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1.
We continue the analysis of the onset of classical behaviour in a scalar field after a continuous phase transition, in which
the system-field, the long wavelength order parameter of the model, interacts with an environment, of its own short-wavelength
modes and other fields, neutral and charged, with which it is expected to interact. We compute the decoherence time for the
system-field modes from the master equation and directly from the decoherence functional (with identical results). In simple
circumstances the order parameter field is classical by the time the transition is complete. 相似文献
2.
We study a nonminimal derivative coupling (NMDC) of scalar field, where the scalar field is coupled to curvature tensor in the five dimensional universal extra dimension model. We apply the Einstein equation and find its solution. First, we consider a special case of pure free scalar field without NMDC and we find that for static extradimension, the solution is equivalent to the standard cosmology with stiff matter. For a general case of pure free scalar field with NMDC, we find that the de Sitter solution is the solution of our model. For this solution, the scalar field evolves linearly in time. In the limit of small Hubble parameter, the general case give us the same solution as in the pure free scalar field. Finally, we perform a dynamical analysis to determine the stability of our model. We find that the extradimension, if it exist, can not be static and always shrinks with the expansion of four dimensional spacetime. 相似文献
3.
The objective of this paper is to discuss the Chameleon Brans–Dicke gravity with non-minimally matter coupling of scalar field. We take modified Holographic Ricci dark energy model in this gravity with its energy density in interaction with energy density of cold dark matter. We assume power-law ansatz for scale factor and scalar field to discuss potential as well as coupling functions in the evolving universe. These reconstructed functions are plotted versus scalar field and time for different values of power component of scale factor n. We observe that potential and coupling functions represent increasing behavior, in particular, consistent results for a specific value of n. Finally, we have examined validity of the generalized second law of thermodynamics and we have observed its validity for all values of n. 相似文献
4.
Alfred Actor 《Zeitschrift fur Physik C Particles and Fields》1980,6(3):223-234
We present a study of classical solutions of the SU(2) Yang-Mills (YM) theory with a massless Higgs doublet, and of the CP n?1 model coupled to a scalar field. In both cases the scalar field tends to suppress instantons but not merons (this is a purely classical effect). In the YM theory a static Wu-Yang-like monopole solution with variable magnetic charge is found and its connection with the meron solution of this theory is discussed. 相似文献
5.
F. Darabi 《International Journal of Theoretical Physics》2012,51(2):501-506
We investigate the necessary condition for the existence of classical Euclidean wormholes in a conformally non-invariant gravitational
model minimally coupled to an scalar field. It is shown that while the original Ricci tensor with positive eigenvalues does
not allow the Euclidean wormholes to occur, under dynamical conformal transformations the Ricci tensor, with respect to the
original metric, is dynamically coupled with the conformal field and its eigenvalues may become negative allowing the Euclidean
wormholes to occur. Therefore, it is conjectured that dynamical conformal transformations may provide us with effective forms of matter sources leading to Euclidean wormholes in conformally non-invariant systems. 相似文献
6.
A scalar field with a pole in its kinetic term is often used to study cosmological inflation; it can also play the role of dark energy, which is called the pole dark energy model. We propose a generalized model where the scalar field may have two or even multiple poles in the kinetic term, and we call it the multi-pole dark energy. We find that the poles can place some restrictions on the values of the original scalar field with a non-canonical kinetic term. After the transformation to the canonical form, we get a flat potential for the transformed scalar field even if the original field has a steep one. The late-time evolution of the universe is obtained explicitly for the two pole model, while dynamical analysis is performed for the multiple pole model. We find that it does have a stable attractor solution, which corresponds to the universe dominated by the potential of the scalar field. 相似文献
7.
Simone Calogero 《Communications in Mathematical Physics》2006,266(2):343-353
The Nordström-Vlasov system describes the kinetic evolution of self-gravitating collisionless matter in the framework of a relativistic scalar theory of gravitation. We prove global existence and uniqueness of classical solutions for the corresponding initial value problem in three dimensions when the initial data for the scalar field are smooth and the initial particle density is smooth with compact support. 相似文献
8.
《Nuclear Physics B》1988,303(4):728-750
We identify the quantum theory of cosmological perturbations with the quantum field theory in curved spacetime with emphasis on its field concept. We materialize this idea by using a coherent state as a quantum analogue of a nontrivial classical field configuration. We present analytic results in a de Sitter universe for the massless and massive minimal free scalar fields. Some new features on the spectrum of perturbations are obtained for the massive case. We also show how such quantum field theories can be derived from quantum gravity using the semiclassical approximation. A physical degree of freedom is picked up from three scalar perturbations in the quantum gravity scalar system and its Schrödinger equation is derived. Peculiar features of quantum fields at imaginary time and its possible implications on boundary conditions for the wave function of the universe are also discussed. 相似文献
9.
In this paper we study the evolution of a flat Friedmann-Robertson-Walker model filled with a perfect fluid and a scalar field
minimally coupled to gravity in higher derivative theory of gravitation. Exact solution of the field equations are obtained
by the assumption of power-law form of the scale factor. A number of evolutionary phases of the universe including the present
accelerating phase are found to exist with scalar field in the higher derivative theory of gravitation. The properties of
scalar field and other physical parameters are discussed in detail. We find that the equation of state parameter for matter
and scalar field are same at late time in each case. We observe that a higher derivative term can hardly be a candidate to
describe the presently observed accelerated expansion. It is only the hypothetical fluids, which provide the late time acceleration.
It is also remarkable that the higher derivative theory does not effect the radiating model of scalar field cosmology. 相似文献
10.
《Physics letters. [Part B]》1986,166(1):75-77
In the presence of a symmetry-breaking term, we discuss the classical stability of a scalar field conformally coupled to five-dimensional gravity. When the scalar field φ has the vacuum expectation values 〈φ〉 = ±μ, this system is classically unstable. 相似文献
11.
In this paper, we have introduced a shell-model of Kraichnan's passive
scalar problem. Different from the original problem, the prescribed
random velocity field is non-Gaussian and $\delta$ correlated in
time, and its introduction is inspired by She and L\'{e}v\^{e}que (Phys. Rev. Lett.
{\bf 72}, 336 (1994)). For comparison, we also give the passive
scalar advected by the Gaussian random velocity field. The
anomalous scaling exponents $H(p)$ of passive scalar advected by
these two kinds of random velocities above are determined for
structure function with values of $p$ up to 15 by Monte Carlo simulations of the
random shell model, with Gear methods used to solve the stochastic
differential equations. We find that the $H(p)$ advected by
the non-Gaussian random velocity is not more anomalous than that
advected by the Gaussian random velocity. Whether the advecting
velocity is non-Gaussian or Gaussian, similar scaling exponents of
passive scalar are obtained with the same molecular diffusivity. 相似文献
12.
In this paper, we study the scalar fields evolving on a FRW brane embedded in a five-dimensional de Sitter bulk. The scale function and the warp factor, solutions of the Einstein equations, are employed in the five-dimensional Gordon equation describing the massive scalar field, whose wave function depends on the cosmic time and on the extra-dimension. We point out the existence of bounded states and find a minimum value of the effective four-dimensional mass. For the test (scalar) field envelope along the extra-dimension, we derive the corresponding Schrödinger-like equation which is formally that for the Pöschl-Teller potential. Accordingly, we have obtained the quantization law for the mass parameter of the tested scalar field. 相似文献
13.
We study the Casimir effect at finite temperature for a massless scalar field in the parallel plates geometry in N spatial dimensions, under various combinations of Dirichlet and Neumann boundary conditions on the plates. We show that in all these cases the entropy, in the limit where energy equipartitioning applies, is a geometrical factor whose sign determines the sign of the Casimir force. 相似文献
14.
Y. P. Rybakov G. N. Shikin Y. A. Popov Bijan Saha 《International Journal of Theoretical Physics》2011,50(11):3421-3431
The important role of scalar field in cosmology was noticed by a number of authors. Due to the fact that the scalar field
possesses zero spin, it was basically considered in isotropic cosmological models. If considered in an anisotropic model,
the linear scalar field does not lead to isotropization of expansion process. One needs to introduce scalar field with nonlinear
potential for the isotropization process to take place. In this paper the general form of scalar field potentials leading
to the asymptotic isotropization in case of Bianchi type-I cosmological model, and inflationary regime in case of isotropic
space-time is obtained. In doing so we solved both direct and inverse problem, where by direct problem we mean to find metric
functions and scalar field for the given potential, whereas, the inverse problem means to find the potential and scalar field
for the given metric function. The scalar field potentials leading to the inflation and isotropization were found both for
harmonic and proper synchronic time. 相似文献
15.
Intermittency is a basic feature of fully developed turbulence, for both velocity and passive scalars.
Intermittency is classically characterized by
Eulerian scaling exponent of structure functions. The same approach can
be used in a Lagrangian framework to characterize the temporal
intermittency of the velocity and passive scalar concentration of a an element of fluid advected by a turbulent intermittent
field. Here we focus on
Lagrangian passive scalar scaling exponents, and discuss their possible links
with Eulerian passive scalar and mixed velocity-passive scalar structure functions.
We provide different transformations between these scaling exponents,
associated to different transformations linking space and time scales.
We obtain four new explicit relations.
Experimental data are needed to test these predictions for Lagrangian passive
scalar scaling exponents. 相似文献
16.
17.
By using the formulation of the reconstruction, we explicitly construct models of k-essence, which unify the inflation in the early universe and the late accelerating expansion of the present universe by a
single scalar field. Due to the higher derivative terms, the solution describing the unification can be stable in the space
of solutions, which makes the restriction for the initial condition relaxed. The higher derivative terms also eliminate tachyon.
Therefore we can construct a model describing the time development, which cannot be realized by a usual inflaton or quintessence
models of the canonical scalar field due to the instability or the existence of tachyon. We also propose a mechanism of the
reheating by the quantum effects coming from the variation of the energy density of the scalar field. 相似文献
18.
Jacob D. Bekenstein 《Annals of Physics》1974,82(2):535-547
The massless scalar field which satisfies a conformally invariant equation is in some respects more interesting than the ordinary one. Unfortunately, few, if any, exact solutions of Einstein's equations for a conformal scalar stress-energy have appeared previously. Here we present a theorem by means of which one can generate two Einstein-conformal scalar solutions from a single Einstein-ordinary scalar solution (of which many are known). As an example we show how to obtain Weyl-like solutions with a conformal scalar field. We obtain and analyze in some detail two families of spherically symmetric static Einstein-conformal scalar solutions. We also exhibit a family of static spherically symmetric Einstein-Maxwell-conformal scalar solutions (parametrized by both electric and scalar charge), which have black-hole geometries but are not genuine black holes. Finally, we present all the Robertson-Walker cosmological models which contain both incoherent radiation and a homogeneous conformal scalar field. One class of these represents open universes which bounce and never pass through a singular state; they circumvent the “singularity theorems” by violating the energy condition. 相似文献
19.
Jacob D Bekenstein 《Annals of Physics》1975,91(1):75-82
Previously it had been thought that a stationary black hole with an exterior devoid of matter can be parametrized only by mass, angular momentum, and electric charge. We show here that scalar charge is also an admissible parameter. Our starting point is a new solution of Einstein's equations with stress-energy of electromagnetic and conformal scalar fields which we presented earlier. It has a black-hole geometry, and is parametrized by electric and scalar charges. Its conformal scalar field is unbounded at the event horizon, and we originally regarded this feature as incompatible with a black hole interpretation. However, following a suggestion of B. DeWitt, we show here that the infinity in the scalar field need not be physically pathological: it is not associated with an infinite potential barrier for test scalar charges; it does not cause the termination of any trajectories of these test particles at finite proper time; and it is not connected with unbounded tidal accelerations between neighboring trajectories. In view of these facts, we now regard the new solution as a genuine black hole solution. 相似文献
20.
M. A. Ganjali 《International Journal of Theoretical Physics》2012,51(8):2380-2391
In this paper, we study the field dynamics in Tortoise coordinate where the equation of motion of a scalar can be written as Schrodinger-like form. We obtain a general form for effective potential by finding the Schrodinger equation for scalar and spinor fields and study its global behavior in some black hole backgrounds in three dimension such as BTZ black holes, new type black holes and black holes with no horizon. 相似文献