217 research outputs found

### Distribution and Fluctuation of Firm Size in the Long-Run

The paper studies empirically and analytically growth and fluctuation of firm size distribution. An empirical analysis is carried out on several data sets on firm size, with emphasis on one-time distribution as well as growth-rate probability distribution. Two well-known scaling laws, Pareto's law and Gibrat's law, are discussed. Some theoretical discussion on their relationship is presented. We also discuss to what extent there may exist economic mechanisms that produce an unequal firm size distribution in the long run. The mechanisms we study have been known in the economic literature since long. Yet, they have not been studied in the context of a dynamic decision problem of the firm. We allow for heterogeneity of firms with respect to certain characteristics. We then show that there are mechanisms at work which may generate a twin-peaked distribution of firm size in the long-run, which will then be tested empiricallyFirm size, Pareto's law, Gibrat's law

### Quantum Control of the Hyperfine Spin of a Cs Atom Ensemble

We demonstrate quantum control of a large spin-angular momentum associated
with the F=3 hyperfine ground state of 133Cs. A combination of time dependent
magnetic fields and a static tensor light shift is used to implement
near-optimal controls and map a fiducial state to a broad range of target
states, with yields in the range 0.8-0.9. Squeezed states are produced also by
an adiabatic scheme that is more robust against errors. Universal control
facilitates the encoding and manipulation of qubits and qudits in atomic ground
states, and may lead to improvement of some precision measurements.Comment: 4 pages, 4 figures (color

### Is Quantum Einstein Gravity Nonperturbatively Renormalizable?

We find considerable evidence supporting the conjecture that four-dimensional
Quantum Einstein Gravity is ``asymptotically safe'' in Weinberg's sense. This
would mean that the theory is likely to be nonperturbatively renormalizable and
thus could be considered a fundamental (rather than merely effective) theory
which is mathematically consistent and predictive down to arbitrarily small
length scales. For a truncated version of the exact flow equation of the
effective average action we establish the existence of a non-Gaussian
renormalization group fixed point which is suitable for the construction of a
nonperturbative infinite cutoff-limit. The truncation ansatz includes the
Einstein-Hilbert action and a higher derivative term.Comment: 18 pages, latex, 3 figure

### Pareto's Law of Income Distribution: Evidence for Germany, the United Kingdom, and the United States

We analyze three sets of income data: the US Panel Study of Income Dynamics
PSID), the British Household Panel Survey (BHPS), and the German Socio-Economic
Panel (GSOEP). It is shown that the empirical income distribution is consistent
with a two-parameter lognormal function for the low-middle income group
(97%-99% of the population), and with a Pareto or power law function for the
high income group (1%-3% of the population). This mixture of two qualitatively
different analytical distributions seems stable over the years covered by our
data sets, although their parameters significantly change in time. It is also
found that the probability density of income growth rates almost has the form
of an exponential function.Comment: Latex2e v1.6; 16 pages with 5 figure

### Breakdown of the mean-field approximation in a wealth distribution model

One of the key socioeconomic phenomena to explain is the distribution of
wealth. Bouchaud and M\'ezard have proposed an interesting model of economy
[Bouchaud and M\'ezard (2000)] based on trade and investments of agents. In the
mean-field approximation, the model produces a stationary wealth distribution
with a power-law tail. In this paper we examine characteristic time scales of
the model and show that for any finite number of agents, the validity of the
mean-field result is time-limited and the model in fact has no stationary
wealth distribution. Further analysis suggests that for heterogeneous agents,
the limitations are even stronger. We conclude with general implications of the
presented results.Comment: 11 pages, 3 figure

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