Papers by Octavio Obregon
Classical and Quantum Gravity, 1999
Making use of supersymmetry breaking selection rules under local n = 2 conformal supersymmetry we... more Making use of supersymmetry breaking selection rules under local n = 2 conformal supersymmetry we are able to obtain a normalizable wavefunction (at zero energy) of the universe for the FRW cosmological model (k = 0). For this purpose it is necessary to `weight' the inner product with the scalar factor R. The appropriate Hermitian operators are constructed and the
In this work, we present several solutions to noncommutative cosmology using the WKB approximatio... more In this work, we present several solutions to noncommutative cosmology using the WKB approximation in noncommutative quantum cosmology.
Several eigenvalue equations that could describe quantum black holes have been proposed in the ca... more Several eigenvalue equations that could describe quantum black holes have been proposed in the canonical quantum gravity approach. In this paper, we choose one of the simplest of these quantum equations to show how the usual Feynman's path integral method can be applied to obtain the corresponding statistical properties. We get a logarithmic correction to the Bekenstein-Hawking entropy as already obtained by other authors by other means.
In this work, we develop and apply the WKB approximation to several examples of noncommutative qu... more In this work, we develop and apply the WKB approximation to several examples of noncommutative quantum cosmology, obtaining the time evolution of the noncommutative universe, this is done starting from a noncommutative quantum formulation of cosmology where the noncommutativity is introduced by a deformation on the minisuperspace variables. This procedure gives a straightforward algorithm to incorporate noncommutativity to cosmology and inflation.
Arxiv preprint gr-qc/0404003, 2004
The assumption of a linearly expanding universe for the JBD-cosmological equations generates a se... more The assumption of a linearly expanding universe for the JBD-cosmological equations generates a set of solutions for the barotropic equations ofstatep = ~Q (a = const.). These solutions turn out to be valid for closed space- except in the case p = 0 which is for open space. The ' gravita- tional constant' which is inversely proportional to the scalar field q~ increases with time if a > -�89 and decreases for a < -k. No solution exists for c~ = �89 The Brans-Dicke parameter ~o is negative ifa < --�89 A set of exact cosmological solutions for the Jordan-Brans and Dicke (JBD) scalar- tensor theory of gravitation is presented. One considers the universe to be homo- geneous and isotropic with a perfect fluid equation of state,p = a~ (c~ ~< 1), and assume that the scale factor R of the Robertson Walker line-element increases linearly with respect to the age of the universe. Some of these solutions, for closed space and particu- lar values of a, have been previously foun...
International Journal of Modern Physics D, 2009
In this paper, we develop and apply the WKB-type approximation to several examples of noncommutat... more In this paper, we develop and apply the WKB-type approximation to several examples of noncommutative quantum cosmology, obtaining the time evolution of the noncommutative universe. This is accomplished by starting from a noncommutative quantum formulation of cosmology, where the noncommutativity is introduced by a deformation on the minisuperspace variables. This procedure gives a straightforward algorithm to incorporate noncommutativity into cosmology and inflation.
Physics Letters B, 1999
Using one-loop effective action in large N and s-wave approximation we discuss the possibility to... more Using one-loop effective action in large N and s-wave approximation we discuss the possibility to induce primordial wormholes at the early Universe. An analytical solution is found for self-consistent primordial wormhole with constant radius. Numerical study gives the wormhole solution with increasing throat radius and increasing red-shift function. There is also some indication to the possibility of a topological phase transition.
AIP Conference Proceedings, 2003
Il Nuovo Cimento B Series 11, 1995
A discussion is given on the restrictions imposed on generalized gravitational Lagrangians by req... more A discussion is given on the restrictions imposed on generalized gravitational Lagrangians by requiring that the Green function, for their corresponding weak-field limit, be of the form ~(t-r)/r, which implies the very physical fact that waves propagate with only one velocity. It is shown that in four dimensions only a Lagrangian proportional to R is allowed and for six dimensions it should be proportional to R'~R~. No powers of combinations of the curvature tensors give a satisfactory theory for dimensions n > 6. PACS 04.20.Cv-Fundamental problems and general formalism. PACS 04.50-Gravity in more than four dimensions, Kaluza-Klein theory, unified field theories, alternative theories of gravity. 1.-Introduction.
We briefly study the dynamics at classical level of the Carrollian limit, with vanishing speed of... more We briefly study the dynamics at classical level of the Carrollian limit, with vanishing speed of light and no possible propagation of signals, for a simply effective action in a flat space with a open string tachyon as scalar field. The canonical analysis of the theory indicates that the equation of motion is of Dirac type contrary to non-relativistic case
Contemporary Mathematics, 2008
ABSTRACT
Foundations of Physics - FOUND PHYS, 2003
The problem of the electromagnetic coupling for spin-3/2 particles is discussed. Following superg... more The problem of the electromagnetic coupling for spin-3/2 particles is discussed. Following supergravity and some previous researches in the field of classical supersymmetric particles, we found that the electromagnetic coupling must not obey a minimal coupling in the sense of coupling the electromagnetic potential, but some kind of an electromagnetic field strength.
Physical Review Letters, 2002
Physical Review D, 1999
Using s-wave and large N approximation the one-loop effective action for 2d dilaton coupled scala... more Using s-wave and large N approximation the one-loop effective action for 2d dilaton coupled scalars and spinors which are obtained by spherical reduction of 4d minimal matter is found. Quantum effective equations for reduced Einstein gravity are written. Their analytical solutions corresponding to 4d Kantowski-Sachs (KS) Universe are presented. For quantum-corrected Einstein gravity we get non-singular KS cosmology which represents 1) quantumcorrected KS cosmology which existed on classical level or 2)purely quantum solution which had no classical limit. The analogy with Nariai BH is briefly mentioned. For purely induced gravity (no Einstein term) we found general analytical solution but all KS cosmologies under discussion are singular. The corresponding equations of motion are reformulated as classical mechanics problem of motion of unit mass particle in some potential V .
Physical Review D, 2000
We study 2 + 1 Chern-Simons gravity at the classical action level. In particular we rederive the ... more We study 2 + 1 Chern-Simons gravity at the classical action level. In particular we rederive the linear combinations of the "standard" and "exotic" Einstein actions, from the (anti) self-duality of the "internal" Lorentzian indices. The relation to a genuine four-dimensional (anti)self-dual topological theory greatly facilitates the analysis and its relation to hyperbolic threedimensional geometry. Finally a non-abelian vector field "dual" action is also obtained.
Uploads
Papers by Octavio Obregon