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Einstein's field equations with variablegravitational coupling G = G(t) and decaying vacuumenergy density = (t) are considered asdescribing matter creation in a cosmological framework.The particle creation rate is determined by thevariation rate of both G and . By consideringsimple phenomenological evolution laws for G and Lambda,an exact solution of the gravitational field equationsfor a flat Friedmann-Robertson-Walker (FRW)space-time is obtained leading to a self-consistentcosmological model describing matter and entropygeneration in the very early Universe. 相似文献
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We propose that the Universe is filled with a massive vector field non-minimally coupled to gravitation. The field equations
of the model are consistently derived, and their application to cosmology is considered. The Friedmann equations acquire an
extra dark-energy component, which is proportional to the mass of the vector particle. This leads to a late-time accelerated
de Sitter type expansion. The free parameters of the model (gravitational coupling constants and initial value of the cosmological
vector field) can be estimated by using the PPN solar system constraints. The mass of the cosmological massive vector particle,
which may represent the main component of the Universe, is of the order of 10-63 g.
PACS 03.70.+k; 11.90.+t; 11.10.Kk 相似文献
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Acta Mathematicae Applicatae Sinica, English Series - We present some exact integrability cases of the extended Liénard equation y″ + f(y)(y′)n + k(y)(y′)m + g(y)y′ +... 相似文献
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Sheikhahmadi Haidar Mohammadi Abolhassan Aghamohammadi Ali Harko Tiberiu Herrera Ramón Corda Christian Abebe Amare Saaidi Khaled 《The European Physical Journal C - Particles and Fields》2019,79(12):1-10
The European Physical Journal C - We study the Yukawa model with one scalar and one axial scalar fields, coupled to N copies of Dirac fermions, in curved spacetime background. The theory possesses... 相似文献
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We rigorously prove that for compact charged general relativistic objects there is a lower bound for the mass–radius ratio.
This result follows from the same Buchdahl type inequality for charged objects, which has been extensively used for the proof
of the existence of an upper bound for the mass–radius ratio. The effect of the vacuum energy (a cosmological constant) on
the minimum mass is also taken into account. Several bounds on the total charge, mass and the vacuum energy for compact charged
objects are obtained from the study of the Ricci scalar invariants. The total energy (including the gravitational one) and
the stability of the objects with minimum mass–radius ratio is also considered, leading to a representation of the mass and
radius of the charged objects with minimum mass–radius ratio in terms of the charge and vacuum energy only. 相似文献
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Karin Hansson Petter Karlström Aron Larsson Harko Verhagen 《Computational & Mathematical Organization Theory》2014,20(2):155-175
Equality within groups is ordinarily taken for granted when technology for e-democracy is conceived and developed. However, inequality in online communication is just as common as in other social contexts. Therefore, we have developed a groupware with the express purpose of illuminating imbalance of power. Inequalities are measured and made visible to users of the system, and they change dynamically as actions are taken by users. The system is based on democratic meeting techniques and is reminiscent of a strategy game based on social media. Each participant’s score within the game is dynamically calculated and reflects that user’s activity, others’ reactions to that activity and reactions to others’ activities. The calculations and weighing mechanisms are open to inspection and change by the users, and hierarchical roles reflecting game levels may be attached to system rights belonging to individual users and user groups. The prototype we present stems from the question of how to conceive of groupware based on diversity and is the result of combining social theory with algorithms for modelling and visualising user hierarchy and status. Empirical user tests suggest improvements to the prototype’s interface, which will be implemented and further evaluated by embedding the algorithms in a system for e-participation. 相似文献