As is well known, in order for the Einstein–Hilbert action to have a well defined variation, and therefore to be used for deriving field equation through the stationary action principle, it has to be amended by the addition of a suitable boundary term. It has recently been claimed that, if one constructs an action by adding this term to the matter action, the Einstein field equations can be der...

A closed Riemannian manifold (Mn, g) is called Einstein if the Ricci tensor of g is a multiple of itself; that is, ric(g) = λ · g. This equation, called the Einstein equation, is a complicated system of second order partial differential equations, and at the present time no general existence results for Einstein metrics are known. However, there are results for many interesting classes of Einst...

The Boyer-Finley equation, or SU(∞)-Toda equation is both a reduction of the self-dual Einstein equations and the dispersionless limit of the 2d-Toda lattice equation. This suggests that there should be a dispersive version of the self-dual Einstein equation which both contains the Toda lattice equation and whose dispersionless limit is the familiar self-dual Einstein equation. Such a system is...

The Boyer-Finley equation, or SU (∞)-Toda equation is both a reduction of the self-dual Einstein equations and the dispersionless limit of the 2d-Toda lattice equation. This suggests that there should be a dispersive version of the self-dual Einstein equation which both contains the Toda lattice equation and whose dispersionless limit is the familiar self-dual Einstein equation. Such a system i...

– We investigate the exact renormalization group (RG) in Einstein gravity coupled to N-component spinor field, working in the effective average action formalism and background field method. The truncated evolution equation is obtained for the Newtonian and cosmological constants. We have shown that screening or antiscreening behaviour of the gravitational coupling depends crucially on the numbe...

We propose that periodically in spaceand time-modulated potentials (dynamic lattices) can efficiently remove the excited (the high-energy and large momentum) components of the trapped Bose-Einstein condensates (BECs) and, consequently, can result in efficient cleaning of the BECs. We prove the idea by numerically solving the mean-field models (the Schrödinger equation for noninteracting condens...

On the basis of an algebraic relation between torsion and a classical spinor field a new interpretation of Einstein-Cartan gravity interacting with a classical spinor field is proposed. In this approach the spinor field becomes an auxiliary field and the dynamical equation for this field (the Heisenberg equation) is a dynamical, gravitational equation for torsion. The simplest version of this t...

For a spatially flat Friedmann model with line element ds 2 = a 2 [da 2 /B(a) − dx 2 − dy 2 − dz 2 ], the 00-component of the Einstein field equation reads 8πGT 00 = 3/a 2 containing no derivative. For a nonlinear Lagrangian L(R), we obtain a second– order differential equation for B instead of the expected fourth-order equation. We discuss this equation for the curvature-saturated model propos...