Probing finite size effects in (λΦ4)4(\lambda \Phi^4)_4 MonteCarlo calculations

The Constrained Effective Potential (CEP) is known to be equivalent to the usual Effective Potential (EP) in the infinite volume limit. We have carried out MonteCarlo calculations based on the two different definitions to get informations on finite size effects. We also compared these calculations with those based on an Improved CEP (ICEP) which takes into account the finite size of the lattice. It turns out that ICEP actually reduces the finite size effects which are more visible near the vanishing of the external source.Comment: LATTICE98(Gauge, Higgs and Yukawa Models

Mass Determination from Constraint Effective Potential

The Constraint Effective Potential (CEP) allows a determination of the mass and other quantities directly, without relying upon asymptotic correlator decays. We report and discuss the results of some mass calculations in $(\lambda \Phi^4)_4$, obtained from CEP and our improved version of CEP (ICEP).Comment: LATTICE99(Higgs, Yukawa, SUSY

A Geometrical Interpretation of Hyperscaling Breaking in the Ising Model

In random percolation one finds that the mean field regime above the upper critical dimension can simply be explained through the coexistence of infinite percolating clusters at the critical point. Because of the mapping between percolation and critical behaviour in the Ising model, one might check whether the breakdown of hyperscaling in the Ising model can also be intepreted as due to an infinite multiplicity of percolating Fortuin-Kasteleyn clusters at the critical temperature T_c. Preliminary results suggest that the scenario is much more involved than expected due to the fact that the percolation variables behave differently on the two sides of T_c.Comment: Lattice2002(spin

A lattice test of alternative interpretations of ``triviality'' in (λΦ4)4(\lambda \Phi^4)_4 theory

There are two physically different interpretations of ``triviality'' in $(\lambda\Phi^4)_4$ theories. The conventional description predicts a second-order phase transition and that the Higgs mass $m_h$ must vanish in the continuum limit if $v$, the physical v.e.v, is held fixed. An alternative interpretation, based on the effective potential obtained in ``triviality-compatible'' approximations (in which the shifted `Higgs' field $h(x)\equiv \Phi(x)-$ is governed by an effective quadratic Hamiltonian) predicts a phase transition that is very weakly first-order and that $m_h$ and $v$ are both finite, cutoff-independent quantities. To test these two alternatives, we have numerically computed the effective potential on the lattice. Three different methods were used to determine the critical bare mass for the chosen bare coupling value. All give excellent agreement with the literature value. Two different methods for obtaining the effective potential were used, as a control on the results. Our lattice data are fitted very well by the predictions of the unconventional picture, but poorly by the conventional picture.Comment: 16 pages, LaTeX, 2 eps figures (acknowledgements added in the replaced version

Crowded space: a review on radar measurements for space debris monitoring and tracking

Space debris monitoring is nowadays a priority for worldwide space agencies, due to the serious threat that these objects present. More and more efforts have been made to extend the network of available radar systems devoted to the control of space. A meticulous review has been done in this paper, in order to find and classify the considerable amounts of data provided by the scientific community that deal with RADAR measurement for the debris monitoring and tracking. The information gathered is organized based on the volume of found data and classified taking into account the geographical location of the facilities

Comment on "Feynman Effective Classical Potential in the Schrodinger Formulation"

We comment on the paper "Feynman Effective Classical Potential in the Schrodinger Formulation"[Phys. Rev. Lett. 81, 3303 (1998)]. We show that the results in this paper about the time evolution of a wave packet in a double well potential can be properly explained by resorting to a variational principle for the effective action. A way to improve on these results is also discussed.Comment: 1 page, 2eps figures, Revte

Assessing pyroclastic fall hazard through field data and numerical simulation: Example from Vesuvius

A general methodology of pyroclastic fall hazard assessment is proposed on the basis of integrated results of field studies and numerical simulations. These approaches result in two different methods of assessing hazard: (1) the ‘‘field frequency,’’ based on the thickness and distribution of past deposits and (2) the ‘‘simulated probability,’’ based on the numerical modeling of tephra transport and fallout. The proposed methodology mostly applies to volcanoes that, by showing a clear correlation between the repose time and the magnitude of the following eruptions, allows the definition of a reference ‘‘maximum expected event’’ (MEE). The application to Vesuvius is shown in detail. Using the field frequency method, stratigraphic data of 24 explosive events in the 3–6 volcanic explosivity index range in the last 18,000 years of activity are extrapolated to a regular grid in order to obtain the frequency of exceedance in the past of a certain threshold value of mass loading (100, 200, 300, and 400 kg/m2). Using the simulated probability method, the mass loading related to the MEE is calculated based on the expected erupted mass (5 1011 kg), the wind velocity profiles recorded during 14 years, and various column heights and grain-size populations. The role of these factors was parametrically studied performing 160,000 simulations, and the probability that mass loading exceeded the chosen threshold at each node was evaluated. As a general rule, the field frequency method results are more reliable in proximal regions, provided that an accurate database of field measurements is available. On the other hand, the simulated probability method better describes events in middle distal areas, provided that the MEE magnitude can be reliably assumed. In the Vesuvius case, the integration of the two methods results in a new fallout hazard map, here presented for a mass loading value of 200 kg/m2