2,467 research outputs found
The challenge for single field inflation with BICEP2 result
The detection of B-mode power spectrum by the BICEP2 collaboration constrains
the tensor-to-scalar ratio for the lensed-CDM
model. The consistency of this big value with the {\em Planck} results requires
a large running of the spectral index. The large values of the tensor-to-scalar
ratio and the running of the spectral index put a challenge to single field
inflation. For the chaotic inflation, the larger the value of the
tensor-to-scalar ratio is, the smaller the value of the running of the spectral
index is. For the natural inflation, the absolute value of the running of the
spectral index has an upper limit.Comment: 4 figures, 3 pages, some references added, PLB in pres
On the effect of the degeneracy between w_0 and w_a
The dynamics of scalar fields as dark energy is well approximated by some
general relations between the equation of state parameter and the
fraction energy density . Based on the approximation, for
slowly-rolling scalar fields, we derived the analytical expressions of
which reduce to the popular Chevallier-Polarski-Linder parametrization with
explicit degeneracy relation between and . The models approximate
the dynamics of scalar fields well and help eliminate the degeneracies among
, and . With the explicit degeneracy relations, we test
their effects on the constraints of cosmological parameters. We find that: (1)
The analytical relations between and for the two models are
consistent with observational data; (2) The degeneracies have little effect on
; (3) The error of was reduced about 30% with the
degeneracy relations.Comment: add discussions on the reconstruction of thawing potentials, Eur.
Phys. J. C in pres
Reform and Competitive Selection in China: An Analysis of Firm Exits
This paper considers aspects of the competitive selection process in China - firm entry, survival, and exit - in an important sector of manufacturing, looking in particular for changes resulting from the latest stage of reforms. Using industry survey data from a province in North-East China, we find substantial differences in the process between ownership types. By conducting a simple decomposition of the aggregate productivity growth and exploring the determinants of firm’s exit using a hazard rate model, we observe a substantial rate of churning of enterprises in the sector, and find that the competitive selection processes operate, for small and collectively owned enterprises (COEs), in a manner consistent with a private market economy. In contrast, such processes appear not to be functioning for state owned enterprises (SOEs). We conclude that competitive selection in China is not providing a sufficiently strong substitute for corporate governance based on ownership.Competition; Exit; Productivity, Hazard Models
Quantum Geometric Tensor in -Symmetric Quantum Mechanics
A series of geometric concepts are formulated for -symmetric
quantum mechanics and they are further unified into one entity, i.e., an
extended quantum geometric tensor (QGT). The imaginary part of the extended QGT
gives a Berry curvature whereas the real part induces a metric tensor on
system's parameter manifold. This results in a unified conceptual framework to
understand and explore physical properties of -symmetric systems
from a geometric perspective. To illustrate the usefulness of the extended QGT,
we show how its real part, i.e., the metric tensor, can be exploited as a tool
to detect quantum phase transitions as well as spontaneous
-symmetry breaking in -symmetric systems.Comment: main text of 5 pages, plus supplementary material of 8 page
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