Physics by Laur Järv
Journal of Cosmology and Astroparticle Physics, 2004
We use phase space methods to investigate closed, flat, and open Friedmann-Robertson-Walker cosmo... more We use phase space methods to investigate closed, flat, and open Friedmann-Robertson-Walker cosmologies with a scalar potential given by the sum of two exponential terms. The form of the potential is motivated by the dimensional reduction of M-theory with non-trivial four-form flux on a maximally symmetric internal space. To describe the asymptotic features of run-away solutions we introduce the concept of a 'quasi fixed point.' We give the complete classification of solutions according to their late-time behavior (accelerating, decelerating, crunch) and the number of periods of accelerated expansion.
Physical Review D, 2010
We consider Friedmann-Lemaître-Robertson-Walker flat cosmological models in the framework of gene... more We consider Friedmann-Lemaître-Robertson-Walker flat cosmological models in the framework of general Jordan frame scalar-tensor theories of gravity with arbitrary coupling function and potential. For the era when the cosmological energy density of the scalar potential dominates over the energy density of ordinary matter, we use a nonlinear approximation of the decoupled scalar field equation for the regime close to the so-called limit of general relativity where the local weak field constraints are satisfied. We give the solutions in cosmological time with a particular attention to the classes of models asymptotically approaching general relativity. The latter can be subsumed under two types: (i) exponential convergence, and (ii) damped oscillations around general relativity. As an illustration we present an example of oscillating dark energy. * [email protected] † [email protected] ‡ [email protected]
International Journal of Modern Physics A, 2009
We study the evolution of homogeneous and isotropic, flat cosmological models within the general ... more We study the evolution of homogeneous and isotropic, flat cosmological models within the general scalar-tensor theory of gravity with arbitrary coupling function and potential and scrutinize its limit to general relativity. Using the methods of dynamical systems for the decoupled equation of the Jordan frame scalar field we find the fixed points of flows in two cases: potential domination and
Proceedings of the Estonian Academy of Sciences, 2010
We consider Friedmann-Lemaître-Robertson-Walker cosmological models in the framework of general s... more We consider Friedmann-Lemaître-Robertson-Walker cosmological models in the framework of general scalar-tensor theories of gravity (STG) with arbitrary coupling functions, set in the Jordan frame. First we describe the general properties of the phase space in the case of barotropic matter fluid and scalar field potential for any spatial curvature (flat, spherical, hyperbolic). Then we address the question under which conditions epochs of accelerated and super-accelerated expansion are possible in STG. For flat models filled with dust matter (and vanishing potential) we give a necessary condition on the coupling function of the scalar field which must be satisfied to allow acceleration and super-acceleration. This is illustrated by a specific example. * [email protected] † [email protected] ‡ [email protected]
Physical Review D, 2007
We consider a Randall-Sundrum two-brane cosmological model in the low energy gradient expansion a... more We consider a Randall-Sundrum two-brane cosmological model in the low energy gradient expansion approximation by Kanno and Soda. It is a scalar-tensor theory with a specific coupling function and a specific potential. Upon introducing the Friedmann-Lemaitre-Robertson-WalkerFLRW metric and perfect fluid matter on both branes in the Jordan frame, the effective dynamical equation for the A-brane (our Universe) scale factor decouples
Physical Review D, 2008
We study the evolution of homogeneous and isotropic, flat cosmological models within the general ... more We study the evolution of homogeneous and isotropic, flat cosmological models within the general scalar-tensor theory of gravity with arbitrary coupling function and potential. After introducing the limit of general relativity we describe the details of the phase space geometry. Using the methods of dynamical systems for the decoupled equation of the Jordan frame scalar field we find the fixed points of flows in two cases: potential domination and matter domination. We present the conditions on the mathematical form of the coupling function and potential which determine the nature of the fixed points (attractor or other). There are two types of fixed points, both are characterized by cosmological evolution mimicking general relativity, but only one of the types is compatible with the Solar System PPN constraints. The phase space structure should also carry over to the Einstein frame as long as the transformation between the frames is regular which however is not the case for the latter (PPN compatible) fixed point.
Physical Review D, 2007
We consider the correspondence between the Jordan frame and the Einstein frame descriptions of sc... more We consider the correspondence between the Jordan frame and the Einstein frame descriptions of scalar-tensor theory of gravitation. We argue that since the redefinition of the scalar field is not differentiable at the limit of general relativity the correspondence between the two frames is lost at this limit. To clarify the situation we analyse the dynamics of the scalar field in different frames for two distinct scalar-tensor cosmologies with specific coupling functions and demonstrate that the corresponding scalar field phase portraits are not equivalent for regions containing the general relativity limit. Therefore the answer to the question whether general relativity is an attractor for the theory depends on the choice of the frame.
Journal of Physics: Conference Series, 2012
Journal of Physics: Conference Series, 2011
We consider Friedmann-Lemaître-Robertson-Walker flat cosmological models in the framework of gene... more We consider Friedmann-Lemaître-Robertson-Walker flat cosmological models in the framework of general Jordan frame scalar-tensor theories of gravity with arbitrary coupling functions, in the era when the energy density of the scalar potential dominates over the energy density of ordinary matter. To study the regime suggested by the local weak field tests (i.e. close to the so-called limit of general relativity) we propose a nonlinear approximation scheme, solve for the phase trajectories, and provide a complete classification of possible solutions. We argue that the topology of phase trajectories in the nonlinear approximation is representative of those of the full system, and thus can tell for which scalar-tensor models general relativity functions as an attractor. To the classes of models which asymptotically approach general relativity we give the solutions also in cosmological time and conclude with some observational implications.
Journal of High Energy Physics, 2003
We construct a family of five-dimensional gauged supergravity actions which describe flop transit... more We construct a family of five-dimensional gauged supergravity actions which describe flop transitions of M-theory compactified on Calabi-Yau threefolds.
Journal of Cosmology and Astroparticle Physics, 2004
We study five-dimensional Kasner cosmologies in a time-dependent Calabi-Yau compactification of M... more We study five-dimensional Kasner cosmologies in a time-dependent Calabi-Yau compactification of M-theory undergoing a flop transition. The dynamics of the additional states, which become massless at the transition point and give rise to a scalar potential, are taken into account using a recently constructed gauged supergravity action. Due to the dynamics of these states the moduli do not show the usual run-away behavior but oscillate around the transition region. Moreover, the solutions typically exhibit short periods of accelerated expansion. We also analyze the interplay between the geometries of moduli space and space-time.
Journal of High Energy Physics, 2002
We present some results of studying certain axially symmetric supergravity geometries correspondi... more We present some results of studying certain axially symmetric supergravity geometries corresponding to a distribution of BPS D6-branes wrapped on K3, obtained as extremal limits of a rotating solution. The geometry's unphysical regions resulting from the wrapping can be repaired by the enhançon mechanism, with the result that there are two nested enhançon shells. For a range of parameters, the two shells merge into a single toroidal surface. Given the quite intricate nature of the geometry, it is an interesting system in which to test previous techniques that have been brought to bear in spherically symmetric situations. We are able to check the consistency of the construction using supergravity surgery techniques, and probe brane results. Implications for the Coulomb branch of (2+1)-dimensional pure SU (N ) gauge theory are extracted from the geometry. Related results for wrapped D4-and D5-brane distributions are also discussed.
Buddhist & Tibetan Studies by Laur Järv
Loeng TÜ orientalistika seminaris 2014
Sissejuhatavaid selgitusi Dharmakīrti suurteose "Pramāṇavārttika" teise peatüki kohta, koostatud ... more Sissejuhatavaid selgitusi Dharmakīrti suurteose "Pramāṇavārttika" teise peatüki kohta, koostatud Tema Pühaduse õpetustele Riias 10.-11. oktoobril 2016, ette kantud TÜ orientalistika seminarides.
Slides for the talk presented at the Baltic Alliance for Asian Studies (BAAS) Conference 2014, at... more Slides for the talk presented at the Baltic Alliance for Asian Studies (BAAS) Conference 2014, at Vilnius University, April 3–4 2014, Panel 2: “Buddhism in texts: interpretations and reinterpretations of Buddhist heritage.”
Slides introducing the documentary "Guge, the Lost Kingdom of Tibet", at Sakya International Budd... more Slides introducing the documentary "Guge, the Lost Kingdom of Tibet", at Sakya International Buddhist Academy 2012.
Tiibeti keelest tõlkinud ja kommenteerinud Laur Järv, valmis Tema Pühaduse XIV dalai-laama õpetus... more Tiibeti keelest tõlkinud ja kommenteerinud Laur Järv, valmis Tema Pühaduse XIV dalai-laama õpetuste tarvis Riias 5.-6. mail 2014.
Ettekande slaidid Eesti Akadeemilise Orientaalseltsi XXIV orientalistikapäevadel "Ida mõttelugu e... more Ettekande slaidid Eesti Akadeemilise Orientaalseltsi XXIV orientalistikapäevadel "Ida mõttelugu eesti keeles: tõlked ja tõlgendused", 28. aprillil 2012 Tartus.
Ettekande slaidid Eesti Akadeemilise Orientaalseltsi XXV orientalistikapäevadel 5. aprillil 2013 ... more Ettekande slaidid Eesti Akadeemilise Orientaalseltsi XXV orientalistikapäevadel 5. aprillil 2013 Tartus.
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Physics by Laur Järv
Buddhist & Tibetan Studies by Laur Järv