Scalar Decay Constant and Yukawa Coupling in Walking Technicolor Models

Based on Refs.1 and 2, we study the couplings of the scalar bound state to the fermions and the weak bosons in walking gauge theories.Comment: 4 pages, 2 figures. Contribution to KMI Inauguration Conference "Quest for the Origin of Particles and the Universe" (KMIIN), 24-26 Nov. 2011, KMI, Nagoya Universit

Scalar Decay Constant and Yukawa Coupling in Walking Gauge Theories

We propose an approach for the calculation of the yukawa coupling through the scalar decay constant and the chiral condensate in the context of the extended technicolor (ETC). We perform the nonperturbative computation of the yukawa coupling based on the improved ladder Schwinger-Dyson equation. It turns out that the yukawa coupling can be larger or smaller than the standard model (SM) value, depending on the number $N_D$ of the weak doublets for each technicolor (TC) index. It is thus nontrivial whether or not the huge enhancement of the production of the scalar via the gluon fusion takes place even for a walking TC model with a colored techni-fermion. For the typical one-family TC model near conformality, it is found that the yukawa coupling is slightly larger than the SM one, where the expected mass of the scalar bound state is around 500 GeV. In this case, the production cross section via the gluon fusion is considerably enhanced, as naively expected, and hence such a scalar can be discovered/excluded at the early stage of the LHC.Comment: 8 pages, 1 figure, typos are corrected. Version to appear in PR

Reconsidering Composite Higgs Loop Effects in the Top Mode Standard Model

Composite Higgs loop effects in the top mode standard model are discussed by using the Miransky-Tanabashi-Yamawaki (MTY) approach based on the Schwinger-Dyson equation. The top mass is obtained as 179 GeV for the Planck scale cutoff (\Lambda \simeq 10^{19} GeV). This result is different from that of the Bardeen-Hill-Lindner (BHL) approach based on the renormalization group equation (RGE), with QCD plus Higgs loop effects included (m_t \simeq 205 GeV). Detailed comparison of the MTY approach with the BHL approach is made. We derive ``RGE'' from the Pagels-Stokar formula by considering the infrared mass as the ``renormalization point''. Then, it is found that the MTY approach including the composite Higgs loop effects is only partially equivalent to the BHL approach with QCD plus Higgs loop effects. The difference essentially results from the treatment of the composite Higgs propagator, or more precisely, of Z_H^{-1}. Our results can be summarized as m_t (Ours) \simeq 1/\sqrt{2} m_t (MTY), in contrast to m_t (BHL) \simeq \sqrt{2/3} m_t (MTY), where m_t (MTY) \simeq 250 GeV is the original MTY prediction without Higgs loop effects.Comment: 20 pages, PTPTeX, 5 EPS figures, 1 Table, to appear in Progress of Theoretical Physic

Chromomagnetic Instability and Gluonic Phase

We briefly report on a recent development in studies of a phase with vector condensates of gluons (gluonic phase) in dense two-flavor quark matter.Comment: 8 pages, 7 figures; talk given at 2006 International Workshop SCGT06, Nagoya, Japan, November 21-24, 200

Composite Z'

We investigate a possibility of a composite Z' vector boson. For the compositeness, the required gauge coupling g in low energy is not so big, g^2/(4\pi) > 0.015 in the case of the U(1)_{B-L} model. We show that the Stueckelberg model is effectively induced in low energy via the fermion loop from the Nambu-Jona-Lasinio (NJL) model having the vectorial four-fermion interaction. In terms of the renormalization group equations (RGE's), this situation is expressed by the compositeness conditions. We find that the solutions of the RGE's with the compositeness conditions are determined by the infrared fixed points. As a result, the ratio of the masses of the extra electroweak singlet scalar and the right-handed neutrino is fixed. The mass of the composite Z' boson contains the contribution \Delta of the Stueckelberg mass term. This nonzero \Delta might be a remnant of a strongly interacting theory in high energy.Comment: 6 pages, 4 figures; version published in PR