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Title: On the Hojman conservation quantities in Cosmology
Authors: Paliathanasis, Andronikos 
Leach, P. G. L. 
Capozziello, Salvatore 
Keywords: Cosmology;Scalar field;Conservation laws
Issue Date: 10-Apr-2016
Publisher: Elsevier
Source: Paliathanasis, A.; Leach, P. G. L. and Capozziello, S. 2016. On the Hojman conservation quantities in Cosmology. Physics Letters B. 755: 8-12.
Journal: Physics letters. B (Online) 
We discuss the application of the Hojman’s Symmetry Approach for the determination of conservation laws in Cosmology, which has been recently applied by various authors in different cosmological models. We show that Hojman’s method for regular Hamiltonian systems, where the Hamiltonian function is one of the involved equations of the system, is equivalent to the application of Noether’s Theorem for generalized transformations. That means that for minimally-coupled scalar field cosmology or other modified theories which are conformally related with scalar-field cosmology, like f (R) gravity, the application of Hojman’s method provide us with the same results with that of Noether’s Theorem. Moreover we study the special Ansatz. φ (t) = φ (a (t)), which has been introduced for a minimally-coupled scalar field, and we study the Lie and Noether point symmetries for the reduced equation. We show that under this Ansatz, the unknown function of the model cannot be constrained by the requirement of the existence of a conservation law and that the Hojman conservation quantity which arises for the reduced equation is nothing more than the functional form of Noetherian conservation laws for the free particle. On the other hand, for f (T ) teleparallel gravity, it is not the existence of Hojman’s conservation laws which provide us with the special function form of f (T ) functions, but the requirement that the reduced second-order differential equation admits a Jacobi Last multiplier, while the new conservation law is nothing else that the Hamiltonian function of the reduced equation.
ISSN: 0370-2693 (print)
1873-2445 (online)
Appears in Collections:Research Publications (Applied Sciences)

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