Suchergebnisse

Within Resonance Chiral Theory and in the context of QCD current correlators at next-to-leading order in 1/N(C), we have analyzed the two-body form factors which include resonances as a final state . The short-distance constraints have been studied. One of the main motivations is the estimation of the chiral low-energy constants at subleading order, that is, keeping full control of the renormalization scale dependence. As an application we show the resonance estimation of some coupling, L(10)(mu_0)=(-4.4 \pm 0.9)10^{-3} and C(87)(mu_0)=(3.1 \pm 1.1)10^{-5}. ; I wish to thank S. Narison for the organization of the conference and A. Pich and J.J. Sanz-Cillero for their helpful comments. This work has been supported in part by the Generalitat under grant GVPRE/2008/413, by the Spanish Government, under grants FPA2007-60323 and CSD2007-00042 (CPAN), and by the EU MRTNCT-2006-035482 (FLAVIAnet).

Using a general effective Lagrangian implementing the chiral symmetry breaking SU(2) L ⊗ SU(2) R → SU(2) L+R , we present a one-loop calculation of the oblique S and T parameters within electroweak strongly-coupled models with a light scalar. Imposing a proper ultraviolet behaviour, we determine S and T at next-to-leading order in terms of a few resonance parameters. The constraints from the global fit to electroweak precision data force the massive vector and axial-vector states to be heavy, with masses above the TeV scale, and suggest that the W + W − and ZZ couplings of the Higgs-like scalar should be close to the Standard Model value. Our findings are generic, since they only rely on soft requirements on the short-distance properties of the underlying strongly-coupled theory, which are widely satisfied in more specific scenarios. ; This work has been supported in part by the Spanish Government and ERDF funds from the European Commission [grants FPA2010-17747, FPA2011-23778, AIC-D-2011-0818, SEV-2012-0249 (Severo Ochoa Program), CSD2007-00042 (Consolider Project CPAN)], the Generalitat Valenciana [PrometeoII/2013/007] and the Comunidad de Madrid [HEPHACOS S2009/ESP-1473]. ; Peer reviewed

We present a one-loop calculation of the oblique S and T parameters within strongly coupled models of electroweak symmetry breaking with a light Higgs-like boson. We use a general effective Lagrangian, implementing the chiral symmetry breaking SU(2)(L) circle times SU(2)(R) -> SU(2)(L+R) with Goldstone bosons, gauge bosons, the Higgs-like scalar, and one multiplet of vector and axial-vector massive resonance states. Using a dispersive representation and imposing a proper ultraviolet behavior, we obtain S and T at the next-to-leading order in terms of a few resonance parameters. The experimentally allowed range forces the vector and axial-vector states to be heavy, with masses above the TeV scale, and suggests that the Higgs-like scalar should have a WW coupling close to the standard model one. Our conclusions are generic and apply to more specific scenarios such as the minimal SO(5)/SO(4) composite Higgs model. ; This work was supported in part by Spanish government Grants No. FPA2007-60323, No. FPA2011-23778, No. CSD2007-00042 (Consolider Project CPAN), and MICINN-INFN No. AIC-D-2011-0818, Italian government Grant No. MIUR-PRIN-2009, National Nature Science Foundation of China Grant No. 0925522, and Universidad CEU Cardenal Herrera Grant No. PRCEU-UCH35/11. J.J.S.-C. thanks G. Cacciapaglia, H. Y. Cai, and H. Q. Zheng for useful discussions. ; Peer reviewed

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