1,402 research outputs found
Japan's Intangible Capital and Valuation of Corporations in a Neoclassical Framework
This paper estimates the economic value in the 1980s and 1990s of corporate as sets in Japan,including both tangible and intangible as sets, based on the neo-classical framework of McGrattan and Prescott(2005). Our estimates use anew micro-data set that comprises the accounting statements of all listed, non-financial companies in Japan. We find that in 1981-86, a period that immediately preceded Japan's so-called "bubble economy", our assessed value of corporate productiveas-sets, net of the value of corporate debt,is approximately equal to the actual stock market value of Japanese corporate equity. The fnding differs from previous results based on studies of aggregated at a sets or based on studies of micro data sets that neglected intangible capital. We also show that the Japanese ratio of the amount of intangible capital stock to the amount of tangible capital stock is comparable to the analogous ratios for the U.S. and U.K.
Decoherence processes of a quantum two-level system coupled to a fermionic environment
We study decoherence processes of an S = 1/2 localized spin coupled to
conduction band electrons in a metal or a semiconductor via an Ising-like
interaction. We derive master equations for the density matrix of the localized
spin, by tracing out all degrees of freedom in the conduction electron system
based on the linked-cluster-expansion technique. It is found that the
decoherence occurs more rapidly for the metallic case than for semiconducting
case.Comment: to appear in J. Appl. Phy
Isocurvature Perturbations of Dark Energy and Dark Matter from the Swampland Conjecture
We point out that the recently proposed Swampland conjecture on the potential
gradient can lead to isocurvature perturbations of dark energy, if the
quintessence field acquires large quantum fluctuations during high-scale
inflation preferred by the conjecture. Also, if the quintessence field is
coupled to a dark sector that contains dark matter, isocurvature perturbation
of dark matter is similarly induced. Both isocurvature perturbations can be
suppressed if the quintessence potential allows a tracker solution in the early
Universe. We find that a vector field of mass meV is an
excellent dark matter candidate in this context, not only because the right
abundance is known to be produced by quantum fluctuations during high-scale
inflation without running afoul of isocurvature bounds, but also because its
coupling to the quintessence does not spoil the flatness of the potential.Comment: 14 pages, 1 figure; (v2) minor changes, Fig. 1 adde
Critical Surface for Explosions of Rotational Core-Collapse Supernovae
The effect of rotation on the explosion of core-collapse supernovae is
investigated systematically in three-dimensional simulations. In order to
obtain the critical conditions for explosion as a function of mass accretion
rate, neutrino luminosity, and specific angular momentum, rigidly rotating
matter was injected from the outer boundary with an angular momentum, which is
increased every 500 ms. It is found that there is a critical value of the
specific angular momentum, above which the standing shock wave revives, for a
given combination of mass accretion rate and neutrino luminosity, i.e. an
explosion can occur by rotation even if the neutrino luminosity is lower than
the critical value for a given mass accretion rate in non-rotational models.
The coupling of rotation and hydrodynamical instabilities plays an important
role to characterize the dynamics of shock revival for the range of specific
angular momentum that are supposed to be realistic. Contrary to expectations
from past studies, the most rapidly expanding direction of the shock wave is
not aligned with the rotation axis. Being perpendicular to the rotation axis on
average, it can be oriented in various directions. Its dispersion is small when
the spiral mode of the standing accretion shock instability (SASI) governs the
dynamics, while it is large when neutrino-driven convection is dominant. As a
result of the comparison between 2D and 3D rotational models, it is found that
m=!0 modes of neutrino-driven convection or SASI are important for shock
revival around the critical surface.Comment: First revised version, submitted to ApJ, 14 pages, 13 figures, 2
table
Three-dimensional Boltzmann-Hydro code for core-collapse in massive stars I. special relativistic treatments
We propose a novel numerical method for solving multi-dimensional, special
relativistic Boltzmann equations for neutrinos coupled to hydrodynamics
equations. It is meant to be applied to simulations of core-collapse
supernovae. We handle special relativity in a non-conventional way, taking
account of all orders of v/c. Consistent treatment of advection and collision
terms in the Boltzmann equations is the source of difficulties, which we
overcome by employing two different energy grids: Lagrangian remapped and
laboratory fixed grids. We conduct a series of basic tests and perform a
one-dimensional simulation of core-collapse, bounce and shock-stall for a
15M_{sun} progenitor model with a minimum but essential set of microphysics. We
demonstrate in the latter simulation that our new code is capable of handling
all phases in core-collapse supernova. For comparison, a non-relativistic
simulation is also conducted with the same code, and we show that they produce
qualitatively wrong results in neutrino transfer. Finally, we discuss a
possible incorporation of general relativistic effects in our method.Comment: 25 pages, 22 figures, submitted to Ap
- …