98 research outputs found
Equation of State and Viscosities from a Gravity Dual of the Gluon Plasma
Employing new precision data of the equation of state of the SU(3) Yang-Mills
theory (gluon plasma) the dilaton potential of a gravity-dual model is adjusted
in the temperature range within a bottom-up approach. The ratio
of bulk viscosity to shear viscosity follows then as for and achieves a maximum value of
at , where is the
non-conformality measure and is the velocity of sound squared, while
the ratio of shear viscosity to entropy density is known as for
the considered set-up with Hilbert action on the gravity side.Comment: 19 pages, 13 figures. Version published in PL
Cross-over versus first-order phase transition in holographic gravity-single-dilaton models of QCD thermodynamics
A dilaton potential is adjusted to recently confirmed lattice QCD
thermodynamics data in the temperature range where is the pseudo-critical temperature. The employed holographic
model is based on a gravity--single-field dilaton dual. We discuss conditions
for enforcing (for the pure gluon plasma) or avoiding (for the QCD quark-gluon
plasma) a first-order phase transition, but still keeping a softest point
(minimum of sound velocity).Comment: 11 pages, 9 figure
Relativistic Expansion of Electron-Positron-Photon Plasma Droplets and Photon Emission
The expansion dynamics of hot electron-positron-photon plasma droplets is
dealt with within relativistic hydrodynamics. Such droplets, envisaged to be
created in future experiments by irradiating thin foils with
counter-propagating ultra-intense laser beams, are sources of flashes of gamma
radiation. Warm electron-positron plasma droplets may be identified and
characterized by a broadened 511 keV line
Origin of Rashba-splitting in the quantized subbands at Bi2Se3 surface
We study the band structure of the topological
insulator (111) surface using angle-resolved photoemission spectroscopy. We
examine the situation where two sets of quantized subbands exhibiting different
Rashba spin-splitting are created via bending of the conduction (CB) and the
valence (VB) bands at the surface. While the CB subbands are strongly Rashba
spin-split, the VB subbands do not exhibit clear spin-splitting. We find that
CB and VB experience similar band bending magnitudes, which means, a
spin-splitting discrepancy due to different surface potential gradients can be
excluded. On the other hand, by comparing the experimental band structure to
first principles LMTO band structure calculations, we find that the strongly
spin-orbit coupled Bi 6 orbitals dominate the orbital character of CB,
whereas their admixture to VB is rather small. The spin-splitting discrepancy
is, therefore, traced back to the difference in spin-orbit coupling between CB
and VB in the respective subbands' regions
Pseudogap and charge density waves in two dimensions
An interaction between electrons and lattice vibrations (phonons) results in
two fundamental quantum phenomena in solids: in three dimensions it can turn a
metal into a superconductor whereas in one dimension it can turn a metal into
an insulator. In two dimensions (2D) both superconductivity and charge-density
waves (CDW) are believed to be anomalous. In superconducting cuprates, critical
transition temperatures are unusually high and the energy gap may stay unclosed
even above these temperatures (pseudogap). In CDW-bearing dichalcogenides the
resistivity below the transition can decrease with temperature even faster than
in the normal phase and a basic prerequisite for the CDW, the favourable
nesting conditions (when some sections of the Fermi surface appear shifted by
the same vector), seems to be absent. Notwithstanding the existence of
alternatives to conventional theories, both phenomena in 2D still remain the
most fascinating puzzles in condensed matter physics. Using the latest
developments in high-resolution angle-resolved photoemission spectroscopy
(ARPES) here we show that the normal-state pseudogap also exists in one of the
most studied 2D examples, dichalcogenide 2H-TaSe2, and the formation of CDW is
driven by a conventional nesting instability, which is masked by the pseudogap.
Our findings reconcile and explain a number of unusual, as previously believed,
experimental responses as well as disprove many alternative theoretical
approaches. The magnitude, character and anisotropy of the 2D-CDW pseudogap are
intriguingly similar to those seen in superconducting cuprates.Comment: 14 pages including figures and supplementary informatio
Arguing on Entropic and Enthalpic First-Order Phase Transitions in Strongly Interacting Matter
Abstract The pattern of isentropes in the vicinity of a first-order phase transition is proposed as a key for a sub-classification. While the confinement-deconfinement transition, conjectured to set in beyond a critical end point in the QCD phase diagram, is often related to an entropic transition and the apparently settled gas-liquid transition in nuclear matter is an enthalphic transition, the conceivable local isentropes w.r.t. "incoming" or "outgoing" serve as another useful guide for discussing possible implications, both in the presumed hydrodynamical expansion stage of heavy-ion collisions and the core-collapse of supernova explosions. Examples, such as the quark-meson model and two-phase models, are shown to distinguish concisely the different transitions
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