5,347 research outputs found
VARs with Mixed Roots Near Unity
Limit theory is developed for nonstationary vector autoregression (VAR) with mixed roots in the vicinity of unity involving persistent and explosive components. Statistical tests for common roots are examined and model selection approaches for discriminating roots are explored. The results are useful in empirical testing for multiple manifestations of nonstationarity -- in particular for distinguishing mildly explosive roots from roots that are local to unity and for testing commonality in persistence.Common roots, Local to unity, Mildly explosive, Mixed roots, Model selection, Persistence, Tests of common roots
Effective field theory description of halo nuclei
Nuclear halos emerge as new degrees of freedom near the neutron and proton
driplines. They consist of a core and one or a few nucleons which spend most of
their time in the classically-forbidden region outside the range of the
interaction. Individual nucleons inside the core are thus unresolved in the
halo configuration, and the low-energy effective interactions are short-range
forces between the core and the valence nucleons. Similar phenomena occur in
clusters of He atoms, cold atomic gases near a Feshbach resonance, and some
exotic hadrons. In these weakly-bound quantum systems universal scaling laws
for s-wave binding emerge that are independent of the details of the
interaction. Effective field theory (EFT) exposes these correlations and
permits the calculation of non-universal corrections to them due to
short-distance effects, as well as the extension of these ideas to systems
involving the Coulomb interaction and/or binding in higher angular-momentum
channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo
nuclei, has been used to compute the properties of single-neutron, two-neutron,
and single-proton halos of s-wave and p-wave type. This review summarizes these
results for halo binding energies, radii, Coulomb dissociation, and radiative
capture, as well as the connection of these properties to scattering
parameters, thereby elucidating the universal correlations between all these
observables. We also discuss how Halo EFT's encoding of the long-distance
physics of halo nuclei can be used to check and extend ab initio calculations
that include detailed modeling of their short-distance dynamics.Comment: 104 pages, 31 figures. Topical Review for Journal of Physics G. v2
incorporates several modifications, particularly to the Introduction, in
response to referee reports. It also corrects multiple typos in the original
submission. It corresponds to the published versio
Quantum Monte Carlo Study of Disordered Fermions
We study a strongly correlated fermionic model with attractive interactions
in the presence of disorder in two spatial dimensions. Our model has been
designed so that it can be solved using the recently discovered meron-cluster
approach. Although the model is unconventional it has the same symmetries of
the Hubbard model. Since the naive algorithm is inefficient, we develop a new
algorithm by combining the meron-cluster technique with the directed-loop
update. This combination allows us to compute the pair susceptibility and the
winding number susceptibility accurately. We find that the s-wave
superconductivity, present in the clean model, does not disappear until the
disorder reaches a temperature dependent critical strength. The critical
behavior as a function of disorder close to the phase transition belongs to the
Berezinsky-Kosterlitz-Thouless universality class as expected. The fermionic
degrees of freedom, although present, do not appear to play an important role
near the phase transition.Comment: published version, more data added to Fig 5 and clarifications in
text, 8 page
Implications of a matter-radius measurement for the structure of Carbon-22
We study Borromean 2n-halo nuclei using effective field theory. We compute
the universal scaling function that relates the mean-square matter radius of
the 2n halo to dimensionless ratios of two- and three-body energies. We use the
experimental value of the rms matter radius of 22C measured by Tanaka et al. to
put constraints on its 2n separation energy and the 20C-n virtual energy. We
also explore the consequences of these constraints for the existence of excited
Efimov states in this nucleus. We find that, for 22C to have an rms matter
radius within 1-sigma of the experimental value, the two-neutron separation
energy of 22C needs to be below 100 keV. Consequently, this three-body halo
system can have an excited Efimov state only if the 20C-n system has a
resonance within 1 keV of the scattering threshold.Comment: 6 pages, 4 figure
Drell-Hearn-Gerasimov Sum-Rule for the Deuteron in Nuclear Effective Field Theory
The Drell-Hearn-Gerasimov sum rule for the deuteron is studied in nuclear
effective field theory. The low-energy theorem for the spin-dependent Compton
amplitude is derived to the next-to-leading order in low-energy
expansion. The spin-dependent photodisintegration cross section
is calculated to the same order, and its contribution to
the dispersive integral is evaluated.Comment: 8 pages, 2 figure
Weight bias 2.0: the effect of perceived weight change on performance evaluation and the moderating role of anti-fat bias
Overweight employees are viewed as lazy, slow, inactive, and even incapable. Even if such attributes are false, this perspective can seriously undermine others' evaluation of their work performance. The current study explores a broader phenomenon of weight bias that has an effect on weight change. In a longitudinal study with a time lag of 6 months, we surveyed 226 supervisor-employee dyads. We found supervisor perceptions of employee weight change notably altered their evaluation of the employee performance from Time 1, especially following low vs. high Time-1 performance evaluation. Meanwhile, the moderating effects among different levels of supervisor anti-fat bias functioned as boundary conditions for such performance evaluation alteration. In particular, the interaction between the Time-1 performance evaluation and the impact of supervisor perception of employee weight change on the Time-2 performance evaluation was significant only if supervisors held a stronger anti-fat bias
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