scholarly journals Vaidya geometries and scalar fields with null gradients

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
Valerio Faraoni ◽  
Andrea Giusti ◽  
Bardia H. Fahim
Keyword(s):  
Scalar Field ◽  
Gordon Equation ◽  
Plane Waves ◽  
Null Geodesic ◽  
Scalar Fields ◽  
Einstein Gravity ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Klein Gordon ◽  
Klein Gordon Equation

AbstractSince, in Einstein gravity, a massless scalar field with lightlike gradient behaves as a null dust, one could expect that it can act as the matter source of Vaidya geometries. We show that this is impossible because the Klein–Gordon equation forces the null geodesic congruence tangent to the scalar field gradient to have zero expansion, contradicting a basic property of Vaidya solutions. By contrast, exact plane waves travelling at light speed and sourced by a scalar field acting as a null dust are possible.

SOLUTION OF THE KLEIN–GORDON EQUATION IN A 2 + 1 CURVED SPACE–TIME

2001 ◽  
Vol 16 (18) ◽  
pp. 1151-1156
Author(s):  
TINA A. HARRIOTT ◽  
J. G. WILLIAMS
Keyword(s):  
Scalar Field ◽  
Bessel Functions ◽  
Gordon Equation ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Whittaker Functions ◽  
Curved Space ◽  
Standard Manner ◽  
Klein Gordon ◽  
Klein Gordon Equation

The Klein–Gordon equation for a massless scalar field is considered for an extended matter source in 2 + 1 dimensions. It is shown how a solution can be found using Whittaker functions and can be normalized in the standard manner. In the point source limit, the solution reduces to the usual expression in terms of Bessel functions.

scholarly journals Proper time and conformal problem in Kaluza–Klein theory

2015 ◽  
Vol 12 (05) ◽  
pp. 1550063
Author(s):  
E. Minguzzi
Keyword(s):  
Scalar Field ◽  
Gordon Equation ◽  
Proper Time ◽  
Inertial Mass ◽  
Scalar Fields ◽  
Conformal Factor ◽  
Klein Theory ◽  
Klein Gordon ◽  
Klein Gordon Equation ◽  
Kaluza Klein

In the traditional Kaluza–Klein theory, the cylinder condition and the constancy of the extra-dimensional radius (scalar field) imply that time-like geodesics on the five-dimensional bundle project to solutions of the Lorentz force equation on spacetime. This property is lost for nonconstant scalar fields, in fact there appears new terms that have been interpreted mainly as new forces or as due to a variable inertial mass and/or charge. Here we prove that the additional terms can be removed if we assume that charged particles are coupled with the same spacetime conformal structure of neutral particles but through a different conformal factor. As a consequence, in Kaluza–Klein theory the proper time of the charged particle might depend on the charge-to-mass ratio and the scalar field. Then we show that the compatibility between the equation of the projected geodesic and the classical limit of the Klein–Gordon equation fixes unambiguously the conformal factor of the coupling metric solving the conformal ambiguity problem of Kaluza–Klein theories. We confirm this result by explicitly constructing the projection of the Klein–Gordon equation and by showing that each Fourier mode, even for a variable scalar field, satisfies the Klein–Gordon equation on the base.

scholarly journals A Central Potential with a Massive Scalar Field in a Lorentz Symmetry Violation Environment

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
R. L. L. Vitória ◽  
H. Belich
Keyword(s):  
Scalar Field ◽  
Gordon Equation ◽  
Mass Term ◽  
Lorentz Symmetry ◽  
Massive Scalar ◽  
Symmetry Violation ◽  
Massive Scalar Field ◽  
Klein Gordon ◽  
Coulomb Type ◽  
Klein Gordon Equation

We investigate the behaviour of a massive scalar field under the influence of a Coulomb-type and central linear central potentials inserted in the Klein-Gordon equation by modifying the mass term in the spacetime with Lorentz symmetry violation. We consider the presence of a background constant vector field which characterizes the breaking of the Lorentz symmetry and show that analytical solutions to the Klein-Gordon equation can be achieved.

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 Does Inflationary Particle Production Suggest a Low-Density Flat Universe?

1999 ◽  
Vol 183 ◽  
pp. 314-314
Author(s):  
Varun Sahni ◽  
Salman Habib
Keyword(s):  
Scalar Field ◽  
Particle Production ◽  
Gordon Equation ◽  
Low Density ◽  
Frw Universe ◽  
Flat Universe ◽  
Klein Gordon ◽  
Klein Gordon Equation

In a FRW Universe a massless nonminimally coupled scalar field satisfies the Klein-Gordon equation.

scholarly journals LATE-TIME TAIL OF A COUPLED SCALAR FIELD IN THE BACKGROUND OF A BLACK HOLE WITH A GLOBAL MONOPOLE

2008 ◽  
Vol 23 (05) ◽  
pp. 359-369 ◽  
Author(s):  
SONGBAI CHEN ◽  
JILIANG JING
Keyword(s):  
Black Hole ◽  
Scalar Field ◽  
Scalar Fields ◽  
Massless Scalar ◽  
Late Time ◽  
Massless Scalar Field ◽  
Global Monopole ◽  
Massive Scalar Field ◽  
Gravitational Fields ◽  
Field Decay

Using the technique of spectral decomposition, we investigated the late-time tails of massless and massive coupled scalar fields in the background of a black hole with a global monopole. We found that due to the existence of the coupling between the scalar and gravitational fields, the massless scalar field decay faster at timelike infinity i+, and so does the massive one in the intermediate late time. But the asymptotically late-time tail for the massive scalar field is not affected and its decay rate is still t-5/6.

scholarly journals The spectral dimension in 2D CDT gravity coupled to scalar fields

2015 ◽  
Vol 30 (13) ◽  
pp. 1550077 ◽  
Author(s):  
J. Ambjørn ◽  
A. Görlich ◽  
J. Jurkiewicz ◽  
H. Zhang
Keyword(s):  
Scalar Field ◽  
Scalar Fields ◽  
Spectral Dimension ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Two Dimensional ◽  
Imaginary Time ◽  
Causal Dynamical Triangulations ◽  
Pure Gravity ◽  
Dynamical Triangulations

Causal Dynamical Triangulations (CDT) provide a non-perturbative formulation of Quantum Gravity assuming the existence of a global time foliation. In our earlier study we analyzed the effect of including d copies of a massless scalar field in the two-dimensional CDT model with imaginary time. For d > 1 we observed the formation of a "blob", somewhat similar to that observed in four-dimensional CDT without matter. In the two-dimensional case the "blob" has a Hausdorff dimension DH = 3. In this paper, we study the spectral dimension DS of the two-dimensional CDT-universe, both for d = 0 (pure gravity) and d = 4. We show that in both cases the spectral dimension is consistent with DS = 2.

scholarly journals THE QUANTUM THEORY OF SCALAR FIELDS ON THE DE SITTER EXPANDING UNIVERSE

2008 ◽  
Vol 23 (16n17) ◽  
pp. 2563-2577 ◽  
Author(s):  
ION I. COTĂESCU ◽  
COSMIN CRUCEAN ◽  
ADRIAN POP
Keyword(s):  
Scalar Field ◽  
Gordon Equation ◽  
Scalar Fields ◽  
Wave Functions ◽  
De Sitter ◽  
Scalar Quantum ◽  
Long Time ◽  
Klein Gordon ◽  
Free Scalar ◽  
Special Time

New quantum modes of the free scalar field are derived in a special time-evolution picture that may be introduced in moving charts of de Sitter backgrounds. The wave functions of these new modes are solutions of the Klein–Gordon equation and energy eigenfunctions, defining the energy basis. This completes the scalar quantum mechanics where the momentum basis is well known for long time. In this enlarged framework the quantization of the scalar field can be done in canonical way obtaining the principal conserved one-particle operators and the Green functions.

scholarly journals Black holes with regular horizons in Maxwell-scalar gravity

1996 ◽  
Vol 74 (1-2) ◽  
pp. 17-28 ◽  
Author(s):  
Slava G. Turyshev
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Scalar Curvature ◽  
Scalar Fields ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Coupling Constant ◽  
Minkowski Space Time ◽  
Special Cases ◽  
Nontrivial Coupling

A class of exact static spherically symmetric solutions of the Einstein–Maxwell gravity coupled to a massless scalar field is obtained in the harmonic coordinates of Minkowski space-time. For each value of the coupling constant a, these solutions are characterized by a set of three parameters, the physical mass μ0, the electric charge Q0 and the scalar-field parameter k. We find that the solutions for both gravitational and electromagnetic fields are not only affected by the scalar field, but also the nontrivial coupling with matter constrains the scalar field itself. In particular, we find that the constant k differs generically from ±1/2, falling into the interval [Formula: see text]. It takes these values only for black holes or in the case when a scalar field [Formula: see text] is totally decoupled from the matter. Our results differ from those previously obtained in that the presence of an arbitrary coupling constant a gives an opportunity to rule out the nonphysical horizons. In one of the special cases, the obtained solution corresponds to a charged dilatonic black hole with only one horizon μ+ and hence to the Kaluza–Klein case. The most remarkable property of this result is that the metric, the scalar curvature, and both the electromagnetic and scalar fields are all regular on this surface. Moreover, while studying the dilaton charge, we found that the inclusion of the scalar field in the theory resulted in a contraction of the horizon. The behavior of the scalar curvature was analysed.

Sign in / Sign up

Export Citation Format

Share Document