Non-Gaussianity from preheating

We consider a two-field model for inflation where the second order metric perturbations can be amplified by a parametric resonance during preheating. We demonstrate that there can arise a considerable enhancement of non-Gaussianity sourced by the local terms generated through the coupled perturbations. We argue that the non-Gaussianity parameter could be as large as f(NL) approximately 50. Our results may provide a useful test of preheating in future cosmic microwave background experiments.     

Production of spin 3/2 particles from vacuum fluctuations

We study the production of spin 3/2 particles in homogeneous scalar and gravitational backgrounds using the mode-mixing Bogolyubov method. Considering only the helicity +/-3/2 states, we can reduce the problem to a standard Dirac fermion calculation and apply the standard techniques in a straightforward way. As an example we consider a specific supergravity inflationary model and calculate the spectrum of gravitinos created during preheating at the end of inflation.     

An alternative method for the evaluation of integral dependent on parameter E in classical non-isothermal kinetics with linear heating rate

We have suggested a straightforward method for the determination of the derivative of the temperature integral with respect to the activation energy.     

Some exact solutions in string cosmology

Some Bianchi-type string-cosmological models are presented here. The physical implications of the models are briefly discussed     

Thermally induced vibrations of a viscoelastic plate

A method for the study of thermally induced vibrations of a viscoelastic plate of arbitrary shape is proposed. The method is based upon the concept of iso-amplitude contour lines on the surface of the plate. It is shown that the time behaviour can be found by assuming a normal mode expansion in terms of the eigenfunctions for the associated elastic plate problem, and the deflection is obtained by using the elastic-viscoelastic analogy. As an illustration of the technique, the vibration of a viscoelastic circular plate under a thermal shock at its centre is discussed, all details of which are illustrated by graphs.     

Simplified approach to the vibration analysis of elastic plates due to sonic boom

A theoretical study of the response of a flat plate to a sonic boom excitation is presented. For such a study, the problem of transient vibrations of elastic plates having clamped or simply supported boundary conditions under a pulse load in the shape of a capital N corresponding to a typical far-field sonic boom disturbance is discussed in a new fashion by using the concept of iso-amplitude contour lines on the surface of the plate. Series solutions consisting of products of eigenfunctions times functions of time are employed to analyse the motions. As an illustration of the technique, an elliptical plate subjected to a typical N wave arriving at normal incidence is chosen as a model because this involves a curvilinear boundary of a relatively simple shape, yet has no simple exact solution. Closed form solutions are obtained for both clamped as well as simply supported edges. The results have technical importance for the prediction of response of window panes and wall-panels to sonic boom. All details are explained by graphs.     

Transverse vibration of membranes of arbitrary shape by the method of constant-deflection contours

A method for approximate computation of the fundamental frequency of membranes of arbitrary shape vibrating harmonically is developed. The method is based upon the concept of contour lines of equal deflection on the surface of the membrane. A similar method for elastic plates has recently been developed by the author in a series of papers. As illustrations of the procedure, the method is applied to the calculation of the gravest mode of an annular, an elliptic, and a parabolic membrane.