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Yuri Shtanov

Publications and source records attributed to Yuri Shtanov.

59 records · Page 4Linked to original sources
arXiv2002

New Cosmological Singularities in Braneworld Models

Higher-dimensional braneworld models which contain both bulk and brane curvature terms in the action admit cosmological singularities of rather unusual form and nature. These `quiescent' singularities, which can occur both during the contracting as well as the expanding phase, are characterised by the fact that while the matter density and Hubble parameter remain finite, all higher derivatives of the scale factor ($\stackrel{..}{a}$, $\stackrel{...}{a}$ etc.) diverge as the cosmological singularity is approached. The singularities are the result of the embedding of the (3+1)-dimensional brane in the bulk and can exist even in an empty homogeneous and isotropic (FRW) universe. The possibility that the present universe may expand into a singular state is discussed.

gr-qc↗
arXiv2001

Recycling the universe using scalar fields

We examine the behaviour of a closed oscillating universe filled with a homogeneous scalar field and find that, contrary to naive expectations, such a universe expands to larger volumes during successive expansion epochs. This intriguing behaviour introduces an arrow of time in a system which is time-reversible. The increase in the maximum size of the universe is closely related to the work done on/by the scalar field during one complete oscillatory cycle which, in turn, is related to the asymmetry in the scalar field equation of state during expansion and collapse. Our analysis shows that scalar fields with polynomial potentials $V(ϕ) = λϕ^q$, $q > 1$ lead to a growing oscillation amplitude for the universe: the increase in amplitude between successive oscillations is more significant for smaller values of $q$. Such behaviour allows for the effective recycling of the universe. A recycled universe can be quite old and can resolve the flatness problem. These results have strong bearing on cosmological models in which the role of dark matter is played by a scalar field. They are also relevant for chaotic inflationary models of the early universe since they demonstrate that, even if the universe fails to inflate the first time around, it will eventually do so during future oscillatory cycles. Thus, the space of initial conditions favourable for chaotic inflation increases significantly.

astro-ph↗
arXiv1997

Space-time description of neutrino flavour oscillations

Recently the issue of EPR-like correlations in the mutual probability of detecting neutrino together with accompanying charged lepton has received a new impetus. In this paper we describe this effect using the propagators of the particles involved in the Schwinger's parametric integral representation. We find this description more simple and more suitable to the purpose than the usual momentum-space analysis. We consider the cases of monochromatic neutrino source, wave packet source, and neutrino creation in a localised space-time region. In the latter case we note that the space-time oscillation amplitude depends on the values of the neutrino masses, and becomes rather small for large relative mass differences (mass hierarchy). We obtain the expressions for the oscillation and coherence lengths in various circumstances. In the region of overlap our results confirm those of Dolgov et al. [hep-ph/9703241].

hep-ph↗
arXiv1995

On Pilot Wave Quantum Cosmology

The de~Broglie--Bohm (pilot wave) formulation of quantum theory appears to be free from the conceptual problems specific to quantum mechanics (problem of measurement) and to quantum cosmology (problem of time). We discuss the issue of quantum equilibrium which arises within its context. We then study the extension of this formulation to the case of gravity and demonstrate that the foliation of spacetime by space-like hypersurfaces obtained during the solution of the quantum problem turns out to be distinguished in general. This means that quantum pilot wave dynamics is not invariant with respect to arbitrary change of foliation, or, in other terms, that quantum non-locality takes place. We also discuss general structure of a realistic pilot wave theory which could describe the universe.

gr-qc↗