7,308 research outputs found
Isentropic thermodynamics in the PNJL model
We discuss the isentropic trajectories on the QCD phase diagram in the
temperature and the quark chemical potential plane using the
Nambu--Jona-Lasinio model with the Polyakov loop coupling (PNJL model). We
impose a constraint on the strange quark chemical potential so that the strange
quark density is zero, which is the case in the ultra relativistic heavy-ion
collisions. We compare our numerical results with the truncated estimates by
the Taylor expansion in terms of the chemical potential to quantify the
reliability of the expansion used in the lattice QCD simulation. We finally
discuss the strange quark chemical potential induced by the strangeness
neutrality condition and relate it to the ratio of the Polyakov loop and the
anti-Polyakov loop.Comment: 9 pages, 9 figure
Mechanics of the turbulent/non-turbulent interface of a jet
We report the results of an experimental investigation of the mechanics and transport processes at the bounding interface between the turbulent and nonturbulent regions of flow in a turbulent jet, which shows the existence of a finite jump in the tangential velocity at the interface. This is associated with small-scale eddying motion at the outward propagating interface (nibbling) by which irrotational fluid becomes turbulent, and this implies that large-scale engulfment is not the dominant entrainment process. Interpretation of the jump as a singular structure yields an essential and significant contribution to the mean shear in the jet mixing region. Finally, our observations provide a justification for Prandtl’s original hypothesis of a constant eddy viscosity in the nonturbulent outer jet region
Color superconducting matter in a magnetic field
We investigate the effect of a magnetic field on cold dense three-flavor
quark matter using an effective model with four-Fermi interactions with
electric and color neutrality taken into account. The gap parameters Delta_1,
Delta_2, and Delta_3 representing respectively the predominant pairing between
down and strange (d-s) quarks, strange and up (s-u) quarks, and up and down
(u-d) quarks, show the de Haas-van Alphen effect, i.e. oscillatory behavior as
a function of the modified magnetic field B that can penetrate the color
superconducting medium. Without applying electric and color neutrality we find
Delta_2 \approx Delta_3 >> Delta_1 for 2 e B / mu_q^2, where e is the modified
electromagnetic coupling constant and mu_q is one third of the baryon chemical
potential. Because the average Fermi surface for each pairing is affected by
taking into account neutrality, the gap structure changes drastically in this
case; we find Delta_1 >> Delta_2 \approx Delta_3 for 2 e B > mu_q^2. We point
out that the magnetic fields as strong as presumably existing inside magnetars
might induce significant deviations from the gap structure Delta_1 \approx
Delta_2 \approx Delta_3 at zero magnetic field.Comment: 5 pages, 3 figure
The problem of repulsive quark interactions - Lattice versus mean field models
We calculate the 2nd and 4th order quark number susceptibilities at zero
baryochemical potential, using a PNJL approach and an approach which includes,
in a single model, quark and hadronic degrees of freedom. We observe that the
susceptibilities are very sensitive to possible quark-quark vector
interactions. Compared to lattice data our results suggest that above any
mean field type of repulsive vector interaction can be excluded from model
calculations. Below our results show only very weak sensitivity on the
strength of the quark and hadronic vector interaction. The best description of
lattice data around is obtained for a case of coexistence of hadronic and
quark degrees of freedom.Comment: 5 pages, 4 figure, version accepted by PL
Effective Model Approach to the Dense State of QCD Matter
The first-principle approach to the dense state of QCD matter, i.e. the
lattice-QCD simulation at finite baryon density, is not under theoretical
control for the moment. The effective model study based on QCD symmetries is a
practical alternative. However the model parameters that are fixed by hadronic
properties in the vacuum may have unknown dependence on the baryon chemical
potential. We propose a new prescription to constrain the effective model
parameters by the matching condition with the thermal Statistical Model. In the
transitional region where thermal quantities blow up in the Statistical Model,
deconfined quarks and gluons should smoothly take over the relevant degrees of
freedom from hadrons and resonances. We use the Polyakov-loop coupled
Nambu--Jona-Lasinio (PNJL) model as an effective description in the quark side
and show how the matching condition is satisfied by a simple ansatz on the
Polyakov loop potential. Our results favor a phase diagram with the chiral
phase transition located at slightly higher temperature than deconfinement
which stays close to the chemical freeze-out points.Comment: 8 pages, 4 figures; Talk at International Workshop on High Density
Nuclear Matter, Cape Town, South Africa, April 6-9, 201
Light emission patterns from stadium-shaped semiconductor microcavity lasers
We study light emission patterns from stadium-shaped semiconductor (GaAs)
microcavity lasers theoretically and experimentally. Performing systematic wave
calculations for passive cavity modes, we demonstrate that the averaging by
low-loss modes, such as those realized in multi-mode lasing, generates an
emission pattern in good agreement with the ray model's prediction. In
addition, we show that the dependence of experimental far-field emission
patterns on the aspect ratio of the stadium cavity is well reproduced by the
ray model.Comment: 5 pages, 4 figure
Views of the Chiral Magnetic Effect
My personal views of the Chiral Magnetic Effect are presented, which starts
with a story about how we came up with the electric-current formula and
continues to unsettled subtleties in the formula. There are desirable features
in the formula of the Chiral Magnetic Effect but some considerations would lead
us to even more questions than elucidations. The interpretation of the produced
current is indeed very non-trivial and it involves a lot of confusions that
have not been resolved.Comment: 19 pages, no figure; typos corrected, references significantly
updated, to appear in Lect. Notes Phys. "Strongly interacting matter in
magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Ye
Classical Phase Space Revealed by Coherent Light
We study the far field characteristics of oval-resonator laser diodes made of
an AlGaAs/GaAs quantum well. The resonator shapes are various oval geometries,
thereby probing chaotic and mixed classical dynamics. The far field pattern
shows a pronounced fine structure that strongly depends on the cavity shape.
Comparing the experimental data with ray-model simulations for a Fresnel
billiard yields convincing agreement for all geometries and reveals the
importance of the underlying classical phase space for the lasing
characteristics.Comment: 4 pages, 5 figures (reduced quality), accepted for publication in
Physical Review Letter
Perimeter of sublevel sets in infinite dimensional spaces
We compare the perimeter measure with the Airault-Malliavin surface measure
and we prove that all open convex subsets of abstract Wiener spaces have finite
perimeter. By an explicit counter-example, we show that in general this is not
true for compact convex domains
High energy cosmic-ray interactions with particles from the Sun
Cosmic-ray protons with energies above eV passing near the Sun may
interact with photons emitted by the Sun and be excited to a
resonance. When the decays, it produces pions which further decay to
muons and photons which may be detected with terrestrial detectors. A flux of
muons, photon pairs (from decay), or individual high-energy photons
coming from near the Sun would be a rather striking signature, and the flux of
these particles is a fairly direct measure of the flux of cosmic-ray nucleons,
independent of the cosmic-ray composition. In a solid angle within
around the Sun the flux of photon pairs is about \SI{1.3e-3}{}
particles/(kmyr), while the flux of muons is about \SI{0.33e-3}{}
particles/(kmyr). This is beyond the reach of current detectors like
the Telescope Array, Auger, KASCADE-Grande or IceCube. However, the muon flux
might be detectable by next-generation air shower arrays or neutrino detectors
such as ARIANNA or ARA. We discuss the experimental prospects in some detail.
Other cosmic-ray interactions occuring close to the Sun are also briefly
discussed.Comment: 8 pages, 11 figure
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