3,999 research outputs found
On the early stage of nucleus-nucleus collisions
A statistical model of the early stage of central nucleus--nucleus (A+A) collisions is developed. We suggest a description of the confined state with several free parameters fitted to a compilation of A+A data at the AGS. For the deconfined state a simple Bag model equation of state is assumed. The model leads to the conclusion that a Quark Gluon Plasma is created in central nucleus--nucleus collisions at the SPS. This result is in quantitative agreement with existing SPS data on pion and strangeness production and gives a natural explanation for their scaling behaviour. The localization and the properties of the transition region are discussed. It is shown that the deconfinement transition can be detected by observation of the characteristic energy dependence of pion and strangeness multiplicities, and by an increase of the event--by--event fluctuations. An attempt to understand the data on J/psi production in Pb+Pb collisions at the SPS within the same approach is presented
Holographic superconductivity in the presence of dark matter: basic issues
The holographic approach to study strongly coupled superconductors in the
presence of dark matter is reviewed. We discuss the influence of dark matter on
the superconducting transition temperature of both s-wave and p-wave
holographic superconductors. The upper critical field, coherence length,
penetration depth of holographic superconductors as well as the metal-insulator
transitions have also been analysed. Issues related to the validity of AdS/CFT
correspondence for the description of superconductors studied in the laboratory
and possible experiments directed towards the detection of dark matter are
discussed. In doing so we shall compare our assumptions and assertions with
those generally accepted in the elementary particle experiments aimed at the
detection of dark matter particles.Comment: 5+ pages, 1 figure, National Conference on Superconductivity 2015,
Karpacz, Polan
Charm estimate from the dilepton spectra in nuclear collisions
A validity of a recent estimate of an upper limit of charm production in central Pb+Pb collisions at 158 AGeV is critically discussed. Within a simple model we study properties of the background subtraction procedure used for an extraction of the charm signal from the analysis of dilepton spectra. We demonstrate that a production asymmetry between positively and negatively charged background muons and a large multiplicity of signal pairs leads to biased results. Therefore the applicability of this procedure for the analysis of nucleus-nucleus data should be reconsidered before final conclusions on the upper limit estimate of charm production could be drawn
Holographic calcualtion of the magneto-transport coefficients in Dirac semimetals
Based on the gauge/gravity correspondence we have calculated the
thermoelectric kinetic and transport characteristics of the strongly
interacting materials in the presence of perpendicular magnetic field. The 3+1
dimensional system with Dirac-like spectrum is considered as a strongly
interacting one if it is close to the particle-hole symmetry point. Transport
in such system has been modeled by the two interacting vector fields. In the
holographic theory the momentum relaxation is caused by axion field and leads
to finite values of the direct current transport coefficients. We have
calculated conductivity tensor in the presence of mutually perpendicular
electric and magnetic fields and temperature gradient. The geometry differs
from that in which magnetic field lies in the same plane as an electric one and
temperature gradient.Comment: 26 pages, 7 figure
Holographic vortices in the presence of dark matter sector
The {\it dark matter} seem to be an inevitable ingredient of the total matter
configuration in the Universe and the knowledge how the {\it dark matter}
affects the properties of superconductors is of vital importance for the
experiments aimed at its direct detection. The homogeneous magnetic field
acting perpendicularly to the surface of (2+1) dimensional s-wave holographic
superconductor in the theory with {\it dark matter} sector has been modeled by
the additional -gauge field representing dark matter and coupled to the
Maxwell one. As expected the free energy for the vortex configuration turns out
to be negative. Importantly its value is lower in the presence of {\it dark
matter} sector. This feature can explain why in the Early Universe first the
web of {\it dark matter} appeared and next on these gratings the ordinary
matter forming cluster of galaxies has formed.Comment: 23 pages, JHEP-styl
P-wave holographic superconductor/insulator phase transitions affected by dark matter sector
The holographic approach to building the p-wave superconductors results in
three different models: the Maxwell-vector, the SU(2) Yang-Mills and the
helical. In the probe limit approximation, we analytically examine the
properties of the first two models in the theory with {\it dark matter} sector.
It turns out that the effect of {\it dark matter} on the Maxwell-vector p-wave
model is the same as on the s-wave superconductor studied earlier. For the
non-Abelian model we study the phase transitions between p-wave holographic
insulator/superconductor and metal/superconductor.
Studies of marginally stable modes in the theory under consideration allow us
to determine features of p-wave holographic droplet in a constant magnetic
field. The dependence of the superconducting transition temperature on the
coupling constant to the {\it dark matter} sector is affected by the
{\it dark matter} density . For the transition
temperature is a decreasing function of . The critical chemical
potential for the quantum phase transition between insulator and metal
depends on the chemical potential of dark matter and for is a
decreasing function of .Comment: 25 pages, 3 figures, JHEP style (included), version accepted for
publication in JHE
- …