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P. V. Moniz

Publications and source records attributed to P. V. Moniz.

At least 37 records · Page 2Linked to original sources

Classical Universe emerging from quantum cosmology without horizon and flatness problems

We apply the complex de Broglie-Bohm formulation of quantum mechanics [1] to a spatially closed homogeneous and isotropic early Universe whose matter content are radiation and dust perfect fluids. We then show that an expanding classical Universe can emerge from an oscillating (with complex scale factor) quantum Universe without singularity. Furthermore, the Universe obtained in this process has no horizon or flatness problems.

gr-qc↗

Quantum cosmological intertwining: Factor ordering and boundary conditions from hidden symmetries

We explore the implications of hidden symmetries present in a particular quantum cosmological setting, extending the results reported in \cite{10,11}. In more detail, our case study is constituted by a spatially closed Friedmann-Lema\^ıtre-Robertson-Walker universe, in the presence of a conformally coupled scalar field. The $su(1,1)$ hidden symmetries of this model, together with the Hamiltonian constraint, lead to the gauge invariance of its corresponding Bargmann indices. We subsequently show that some factor-ordering choices can be related to the allowed spectrum of Bargmann indices and hence, to the hidden symmetries. Moreover, the presence of those hidden symmetries also implies a set of appropriate boundary conditions to choose from. In summary, our results suggest that factor ordering and boundary conditions can be intertwined when a quantum cosmological model has hidden symmetries.

gr-qc↗

On the relation between boundary proposals and hidden symmetries of the extended pre-big bang quantum cosmology

A framework associating quantum cosmological boundary conditions to minisuperspace hidden symmetries has been introduced in \cite{7}. The scope of the application was, notwithstanding the novelty, restrictive because it lacked a discussion involving realistic matter fields. Therefore, in the herein letter, we extend the framework scope to encompass elements from a scalar-tensor theory in the presence of a cosmological constant. More precisely, it is shown that hidden minisuperspace symmetries present in a pre-big bang model suggest a process from which boundary conditions can be selected.

gr-qc↗

Quantum cosmology, minimal length and holography

We study the effects of a generalized uncertainty principle on the classical and quantum cosmology of a closed Friedmann Universe whose matter content is either a dust or a radiation fluid. More concretely, assuming the existence of a minimal length, we show that the entropy will constitute a Dirac observable. In addition, 't Hooft conjecture on the cosmological holographic principle is also investigated. We describe how this holographic principle is satisfied for large values of a quantum number, $n$. This occurs when the entropy is computed in terms of the minimal area.

gr-qc↗

Dirac observables and boundary proposals in quantum cosmology

We study the reduced phase space quantization of a closed Friedmann Universe, where matter content is constituted by two (no-interacting) fluids, namely dust (or cold dark matter) and radiation. It is shown that, for this particular model, specific boundary conditions can be related to the algebra of Dirac observables.

gr-qc↗

Gravitational Collapse of a Homogeneous Scalar Field in Deformed Phase Space

We study the gravitational collapse of a homogeneous scalar field, minimally coupled to gravity, in the presence of a particular type of dynamical deformation between the canonical momenta of the scale factor and of the scalar field. In the absence of such a deformation, a class of solutions can be found in the literature [R. Goswami and P. S. Joshi, arXiv:gr-qc/0410144], %\cite{JG04}, whereby a curvature singularity occurs at the collapse end state, which can be either hidden behind a horizon or be visible to external observers. However, when the phase-space is deformed, as implemented herein this paper, we find that the singularity may be either removed or instead, attained faster. More precisely, for negative values of the deformation parameter, we identify the emergence of a negative pressure term, which slows down the collapse so that the singularity is replaced with a bounce. In this respect, the formation of a dynamical horizon can be avoided depending on the suitable choice of the boundary surface of the star. Whereas for positive values, the pressure that originates from the deformation effects assists the collapse toward the singularity formation. In this case, since the collapse speed is unbounded, the condition on the horizon formation is always satisfied and furthermore the dynamical horizon develops earlier than when the phase-space deformations are absent. These results are obtained by means of a thoroughly numerical discussion.

gr-qc↗

Quantum Cosmological Multidimensional Einstein-Yang-Mills Model in a $R \times S^3 \times S^d$ Topology

The quantum cosmological version of the multidimensional Einstein-Yang-Mills model in a $R \times S^3 \times S^d$ topology is studied in the framework of the Hartle-Hawking proposal. In contrast to previous work in the literature, we consider Yang-Mills field configurations with non-vanishing time-dependent components in both $S^3$ and $S^d$ spaces. We obtain stable compactifying solutions that do correspond to extrema of the Hartle-Hawking wave function of the Universe. Subsequently, we also show that the regions where 4-dimensional metric behaves classically or quantum mechanically (i.e. regions where the metric is Lorentzian or Euclidean) will depend on the number, $d$, of compact space dimensions.

gr-qc↗

Origin of Structure in a Supersymmetric Quantum Universe

In this report we advance the current repertoire of quantum cosmological models to incorporate inhomogenous field modes in a supersymmetric manner. In particular, we introduce perturbations about a supersymmetric FRW model. A quantum state of our model has properties typical of the no-boundary (Hartle--Hawking) proposal. This solution may then lead to a scale--free spectrum of density perturbations.

gr-qc↗

Can we obtain Conserved Currents in Supersymmetric Quantum Cosmology?

In this paper we report whether conserved currents can be sensibly defined in supersymmetric minisuperspaces. Our analysis deals with a k=1 FRW model. Supermatter in the form of scalar supermultiplets is included. We show that conserved currents cannot be adequately established except for some very simple scenarios.

gr-qc↗

Conserved Currents in Supersymmetric Quantum Cosmology?

In this paper we investigate whether conserved currents can be sensibly defined in supersymmetric minisuperspaces. Our analysis deals with k=1 FRW and Bianchi class--A models. Supermatter in the form of scalar supermultiplets is included in the former. Moreover, we restrict ourselves to the first-order differential equations derived from the Lorentz and supersymmetry constraints. The ``square-root'' structure of N=1 supergravity was our motivation to contemplate this interesting research. We show that conserved currents cannot be adequately established except for some very simple scenarios. Otherwise, conservation equations may only be obtained from Wheeler-DeWitt--like equations, which are derived from the supersymmetric algebra of constraints. Two appendices are included. In appendix A we describe some interesting features of quantum FRW cosmologies with complex scalar fields when supersymmetry is present. In particular, we explain how the Hartle-Hawking state can now be satisfactorily identified. In appendix B we initiate a discussion about the retrieval of classical properties from supersymmetric quantum cosmologies.

gr-qc↗

From Reissner-Nordström quantum states to charged black holes mass evaporation

In this report we describe quantum Reissner-Nordström (RN) black-holes interacting with a complex scalar field. Our analysis is characterized by solving a Wheeler-DeWitt equation in the proximity of an apparent horizon of the RN space-time. Subsequently, we obtain a wave-function $Ψ_{RN}[M, Q]$ representing the RN black-hole. A special emphasis is given to the evolution of the mass-charge rate affected by Hawking radiation. More details can be found in gr-qc/9709080.

hep-th↗

Wave Function for the Reissner-Nordström Black-Hole

We study the quantum behaviour of Reissner-Nordström (RN) black-holes interacting with a complex scalar field. A Maxwell field is also present. Our analysis is based on M. Pollock's method and is characterized by solving a Wheeler-DeWitt equation in the proximity of an apparent horizon of the RN space-time. Subsequently, we obtain a wave-function $Ψ_{RN}[M, Q]$ representing the RN black-hole when its charge, $\mid Q \mid$, is small in comparison with its mass, $M$. We then compare quantum-mechanically the cases of $(i)$ $Q = 0$ and $(ii)$ $M \geq \mid Q \mid \neq 0 $. A special emphasis is given to the evolution of the mass-charge rate affected by Hawking radiation.

gr-qc↗

Why two makes it more attractive than just with one... or Bianchi class-A models and Reissner-Nordström Black Holes in Quantum N=2 Supergravity

Bianchi class-A models and Reissner-Nordstrom (RN) black hole scenarios are considered from the point of view of quantum N=2 Supergravity. It is shown that the presence of Maxwell fields in the supersymmetry constraints implies a non-conservation of the fermion number present in Bianchi class-A models. This effect corresponds to a mixing between different (Lorentz invariant) fermionic sectors in the wave function of the Universe. Quantum states are constituted by exponentials of N=2 supersymmetric Chern-Simons functionals. With respect to the RN case, we analyse some problems and features present in a reduced model with supersymmetry. Lines of subsequent research work are then provided.

hep-th↗

Wave Function of a Supersymmetric FRW Model with Vector Fields

A specific Friedmann-Roberstson-Walker (FRW) model derived from the theory of N=1 supergravity with gauged supermatter is considered in this paper. The supermatter content is restricted to a vector supermultiplet. The corresponding Lorentz and supersymmetry quantum constraints are then derived. Non-trivial solutions are subsquently found. A no-boundary solution is identified while another state may be interpreted as a wormhole solution.

hep-th↗

Supersymmetric Quantum Cosmology --- Shaken not stirred

The canonical quantization of $N=1$ and $N=2$ supergravity theories is reviewed in this report. A special emphasis is given to the topic of supersymmetric Bianchi class-A and FRW minisuperspaces, namely in the presence of supermatter fields. The quantization of the general theory (including supermatter) is also contemplated. The issue of quantum physical states is subsequently analysed. A discussion on further research problems still waiting to be addressed is included. An extensive and updated bibliography concludes this review.

gr-qc↗

`` Rerum Universitas Sententia ex Susy'' (A View of the Universe according to Supersymmetry)

The question if conserved currents can be sensibly defined in supersymmetric minisuperspaces is investigated in this essay. The objective is to employ exclusively the differential equations obtained {\em directly} from the Lorentz and supersymmetry quantum constraints. The ``square-root'' structure of N=1 supergravity is the motivation to contemplate this tempting idea. However, it is shown that such prospect is not feasible but for some very simple scenarios. Otherwise, conserved currents (and consistent probability densities) can be derived from subsequent Wheeler-DeWitt like equations obtained from the supersymmetric algebra of constraints.

gr-qc↗