly coupled anisotropic plasma
We study the energy loss of a rotating infinitely massive quark moving, at
constant velocity, through an anisotropic strongly-coupled N=4 plasma from
holography. It is shown that, similar to the isotropic plasma, the energy loss
of the rotating quark is due to either the drag force or radiation with a
continuous crossover from drag-dominated regime to the radiation dominated
regime. We find that the anisotropy has a significant effect on the energy loss
of the heavy quark, specially in the crossover regime. We argue that the energy
loss due to radiation in anisotropic media is less than the isotropic case.
Interestingly this is similar to analogous calculations for the energy loss in
weakly coupled anisotropic plasma.Comment: 26+1 pages, 10 figures, typos fixe
Inverse magnetic catalysis in dense holographic matter
We study the chiral phase transition in a magnetic field at finite
temperature and chemical potential within the Sakai-Sugimoto model, a
holographic top-down approach to (large-N_c) QCD. We consider the limit of a
small separation of the flavor D8-branes, which corresponds to a dual field
theory comparable to a Nambu-Jona Lasinio (NJL) model. Mapping out the surface
of the chiral phase transition in the parameter space of magnetic field
strength, quark chemical potential, and temperature, we find that for small
temperatures the addition of a magnetic field decreases the critical chemical
potential for chiral symmetry restoration - in contrast to the case of
vanishing chemical potential where, in accordance with the familiar phenomenon
of magnetic catalysis, the magnetic field favors the chirally broken phase.
This "inverse magnetic catalysis" (IMC) appears to be associated with a
previously found magnetic phase transition within the chirally symmetric phase
that shows an intriguing similarity to a transition into the lowest Landau
level. We estimate IMC to persist up to 10^{19} G at low temperatures.Comment: 42 pages, 11 figures, v3: extended discussion; new appendix D;
references added; version to appear in JHE
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