%0 Journal Article
%T "Power-laws f(R) theories are cosmologically unacceptable"
%+ Laboratoire de Physique Théorique et Astroparticules (LPTA)
%A Amendola, L.
%A Polarski, D.
%A Tsujikawa, S.
%Z 3 pages
%< avec comité de lecture
%Z PTA/06-31
%@ 0218-2718
%J International Journal of Modern Physics D
%I World Scientific Publishing
%V 16
%P 1555-1561
%8 2007
%D 2007
%Z astro-ph/0605384
%R 10.1142/S0218271807010936
%Z Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]
%Z Physics [physics]/General Relativity and Quantum Cosmology [gr-qc]
%Z Physics [physics]/High Energy Physics - Phenomenology [hep-ph]
%Z Physics [physics]/High Energy Physics - Theory [hep-th]
%Z Sciences of the Universe [physics]/Astrophysics [astro-ph]Journal articles
%X In the recent paper astro-ph/0603703 we have shown that $f(R)=R+\mu R^n$ modified gravity dark energy models are not cosmologically viable because during the matter era that precedes the accelerated stage the cosmic expansion is $a ~ t^{1/2}$ rather than $t^{2/3}$. In this short note we wish to comment on the recent paper astro-ph/0604431 which criticised our results. We show here that the $R^n$ models presented in astro-ph/0604431 cannot generate a stage with $a ~ t^{2/3}$ preceding a stage of accelerated expansion. Hence, though acceptable $f(R)$ dark energy models might exist, the $R^n$ models presented in astro-ph/0604431 are not viable, confirming our previous results.
%G English
%L in2p3-00115597
%U https://hal.in2p3.fr/in2p3-00115597
%~ IN2P3
%~ LPTA
%~ CNRS
%~ UNIV-MONTP2
%~ UNIV-MONTPELLIER
%~ UM1-UM2