10,156 research outputs found
Production rates for hadrons, pentaquarks and , and di-baryon in relativistic heavy ion collisions by a quark combination model
The hadron production in relativistic heavy ion collisions is well described
by the quark combination model. The mixed ratios for various hadrons and the
transverse momentum spectra for long-life hadrons are predicted and agree with
recent RHIC data. The production rates for the pentaquarks , and the di-baryon are estimated, neglecting
the effect from the transition amplitude for constituent quarks to form an
exotic state.Comment: The difference between our model and other combination models is
clarified. The scaled transverse momentum spectra for pions, kaons and
protoms at both 130 AGeV and 200 AGeV are given, replacing the previous
results in transverse momentum spectr
Multidimensional entropy landscape of quantum criticality
The Third Law of Thermodynamics states that the entropy of any system in
equilibrium has to vanish at absolute zero temperature. At nonzero
temperatures, on the other hand, matter is expected to accumulate entropy near
a quantum critical point (QCP), where it undergoes a continuous transition from
one ground state to another. Here, we determine, based on general thermodynamic
principles, the spatial-dimensional profile of the entropy S near a QCP and its
steepest descent in the corresponding multidimensional stress space. We
demonstrate this approach for the canonical quantum critical compound
CeCu6-xAux near its onset of antiferromagnetic order. We are able to link the
directional stress dependence of S to the previously determined geometry of
quantum critical fluctuations. Our demonstration of the multidimensional
entropy landscape provides the foundation to understand how quantum criticality
nucleates novel phases such as high-temperature superconductivity.Comment: 14 pages, 4 figure
Semiclassical Analysis of Extended Dynamical Mean Field Equations
The extended Dynamical Mean Field Equations (EDMFT) are analyzed using
semiclassical methods for a model describing an interacting fermi-bose system.
We compare the semiclassical approach with the exact QMC (Quantum Montecarlo)
method. We found the transition to an ordered state to be of the first order
for any dimension below four.Comment: RevTex, 39 pages, 16 figures; Appendix C added, typos correcte
Quantum criticality in spin chains with non-ohmic dissipation
We investigate the critical behavior of a spin chain coupled to bosonic baths
characterized by a spectral density proportional to , with .
Varying changes the effective dimension of the
system, where is the dynamical critical exponent and the number of spatial
dimensions is set to one. We consider two extreme cases of clock models,
namely Ising-like and U(1)-symmetric ones, and find the critical exponents
using Monte Carlo methods. The dynamical critical exponent and the anomalous
scaling dimension are independent of the order parameter symmetry for
all values of . The dynamical critical exponent varies continuously from for to for , and the anomalous scaling dimension
evolves correspondingly from to . The latter
exponent values are readily understood from the effective dimensionality of the
system being for , while for the anomalous
dimension takes the well-known exact value for the 2D Ising and XY models,
since then . A noteworthy feature is, however, that
approaches unity and approaches 1/4 for values of , while naive
scaling would predict the dissipation to become irrelevant for . Instead,
we find that for for both Ising-like and U(1)
order parameter symmetry. These results lead us to conjecture that for all
site-dissipative chains, these two exponents are related by the scaling
relation . We also connect our results to
quantum criticality in nondissipative spin chains with long-range spatial
interactions.Comment: 8 pages, 6 figure
Hall effect in heavy-fermion metals
The heavy fermion systems present a unique platform in which strong
electronic correlations give rise to a host of novel, and often competing,
electronic and magnetic ground states. Amongst a number of potential
experimental tools at our disposal, measurements of the Hall effect have
emerged as a particularly important one in discerning the nature and evolution
of the Fermi surfaces of these enigmatic metals. In this article, we present a
comprehensive review of Hall effect measurements in the heavy-fermion
materials, and examine the success it has had in contributing to our current
understanding of strongly correlated matter. Particular emphasis is placed on
its utility in the investigation of quantum critical phenomena which are
thought to drive many of the exotic electronic ground states in these systems.
This is achieved by the description of measurements of the Hall effect across
the putative zero-temperature instability in the archetypal heavy-fermion metal
YbRhSi. Using the CeIn (with Co, Ir) family of systems as
a paradigm, the influence of (antiferro-)magnetic fluctuations on the Hall
effect is also illustrated. This is compared to prior Hall effect measurements
in the cuprates and other strongly correlated systems to emphasize on the
generality of the unusual magnetotransport in materials with non-Fermi liquid
behavior.Comment: manuscript accepted in Adv. Phy
Global Phase Diagram of the Kondo Lattice: From Heavy Fermion Metals to Kondo Insulators
We discuss the general theoretical arguments advanced earlier for the T=0
global phase diagram of antiferromagnetic Kondo lattice systems, distinguishing
between the established and the conjectured. In addition to the well-known
phase of a paramagnetic metal with a "large" Fermi surface (P_L), there is also
an antiferromagnetic phase with a "small" Fermi surface (AF_S). We provide the
details of the derivation of a quantum non-linear sigma-model (QNLsM)
representation of the Kondo lattice Hamiltonian, which leads to an effective
field theory containing both low-energy fermions in the vicinity of a Fermi
surface and low-energy bosons near zero momentum. An asymptotically exact
analysis of this effective field theory is made possible through the
development of a renormalization group procedure for mixed fermion-boson
systems. Considerations on how to connect the AF_S and P_L phases lead to a
global phase diagram, which not only puts into perspective the theory of local
quantum criticality for antiferromagnetic heavy fermion metals, but also
provides the basis to understand the surprising recent experiments in
chemically-doped as well as pressurized YbRh2Si2. We point out that the AF_S
phase still occurs for the case of an equal number of spin-1/2 local moments
and conduction electrons. This observation raises the prospect for a global
phase diagram of heavy fermion systems in the Kondo-insulator regime. Finally,
we discuss the connection between the Kondo breakdown physics discussed here
for the Kondo lattice systems and the non-Fermi liquid behavior recently
studied from a holographic perspective.Comment: (v3) leftover typos corrected. (v2) Published version. 32 pages, 4
figures. Section 7, on the connection between the Kondo lattice systems and
the holographic models of non-Fermi liquid, is expanded. (v1) special issue
of JLTP on quantum criticalit
Advancing Solar Irradiance Measurement for Climate-Related Studies: Accurate Constraint on Direct Aerosol Radiative Effect (DARE)
Earth's climate is driven primarily by solar radiation. As summarized in various IPCC reports, the global average of radiative forcing for different agents and mechanisms, such as aerosols or CO2 doubling, is in the range of a few W/sq m. However, when solar irradiance is measured by broadband radiometers, such as the fleet of Eppley Precision Solar Pyranometers (PSP) and equivalent instrumentation employed worldwide, the measurement uncertainty is larger than 2% (e.g., WMO specification of pyranometer, 2008). Thus, out of the approx. 184 W/sq m (approx.263 W/sq m if cloud-free) surface solar insolation (Trenberth et al. 2009), the measurement uncertainty is greater than +/-3.6 W/sq m, overwhelming the climate change signals. To discern these signals, less than a 1 % measurement uncertainty is required and is currently achievable only by means of a newly developed methodology employing a modified PSP-like pyranometer and an updated calibration equation to account for its thermal effects (li and Tsay, 2010). In this talk, we will show that some auxiliary measurements, such as those from a collocated pyrgeometer or air temperature sensors, can help correct historical datasets. Additionally, we will also demonstrate that a pyrheliometer is not free of the thermal effect; therefore, comparing to a high cost yet still not thermal-effect-free "direct + diffuse" approach in measuring surface solar irradiance, our new method is more economical, and more likely to be suitable for correcting a wide variety of historical datasets. Modeling simulations will be presented that a corrected solar irradiance measurement has a significant impact on aerosol forcing, and thus plays an important role in climate studies
Correlation Induced Insulator to Metal Transitions
We study a spinless two-band model at half-filling in the limit of infinite
dimensions. The ground state of this model in the non-interacting limit is a
band-insulator. We identify transitions to a metal and to a charge-Mott
insulator, using a combination of analytical, Quantum Monte Carlo, and zero
temperature recursion methods. The metallic phase is a non-Fermi liquid state
with algebraic local correlation functions with universal exponents over a
range of parameters.Comment: 12 pages, REVTE
Heavy Fermions and Quantum Phase Transitions
Quantum phase transitions arise in many-body systems due to competing
interactions that promote rivaling ground states. Recent years have seen the
identification of continuous quantum phase transitions, or quantum critical
points, in a host of antiferromagnetic heavy-fermion compounds. Studies of the
interplay between the various effects have revealed new classes of quantum
critical points, and are uncovering a plethora of new quantum phases. At the
same time, quantum criticality has provided fresh insights into the electronic,
magnetic, and superconducting properties of the heavy-fermion metals. We review
these developments, discuss the open issues, and outline some directions for
future research.Comment: review article, 26 pages, 4 figure
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