scholarly journals On the Particle-Defining Modes for a Free Neutral Scalar Field in Spatially Homogeneous and Isotropic Universes

1981 ◽  
Vol 65 (2) ◽  
pp. 507-524 ◽  
Author(s):  
H. Kodama
Keyword(s):  
Scalar Field ◽  
Neutral Scalar ◽  
Spatially Homogeneous

scholarly journals The Casimir energy anomaly for a point interaction

2020 ◽  
Vol 35 (03) ◽  
pp. 2040008
Author(s):  
Davide Fermi
Keyword(s):  
Scalar Field ◽  
Casimir Energy ◽  
Point Interaction ◽  
Boundary Term ◽  
Intrinsic Nature ◽  
Neutral Scalar

The Casimir energy for a massless, neutral scalar field in presence of a point interaction is analyzed using a general zeta-regularization approach developed in earlier works. In addition to a regular bulk contribution, there arises an anomalous boundary term which is infinite despite renormalization. The intrinsic nature of this anomaly is briefly discussed.

scholarly journals Wave-like spatially homogeneous models of Stäckel spacetimes (2.1) type in the scalar-tensor theory of gravity

2020 ◽  
Vol 35 (33) ◽  
pp. 2050275
Author(s):  
Konstantin Osetrin ◽  
Altair Filippov ◽  
Evgeny Osetrin
Keyword(s):  
Scalar Field ◽  
Explicit Form ◽  
Scalar Tensor Theory ◽  
Tensor Theory ◽  
Test Particles ◽  
Homogeneous Wave ◽  
General Scalar ◽  
Spatially Homogeneous ◽  
Theory Of Gravity ◽  
The Universe

Six exact solutions are obtained in the general scalar-tensor theory of gravity related to spatially homogeneous wave-like models of the Universe. Wave-like spacetime models allow the existence of privileged coordinate systems where the eikonal equation and the Hamilton–Jacobi equation of test particles can be integrated by the method of complete separation of variables with the separation of isotropic (wave) variables on which the space metric depends (non-ignored variables). An explicit form of the scalar field and two functions of the scalar field that are part of the general scalar-tensor theory of gravity are found. The explicit form of the eikonal function and the action function for test particles in the considered models is given. The obtained solutions are of type III according to the Bianchi classification and type N according to the Petrov classification. Wave-like spatially homogeneous spacetime models can describe primordial gravitational waves of the Universe.

THERMAL SQUEEZING AND DENSITY FLUCTUATIONS IN SEMICLASSICAL THEORY OF GRAVITY

2001 ◽  
Vol 16 (11) ◽  
pp. 707-717 ◽  
Author(s):  
P. K. SURESH
Keyword(s):  
Scalar Field ◽  
Coherent State ◽  
Density Fluctuation ◽  
Density Fluctuations ◽  
Semiclassical Theory ◽  
Squeezed State ◽  
State Representation ◽  
Walker Metric ◽  
Spatially Homogeneous ◽  
Theory Of Gravity

A thermal squeezed state representation is constructed for each mode of a quantized scalar field in a spatially homogeneous and flat Robertson–Walker metric and the validity of semiclassical Einstein equation by analyzing the density fluctuation is examined. The density fluctuation in thermal squeezed state is very large and therefore the semiclassical theory may not be valid for squeezing parameter more than unity, however the theory holds when the associated squeezing parameter is much less than the unity. Further noted that the semiclassical theory is consistent in thermal coherent state formalism. The present study can account for the density fluctuations due to the thermal and quantum effects in semiclassical theory of gravity.

Spontaneous breakdown of symmetry in axiomatic theory

1965 ◽  
Vol 287 (1411) ◽  
pp. 510-518 ◽  
Keyword(s):  
Scalar Field ◽  
Broken Symmetry ◽  
Positive Energy ◽  
Linear Functionals ◽  
Axiomatic Theory ◽  
Spontaneous Breakdown ◽  
Positive Linear Functionals ◽  
Neutral Scalar ◽  
Local Operators ◽  
Conserved Current

We prove two results; the first is that it is possible to prove Goldstone’s theorem in a Wightman theory in which there is a conserved current with a meaning for a sharp time and which generates a broken symmetry. The second is that for such theories there exist infinitely many positive linear functionals on the algebra of quasi-local operators, that are Lorentz invariant and lead to a theory with positive energy. That is, we may regard the vacuum functional as non-unique. These two results are illustrated in the theory of the free massless neutral scalar field.

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