10,151 research outputs found
Inequalities for low-energy symmetric nuclear matter
Using effective field theory we prove inequalities for the correlations of
two-nucleon operators in low-energy symmetric nuclear matter. For physical
values of operator coefficients in the effective Lagrangian, the S = 1, I = 0
channel correlations must have the lowest energy and longest correlation length
in the two-nucleon sector. This result is valid at nonzero density and
temperature.Comment: 9 page
Lattice Monte Carlo calculations for unitary fermions in a finite box
We perform lattice Monte Carlo simulations for up to 66 unitary fermions in a
finite box using a highly improved lattice action for nonrelativistic spin 1/2
fermions. We obtain a value of for the Bertsch
parameter, defined as the energy of the unitary Fermi gas measured in units of
the free gas energy in the thermodynamic limit. In addition, for up to four
unitary fermions, we compute the spectrum of the lattice theory by exact
diagonalization of the transfer matrix projected onto irreducible
representations of the octahedral group for small to moderate size lattices,
providing an independent check of our few-body simulation results. We compare
our exact numerical and simulation results for the spectrum to benchmark
studies of other research groups, as well as perform an extended analysis of
our lattice action improvement scheme, including an analysis of the errors
associated with higher partial waves and finite temporal discretization.Comment: Significant revisions from previous version. Included data at a
larger volume and performed an infinite volume extrapolation of the Bertsch
parameter. Published versio
Zone Determinant Expansions for Nuclear Lattice Simulations
We introduce a new approximation to nucleon matrix determinants that is
physically motivated by chiral effective theory. The method involves breaking
the lattice into spatial zones and expanding the determinant in powers of the
boundary hopping parameter.Comment: 20 pages, 6 figures, revtex4 (version to appear in PRC
J/\Psi production in two-photon collisions at next-to-leading order
In this paper, we report on the calculation of the cross section of J/\Psi
plus jet inclusive production in direct two-photon collisions at
next-to-leading order within the factorization formalism of nonrelativistic
quantum chromodynamics (NRQCD). Theoretical predictions for the future e^+e^-
linear collider TESLA are also presented.Comment: 5 pages, 2 figures, talk given at the 7th DESY Workshop on Elementary
Particle Theory: Loops and Legs in Quantum Field Theory, Zinnowitz, Germany,
25-30 April, 2004: added references for section
The Rich Mid-Infrared Environments of Two Highly-Obscured X-ray Binaries: Spitzer Observations of IGR J16318-4848 and GX 301-2
We present the results of Spitzer mid-infrared spectroscopic observations of
two highly-obscured massive X-ray binaries: IGR J16318-4848 and GX301-2. Our
observations reveal for the first time the extremely rich mid-infrared
environments of this type of source, including multiple continuum emission
components (a hot component with T > 700 K and a warm component with T ~ 180 K)
with apparent silicate absorption features, numerous HI recombination lines,
many forbidden ionic lines of low ionization potentials, and pure rotational H2
lines. This indicates that both sources have hot and warm circumstellar dust,
ionized stellar winds, extended low-density ionized regions, and
photo-dissociated regions. It appears difficult to attribute the total optical
extinction of both sources to the hot and warm dust components, which suggests
that there could be an otherwise observable colder dust component responsible
for the most of the optical extinction and silicate absorption features. The
observed mid-infrared spectra are similar to those from Luminous Blue
Variables, indicating that the highly-obscured massive X-ray binaries may
represent a previously unknown evolutionary phase of X-ray binaries with
early-type optical companions. Our results highlight the importance and utility
of mid-infrared spectroscopy to investigate highly-obscured X-ray binaries.Comment: To appear in ApJ Letter
N-acetylglucosamine 6-Phosphate Deacetylase (nagA) Is Required for N-acetyl Glucosamine Assimilation in Gluconacetobacter xylinus
Metabolic pathways for amino sugars (N-acetylglucosamine; GlcNAc and glucosamine;
Gln) are essential and remain largely conserved in all three kingdoms of life,
i.e., microbes, plants and animals. Upon uptake, in the cytoplasm these amino
sugars undergo phosphorylation by phosphokinases and subsequently deacetylation
by the enzyme N-acetylglucosamine 6-phosphate deacetylase
(nagA) to yield glucosamine-6-phosphate and acetate, the first committed step
for both GlcNAc assimilation and amino-sugar-nucleotides biosynthesis. Here we
report the cloning of a DNA fragment encoding a partial nagA gene and its
implications with regard to amino sugar metabolism in the cellulose producing
bacterium Glucoacetobacter xylinus (formally known as
Acetobacter xylinum). For this purpose, nagA was disrupted
by inserting tetracycline resistant gene (nagA::tetr; named as
ΔnagA) via homologous recombination. When compared to glucose fed
conditions, the UDP-GlcNAc synthesis and bacterial growth (due to lack of GlcNAc
utilization) was completely inhibited in nagA mutants. Interestingly, that
inhibition occured without compromising cellulose production efficiency and its
molecular composition under GlcNAc fed conditions. We conclude that nagA plays
an essential role for GlcNAc assimilation by G. xylinus thus is
required for the growth and survival for the bacterium in presence of GlcNAc as
carbon source. Additionally, G. xylinus appears to possess the
same molecular machinery for UDP-GlcNAc biosynthesis from GlcNAc precursors as
other related bacterial species
Non-thermalization in trapped atomic ion spin chains
Linear arrays of trapped and laser cooled atomic ions are a versatile
platform for studying emergent phenomena in strongly-interacting many-body
systems. Effective spins are encoded in long-lived electronic levels of each
ion and made to interact through laser mediated optical dipole forces. The
advantages of experiments with cold trapped ions, including high spatiotemporal
resolution, decoupling from the external environment, and control over the
system Hamiltonian, are used to measure quantum effects not always accessible
in natural condensed matter samples. In this review we highlight recent work
using trapped ions to explore a variety of non-ergodic phenomena in long-range
interacting spin-models which are heralded by memory of out-of-equilibrium
initial conditions. We observe long-lived memory in static magnetizations for
quenched many-body localization and prethermalization, while memory is
preserved in the periodic oscillations of a driven discrete time crystal state.Comment: 14 pages, 5 figures, submitted for edition of Phil. Trans. R. Soc. A
on "Breakdown of ergodicity in quantum systems
Quasifree kaon-photoproduction from nuclei in a relativistic approach
We compute the recoil polarization of the lambda-hyperon and the photon
asymmetry for the quasifree photoproduction of kaons in a relativistic
impulse-approximation approach. Our motivation for studying polarization
observables is threefold. First, polarization observables are more effective
discriminators of subtle dynamics than the unpolarized cross section. Second,
earlier nonrelativistic calculations suggest an almost complete insensitivity
of polarization observables to distortions effects. Finally, this insensitivity
entails an enormous simplification in the theoretical treatment. Indeed, by
introducing the notion of a ``bound-nucleon propagator'' we exploit Feynman's
trace techniques to develop closed-form, analytic expressions for all
photoproduction observables. Moreover, our results indicate that polarization
observables are also insensitive to relativistic effects and to the nuclear
target. Yet, they are sensitive to the model parameters, making them ideal
tools for the study of modifications to the elementary amplitude --- such as in
the production, propagation, and decay of nucleon resonances --- in the nuclear
medium.Comment: 15 pages and 6 figures - submitted to PR
Meson Condensation in Dense Matter Revisited
The results for meson condensation in the literature vary markedly depending
on whether one uses chiral perturbation theory or the current-algebra-plus-PCAC
approach. To elucidate the origin of this discrepancy, we re-examine the role
of the sigma-term in meson condensation. We find that the resolution of the
existing discrepancy requires a knowledge of terms in the Lagrangian that are
higher order in density than hitherto considered.Comment: 10pages, USC(NT)-94-
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