Invisible Events with Radiative Photons at LEP

A study of the radiative neutrino counting reaction $e^+ e^- \to \nu {\bar \nu} \gamma$ at LEP1 and LEP2 energies is presented. An approximate expression for the spectrum of the observed photon is derived within the framework of the $p_t$-dependent structure function approach. This is compared with an exact expression and found in agreement within the foreseen experimental accuracy. This model describing single-photon radiation can be applied to the more general case of initial-state single-photon emission accompanying invisible final-state events. Higher-order QED corrections due to undetected initial-state radiation are also included. The implementation in a Monte Carlo event generator is briefly described.Comment: 10 pages, LaTeX, 7 figures available via anonymous ftp at: ftp://cobra1.pv.infn.it/pub/phot/, files fig#n.ps with #=1,...,

Revealing the large extra dimension effective interaction at an e^+e^- collider with polarized beams

Contactlike nonstandard effective interactions can be revealed through deviations of observables from the Standard Model predictions. If such deviations were observed, the relevant source should be identified among the possible models that could explain them. We estimate the expected discrimination reach on the ADD model of gravity in large compactified extra dimensions, against the compositeness-inspired four-fermion contact interaction. As basic observables we take the differential cross sections for fermion-pair production at a 0.5-1 TeV electron-positron linear collider with both beams longitudinally polarized. For the four-fermion contact interaction, we assume a general linear combination of the individual models with definite chiralities, and arbitrary coupling constants. Accordingly, the estimated identification reach on the ADD scenario can be considered as `model-independent'. We emphasize the substantial role of beams polarization in enhancing the identification sensitivity.Comment: 14 pages, 2 figure

A Path Integral Way to Option Pricing

An efficient computational algorithm to price financial derivatives is presented. It is based on a path integral formulation of the pricing problem. It is shown how the path integral approach can be worked out in order to obtain fast and accurate predictions for the value of a large class of options, including those with path-dependent and early exercise features. As examples, the application of the method to European and American options in the Black-Scholes model is illustrated. A particularly simple and fast semi-analytical approximation for the price of American options is derived. The results of the algorithm are compared with those obtained with the standard procedures known in the literature and found to be in good agreement.Comment: 20 pages, 2 figures, 3 table

O(α2){\cal O} (\alpha^2) Next-to-Leading Photonic Corrections to Small-Angle Bhabha Scattering in the Structure Function Formalism

A general method for computing ${\cal O} (\alpha^2)$ and higher-order next-to-leading photonic corrections is presented and applied to the precision calculation of the small-angle Bhabha scattering cross section in the phase-space region of interest for the luminosity measurement at LEP. The formulation is based on a proper matching of exact $\cal O (\alpha)$ results with higher-order corrections in the Structure Function formalism. The results of the approach are analytically compared with theoretical calculations, both for $s$- and $t$-channel processes, available for simple Event Selections. Numerical predictions for realistic Event Selections are also provided and critically compared with the ones existing in the literature.Comment: 16 pages, gzip'ed uuencoded tar fil

Distinguishing New Physics Scenarios at a Linear Collider with Polarized Beams

Numerous non-standard dynamics are described by contact-like effective interactions that can manifest themselves through deviations of the cross sections from the Standard Model predictions. If one such deviation were observed, one should try to identify to a given confidence level the actual source among the possible non-standard interactions that in principle can explain it. We here estimate the potential identification reach on different New Physics effective interactions, obtainable from the angular distributions of lepton pair production processes at the planned International Linear Collider with polarized beams. The models discussed are the interactions based on gravity in large and in TeV^{-1} extra dimensions and the compositeness-inspired four-fermion contact interactions. The availability of both beams polarized in many cases plays an essential role in enhancing the identification sensitivity.Comment: 21 pages, LaTex, 11 figures. One author was missing from the previous version. The authors list has been completed, no other change

Six-Fermion Calculation of Intermediate-mass Higgs Boson Production at Future e+e−e^+ e^- Colliders

The production of an intermediate-mass Higgs boson in processes of the kind $e^+ e^- \to 6$ fermions at the energies of future linear colliders is studied. The recently developed and fully automatic algorithm/code ALPHA is used to compute the tree-level scattering amplitudes for the reactions $e^+ e^- \to \mu^+ \mu^- \tau^- \bar\nu_{\tau} u \bar d, \mu^+ \mu^- e^- \bar\nu_{e} u \bar d$. The code has been interfaced with the Monte Carlo program HIGGSPV/WWGENPV, properly adapted to 6-fermion production, in order to provide realistic results, both in the form of cross sections and event samples at the partonic level. Phenomenological results, that incorporate the effects of initial-state radiation and beamstrahlung, are shown and commented, emphasizing the potentials of full six-fermion calculations for precise background evaluation as well as for detailed studies of the fundamental properties of the Higgs particle.Comment: 31 pages, LaTeX, 15 eps low-resolution figures include

Relativistic Spontaneous Localization: A Proposal

A new proposal for a Lorentz-invariant spontaneous localization theory is presented. It is based on the choice of a suitable set of macroscopic quantities to be stochastically induced to have definite values. Such macroscopic quantities have the meaning of a time-integrated amount of a microscopically defined quantity called stuff related to the presence of massive particles