1,450 research outputs found
Is \lq\lq Heavy Quark Damping Rate Puzzle'' in Hot QCD Really the Puzzle?
Within the framework of perturbative resummation scheme of Pisarski and
Braaten, the decay- or damping-rate of a moving heavy quark (muon) to leading
order in weak coupling in hot QCD (QED) is examined. Although, as is well
known, the conventionally-defined damping rate diverges logarithmically at the
infrared limit, shown is that no such divergence appears in the physically
measurable decay rate. The cancellation occurs between the contribution from
the \lq\lq real'' decay diagram and the contribution from the diagrams with
\lq\lq thermal radiative correction''.Comment: 13pages, OCU-PHYS-15
Efficient variational approach to dynamics of a spatially extended bosonic Kondo model
We develop an efficient variational approach to studying dynamics of a
localized quantum spin coupled to a bath of mobile spinful bosons. We use
parity symmetry to decouple the impurity spin from the environment via a
canonical transformation and reduce the problem to a model of the interacting
bosonic bath. We describe coherent time evolution of the latter using bosonic
Gaussian states as a variational ansatz. We provide full analytical expressions
for equations describing variational time evolution that can be applied to
study in- and out-of-equilibrium phenomena in a wide class of quantum impurity
problems. In the accompanying paper [Y. Ashida {\it et al.}, Phys. Rev. Lett.
123, 183001 (2019)], we present a concrete application of this general
formalism to the analysis of the Rydberg Central Spin Model, in which the
spin-1/2 Rydberg impurity undergoes spin-changing collisions in a dense cloud
of two-component ultracold bosons. To illustrate new features arising from
orbital motion of the bath atoms, we compare our results to the Monte Carlo
study of the model with spatially localized bosons in the bath, in which random
positions of the atoms give rise to random couplings of the standard central
spin model.Comment: 15 pages, 6 figures. See also Phys. Rev. Lett. 123, 183001 (2019)
[arXiv:1905.08523
Quantum Rydberg Central Spin Model
We consider dynamics of a Rydberg impurity in a cloud of ultracold bosonic
atoms in which the Rydberg electron can undergo spin-changing collisions with
surrounding atoms. This system realizes a new type of the quantum impurity
problem that compounds essential features of the Kondo model, the Bose polaron,
and the central spin model. To capture the interplay of the Rydberg-electron
spin dynamics and the orbital motion of atoms, we employ a new variational
method that combines an impurity-decoupling transformation with a Gaussian
ansatz for the bath particles. We find several unexpected features of this
model that are not present in traditional impurity problems, including
interaction-induced renormalization of the absorption spectrum that eludes
simple explanations from molecular bound states, and long-lasting oscillations
of the Rydberg-electron spin. We discuss generalizations of our analysis to
other systems in atomic physics and quantum chemistry, where an electron
excitation of high orbital quantum number interacts with a spinful quantum
bath.Comment: 6 pages, 5 figures. See also Phys. Rev. A 100, 043618 (2019)
[arXiv:1905.09615
Finite-temperature reaction-rate formula: Finite volume system, detailed balance, limit, and cutting rules
A complete derivation, from first principles, of the reaction-rate formula
for a generic process taking place in a heat bath of finite volume is given. It
is shown that the formula involves no finite-volume correction. Through
perturbative diagrammatic analysis of the resultant formula, the
detailed-balance formula is derived. The zero-temperature limit of the formula
is discussed. Thermal cutting rules, which are introduced in previous work, are
compared with those introduced by other authors.Comment: 35pages (text) plus 4pages (figures
Many-body interferometry of magnetic polaron dynamics
The physics of quantum impurities coupled to a many-body environment is among
the most important paradigms of condensed matter physics. In particular, the
formation of polarons, quasiparticles dressed by the polarization cloud, is key
to the understanding of transport, optical response, and induced interactions
in a variety of materials. Despite recent remarkable developments in ultracold
atoms and solid-state materials, the direct measurement of their ultimate
building block, the polaron cloud, has remained a fundamental challenge. We
propose and anlalyze a unique platform to probe time-resolved dynamics of
polaron-cloud formation with an interferometric protocol. We consider an
impurity atom immersed in a two-component Bose-Einstein condensate, where the
impurity generates spin-wave excitations that can be directly measured by the
Ramsey interference of surrounding atoms. The dressing by spin waves leads to
the formation of magnetic polarons and reveals a unique interplay between few-
and many-body physics that is signified by single- and multi-frequency
oscillatory dynamics corresponding to the formation of many-body bound states.
Finally, we discuss concrete experimental implementations in ultracold atoms.Comment: 6+6 pages, 3+2 figures. See also Research highlight
[doi:10.1038/s41567-018-0088-x] in Nature Physic
Dimensionality dependence of optical nonlinearity and relaxation dynamics in cuprates
Femtosecond pump-probe measurements find pronounced dimensionality dependence
of the optical nonlinearity in cuprates. Although the coherent two-photon
absorption (TPA) and linear absorption bands nearly overlap in both quasi-one
and two-dimensional (1D and 2D) cuprates, the TPA coefficient is one order of
magnitude smaller in 2D than in 1D. Furthermore, picosecond recovery of optical
transparency is observed in 1D cuprates, while the recovery in 2D involves
relaxation channels with a time scales of tens of picoseconds. The experimental
results are interpreted within the two-band extended Hubbard model.Comment: 10 pages, 4 figure
A new technique using a rubber balloon in emergency second trimester cerclage for fetal membrane prolapse
The definitive version is available at www.blackwell-synergy.comArticleJOURNAL OF OBSTETRICS AND GYNAECOLOGY RESEARCH. 34(6):935-940 (2008)journal articl
Two tricritical lines from a Ginzburg-Landau expansion: application to the LOFF phase
We study the behavior of the two plane waves configuration in the LOFF phase
close to T=0. The study is performed by using a Landau-Ginzburg expansion up to
the eighth order in the gap. The general study of the corresponding grand
potential shows, under the assumption that the eighth term in the expansion is
strictly positive, the existence of two tricritical lines. This allows to
understand the existence of a second tricritical point for two antipodal plane
waves in the LOFF phase and justifies why the transition becomes second order
at zero temperature. The general analysis done in this paper can be applied to
other cases.Comment: LaTex file, 15 pages, 6 figure
Energy and pressure densities of a hot quark-gluon plasma
We calculate the energy and hydrostatic pressure densities of a hot
quark-gluon plasma in thermal equilibrium through diagrammatic analyses of the
statistical average, , of the
energy-momentum-tensor operator . To leading order at high
temperature, the energy density of the long wave length modes is consistently
extracted by applying the hard-thermal-loop resummation scheme to the
operator-inserted no-leg thermal amplitudes .
We find that, for the long wave length gluons, the energy density, being
positive, is tremendously enhanced as compared to the noninteracting case,
while, for the quarks, no noticeable deviation from the noninteracting case is
found.Comment: 33 pages. Figures are not include
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