Null dominant energy condition

C Some defective warp drives Some of the recently proposed warp drive spacetimes are defective for other reasons. This then leads to delta functions in the Christoffel symbols, squares of delta functions in the Riemann tensor, and cubes of delta functions in the Bianchi identities. This is mathematically and physically not viable.

This is simply not viable for describing a warp drive spacetime. This is not a warp drive spacetime. So if this claim were to be true, if these models truly were solutions of the Einstein equations with the specified source, one would have a warp drive spacetime satisfying the NEC, which we have just shown to be impossible. The point here is that the author of [1] has not actually solved the Einstein equations, he has only solved part of the Einstein equations — for the density, flux, and trace of the stress.

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D 77 , Appleby, R. It was proposed [21] that p-adic string theories provide lattice discretization to the world-sheet of ordinary strings. As a result of these developments, some nontrivial features of ordinary string In [19, 20] the instability problem has been reduced to the problem of such choose of the effective theory parameters that the instability turns out to be essential only at times that are not descri When our works overlap, our results agree with each other.

We use the Lagrangian approach mainly to have an alternati A idea that could solve the problems is that terms with high order derivatives can be treated as corrections valued only at small energies below the physical cut-off [24, 25]. This approach implies It has been remarkably successful as a classical theory of gravitational interactions from scales of millimeters through to kiloparsecs.

Thus a Documents: Advanced Search Include Citations. Authors: Advanced Search Include Citations. Add To MetaCart. Joukovskaya, Sergey Yu. Vernov , A general class of cosmological models driven by a non-local scalar field inspired by string field theories is studied. In particular cases the scalar field is a string dilaton or a string tachyon. A distinguished feature of these models is a crossing of the phantom divide. We reveal the nature of Abstract - Cited by 23 6 self - Add to MetaCart A general class of cosmological models driven by a non-local scalar field inspired by string field theories is studied.

We reveal the nature of this phenomena showing that it is caused by an equivalence of the initial non-local model to a model with an infinite number of local fields some of which are ghosts. Deformations of the model that admit exact solutions are constructed. These deformations contain locking potentials that stabilize solutions.

Bouncing and accelerating solutions are presented. Differential equations of infinite order are an increasingly important class of equations in theoretical physics.

Such equations are ubiquitous in string field theory and have recently attracted considerable interest also from cosmologists.