scholarly journals A NAKED SINGULARITY STABLE UNDER SCALAR FIELD PERTURBATIONS

2013 ◽  
Vol 22 (04) ◽  
pp. 1350015 ◽  
Author(s):  
AMRUTA SADHU ◽  
VARDARAJAN SUNEETA
Keyword(s):  
Scalar Field ◽  
String Theory ◽  
Naked Singularity ◽  
Stability Result ◽  
Cosmic Censorship ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
The Stability ◽  
Cosmic Censorship Conjecture

We prove the stability of a spacetime with a naked singularity under scalar field perturbations, where the perturbations are regular at the singularity. This spacetime, found by Janis, Newman and Winicour and independently by Wyman, is sourced by a massless scalar field and also arises as a certain limit of a class of charged dilatonic solutions in string theory. This stability result opens up specific questions for investigation related to the cosmic censorship conjecture and the mechanism by which it is implemented in nature.

scholarly journals Cosmological bounce in Horndeski theory and beyond

2018 ◽  
Vol 191 ◽  
pp. 07013 ◽  
Author(s):  
R. Kolevatov ◽  
S. Mironov ◽  
V. Rubakov ◽  
N. Sukhov ◽  
V. Volkova
Keyword(s):  
General Relativity ◽  
Scalar Field ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Cosmological Solutions ◽  
The Stability ◽  
The Way

We discuss the stability of the classical bouncing solutions in the general Horndeski theory and beyond Horndeski theory. We restate the no-go theorem, showing that in the general Horndeski theory there are no spatially flat non-singular cosmological solutions which are stable during entire evolution. We show the way to evade the no-go in beyond Horndeski theory and give two specific examples of bouncing solutions, whose asymptotic past and future or both are described by General Relativity (GR) with a conventional massless scalar field. Both solutions are free of any pathologies at all times.

GRAVITATIONAL COLLAPSE OF A SELF-INTERACTING SCALAR FIELD

2007 ◽  
Vol 22 (01) ◽  
pp. 65-74 ◽  
Author(s):  
RITUPARNO GOSWAMI ◽  
PANKAJ S. JOSHI
Keyword(s):  
Black Hole ◽  
Scalar Field ◽  
Gravitational Collapse ◽  
Energy Condition ◽  
Dynamical Evolution ◽  
Naked Singularity ◽  
Cosmic Censorship ◽  
Weak Energy Condition ◽  
Scalar Field Models ◽  
Cosmic Censorship Conjecture

We construct and study here a class of collapsing scalar field models with a nonzero potential. The weak energy condition is satisfied by the collapsing configuration and it is shown that the end state of collapse could be either a black hole or a naked singularity. It is seen that physically it is the rate of collapse that governs these outcomes of the dynamical evolution. The implications for the cosmic censorship conjecture are discussed.

scholarly journals Critical phenomena in gravitational collapse of Husain–Martinez–Nunez scalar field

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Xiaobao Wang ◽  
Xiaoning Wu ◽  
Sijie Gao
Keyword(s):  
Scalar Field ◽  
Critical Phenomena ◽  
Gravitational Collapse ◽  
Naked Singularity ◽  
Extrinsic Curvature ◽  
Analytical Models ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Self Similarity ◽  
Metric Function

Abstract We construct analytical models to study the critical phenomena in gravitational collapse of the Husain-Martinez-Nunez massless scalar field. We first use the cut-and-paste technique to match the conformally flat solution ($$c=0$$c=0 ) onto an outgoing Vaidya solution. To guarantee the continuity of the metric and the extrinsic curvature, we prove that the two solutions must be joined at a null hypersurface and the metric function in Vaidya spacetime must satisfy certain constraints. We find that the mass of the black hole in the resulting spacetime takes the form $$M\propto (p-p^*)^\gamma $$M∝(p-p∗)γ, where the critical exponent $$\gamma $$γ is equal to 0.5. For the case $$c\ne 0$$c≠0, we show that the scalar field must be joined onto two pieces of Vaidya spacetimes to avoid a naked singularity. We also derive the power-law mass formula with $$\gamma =0.5$$γ=0.5. Compared with previous analytical models which were constructed from a different scalar field with continuous self-similarity, we obtain the same value of $$\gamma $$γ. However, we show that the solution with $$c\ne 0$$c≠0 is not self-similar. Therefore, we provide a rare example that a scalar field without self-similarity also possesses the features of critical collapse.

scholarly journals STATIC SPHERICALLY SYMMETRIC SCALAR FIELD SPACETIMES WITH C0 MATCHING

2011 ◽  
Vol 26 (17) ◽  
pp. 1281-1290 ◽  
Author(s):  
SWASTIK BHATTACHARYA ◽  
PANKAJ S. JOSHI
Keyword(s):  
Scalar Field ◽  
Naked Singularity ◽  
Scalar Fields ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Spherically Symmetric ◽  
Curvature Singularity ◽  
Einstein Theory ◽  
Full Class ◽  
Strong Curvature

All the classes of static massless scalar field models currently available in the Einstein theory of gravity necessarily contain a strong curvature naked singularity. We obtain here a family of solutions for static massless scalar fields coupled to gravity, which does not have any strong curvature singularity. This class of models contain a thin shell of singular matter, which has a physical interpretation. The central curvature singularity is, however, avoided which is common to all static massless scalar field spacetime models known so far. Our result thus points out that the full class of solutions in this case may contain non-singular models, which is an intriguing possibility.

scholarly journals NAKED SINGULARITIES IN THREE-DIMENSIONS

2003 ◽  
Vol 12 (05) ◽  
pp. 791-799
Author(s):  
G. OLIVEIRA-NETO
Keyword(s):  
Scalar Field ◽  
Analytical Solution ◽  
Cosmic Censorship ◽  
The Self ◽  
Three Dimensions ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Naked Singularities ◽  
Asymptotically Flat ◽  
Self Similar

We study an analytical solution to the Einstein's equations in (2+1)-dimensions, representing the self-similar collapse of a circularly symmetric, minimally coupled, massless, scalar field. Depending on the value of certain parameters, this solution represents the formation of naked singularities. Since our solution is asymptotically flat, these naked singularities may be relevant for the weak cosmic censorship conjecture in (2+1)-dimensions.

scholarly journals Vacuum Polarization in a Zero-Width Potential: Self-Adjoint Extension

Universe ◽  
2021 ◽  
Vol 7 (5) ◽  
pp. 127
Author(s):  
Yuri V. Grats ◽  
Pavel Spirin
Keyword(s):  
Scalar Field ◽  
Vacuum Polarization ◽  
Dimensional Regularization ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Field Approximation ◽  
Dimensional Euclidean Space ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Adjoint Extension

The effects of vacuum polarization associated with a massless scalar field near pointlike source with a zero-range potential in three spatial dimensions are analyzed. The “physical” approach consists in the usage of direct delta-potential as a model of pointlike interaction. We use the Perturbation theory in the Fourier space with dimensional regularization of the momentum integrals. In the weak-field approximation, we compute the effects of interest. The “mathematical” approach implies the self-adjoint extension technique. In the Quantum-Field-Theory framework we consider the massless scalar field in a 3-dimensional Euclidean space with an extracted point. With appropriate boundary conditions it is considered an adequate mathematical model for the description of a pointlike source. We compute the renormalized vacuum expectation value ⟨ϕ2(x)⟩ren of the field square and the renormalized vacuum averaged of the scalar-field’s energy-momentum tensor ⟨Tμν(x)⟩ren. For the physical interpretation of the extension parameter we compare these results with those of perturbative computations. In addition, we present some general formulae for vacuum polarization effects at large distances in the presence of an abstract weak potential with finite-sized compact support.

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