43,780 research outputs found
What kinds of coordinate can keep the Hawking temperature invariant for the static spherically symmetric black hole?
By studying the Hawking radiation of the most general static spherically
symmetric black hole arising from scalar and Dirac particles tunnelling, we
find the Hawking temperature is invariant in the general coordinate
representation (\ref{arbitrary1}), which satisfies two conditions: a) its
radial coordinate transformation is regular at the event horizon; and b) there
is a time-like Killing vector.Comment: 10 page
Cusp-scaling behavior in fractal dimension of chaotic scattering
A topological bifurcation in chaotic scattering is characterized by a sudden
change in the topology of the infinite set of unstable periodic orbits embedded
in the underlying chaotic invariant set. We uncover a scaling law for the
fractal dimension of the chaotic set for such a bifurcation. Our analysis and
numerical computations in both two- and three-degrees-of-freedom systems
suggest a striking feature associated with these subtle bifurcations: the
dimension typically exhibits a sharp, cusplike local minimum at the
bifurcation.Comment: 4 pages, 4 figures, Revte
Power-Law Distributions in Circulating Money: Effect of Preferential Behavior
We introduce preferential behavior into the study on statistical mechanics of
money circulation. The computer simulation results show that the preferential
behavior can lead to power laws on distributions over both holding time and
amount of money held by agents. However, some constraints are needed in
generation mechanism to ensure the robustness of power-law distributions.Comment: 4 pages, 2 figure
NMR Determination of an Incommensurate Helical Antiferromagnetic Structure in EuCo2As2
We report Eu, As and Co nuclear magnetic resonance
(NMR) results on EuCoAs single crystal. Observations of Eu and
As NMR spectra in zero magnetic field at 4.3 K below an
antiferromagnetic (AFM) ordering temperature = 45 K and its
external magnetic field dependence clearly evidence an incommensurate helical
AFM structure in EuCoAs. Furthermore, based on Co NMR data in
both the paramagnetic and the incommensurate AFM states, we have determined the
model-independent value of the AFM propagation vector = (0, 0, 0.73
0.07)2/ where is the lattice parameter. Thus the
incommensurate helical AFM state was characterized by only NMR data with
model-independent analyses, showing NMR to be a unique tool for determination
of the spin structure in incommensurate helical AFMs.Comment: 6 pages, 4 figures, accepted for publication in Phys.Rev.
Evolution of the Fermi surface with carrier concentration in Bi_2Sr_2CaCu_2O_{8+\delta}
We show, by use of angle-resolved photoemission spectroscopy, that underdoped
Bi_2Sr_2CaCu_2O_{8+\delta} appears to have a large Fermi surface centered at
(\pi,\pi), even for samples with a T_c as low as 15 K. No clear evidence of a
Fermi surface pocket around (\pi/2,\pi/2) has been found. These conclusions are
based on a determination of the minimum gap locus in the pseudogap regime T_c <
T < T^*, which is found to coincide with the locus of gapless excitations in
momentum space (Fermi surface) determined above T^*. These results suggest that
the pseudogap is more likely of precursor pairing rather than magnetic origin.Comment: 4 pages, revtex, 4 postscript color figure
The physics of the stripe quantum critical point in the superconducting cuprates
We elaborate on several observable consequences of the Quantum-Critical-Point
scenario. In particular we show that the strong k-dependent scattering of the
quasiparticles with the quasi-critical charge and spin fluctuations reproduces
the main features of the low-energy spectral weights and of the observed Fermi
surfaces. In the underdoped cuprates the attractive k-dependent charge
scattering drives the formation of the pseudogap at the M points below the
crossover temperature T^*. In this context we discuss models for pseudogap
formation with relevant scattering in the particle-particle and particle-hole
channels. The experimental consequences for the pair-fluctuation and for the
pseudogap behavior are investigated.Comment: 4 pages, 2 enclosed figures, Proceedings of M2S-HTS
Symmetry, symmetry breaking, and pion parton distributions
Pion valence, glue and sea distributions are calculated using a continuum
approach to the two valence-body bound-state problem. Since the framework is
symmetry preserving, physical features of the distributions are properly
expressed. The analysis reveals that the emergent phenomenon of dynamical
chiral symmetry breaking causes a hardening of the valence-quark distribution
function, . Nevertheless, this distribution exhibits the behaviour predicted by quantum chromodynamics (QCD). At the scale
GeV, the following momentum fractions are predicted: , ,
. Evolving to GeV, the
result for agrees with that computed using lattice QCD. These
outcomes should both spur improved analyses of existing experiments and
stimulate efforts to obtain new data on the pion distribution functions using
available and envisioned facilities.Comment: 13 pages, 7 figures, 2 table
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