共查询到20条相似文献,搜索用时 9 毫秒
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Sante Carloni Emilio Elizalde Sergei Odintsov 《General Relativity and Gravitation》2010,42(7):1667-1705
The 1+3 covariant approach and the covariant gauge-invariant approach to perturbations are used to analyze in depth conformal
transformations in cosmology. Such techniques allow us to obtain insights on the physical meaning of these transformations
when applied to non-standard gravity. The results obtained lead to a number of general conclusions on the change of some key
quantities describing any two conformally related cosmological models. For example, even if some of the geometrical properties
of the cosmology are preserved (homogeneous and isotropic Universes are mapped into homogeneous and isotropic universes),
it can happen that decelerating cosmologies can be mapped into accelerated ones. From the point of view of the cosmological
perturbations it is shown how these fluctuation transform. We find that first-order vector and tensor perturbations equations
are left unchanged in their structure by the conformal transformation, but this cannot be said of the scalar perturbations,
which present differences in their evolutionary features. The results obtained are then explicitly interpreted and verified
with the help of some clarifying examples based on f(R)-gravity cosmologies. 相似文献
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We study the problem of the behaviour of cosmological gravitational waves under conformal transformations. In spite of the apparent triviality of this question, the informations we can obtain from gravitational waves in the so-called Einstein's and Jordan's frame are not the same, mainly with respect to the choice of the initial conditions and of graviton production. The only exception seems to occur in string cosmology due to the duality properties. 相似文献
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Hawking radiation from the charged and magnetized BTZ black hole via covariant anomaly 总被引:1,自引:0,他引:1 下载免费PDF全文
This paper discusses Hawking radiation from the charged and
magnetized Ba?ados--Teitelboim--Zanelli (BTZ) black hole from
the viewpoint of anomaly, initiated by Robinson and Wilczek
recently. It reconstructs the electromagnetic field tensor and the
Lagrangian of the field corresponding to the source with electric
and magnetic charges to redefine an equivalent charge and gauge
potential. It employs the covariant anomaly cancellation method to
determine the compensating fluxes of charge flow and energy-momentum
tensor, which are shown to match with those of the 2-dimensional
blackbody radiation at the Hawking temperature exactly. 相似文献
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The growth of the perturbation density in a baryon substance due to a nonstationary character of the equation of state of
nonbaryon matter in the Universe is studied. It is shown that the perturbations evolve slower than within the Friedmann cosmological
model.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 61–67, March, 2009. 相似文献
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The nonminimal coupling of a massive self-interacting scalar field with a gravitational field is studied. Spontaneous symmetry
breaking occurs in the open universe even when the sign on the mass term is positive. In contrast to grand unified theories,
symmetry breakdown is more important for the early universe and it is restored only in the limit of an infinite expansion.
Symmetry breakdown is shown to occur in flat and closed universes when the mass term carries a wrong sign. The model has a
naturally defined effective gravitational coupling coefficient which is rendered time-dependent due to the novel symmetry
breakdown. It changes sign below a critical value of the cosmic scale factor indicating the onset of a repulsive field. The
presence of the mass term severely alters the behaviour of ordinary matter and radiation in the early universe. The total
energy density becomes negative in a certain domain. These features make possible a nonsingular cosmological model for an
open universe. The model is also free from the horizon and the flatness problems. 相似文献
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Adopting the anomaly cancellation method, initiated by Robinson and
Wilczek recently, this paper discusses Hawking radiation from the
dilaton--(anti) de Sitter black hole. To save the underlying gauge
and general covariance, it introduces covariant fluxes of gauge and
energy--momentum tensor to cancel the gauge and gravitational
anomalies. The result shows that the introduced compensating fluxes
are equivalent to those of a 2-dimensional blackbody radiation at
Hawking temperature with appropriate chemical potential. 相似文献
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K. Sridhar 《Pramana》2007,69(5):719-725
The international linear collider (ILC) is likely to provide us important insights into physics sector that may supersede
our current paradigm, viz., the standard model. In anticipation of the possibility that the ILC may come up in the middle
of the next decade, several groups are vigourously investigating its potential to explore this new sector of physics. The
Linear Collider Workshop in Bangalore (LCWS06) had several presentations of such studies which looked at supersymmetry, extra
dimensions and other exotic possibilities which the ILC may help us discover or understand. Some papers also looked at the
understanding of cosmology that may emerge from studies at the ILC. This paper summarises these presentations.
相似文献
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The influence of homogeneous surface perturbations on the surface critical behavior of the two-dimensional Ising model is studied through finite-size scaling and conformal invariance. Quantum chains of up to 2000 spins are studied in the fermionic version of the model. The results are deduced from the numerical solution of an eigenvalue equation for the excitation spectrum and show that conformal invariance still works for irrelevant surface perturbations. 相似文献
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Brian J. Orr 《Molecular physics》2018,116(23-24):3666-3700
ABSTRACTVarious forms of time-resolved optical double-resonance spectroscopy facilitate rotationally resolved measurements of collision-induced intramolecular vibration-to-vibration (V–V) energy-transfer processes, which take a gas-phase polyatomic molecule from one distinct rovibrational energy level to another. Of longstanding mechanistic interest are questions concerning the extent to which such V–V energy transfer (ET) may be influenced by intramolecular perturbations – notably Fermi resonance (and other anharmonic mixing effects) and Coriolis coupling – within polyatomic molecular rovibrational manifolds of interest. It is evident that quantum-mechanical interference effects can arise, either inhibiting or enhancing the probability of collision-induced ET in perturbed rovibrational manifolds of certain small gas-phase polyatomic molecules, notably CO2, D2CO and C2H2. This article focuses on a blend of high-resolution rovibrational spectroscopy (characterising initial and final molecular levels and their intramolecular perturbations) and collision dynamics (with colliding molecules defined in terms of isolated-molecule spectroscopic basis states). It aims to offer fresh insights and to consider some apparent mechanistic anomalies (e.g. collision-induced quasi-continuous background effects in the 4νCH rovibrational manifold of C2H2). Various reported experiments and related theoretical treatments are critically re-examined, in order to pose and address mechanistic questions some of which still challenge detailed understanding. 相似文献
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In this paper we consider the problem of a charged harmonic oscillator under the influence of a constant magnetic field. The system is assumed to be isotropic and the magnetic field is applied along the z-axis. The canonical transformation is invoked to remove the interaction term and the system is reduced to a model containing the second harmonic generation. Two classes of the real and complex quadratic invariants (constants of motion) are obtained. We have employed the Lie algebraic technique to find the most general solution for the wave function for both real and complex invariants. Some discussions related to the advantage of using the quadratic invariants to solve the Cauchy problem instead of the direct use of the Hamiltonian itself are also given. 相似文献
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The purpose of the paper is to formulate multi-soliton solutions for the nonlocal Hirota equations via the Riemann–Hilbert (RH) approach. The RH problems are constructed and the zero structures are studied via performing spectral analysis of the Lax pair. Then we consider three types of nonlocal Hirota equations by discussing different symmetry reductions of the potential matrix. On the basis of the resulting matrix RH problem under the restriction of the reflectionless case, we successfully obtain the multi-soliton solutions of the nonlocal Hirota equations. 相似文献
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本文采用分数维方法, 在讨论Al0.3Ga0.7As衬底上GaAs薄膜的分数维基础上, 计算了GaAs薄膜中的极化子结合能和有效质量. 随着薄膜厚度的增加, 极化子结合能和质量变化单调地减小. 当薄膜厚度Lw<70 Å并且衬底厚度Lb<200 Å时, 衬底厚度的变化对薄膜中极化子的结合能和质量变化的影响比较显著, 随着衬底厚度的增加, 薄膜中极化子的结合能和质量变化逐渐变大; 当薄膜厚度Lw>70 Å或者衬底厚度Lb>200 Å时, 衬底厚度的变化对薄膜中极化子的结合能和质量变化的影响不显著. 研究结果为GaAs薄膜电子和光电子器件的研究和应用提供参考.
关键词:
分数维方法
GaAs薄膜
极化子
低维异质结构 相似文献
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In this paper we continue our consideration of closed-packed dimers on the kagome lattice. Using the Pfaffian approach we evaluate the correlation between dimers on two lattice edges. It is found that the correlation is extremely short-ranged in the case of symmetric dimers weights. Explicit expressions for the nonvanishing correlations are obtained for two dimers in the interior of a large lattice. We also describe a Grassmannian functional integral approach, and use it to evaluate the dimer generating function and correlation functions. 相似文献
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A scattering matrix approach to quantum pumping: beyond the small-AC-driving-amplitude limit 下载免费PDF全文
In the adiabatic and weak-modulation quantum pump, net electron flow is driven from one reservoir to another by absorbing or emitting an energy quantum hω from or to the reservoirs. This paper considers high-order dependence of the scattering matrix on the time. Non-sinusoidal behaviour of strong pumping is revealed. The relation between the pumped current and the ac driving amplitude varies from power of 2, 1 to 1/2 when stronger modulation is exerted. Open experimental observation can be interpreted by multi-energy-quantum-related processes. 相似文献
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A. Viana J.-L. Coulomb L.-L. Rouve G. Cauffet 《Journal of magnetism and magnetic materials》2010,322(2):186-189
The Langevin equation is classically used to model the anhysteretic magnetization curve. A modified version of this equation has been introduced by Jiles to take into account the effects of magnetostriction on the anhysteretic magnetization behavior when a ferromagnetic material undergoes mechanical stresses. The numerical resolution of the modified Langevin equation is usually performed with a root-finding algorithm. In this paper, a differential form of the modified Langevin equation is proposed, allowing a faster numerical resolution. 相似文献