Dynamics of adaptive agents with asymmetric information

We apply path-integral techniques to study the dynamics of agent-based models with asymmetric information structures. In particular, we devise a batch version of a model proposed originally by Berg et al. [Quant. Fin. 1 (2001) 203], and convert the coupled multi-agent processes into an effective-agent problem from which the dynamical order parameters in ergodic regimes can be derived self-consistently together with the corresponding phase structure. Our dynamical study complements and extends the available static theory. Results are confirmed by numerical simulations.Comment: minor revision of text, accepted by JSTA

Experimental study of Pomeron

A Pomeron phenomenon remains a mystery. A short review of the experimental situation in diffractive physics and an account of some spectacular manifestations of the Pomeron are given.Comment: 17 pages, 7 Figs, LATEX. Talk given at the conference "From the smallest to largest distances", ITEP, Moscow, 24-26 May 2001. Changes: Fig.2 replace

Locating very high energy gamma ray sources with arc minute accuracy

The angular accuracy of gamma-ray detectors is intrinsically limited by the physical processes involved in photon detection. Although a number of point-like sources were detected by the COS-B satellite, only two were unambiguously identified by time signature with counterparts at longer wavelengths. By taking advantage of the extended longitudinal structure of Very High Energy gamma-ray showers, measurements in the TeV energy range can pinpoint source coordinates to arc minute accuracy. This was demonstrated using Cerenkov air shower imaging techniques. With two telescopes in coincidence, the individual event circular probable error will be 0.13 deg. The half-cone angle of the field of view is effectively 1 deg

The role of uncertainty, sentiment and cross-country interactions in G7 output dynamics

Output fluctuations in the G7 are characterised using a VAR model of countries' actual and expected outputs and uncertainty over these. New measures are developed to quantify the relative importance of economic prospects-versus-uncertainty, global-versus-national effects and fundamentals-versus-sentiment for countries' persistent output movements. National and global contributions are found to be equally important across the G7 although considerable differences exist between countries. Uncertainty, and especially cross-country uncertainty, is important in propagating the effects of shocks and generates around 20% of countries' persistent output movements on average. Fundamentals dominate output movements although, with an 80:20 split, sentiment plays a non-negligible role

The Host Galaxy of GRB 990123

We present deep images of the field of gamma-ray burst (GRB) 990123 obtained in a broad-band UV/visible bandpass with the Hubble Space Telescope, and deep near-infrared images obtained with the Keck-I 10-m telescope. Both the HST and Keck images show that the optical transient (OT) is clearly offset by 0.6 arcsec from an extended object, presumably the host galaxy. This galaxy is the most likely source of the metallic-line absorption at z = 1.6004 seen in the spectrum of the OT. With magnitudes V_{C} ~ 24.6 +/- 0.2 and K = 21.65 +/- 0.30 mag this corresponds to an L ~ 0.7 L_* galaxy, assuming that it is located at z = 1.6. The estimated unobscured star formation rate is SFR ~ 6 M_sun/yr, which is not unusually high for normal galaxies at comparable redshifts. The strength of the observed metallic absorption lines is suggestive of a relatively high metallicity of the gas, and thus of a chemically evolved system which may be associated with a massive galaxy. It is also indicative of a high column density of the gas, typical of damped Ly-alpha systems at high redshifts. We conclude that this is the host galaxy of GRB 990123. No other obvious galaxies are detected within the same projected radius from the OT. There is thus no evidence for strong gravitational lensing magnification of this burst, and some alternative explanation for its remarkable energetics may be required. The observed offset of the OT from the center of its apparent host galaxy, 5.5 +/- 0.9 proper kpc (projected) in the galaxy's rest-frame, both refutes the possibility that GRBs are related to galactic nuclear activity and supports models of GRBs which involve the death and/or merger of massive stars. Further, the HST image suggests an intimate connection of GRB 990123 and a star-forming region.Comment: Updated references. 12 pages including 3 Postscript figures. Camera- ready reproductions of the figures can be found at http://astro.caltech.edu/~jsb/GRB/grb990123.htm

Continuous optical monitoring during the prompt emission of GRB 060111B

We present the time-resolved optical emission of GRB 060111B during its prompt phase, measured with the TAROT robotic observatory. This is the first time that the optical emission from a gamma-ray burst has been continuously monitored with a temporal resolution of a few seconds during the prompt gamma-ray phase. The temporal evolution of the prompt optical emission at the level of several seconds is used to provide a clue to the origin of this emission. The optical emission was found to decay steadily from our first measure, 28s after the trigger, in contrast to the gamma-ray emission, which exhibits strong variability at the same time. This behaviour strongly suggests that the optical emission is due to the reverse shock

Very High Energy Gamma-Ray Emission from the Blazar Markarian 421

Very high energy gamma-ray emission from the BL Lac object Markarian 421 has been detected over three observing seasons on 59 nights between April 1992 and June 1994 with the Whipple 10-meter imaging Cherenkov telescope. During its initial detection in 1992, its flux above 500 GeV was 1.6$\times$10$^{-11}$photons cm$^{-2}$ s$^{-1}$. Observations in 1993 confirmed this level of emission. For observations made between December 1993 and April 1994, its intensity was a factor of 2.2$\pm$0.5 lower. Observations on 14 and 15 May, 1994 showed an increase over this quiescent level by a factor of $\sim$10 (Kerrick et al. 1995). This strong outburst suggests that 4 episodes of increased flux measurements on similar time scales in 1992 and 1994 may be attributed to somewhat weaker outbursts. The variability of the TeV gamma-ray emission from Markarian 421 stands in contrast to EGRET observations (Lin et al. 1994) which show no evidence for variability.Comment: gzip compressed tar file including LaTeX text and 4 postscript figures (14 pages total incl. 4 tables), accepted for publication in the Astrophysical Journal. Contact address is [email protected]