scholarly journals Existence of Einstein static universes and their stability in fourth-order theories of gravity

2008 ◽  
Vol 78 (4) ◽  
Author(s):  
Rituparno Goswami ◽  
Naureen Goheer ◽  
Peter K S Dunsby
Keyword(s):  
Fourth Order ◽  
Theories Of Gravity

scholarly journals CURVATURE QUINTESSENCE

2002 ◽  
Vol 11 (04) ◽  
pp. 483-491 ◽  
Author(s):  
SALVATORE CAPOZZIELLO
Keyword(s):  
Scalar Field ◽  
Fourth Order ◽  
Order Theory ◽  
Cosmic Acceleration ◽  
Accelerated Expansion ◽  
Conformal Transformations ◽  
Effective Pressure ◽  
Alternative Scheme ◽  
Theories Of Gravity ◽  
Jordan And Einstein Frames

The issues of quintessence and cosmic acceleration can be discussed in the framework of higher order theories of gravity. We can define effective pressure and energy density directly connected to the Ricci scalar of curvature of a generic fourth order theory and then ask for the conditions to get an accelerated expansion. Exact accelerated expanding solutions can be achieved for several fourth order theories so that we get an alternative scheme to the standard quintessence scalar field, minimally coupled to gravity, usually adopted. We discuss also conformal transformations in order to see the links of quintessence between the Jordan and Einstein frames.

scholarly journals Ghost problems from Pauli–Villars to fourth-order quantum gravity and their resolution

2020 ◽  
Vol 29 (14) ◽  
pp. 2043009
Author(s):  
Philip D. Mannheim
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Hilbert Space ◽  
Quantum Gravity ◽  
Fourth Order ◽  
Quantum Field ◽  
Quantum Theories ◽  
Inner Products ◽  
History Of ◽  
Theories Of Gravity

We review the history of the ghost problem in quantum field theory from the Pauli–Villars regulator theory to currently popular fourth-order derivative quantum gravity theories. While these theories all appear to have unitarity-violating ghost states with negative norm, we show that in fact these ghost states only appear because the theories are being formulated in the wrong Hilbert space. In these theories, the Hamiltonians are not Hermitian but instead possess an antilinear symmetry. Consequently, one cannot use inner products that are built out of states and their Hermitian conjugates. Rather, one must use inner products built out of states and their conjugates with respect to the antilinear symmetry, and these latter inner products are positive. In this way, one can build quantum theories of gravity in four spacetime dimensions that are unitary.

Children’s Recall of Approximations to English

1973 ◽  
Vol 16 (2) ◽  
pp. 201-212 ◽  
Author(s):  
Elizabeth Carrow ◽  
Michael Mauldin
Keyword(s):  
Language Development ◽  
Fourth Order ◽  
Third Order ◽  
Memory Processes ◽  
The Third ◽  
General Index ◽  
General Linguistic

As a general index of language development, the recall of first through fourth order approximations to English was examined in four, five, six, and seven year olds and adults. Data suggested that recall improved with age, and increases in approximation to English were accompanied by increases in recall for six and seven year olds and adults. Recall improved for four and five year olds through the third order but declined at the fourth. The latter finding was attributed to deficits in semantic structures and memory processes in four and five year olds. The former finding was interpreted as an index of the development of general linguistic processes.

Exploring the Fourth Order

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Barend KLITSIE ◽  
Rebecca PRICE ◽  
Christine DE LILLE
Keyword(s):  
Action Research ◽  
Fourth Order ◽  
Subject Matter ◽  
Action Research Project ◽  
Research Project ◽  
Building Trust ◽  
Current Business

Companies are organised to fulfil two distinctive functions: efficient and resilient exploitation of current business and parallel exploration of new possibilities. For the latter, companies require strong organisational infrastructure such as team compositions and functional structures to ensure exploration remains effective. This paper explores the potential for designing organisational infrastructure to be part of fourth order subject matter. In particular, it explores how organisational infrastructure could be designed in the context of an exploratory unit, operating in a large heritage airline. This paper leverages insights from a long-term action research project and finds that building trust and shared frames are crucial to designing infrastructure that affords the greater explorative agenda of an organisation.

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