New Constraints on Quantum Gravity from X-ray and Gamma-Ray Observations

One aspect of the quantum nature of spacetime is its "foaminess" at very small scales. Many models for spacetime foam are defined by the accumulation power $\alpha$, which parameterizes the rate at which Planck-scale spatial uncertainties (and thephase shifts they produce) may accumulate over large path-lengths. Here $\alpha$ is defined by theexpression for the path-length fluctuations, $\delta \ell$, of a source at distance $\ell$, wherein $\delta \ell \simeq \ell^{1 - \alpha} \ell_P^{\alpha}$, with $\ell_P$ being the Planck length. We reassess previous proposals to use astronomical observations ofdistant quasars and AGN to test models of spacetime foam. We show explicitly how wavefront distortions on small scales cause the image intensity to decay to the point where distant objects become undetectable when the path-length fluctuations become comparable to the wavelength of the radiation. We use X-ray observations from {\em Chandra} to set the constraint $\alpha \gtrsim 0.58$, which rules out the random walk model (with $\alpha = 1/2$). Much firmer constraints canbe set utilizing detections of quasars at GeV energies with {\em Fermi}, and at TeV energies with ground-based Cherenkovtelescopes: $\alpha \gtrsim 0.67$ and $\alpha \gtrsim 0.72$, respectively. These limits on $\alpha$ seem to rule out $\alpha = 2/3$, the model of some physical interest.Comment: 11 pages, 9 figures, ApJ, in pres

Privatization Versus Competition: Changing Enterprise Behavior in Russia

We investigate whether competitive forces and privatization have yet began to play an efficiency-enhancing role in Russia. We also explore the economic effects of harder budget constraints on enterprise behavior. The empirical work is based on a large enterprise panel of Russian firms 1990-94, representing around 10% of Russian manufacturing output. We conclude that privatization is having an impact on enterprise efficiency and restructuring but domestic market structure and harder budget constraints for the most part are not. Intriguingly, Russian firms are found to be sensitive to the degree of import penetration.http://deepblue.lib.umich.edu/bitstream/2027.42/39460/3/wp70.pd

Multiwavelength transit observations of the candidate disintegrating planetesimals orbiting WD 1145+017

We present multiwavelength, ground-based follow-up photometry of the white dwarf WD 1145+017, which has recently been suggested to be orbited by up to six or more short-period, low-mass, disintegrating planetesimals. We detect nine significant dips in flux of between 10% and 30% of the stellar flux in our ~32 hr of photometry, suggesting that WD 1145+017 is indeed being orbited by multiple, short-period objects. Through fits to the asymmetric transits that we observe, we confirm that the transit egress is usually longer than the ingress, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. The precise orbital periods of the planetesimals are unclear, but at least one object, and likely more, have orbital periods of ~4.5 hr. We are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. Our high-precision photometry also displays low-amplitude variations, suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. We compare the transit depths in the V- and R-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions, the radius of single-size particles in the cometary tails streaming behind the planetesimals must be ~0.15 μm or larger, or ~0.06 μm or smaller, with 2σ confidence

Privatization Versus Competition: Changing Enterprise Behavior in Russia

We investigate whether competitive forces and privatization have yet began to play an efficiency-enhancing role in Russia. We also explore the economic effects of harder budget constraints on enterprise behavior. The empirical work is based on a large enterprise panel of Russian firms 1990-94, representing around 10% of Russian manufacturing output. We conclude that privatization is having an impact on enterprise efficiency and restructuring but domestic market structure and harder budget constraints for the most part are not. Intriguingly, Russian firms are found to be sensitive to the degree of import penetration.privatization, competition, economic transition

Collisions of Free Floating Planets with Evolved Stars in Globular Clusters

We estimate the rate of collisions between stars and free-floating planets (FFPs) in globular clusters, in particular the collision of FFPs with red giant branch (RGB) stars. Recent dynamical simulations imply that the density of such objects could exceed million per cubic parsec near the cores of rich globular clusters. We show that in these clusters 5-10 per cents of all RGB stars near the core would suffer a collision with a FFP, and that such a collision can spin up the RGB star's envelope by an order of magnitude. In turn, the higher rotation rates may lead to enhanced mass-loss rates on the RGB, which could result in bluer horizontal branch (HB) stars. Hence, it is plausible that the presence of a large population of FFPs in a globular cluster can influence the distribution of stars on the HB of that cluster to a detectable degree.Comment: 10 pages, Accepted by ApJ Letter

Multiwavelength Transit Observations of the Candidate Disintegrating Planetesimals Orbiting WD 1145+017

We present multiwavelength, multi-telescope, ground-based follow-up photometry of the white dwarf WD 1145+017, that has recently been suggested to be orbited by up to six or more, short-period, low-mass, disintegrating planetesimals. We detect 9 significant dips in flux of between 10% and 30% of the stellar flux from our ground-based photometry. We observe transits deeper than 10% on average every ~3.6 hr in our photometry. This suggests that WD 1145+017 is indeed being orbited by multiple, short-period objects. Through fits to the multiple asymmetric transits that we observe, we confirm that the transit egress timescale is usually longer than the ingress timescale, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. The precise orbital periods of the planetesimals in this system are unclear from the transit-times, but at least one object, and likely more, have orbital periods of ~4.5 hours. We are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. Our high precision photometry also displays low amplitude variations suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. For the significant transits we observe, we compare the transit depths in the V- and R-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions the radius of single-size particles in the cometary tails streaming behind the planetesimals in this system must be ~0.15 microns or larger, or ~0.06 microns or smaller, with 2-sigma confidence.Comment: 16 pages, 12 figures, submitted to ApJ on October 8th, 201