639 research outputs found
Energy scales of Lu(1-x)Yb(x)Rh2Si2 by means of thermopower investigations
We present the thermopower S(T) and the resistivity rho(T) of
Lu(1-x)Yb(x)Rh2Si2 in the temperature range 3 K < T < 300 K. S(T) is found to
change from two minima for dilute systems (x < 0.5) to a single large minimum
in pure YbRh2Si2. A similar behavior has also been found for the magnetic
contribution to the resistivity rho_mag(T). The appearance of the low-T extrema
in S(T) and rho_mag(T) is attributed to the lowering of the Kondo scale with
decreasing x. The evolution of the characteristic energy scales for both the
Kondo effect and the crystal electric field splitting are deduced. An
extrapolation allows to estimate the Kondo temperature of YbRh2Si2 to 29 K.Comment: 15 pages, 4 figures, accepted in Phys. Rev.
Divergence of the Grueneisen Ratio at Quantum Critical Points in Heavy Fermion Metals
We present low-temperature volume thermal expansion, , and specific
heat, , measurements on high-quality single crystals of CeNi2Ge2 and
YbRh2(SiGe) which are located very near to quantum
critical points. For both systems, shows a more singular temperature
dependence than , and thus the Grueneisen ratio
diverges as T --> 0. For CeNi2Ge2, our results are in accordance with the
spin-density wave (SDW) scenario for three-dimensional critical
spin-fluctuations. By contrast, the observed singularity in
YbRh2_{0.95}_{0.05}_2$ cannot be explained by the itinerant SDW
theory but is qualitatively consistent with a locally quantum critical picture.Comment: 11 pages, 4 figure
Role of spin-orbit coupling on the spin triplet pairing in Na_{x}CoO_{2}yH_{2}O I: d-vector under zero magnetic field
The d-vector in possibile spin triplet superconductor Na_{x}CoO_{2}yH_{2}O is
microscopically investigated on the basis of the multi-orbital Hubbard model
including the atomic spin-orbit coupling. As a result of the perturbation
theory, we obtain the stable spin triplet superconductivity where the p-wave
and f-wave states can be stabilized. If we neglect the spin-orbit coupling,
superconducting state has 6-fold (3-fold) degeneracy in the p-wave (f-wave)
state. This degeneracy is lifted by the spin-orbit coupling. We determine the
d-vector within the linearlized Dyson-Gorkov equation. It is shown that the
d-vector is always along the plane when the pairing symmetry is p-wave, while
it depends on the parameters in case of the f-wave state. The lifting of
degeneracy is significant in the p-wave state while it is very small in the
f-wave state. This is because the first order term with respect to the
spin-orbit coupling is effective in the former case, while it is ineffective in
the latter case. The consistency of these results with NMR and \muSR
measurements are discussed.Comment: To appear in J. Phys. Soc. Jpn. 74 (2005) No.
Resonances and fluctuations of strange particle in 200 GeV Au-Au collisions
We perform an analysis of preliminary data on strange particles yields and
fluctuations within the Statistical hadronization model. We begin by describing
the theoretical disagreements between different statistical models currently on
the market. We then show how the simultaneous analysis of yields and
fluctuations can be used to differentiate between the different models, and
determine if one of them can be connected to underlying physics. We perform a
study on a RHIC 200 GeV data sample that includes stable particles, resonances,
and the event-by-event fluctuation of the ratio. We show that the
equilibrium statistical model can not describe the fluctuation, unless an
unrealistically small volume is assumed. Such small volume then makes it
impossible to describe the total particle multiplicity. The non-equilibrium
model,on the other hand, describes both the fluctuation and yields
acceptably due to the extra boost to the fluctuation provided by the high
pion chemical potential. and abundance is described
within error bars, but the is under-predicted to 1.5 standard
deviations. We suggest further measurements that have the potential to test the
non-equilibrium model, as well as gauge the effect of re-interactions between
hadronization and freeze-out.Comment: References added, equations corrected. As accepted for publication by
Journal of Physics
Thermal multifragmentation in p + Au interactions at 2.16, 3.6 and 8.1 GeV incident energies
Multiple emission of intermediate-mass fragments has been studied for the collisions p + Au at 2.16, 3.6 and 8.1 GeV with the FASA setup. The mean IMF multiplicities for events with at least one IMF are equal to 1.7, 1.9 and 2.1 (±0.2) respectively. The multiplicity, charge distributions and kinetic energy spectra of IMF are described in the framework of a intranuclear cascade model followed by the statistical multifragmentation model. However, between the two parts of the calculation the excitation energies and the residual masses and charges are modified to take into account the losses during expansion. The results support a scenario of true thermal multifragmentation of a hot and expanded target spectator
Hadron Production in Heavy Ion Collisions
We review hadron production in heavy ion collisions with emphasis on pion and
kaon production at energies below 2 AGeV and on partonic collectivity at RHIC
energies.Comment: 31 pages, 26 figures, accepted for publication in Landolt-Boernstein
Volume 1-23
Recent astrophysical and accelerator based results on the Hadronic Equation of State
In astrophysics as well as in hadron physics progress has recently been made
on the determination of the hadronic equation of state (EOS) of compressed
matter. The results are contradictory, however. Simulations of heavy ion
reactions are now sufficiently robust to predict the stiffness of the (EOS)
from (i) the energy dependence of the ratio of from Au+Au and C+C
collisions and (ii) the centrality dependence of the multiplicities. The
data are best described with a compressibility coefficient at normal nuclear
matter density around 200 MeV, a value which is usually called
``soft'' The recent observation of a neutron star with a mass of twice the
solar mass is only compatible with theoretical predictions if the EOS is stiff.
We review the present situation.Comment: invited talk Strange Quark Matter Conference SQM06 in Los Angele
Thermal Dileptons at LHC
We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb
collisions at LHC. Hadronic emission in the low-mass region is calculated using
in-medium spectral functions of light vector mesons within hadronic many-body
theory. In the intermediate-mass region thermal radiation from the Quark-Gluon
Plasma, evaluated perturbatively with hard-thermal loop corrections, takes
over. An important source over the entire mass range are decays of correlated
open-charm hadrons, rendering the nuclear modification of charm and bottom
spectra a critical ingredient.Comment: 2 pages, 2 figures, contributed to Workshop on Heavy Ion Collisions
at the LHC: Last Call for Predictions, Geneva, Switzerland, 14 May - 8 Jun
2007 v2: acknowledgment include
Charge separation relative to the reaction plane in Pb-Pb collisions at TeV
Measurements of charge dependent azimuthal correlations with the ALICE
detector at the LHC are reported for Pb-Pb collisions at TeV. Two- and three-particle charge-dependent azimuthal correlations in
the pseudo-rapidity range are presented as a function of the
collision centrality, particle separation in pseudo-rapidity, and transverse
momentum. A clear signal compatible with a charge-dependent separation relative
to the reaction plane is observed, which shows little or no collision energy
dependence when compared to measurements at RHIC energies. This provides a new
insight for understanding the nature of the charge dependent azimuthal
correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286
A note on comonotonicity and positivity of the control components of decoupled quadratic FBSDE
In this small note we are concerned with the solution of Forward-Backward
Stochastic Differential Equations (FBSDE) with drivers that grow quadratically
in the control component (quadratic growth FBSDE or qgFBSDE). The main theorem
is a comparison result that allows comparing componentwise the signs of the
control processes of two different qgFBSDE. As a byproduct one obtains
conditions that allow establishing the positivity of the control process.Comment: accepted for publicatio
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