Total Cross Sections and Event Properties from Real to Virtual Photons

A model for total cross sections with virtual photons is presented. In particular gamma*-p and gamma*-gamma* cross sections are considered. Our approach extends on a model for photoproduction, where the total cross section is subdivided into three distinct event classes: direct, VMD and anomalous. With increasing photon virtuality, the latter two decrease in importance. Instead Deep Inelastic Scattering dominates, with the direct class being the O(alpha_s) correction thereof. Hence, the model provides a smooth transition between the two regions. By the breakdown into different event classes, one may aim for a complete picture of all event properties.Comment: 1+5 pages, LaTeX2e, 2 eps figures, to appear in the Proceedings of the International Conference on the Structure and Interactions of the Photon; Photon 2000, 26th-31st August 2000, Ambleside, Englan

Jet Production by Real and Virtual Photons

The production of jets is studied in collisions of virtual photons, specifically for applications at HERA. Photon flux factors are convoluted with matrix elements involving either direct or resolved photons and, for the latter, with parton distributions of the photon. Special emphasis is put on the range of uncertainty in the modeling of the resolved component. The resulting model is compared with existing data and further tests are proposed.Comment: 1+13 pages, LaTeX2e, 16 eps figures, to appear in the Proceedings of the DESY Workshop on "Monte Carlo Generators for HERA Physics

Common Currency, Common Market?

Does the common currency promote goods market integration within the EMU? We argue that such an effect is likely, but that the mechanism typically proposed – lover costs of arbitrage because of increased price transparency – is likely to be of minor importance. Instead we sketch a duopoly model which stresses that lover possibility of future real exchange rate variability lowers the option value of being able to price discriminate. The euro would promote market integration because it is less valuable for firms to segment markets. In addition we argue that fairness concerns and less risk associated with third party arbitrage may be potentially important.exchange rate pass-through; law of one price; EMU; price discrimination; price transparency; real options

Idealized computational models for auditory receptive fields

This paper presents a theory by which idealized models of auditory receptive fields can be derived in a principled axiomatic manner, from a set of structural properties to enable invariance of receptive field responses under natural sound transformations and ensure internal consistency between spectro-temporal receptive fields at different temporal and spectral scales. For defining a time-frequency transformation of a purely temporal sound signal, it is shown that the framework allows for a new way of deriving the Gabor and Gammatone filters as well as a novel family of generalized Gammatone filters, with additional degrees of freedom to obtain different trade-offs between the spectral selectivity and the temporal delay of time-causal temporal window functions. When applied to the definition of a second-layer of receptive fields from a spectrogram, it is shown that the framework leads to two canonical families of spectro-temporal receptive fields, in terms of spectro-temporal derivatives of either spectro-temporal Gaussian kernels for non-causal time or the combination of a time-causal generalized Gammatone filter over the temporal domain and a Gaussian filter over the logspectral domain. For each filter family, the spectro-temporal receptive fields can be either separable over the time-frequency domain or be adapted to local glissando transformations that represent variations in logarithmic frequencies over time. Within each domain of either non-causal or time-causal time, these receptive field families are derived by uniqueness from the assumptions. It is demonstrated how the presented framework allows for computation of basic auditory features for audio processing and that it leads to predictions about auditory receptive fields with good qualitative similarity to biological receptive fields measured in the inferior colliculus (ICC) and primary auditory cortex (A1) of mammals.Comment: 55 pages, 22 figures, 3 table

Jet Production by Virtual Photons

The production of jets is studied in collisions of virtual photons, gamma*-p and gamma*-gamma*, specifically for applications at HERA and LEP2. Photon flux factors are convoluted with matrix elements involving either direct or resolved photons and, for the latter, with parton distributions of the photon. Special emphasis is put on the range of uncertainty in the modeling of the resolved component. The resulting model is compared with existing data.Comment: 1+36 pages, LaTeX2e, 63 eps figures, submitted to Eur. Phys. J.

Effects of Longitudinal Photons

The description of longitudinal photons is far from trivial, and their phenomenological importance is largely unknown. While the cross section for direct interactions is calculable, an even more important contribution could come from resolved states. In the development of our model for the interactions of (real and) virtual photons, we have modeled resolved longitudinal effects by simple multiplicative factors on the resolved transverse-photon contributions. Recently, a first set of parton distributions for longitudinal virtual photons has been presented by Ch\'yla. We therefore compare their impact on some representative distributions, relative to the simpler approaches.Comment: 1+14 pages, LaTeX2e, 5 eps figures, submitted to Phys. Lett.

Some thoughts on how to match Leading Log Parton Showers with NLO Matrix Elements

We propose a scheme that could offer a convenient Monte Carlo sampling of next-to-leading-order matrix elements and, at the same time, allow the interfacing of such parton configurations with a parton-shower approach for the estimation of higher-order effects. No actual implementation exists so far, so this note should only be viewed as the outline of a possible road for the future, submitted for discussion.Comment: 5 pages, LaTeX, no figures, to appear in the Proceedings of the DESY Workshop on "Monte Carlo Generators for HERA Physics

Total Cross Sections and Event Properties from Real to Virtual Photons

A model for total cross sections with virtual photons is presented. In particular gamma*-p and gamma*-gamma* cross sections are considered. Our approach extends on a model for photoproduction, where the total cross section is subdivided into three distinct event classes: direct, VMD and anomalous. With increasing photon virtuality, the latter two decrease in importance. Instead Deep Inelastic Scattering dominates, with the direct class being the O(alpha_s) correction thereof. Hence, the model provides a smooth transition between the two regions. By the breakdown into different event classes, one may aim for a complete picture of all event properties.Comment: 1+34 pages, LaTeX2e, 24 eps figures, submitted to J. High Energy Phy