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The structure and energetics of the ring isomers of C(4n+2) (n=3-5) carbon clusters were studied by using coupled-cluster singles and doubles excitation theory to overcome the vast differences existing in the literature. The results obtained in the present study clearly indicate that C₁₄, C₁₈, and C₂₂ carbon rings have bond-length and bond-angle alternated acetylenic minimum energy structures. Contrarily, density functional theory calculations were unable to predict these acetylenic-type structures and they ended up with the cumulenic structures. It is found from the coupled-cluster studies that the lowest-energy ring isomer for the first two members of C(4n+2) series is a bond-angle alternated cumulenic D((2n+1)h) symmetry structure while the same for the remaining members is a bond-length and bond-angle alternated C((2n+1)h) symmetry structure. In C(4n+2) carbon rings, Peierls-type distortion, transformation from bond-angle alternated to bond-length alternated minimum energy structures, occurs at C₁₄ carbon ring. ; This study was supported by the RSS21 project and a Grant-in-Aid for Scientific Research No. 17064017 of MEXT, Government of Japan.

International audience ; Political attention has increasingly focused on limiting warming to 2°C. However, there is no consensus on both questions "Is the 2°C target achievable?" and "What should be done with this target that becomes increasingly difficult to achieve?". This paper aims at disentangling the points of deep uncertainty underlying this absence on consensus. It first gives simple visualizations of the challenge posed by the 2°C target and shows how key assumptions (on the points of deep uncertainty) influence the answer to the target achievability question. It then proposes an "uncertainties and decisions tree", linking different beliefs on climate change, the achievability of different policies, and current international policy dynamics to various options to move forward on climate change.

International audience ; Political attention has increasingly focused on limiting warming to 2°C. However, there is no consensus on both questions "Is the 2°C target achievable?" and "What should be done with this target that becomes increasingly difficult to achieve?". This paper aims at disentangling the points of deep uncertainty underlying this absence on consensus. It first gives simple visualizations of the challenge posed by the 2°C target and shows how key assumptions (on the points of deep uncertainty) influence the answer to the target achievability question. It then proposes an "uncertainties and decisions tree", linking different beliefs on climate change, the achievability of different policies, and current international policy dynamics to various options to move forward on climate change.

International audience ; Political attention has increasingly focused on limiting warming to 2°C. However, there is no consensus on both questions "Is the 2°C target achievable?" and "What should be done with this target that becomes increasingly difficult to achieve?". This paper aims at disentangling the points of deep uncertainty underlying this absence on consensus. It first gives simple visualizations of the challenge posed by the 2°C target and shows how key assumptions (on the points of deep uncertainty) influence the answer to the target achievability question. It then proposes an "uncertainties and decisions tree", linking different beliefs on climate change, the achievability of different policies, and current international policy dynamics to various options to move forward on climate change.

International audience ; Political attention has increasingly focused on limiting warming to 2°C. However, there is no consensus on both questions "Is the 2°C target achievable?" and "What should be done with this target that becomes increasingly difficult to achieve?". This paper aims at disentangling the points of deep uncertainty underlying this absence on consensus. It first gives simple visualizations of the challenge posed by the 2°C target and shows how key assumptions (on the points of deep uncertainty) influence the answer to the target achievability question. It then proposes an "uncertainties and decisions tree", linking different beliefs on climate change, the achievability of different policies, and current international policy dynamics to various options to move forward on climate change.

International audience ; Political attention has increasingly focused on limiting warming to 2°C. However, there is no consensus on both questions "Is the 2°C target achievable?" and "What should be done with this target that becomes increasingly difficult to achieve?". This paper aims at disentangling the points of deep uncertainty underlying this absence on consensus. It first gives simple visualizations of the challenge posed by the 2°C target and shows how key assumptions (on the points of deep uncertainty) influence the answer to the target achievability question. It then proposes an "uncertainties and decisions tree", linking different beliefs on climate change, the achievability of different policies, and current international policy dynamics to various options to move forward on climate change.

International audience ; Political attention has increasingly focused on limiting warming to 2°C. However, there is no consensus on both questions "Is the 2°C target achievable?" and "What should be done with this target that becomes increasingly difficult to achieve?". This paper aims at disentangling the points of deep uncertainty underlying this absence on consensus. It first gives simple visualizations of the challenge posed by the 2°C target and shows how key assumptions (on the points of deep uncertainty) influence the answer to the target achievability question. It then proposes an "uncertainties and decisions tree", linking different beliefs on climate change, the achievability of different policies, and current international policy dynamics to various options to move forward on climate change.

9 páginas, 3 figuras.-- ISI article identifier:000266408300099.-- ArXiv pre-print avaible at:http://arxiv.org/abs/0903.2440 ; The precision obtainable in phenomenological applications of chiral perturbation theory is currently limited by our lack of knowledge on the low-energy constants (LECs). The assumption that the most important contributions to the LECs come from the dynamics of the low-lying resonances, often referred to as the resonance saturation hypothesis, has stimulated the use of large-N-C resonance Lagrangians in order to obtain explicit values for the LECs. We study the validity of the resonance saturation assumption at the next-to-leading order in the 1/N-C expansion within the framework of resonance chiral theory. We find that, by imposing QCD short-distance constraints, the chiral couplings can be written in terms of the resonance masses and couplings and do not depend explicitly on the coefficients of the chiral operators in the Goldstone boson sector of resonance chiral theory. As we argue, this is the counterpart formulation of the resonance saturation statement in the context of the resonance Lagrangian. Going beyond leading order in the 1/N-C counting allows us to keep full control of the renormalization scale dependence of the LEC estimates. ; We want to thank P. Masjuan, S. Peris, A. Pich, and J. Portole´s for their comments on the manuscript. This work is supported in part by the Universidad CEU Cardenal Herrera (Grant No. PRCEU-UCH20/08), by the Generalitat de Catalunya (Grant No. SGR2005-00916), by the Spanish Government (No. FPA2007-60323, No. FPA2008-01430, the Juan de la Cierva program and Consolider-Ingenio 2010 No. CSD2007-00042, CPAN) and by the EU No. MRTN-CT-2006-035482 (FLAVIAnet). P. R. acknowledges support from the DFG Sonderforschungsbereich/Transregio 9 ''Computergestu ¨tzte Theoretische Teilchenphysik''. ; Peer reviewed