358 research outputs found
Ward identities for the Anderson impurity model: derivation via functional methods and the exact renormalization group
Using functional methods and the exact renormalization group we derive Ward
identities for the Anderson impurity model. In particular, we present a
non-perturbative proof of the Yamada-Yosida identities relating certain
coefficients in the low-energy expansion of the self-energy to thermodynamic
particle number and spin susceptibilities of the impurity. Our proof underlines
the relation of the Yamada-Yosida identities to the U(1) x U(1) symmetry
associated with particle number and spin conservation in a magnetic field.Comment: 8 pages, corrected statements about infintite flatband limi
The Importance of Reciprocity: Investigating Individual Differences Underlying Conditional Cooperation
Several models of social preferences have been developed at the intersection of social psychology and behavioral economics, such as social value orientation (SVO) and conditional cooperation. Whereas SVO is well researched in its dispositional and situational correlates, we aim to locate conditional cooperation within the HEXACO personality model, particularly expecting a relation to reactive vs. active prosociality (i.e., Agreeableness vs. Honesty-Humility). Contrary to our expectations, however, in two preregistered, incentivized studies (n total = 521) conditional cooperation was neither related to Agreeableness nor to Honesty-Humility. When investigating the relation between SVO and conditional cooperation, we conceptually replicate a positive relation between both (pro-)social preferences. Surprisingly, while prosocials coincide with conditional cooperators, even most individualists who maximize their outcome in unilateral giving turn to conditionally cooperative behavior in strategic interactions. This underlines the importance of shaping situations as reciprocal acts to elicit cooperative behavior from originally self-interested individuals
Classical Phase Fluctuations in Incommensurate Peierls Chains
In the pseudogap regime of one-dimensional incommensurate Peierls systems,
fluctuations of the phase of the order parameter prohibit the emergence of
long-range order and generate a finite correlation length. For classical phase
fluctuations, we present exact results for the average electronic density of
states, the mean localization length, the electronic specific heat and the spin
susceptibility at low temperatures. Our results for the susceptibility give a
good fit to experimental data.Comment: 4 Revtex pages, 4 figures, submitted to Phys. Rev. Let
Algorithm for obtaining the gradient expansion of the local density of states and the free energy of a superconductor
We present an efficient algorithm for obtaining the gauge-invariant gradient
expansion of the local density of states and the free energy of a clean
superconductor. Our method is based on a new mapping of the semiclassical
linearized Gorkov equations onto a pseudo-Schroedinger equation for a
three-component wave-function psi(x), where one component is directly related
to the local density of states. Because psi(x) satisfies a linear equation of
motion, successive terms in the gradient expansion can be obtained by simple
linear iteration. Our method works equally well for real and complex order
parameter, and in the presence of arbitrary external fields. We confirm a
recent calculation of the fourth order correction to the free energy by
Kosztin, Kos, Stone and Leggett [Phys. Rev. B 58, 9365 (1998)], who obtained a
discrepancy with an earlier result by Tewordt [Z. Phys. 180, 385 (1964)]. We
also give the fourth order correction to the local density of states, which has
not been published before.Comment: 12 preprint pages, added remark concerning Eilenberger equation,
accepted for publication in Phys. Rev.
Tunneling Density of States of the Interacting Two-Dimensional Electron Gas
We investigate the influence of electron--electron interactions on the
density of states of a ballistic two--dimensional electron gas. The density of
states is determined nonperturbatively by means of path integral techniques
allowing for reliable results near the Fermi surface, where perturbation theory
breaks down. We find that the density of states is suppressed at the Fermi
level to a finite value. This suppression factor grows with decreasing electron
density and is weakened by the presence of gates.Comment: 4 pages, 2 figures; slightly shortened version published in PR
Porcine endogenous retroviruses PERV A and A/C recombinant are insensitive to a range of divergent mammalian TRIM5Â proteins including human TRIM5
The potential risk of cross-species transmission of porcine endogenous retroviruses (PERV) to humans has slowed the development of xenotransplantation, using pigs as organ donors. Here, we show that PERVs are insensitive to restriction by divergent TRIM5{alpha} molecules despite the fact that they strongly restrict a variety of divergent lentiviruses. We also show that the human PERV A/C recombinant clone 14/220 reverse transcribes with increased efficiency in human cells, leading to significantly higher infectivity. We conclude that xenotransplantation studies should consider the danger of highly infectious TRIM5{alpha}-insensitive human-tropic PERV recombinants
Some remarks about pseudo gap behavior of nearly antiferromagnetic metals
In the antiferromagnetically ordered phase of a metal, gaps open on parts of
the Fermi surface if the Fermi volume is sufficiently large. We discuss simple
qualitative and heuristic arguments under what conditions precursor effects,
i.e. pseudo gaps, are expected in the paramagnetic phase of a metal close to an
antiferromagnetic quantum phase transition. At least for weak interactions, we
do not expect the formation of pseudo gaps in a three dimensional material.
According to our arguments, the upper critical dimension d_c for the formation
of pseudo gaps is d_c=2. However, at the present stage we cannot rule out a
higher upper critical dimension, 2 < d_c <= 3. We also discuss briefly the role
of statistical interactions in pseudo gap phases.Comment: 6 pages, accepted in PRB, relevant references added, several small
change
Ferromagnetic Luttinger Liquids
We study weak itinerant ferromagnetism in one-dimensional Fermi systems using
perturbation theory and bosonization. We find that longitudinal spin
fluctuations propagate ballistically with velocity v_m << v_F, where v_F is the
Fermi velocity. This leads to a large anomalous dimension in the spin-channel
and strong algebraic singularities in the single-particle spectral function and
in the transverse structure factor for momentum transfers q ~ 2 Delta/v_F,
where 2 Delta is the exchange splitting.Comment: 4 pages, 3 figure
Exact Results for the Crossover from Gaussian to Non-Gaussian Order Parameter Fluctuations in Quasi One-Dimensional Electronic Systems
The physics of quasi one-dimensional Peierls systems is dominated by order
parameter fluctuations. We present an algorithm which allows for the first time
to exactly calculate physical properties of the electrons gas coupled to
classical order parameter fluctuations. The whole range from the Gaussian
regime dominated by amplitude fluctuations to the non-Gaussian regime dominated
by phase fluctuations is accessible. Our results provide insight into the
'pseudogap' phenomenon occurring in underdoped high-temperature
superconductors, quasi one-dimensional organic conductors and liquid metals.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Optical conductivity of a quasi-one-dimensional system with fluctuating order
We describe a formally exact method to calculate the optical conductivity of
a one-dimensional system with fluctuating order. For classical phase
fluctuations we explicitly determine the optical conductivity by solving two
coupled Fokker-Planck equations numerically. Our results differ considerably
from perturbation theory and in contrast to Gaussian order parameter
fluctuations show a strong dependence on the correlation length.Comment: 7 pages, 2 figure
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