1,269 research outputs found
Trust in the Shadow of the Courts
If contract enforcers must be randomly selected from the same population and thus are as opportunistic as ordinary traders could a system of adjudication nevertheless increase the degree to which contractual obligations on large anonymous markets are fulfilled? Adopting an indirect evolutionary approach with endogenous preference formation it can be shown that without superior behaviour of adjudicators an adjudication system can induce untrustworthy traders to behave as if trustworthy. However, in the presence of occasional mistakes adjudication will merely slow down but not fully eliminate the evolutionary advantage of untrustworthy types. Only if arbitrators become judges who receive a fixed income occasional mistakes will not favour untrustworthy types. But even then under non-optimal court politics and unfavourable parameter constellations in a low trust environment the introduction of courts may in fact contribute to the crowding out of the trustworthy.
Time-resolved collapse and revival of the Kondo state near a quantum phase transition
One of the most successful paradigms of many-body physics is the concept of
quasiparticles: excitations in strongly interacting matter behaving like weakly
interacting particles in free space. Quasiparticles in metals are very robust
objects. Yet, when a system's ground state undergoes a qualitative change at a
quantum critical point (QCP), the quasiparticles may disintegrate and give way
to an exotic quantum-fluid state of matter. The nature of this breakdown is
intensely debated, because the emergent quantum fluid dominates the material
properties up to high temperature and might even be related to the occurence of
superconductivity in some compounds. Here we trace the dynamics of
heavy-fermion quasiparticles in CeCuAu and monitor their
evolution towards the QCP in time-resolved experiments, supported by many-body
calculations. A terahertz pulse disrupts the many-body heavy-fermion state.
Under emission of a delayed, phase-coherent terahertz reflex the heavy-fermion
state recovers, with a coherence time 100 times longer than typically
associated with correlated metals. The quasiparticle weight collapses towards
the QCP, yet its formation temperature remains constant -- phenomena believed
to be mutually exclusive. Coexistence in the same experiment calls for
revisions in our view on quantum criticality.Comment: Published version, including data on CeCu6, CeCu5.9Au0.1, and
CeCu5Au1 and extended Supplementary Information. 7 pages, 4 figures,
Supplementary Information: 5 pages, 3 figure
Cascade of magnetic field induced Lifshitz transitions in the ferromagnetic Kondo lattice material YbNi4P2
A ferromagnetic quantum critical point is thought not to exist in two and
three-dimensional metallic systems yet is realized in the Kondo lattice
compound YbNi4(P,As)2, possibly due to its one-dimensionality. It is crucial to
investigate the dimensionality of the Fermi surface of YbNi4P2 experimentally
but common probes such as ARPES and quantum oscillation measurements are
lacking. Here, we studied the magnetic field dependence of transport and
thermodynamic properties of YbNi4P2. The Kondo effect is continuously
suppressed and additionally we identify nine Lifshitz transitions between 0.4
and 18 T. We analyze the transport coefficients in detail and identify the type
of Lifshitz transitions as neck or void type to gain information on the Fermi
surface of YbNi4P2. The large number of Lifshitz transitions observed within
this small energy window is unprecedented and results from the particular flat
renormalized band structure with strong 4f-electron character shaped by the
Kondo lattice effect.Comment: 6 pages, 4 figure
Valence-transition-induced changes of the electronic structure in EuPdSi
We present results of hard X-ray angle-resolved photoemission spectroscopy
and photoemission diffraction measurements performed on high-quality single
crystals of the valence transition compound EuPdSi for temperatures
25~K T 300~K. At low temperatures we observe a Eu valence
, % occupation number , which decreases to for
temperatures above the valence transition around ~K. The
experimental valence numbers resulting from an evaluation of the Eu(III)/Eu(II)
core levels, are used for calculating band structures using density
functional theory. The valence transition significantly changes the band
structure as determined by angle-resolved photoemission spectroscopy. In
particular, the Eu valence bands are shifted to lower binding energies
with increasing Eu occupancy. To a lesser extent, bands derived from the
Si and Pd orbitals are also affected. This observation suggests a
partial charge transfer between Eu and Pd/Si sites. Comparison with {\it
ab-initio} theory shows a good agreement with experiment, in particular
concerning the unequal band shift with increasing Eu occupancy
Study of and and
We study the decays of and to the final states
and based on a single
baryon tag method using data samples of
and events collected with
the BESIII detector at the BEPCII collider. The decays to
are observed for the first time. The
measured branching fractions of and
are in good agreement with, and much
more precise, than the previously published results. The angular parameters for
these decays are also measured for the first time. The measured angular decay
parameter for , , is found to be negative, different to the other
decay processes in this measurement. In addition, the "12\% rule" and isospin
symmetry in the and and
systems are tested.Comment: 11 pages, 7 figures. This version is consistent with paper published
in Phys.Lett. B770 (2017) 217-22
Measurement of azimuthal asymmetries in inclusive charged dipion production in annihilations at = 3.65 GeV
We present a measurement of the azimuthal asymmetries of two charged pions in
the inclusive process based on a data set of 62
at the center-of-mass energy GeV collected with
the BESIII detector. These asymmetries can be attributed to the Collins
fragmentation function. We observe a nonzero asymmetry, which increases with
increasing pion momentum. As our energy scale is close to that of the existing
semi-inclusive deep inelastic scattering experimental data, the measured
asymmetries are important inputs for the global analysis of extracting the
quark transversity distribution inside the nucleon and are valuable to explore
the energy evolution of the spin-dependent fragmentation function.Comment: 7 pages, 5 figure
Measurement of the Cross Section between 600 and 900 MeV Using Initial State Radiation
We extract the cross section in the energy
range between 600 and 900 MeV, exploiting the method of initial state
radiation. A data set with an integrated luminosity of 2.93 fb taken at
a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII
collider is used. The cross section is measured with a systematic uncertainty
of 0.9%. We extract the pion form factor as well as the
contribution of the measured cross section to the leading order hadronic vacuum
polarization contribution to . We find this value to be
.Comment: 14 pages, 7 figures, accepted by PL
Study of
We present an analysis of the decay based
on data collected by the BESIII experiment at the resonance. Using
a nearly background-free sample of 18262 events, we measure the branching
fraction . For GeV/ the partial branching fraction is
. A partial wave analysis shows that the dominant
component is accompanied by an \emph{S}-wave contribution accounting for
of the total rate and that other components are
negligible. The parameters of the resonance and of the
form factors based on the spectroscopic pole dominance predictions are also
measured. We also present a measurement of the helicity
basis form factors in a model-independent way.Comment: 17 pages, 6 figure
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