7,193 research outputs found
NMR relaxation rate and dynamical structure factors in nematic and multipolar liquids of frustrated spin chains under magnetic fields
Recently, it has been shown that spin nematic (quadrupolar) or higher
multipolar correlation functions exhibit a quasi long-range order in the wide
region of the field-induced Tomonaga-Luttinger-liquid (TLL) phase in spin-1/2
zigzag chains. In this paper, we point out that the temperature dependence of
the NMR relaxation rate 1/T_1 in these multipolar TLLs is qualitatively
different from that in more conventional TLLs of one-dimensional quantum
magnets (e.g., the spin-1/2 Heisenberg chain); 1/T_1 decreases with lowering
temperature in multipolar TLL. We also discuss low-energy features in spin
dynamical structure factors which are characteristic of the multipolar TLL
phases.Comment: 4+epsilon pages, 2 figures, published versio
Entropy production and isotropization in Yang-Mills theory with use of quantum distribution function
We investigate thermalization process in relativistic heavy ion collisions in
terms of the Husimi-Wehrl (HW) entropy defined with the Husimi function, a
quantum distribution function in a phase space. We calculate the semiclassical
time evolution of the HW entropy in Yang-Mills field theory with the
phenomenological initial field configuration known as the McLerran-Venugopalan
model in a non-expanding geometry, which has instabilty triggered by initial
field fluctuations. HW-entropy production implies the thermalization of the
system and it reflects the underlying dynamics such as chaoticity and
instability. By comparing the production rate with the Kolmogorov-Sina\"i rate,
we find that the HW entropy production rate is significantly larger than that
expected from chaoticity. We also show that the HW entropy is finally saturated
when the system reaches a quasi-stationary state. The saturation time of the HW
entropy is comparable with that of pressure isotropization, which is around
fm/c in the present calculation in the non-expanding geometry.Comment: 17 pages, 5 figure
Entropy production in quantum Yang-Mills mechanics in semi-classical approximation
We discuss thermalization of isolated quantum systems by using the
Husimi-Wehrl entropy evaluated in the semiclassical treatment. The Husimi-Wehrl
entropy is the Wehrl entropy obtained by using the Husimi function for the
phase space distribution. The time evolution of the Husimi function is given by
smearing the Wigner function, whose time evolution is obtained in the
semiclassical approximation. We show the efficiency and usefullness of this
semiclassical treatment in describing entropy production of a couple of quantum
mechanical systems, whose classical counter systems are known to be chaotic. We
propose two methods to evaluate the time evolution of the Husimi-Wehrl entropy,
the test-particle method and the two-step Monte-Carlo method. We demonstrate
the characteristics of the two methods by numerical calculations, and show that
the simultaneous application of the two methods ensures the reliability of the
results of the Husimi-Wehrl entropy at a given time.Comment: 11 pages, 8 figure
Study of entropy production in Yang-Mills theory with use of Husimi function
Understanding the thermalization process in a pure quantum system is a
challenge in theoretical physics. In this work, we explore possible
thermalization mechanism in Yang-Mills(YM) theory by using a positive
semi-definite quantum distribution function called a Husimi function which is
given by a coarse graining of the Wigner function within the minimum
uncertainty. Then entropy is defined in terms of the Husimi function, which is
called the Husimi-Wehrl(HW) entropy. We propose two numerical methods to
calculate the HW entropy. We find that it is feasible to apply the
semi-classical approximation with the use of classical YM equation. It should
be noted that the semi-classical approximation is valid in the systems of
physical interest including the early stage of heavy-ion collisions. Using a
product ansatz for the Husimi function, which is confirmed to reproduce the HW
entropy within 20% error (overestimate) for a few-body quantum system, we
succeed in a numerical evaluation of HW entropy of YM fields and show that it
surely has a finite value and increases in time.Comment: 7 pages, 5 figures, Proceeding of the 33rd International Symposium on
Lattice Field Theory (Lattice 2015), 14-18 July 2015, Kobe International
Conference Center, Kobe, Japa
A new measurement of thermal conductivity of amorphous ice and its implications for the thermal evolution of comets
Very slowly deposited amorphous ice has a thermal conductivity about four orders of magnitude or more smaller than hitherto estimated. Using the exceedingly low value of the thermal conductivity of comets deduced from the properties of amorphous ice leads to the expectation that internal heating of comets is negligible below the outer several tens of centimeters
Solitons in Chern-Simons theories of nonrelativistic CP^{N-1} models: Spin textures in the quantum Hall effect
Topological solitons in CP^{N-1} models coupled with Chern-Simons gauge
theory and a Hopf term are studied both analytically and numerically.These
models are low-energy effective theories for the quantum Hall effect with
internal degrees of freedom, like that in bilayer electron systems. We
explicitly show that the CP^{N-1} models describe quite well spin textures in
the original Chern-Simons theory of bosonized electrons.Comment: Latex, 19 pages, 6 figure
Electromagnetic radiation due to naked singularity formation in self-similar gravitational collapse
Dynamical evolution of test fields in background geometry with a naked
singularity is an important problem relevant to the Cauchy horizon instability
and the observational signatures different from black hole formation. In this
paper we study electromagnetic perturbations generated by a given current
distribution in collapsing matter under a spherically symmetric self-similar
background. Using the Green's function method, we construct the formula to
evaluate the outgoing energy flux observed at the future null infinity. The
contributions from "quasi-normal" modes of the self-similar system as well as
"high-frequency" waves are clarified. We find a characteristic power-law time
evolution of the outgoing energy flux which appears just before naked
singularity formation, and give the criteria as to whether or not the outgoing
energy flux diverges at the future Cauchy horizon.Comment: 20 pages, 7 figures, references added to match the published versio
Stability of quantum states of finite macroscopic systems against classical noises, perturbations from environments, and local measurements
We study the stability of quantum states of macroscopic systems of finite
volume V, against weak classical noises (WCNs), weak perturbations from
environments (WPEs), and local measurements (LMs). We say that a pure state is
`fragile' if its decoherence rate is anomalously great, and `stable against
LMs' if the result of a LM is not affected by another LM at a distant point. By
making full use of the locality and huge degrees of freedom, we show the
following: (i) If square fluctuation of every additive operator is O(V) or less
for a pure state, then it is not fragile in any WCNs or WPEs. (ii) If square
fluctuations of some additive operators are O(V^2) for a pure state, then it is
fragile in some WCNs or WPEs. (iii) If a state (pure or mixed) has the `cluster
property,' then it is stable against LMs, and vice versa. These results have
many applications, among which we discuss the mechanism of symmetry breaking in
finite systems.Comment: 6 pages, no figure.Proof of the theorem is described in the revised
manuscrip
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