17,664 research outputs found
A Rigorous Proof of Fermi Liquid Behavior for Jellium Two-Dimensional Interacting Fermions
Using the method of continuous constructive renormalization group around the
Fermi surface, it is proved that a jellium two-dimensional interacting system
of Fermions at low temperature remains analytic in the coupling constant
for where is some numerical constant
and is the temperature. Furthermore in that range of parameters, the first
and second derivatives of the self-energy remain bounded, a behavior which is
that of Fermi liquids and in particular excludes Luttinger liquid behavior. Our
results prove also that in dimension two any transition temperature must be
non-perturbative in the coupling constant, a result expected on physical
grounds. The proof exploits the specific momentum conservation rules in two
dimensions.Comment: 4 pages, no figure
Ultralight reactive metal foams produced as structural shapes in space: System design
This autonomous experiment for foaming metals in space involved: (1) payload support structure; (2) furnace and foaming apparatus; (3) electronic controls; (4) battery power; and (5) metallurgy. Emphasis was laid on a modular design which was easily modifiable and which offered maximum durability, safety, and failure tolerance
Spectral Function of 2D Fermi Liquids
We show that the spectral function for single-particle excitations in a
two-dimensional Fermi liquid has Lorentzian shape in the low energy limit.
Landau quasi-particles have a uniquely defined spectral weight and a decay rate
which is much smaller than the quasi-particle energy. By contrast, perturbation
theory and the T-matrix approximation yield spurious deviations from Fermi
liquid behavior, which are particularly pronounced for a linearized dispersion
relation.Comment: 6 pages, LaTeX2e, 5 EPS figure
Analysis of IUE observations of CS in Comet Bradfield (1979 l)
The high resolution rotational band profiles were fitted with theoretical band profiles which are derived using a Boltzmann temperature of 70 K. A very rapid variation with heliocentric distance for the CS brightness was found. The implications of these results for models of the coma along with the origin of the CS species are discussed
Statistical Complexity of Simple 1D Spin Systems
We present exact results for two complementary measures of spatial structure
generated by 1D spin systems with finite-range interactions. The first, excess
entropy, measures the apparent spatial memory stored in configurations. The
second, statistical complexity, measures the amount of memory needed to
optimally predict the chain of spin values. These statistics capture distinct
properties and are different from existing thermodynamic quantities.Comment: 4 pages with 2 eps Figures. Uses RevTeX macros. Also available at
http://www.santafe.edu/projects/CompMech/papers/CompMechCommun.htm
Conserving and gapless approximations for the composite bosons in terms of the constituent fermions
A long-standing problem with the many-body approximations for interacting
condensed bosons has been the dichotomy between the ``conserving'' and
``gapless'' approximations, which either obey the conservations laws or satisfy
the Hugenholtz-Pines condition for a gapless excitation spectrum, in the order.
It is here shown that such a dichotomy does not exist for a system of composite
bosons, which form as bound-fermion pairs in the strong-coupling limit of the
fermionic attraction. By starting from the constituent fermions, for which
conserving approximations can be constructed for any value of the mutual
attraction according to the Baym-Kadanoff prescriptions, it is shown that these
approximations also result in a gapless excitation spectrum for the boson-like
propagators in the broken-symmetry phase. This holds provided the corresponding
equations for the fermionic single- and two-particle Green's functions are
solved self-consistently.Comment: 4 pages, 1 figur
On the Stability and Single-Particle Properties of Bosonized Fermi Liquids
We study the stability and single-particle properties of Fermi liquids in
spatial dimensions greater than one via bosonization. For smooth non-singular
Fermi liquid interactions we obtain Shankar's renormalization- group flows and
reproduce well known results for quasi-particle lifetimes. We demonstrate by
explicit calculation that spin-charge separation does not occur when the Fermi
liquid interactions are regular. We also explore the relationship between
quantized bosonic excitations and zero sound modes and present a concise
derivation of both the spin and the charge collective mode equations. Finally
we discuss some aspects of singular Fermi liquid interactions.Comment: 13 pages plus three postscript figures appended; RevTex 3.0;
BUP-JBM-
The X-ray spectrum of Fe XVII revisited with a multi-ion model
The theoretical intensities of the soft X-ray Fe XVII lines arising from
2l-3l' transitions are reexamined using a three-ion collisional-radiative model
that includes the contributions to line formation of radiative recombination
(RR), dielectronic recombination (DR), resonant excitation (RE), and
inner-shell collisional ionization (CI), in addition to the usual contribution
of collisional excitation (CE). These additional processes enhance mostly the
2p-3s lines and not the 2p-3d lines. Under coronal equilibrium conditions, in
the electron temperature range of 400 to 600 eV where the Fe XVII line
emissivities peak, the combined effect of the additional processes is to
enhance the 2p-3s lines at 16.78, 17.05, and 17.10 A, by ~ 25%, 30%, and 55%,
respectively, compared with their traditional, single-ion CE values. The weak
2p-3d line at 15.45 A is also enhanced by up to 20%, while the other 2p-3d
lines are almost unaffected. The effects of DR and RE are found to be dominant
in this temperature range (400 - 600 eV), while that of CI is 3% at the most,
and the contribution of RR is less than 1%. At lower temperatures, where the Fe
XVII / Fe XVIII abundance ratio is high, the RE effect dominates. However, as
the temperature rises and the Fe XVIII abundance increases, the DR effect takes
over.
The newly calculated line powers can reproduce most of the often observed
high values of the (I17.05 + I17.10) / I15.01 intensity ratio. The importance
of ionization and recombination processes to the line strengths also helps to
explain why laboratory measurements in which CE is essentially the sole
mechanism agree well with single-ion calculations, but do not reproduce the
astrophysically observed ratios.Comment: Submitted to Ap
Functional renormalization group approach to correlated fermion systems
Numerous correlated electron systems exhibit a strongly scale-dependent
behavior. Upon lowering the energy scale, collective phenomena, bound states,
and new effective degrees of freedom emerge. Typical examples include (i)
competing magnetic, charge, and pairing instabilities in two-dimensional
electron systems, (ii) the interplay of electronic excitations and order
parameter fluctuations near thermal and quantum phase transitions in metals,
(iii) correlation effects such as Luttinger liquid behavior and the Kondo
effect showing up in linear and non-equilibrium transport through quantum wires
and quantum dots. The functional renormalization group is a flexible and
unbiased tool for dealing with such scale-dependent behavior. Its starting
point is an exact functional flow equation, which yields the gradual evolution
from a microscopic model action to the final effective action as a function of
a continuously decreasing energy scale. Expanding in powers of the fields one
obtains an exact hierarchy of flow equations for vertex functions. Truncations
of this hierarchy have led to powerful new approximation schemes. This review
is a comprehensive introduction to the functional renormalization group method
for interacting Fermi systems. We present a self-contained derivation of the
exact flow equations and describe frequently used truncation schemes. Reviewing
selected applications we then show how approximations based on the functional
renormalization group can be fruitfully used to improve our understanding of
correlated fermion systems.Comment: Review article, final version, 59 pages, 28 figure
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