9,795 research outputs found
Relativistic BCS-BEC Crossover at Zero Temperature
We investigate the BCS-BEC crossover at zero temperature in the frame of a
relativistic model. The universality of the BCS-BEC crossover for
non-relativistic systems breaks down in relativistic case and the crossover can
be induced by changing the density. When the effective scattering length is
much less than the fermion Compton wavelength, we recover the non-relativistic
result if the gas is initially in non-relativistic state. At ultra-strong
coupling where the scattering length is of the order of the Compton wavelength,
a new BEC state appears. In this state the condensed bosons become nearly
massless and anti-fermions are excited. The behavior of the Goldstone mode and
the mixing between the amplitude and phase modes are significantly different in
different condensed regions.Comment: 8 pages, 3 figures. V2: typos corrected, a comment on mean field
theory adde
Spin current through an ESR quantum dot: A real-time study
The spin transport in a strongly interacting spin-pump nano-device is studied
using the time-dependent variational-matrix-product-state (VMPS) approach. The
precession magnetic field generates a dissipationless spin current through the
quantum dot. We compute the real time spin current away from the equilibrium
condition. Both transient and stationary states are reached in the simulation.
The essentially exact results are compared with those from the Hartree-Fock
approximation (HFA). It is found that correlation effect on the physical
quantities at quasi-steady state are captured well by the HFA for small
interaction strength. However the HFA misses many features in the real time
dynamics. Results reported here may shed light on the understanding of the
ultra-fast processes as well as the interplay of the non-equilibrium and
strongly correlated effect in the transport properties.Comment: 5 pages, 5 figure
Quark and Gluon Condensates in Isospin Matter
Applying the Hellmann-Feynman theorem to a charged pion gas, the quark and
gluon condensates at low isospin density are determined by precise pion
properties. At intermediate density around , from both the
estimation for the dilute pion gas and the calculation with Nambu--Jona-Lasinio
model, the quark condensate is strongly and monotonously suppressed, while the
gluon condensate is enhanced and can be larger than its vacuum value. This
unusual behavior of the gluon condensate is universal for Bose condensed matter
of mesons. Our results can be tested by lattice calculations at finite isospin
density.Comment: 4 pages, 2 figures. Published version in PR
Liquid Crystal-Solid Interface Structure at the Antiferroelectric-Ferroelectric Phase Transition
Total Internal Reflection (TIR) is used to probe the molecular organization
at the surface of a tilted chiral smectic liquid crystal at temperatures in the
vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are
interpreted using an exact analytical solution of a real model for
ferroelectric order at the surface. In the mixture T3, ferroelectric surface
order is expelled with the bulk ferroelectric-antiferroelectric transition. The
conditions for ferroelectric order at the surface of an antiferroelectric bulk
are presented
Modeling soil organic carbon change in croplands of China
Using 1990 conditions, we modeled carbon (C) and nitrogen (N) biogeochemical cycles in croplands of China (and, for comparison, the United States) to estimate the annual soil organic-carbon (SOC) balance for all cropland. Overall, we estimate that China\u27s croplands lost 1.6% of their SOC (to a depth of 0.3 m) in 1990, and that U.S. cropland lost 0.1%. A key element in this difference was that ∼25% of aboveground crop residue in China was returned to the soil, compared to ∼90% in the United States. In China, SOC losses were greatest in the northeast (∼103 kg C·ha–1·yr–1), and were generally smaller (\u3c0.5 × 103 kg C·ha–1·yr–1) in regions with a longer cultivation history. Some regions showed SOC gains, generally \u3c103 kg C·ha–1·yr–1. Reduced organic-matter input to China\u27s cropland soils, and lower overall SOC levels in those soils, led to lower levels of N mineralization in the simulations, consistent with higher rates of synthetic-fertilizer application in China. C and N cycles are closely linked to soil fertility, crop yield, and non-point-source environmental pollution
The Radiative Decay of Vector Mesons
In this paper, radiative decays , are studied
systematically in the U(3)_L\timesU(3)_R chiral theory of mesons. The
theoretical differential spectrum with respect to photon energy and branch
ratio for agree well with the experimental data.
Differential spectrums and branch ratios for are predicted. The process is relevant to precision measurment of CP-violation
parameters in the kaon systerm at a -factory. We give a complete estimate
of the branch ratio for this decay process by including scalar resonance poles, nonresonant smooth amplitude and an abnormal parity process with
pole which hasn't been considered before. We conclude that processes with
intermediate do not pose a potential background problem for CP violation experiments.Comment: Revtex file, 12 pages, 9 eps figure
Soft Photons from Off-shell Particles in a Hot Plasma
Considering the propagation of off-shell particles in the framework of
thermal field theory, we present the general formalism for the calculation of
the production rate of soft photons and dileptons from a hot plasma. This
approach is illustrated with an electrodynamic plasma. The photon production
rate from strongly interacting quarks in the quark-gluon plasma, which might be
formed in ultrarelativistic heavy ion collisions, is calculated in the
previously unaccessible regime of photon energies of the order of the plasma
temperature within an effective field theory incorporating dynamical chiral
symmetry breaking.Comment: 8 pages in RevTeX format, 3 figures uuencoded postscript added. Also
available by anonymous ftp at ftp://tpri6c.gsi.de/pub/phenning/qh95ga
There and back again: Solar cycle effects in future measurements of low-energy atmospheric neutrinos
We study the impact of time-dependent solar cycles in the atmospheric
neutrino rate at DUNE and Hyper-Kamiokande (HK), focusing in particular on the
flux below 1 GeV. Including the effect of neutrino oscillations for the
upward-going component that travels through the Earth, we find that across the
solar cycle the amplitude of time variation is about at DUNE, and at HK. At DUNE, the ratio of up/down-going events ranges from 0.45 to
0.85, while at HK, it ranges from 0.75 to 1.5. Over the 11-year solar cycle, we
find that the estimated statistical significance for observing time modulation
of atmospheric neutrinos is for DUNE and for HK. Flux
measurements at both DUNE and HK will be important for understanding
systematics in the low-energy atmospheric flux as well as for understanding the
effect of oscillations in low-energy atmospheric neutrinos.Comment: 6 pages (including one appendix), 5 figures. Comments welcom
Time-Dependent Gutzwiller Theory for Multiband Hubbard Models
Based on the variational Gutzwiller theory, we present a method for the
computation of response functions for multiband Hubbard models with general
local Coulomb interactions. The improvement over the conventional random-phase
approximation is exemplified for an infinite-dimensional two-band Hubbard model
where the incorporation of the local multiplet-structure leads to a much larger
sensitivity of ferromagnetism on the Hund coupling. Our method can be
implemented into LDA+Gutzwiller schemes and will therefore be an important tool
for the computation of response functions for strongly correlated materials.Comment: 4 pages, 3 figure
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