A straightforward application of the variational principle to null strings meets difficulties since string’s world-sheets are degenerate. It is known that the variational principle in this case can ...be formulated with the help of two-vector density on the string world-sheet which plays a role of Lagrange multipliers. It is shown that recently suggested stress-energy tensor of null strings can be derived by variation over the background metric of the action used to describe tensionless limit in the string theory. One of the Lagrange multipliers is related to the energy of the null string.
Model crack with a scalable linear parameter Glagolev, V V; Glagolev, L V; Fursaev, A A ...
Journal of physics. Conference series,
04/2019, Letnik:
1203, Številka:
1
Journal Article
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The cracked body strain problem is considered in a linearly elastic formulation on the basis of the interaction layer (IL) concept for loading with opening mode or shear. The stress state in the IL ...is determined on the basis of the average-thickness characteristics of the stressed and strained state (SSS). The proposed problem formulation includes the linear parameter (LP). The wedge force-to-IL thickness relation is derived proceeding from the problem's analytical solution to a beam approximation. It is shown that it is possible to use the energy product of the linear size and the increment in the layer's specific free energy as the generic criterion of destruction. The established association of the specimen size with the critical force ensures is found out to ensure the independence of the critical force from the IL thickness to a desired degree of precision. The resulting and the conventional solution for a notch in the form of mathematical cut are compared to determine the assumptions on which Griffith's criterion concurs with the EP criterion.
Distributional geometry of squashed cones Fursaev, Dmitri V.; Patrushev, Alexander; Solodukhin, Sergey N.
Physical review. D, Particles, fields, gravitation, and cosmology,
08/2013, Letnik:
88, Številka:
4
Journal Article
A regularization procedure developed by D. V. Fursaev and S. N. Solodukhin, Phys. Rev. D 52, 2133 (1995) for the integral curvature invariants on manifolds with conical singularities is generalized ...to the case of squashed cones. In general, the squashed conical singularities do not have rotational O(2) symmetry in a subspace orthogonal to a singular surface capital sigma so that the surface is allowed to have extrinsic curvatures. A new feature of the squashed conical singularities is that the surface terms in the integral invariants, in the limit of a small angle deficit, now depend also on the extrinsic curvatures of capital sigma . A case of invariants which are quadratic polynomials of the Riemann curvature is elaborated in different dimensions and applied to several problems related to entanglement entropy. The results are in complete agreement with computations of the logarithmic terms in entanglement entropy of 4D conformal theories S. N. Solodukhin, Phys. Lett. B 665, 305 (2008). Among other applications of the suggested method are logarithmic terms in entanglement entropy of nonconformal theories and a holographic formula for entanglement entropy in theories with gravity duals.
Gravitational shockwaves are geometries where components of the transverse curvature have abrupt behaviour across null hypersurfaces, which are fronts of the waves. We develop a general approach to ...describe classical field theories on such geometries in a linearized approximation, by using free scalar fields as a model. Perturbations caused by shockwaves exist above the wave front and are solutions to a characteristic Cauchy problem with initial data on the wave front determined by a supertranslation of ingoing fields. A special attention is paid to perturbations of fields of pointlike sources generated by plane-fronted gravitational shockwaves. One has three effects: conversion of non-stationary perturbations into an outgoing radiation, a spherical scalar shockwave which appears when the gravitational wave hits the source, and a plane scalar shockwave accompanying the initial gravitational wave. Our analysis is applicable to gravitational shockwaves of a general class including geometries sourced by null particles and null branes.
The statistical-mechanical origin of the Bekenstein-Hawking entropy
S
BH in the induced gravity is discussed. In the framework of the induced gravity models the Einstein action arises as the low ...energy limit of the effective action of quantum fields. The induced gravitational constant is determined by the masses of the heavy constituents. We established the explicit relation between the statistical entropy of the constituent fields and the black hole entropy
S
BH.
Null cosmic strings are shown to disturb gravitational fields of massive bodies and create outgoing gravitational waves (GW). Perturbations of the metric caused by a straight null string and a ...point-like massive source are found as solutions to linearized Einstein equations on a flat space-time. An analytic approximation for their asymptotic at future null infinity is derived. A space-time created by the source and the string is shown to have asymptotically polyhomogeneous form. We calculate GW flux in such space-times and demonstrate that the averaged intensity of the radiation is maximal in the direction of the string motion. Opportunities to detect null string generated gravity waves are briefly discussed.
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