arXiv subjects
Publications and source records attributed to M. Tanabashi.
We review the ILC capabilities to explore the electroweak (EW) sector of the SM at high precision and the prospects of unveiling signals of BSM physics, either through the presence of new particles in higher-order corrections or via direct production of extra EW gauge bosons. This includes electroweak precision observables, global fits to the SM Higgs boson mass as well as triple and quartic gauge boson couplings.
This talk reviews recent progress in Higgsless models of electroweak symmetry breaking, and summarizes relevant points of model-building and phenomenology.
We investigate dynamical chiral symmetry breaking in vector-like gauge theories in $D$ dimensions with ($D-4$) compactified extra dimensions, based on the gap equation (Schwinger-Dyson equation) and the effective potential for the bulk gauge theories within the improved ladder approximation. The non-local gauge fixing method is adopted so as to keep the ladder approximation consistent with the Ward-Takahashi identities. Using the one-loop $\bar{\rm MS}$ gauge coupling of the truncated KK effective theory which has a nontrivial ultraviolet fixed point (UV-FP) $g_*$ for the (dimensionless) bulk gauge coupling ${\hat g}$, we find that there exists a critical number of flavors, $N_f^{\rm crit}$ ($\simeq 4.2, 1.8$ for $D=6, 8$ for SU(3) gauge theory): For $N_f > N_f^{\rm crit}$, the dynamical chiral symmetry breaking takes place not only in the ``strong-coupling phase'' (${\hat g} >g_*$) but also in the ``weak-coupling phase'' (${\hat g} <g_*$) when the cutoff is large enough. For $N_f < N_f^{\rm crit}$, on the other hand, only the strong-coupling phase is a broken phase and we can formally define a continuum (infinite cutoff) limit, so that the physics is insensitive to the cutoff in this case. We also perform a similar analysis using the one-loop ``effective gauge coupling''. We find the $N_f^{\rm crit}$ turns out to be a value similar to that of the $\bar{\rm MS}$ case, notwithstanding the enhancement of the coupling compared with that of the $\bar{\rm MS}$.
Non-decoupling effects of heavy particles present in beyond-the-standard models are studied for the triple gauge boson vertices $γW^+W^-$ and $Z^0W^+W^-$. We show from a general argument that the non-decoupling effects are described by four independent parameters, in comparison with the three parameters $S$, $T$ and $U$ in the oblique corrections. These four parameters of the effective triple gauge boson vertices are computed in two beyond-the-standard models. We also study the relation of the four parameters to the $S$, $T$, $U$ parameters, relying on an operator analysis.
We consider CP violating effects in the decays $τ\rightarrow (3π)ν_τ$ where both the ${\rm J}^{\rm P}=1^+$ resonance, $a_1$, and ${\rm J}^{\rm P}=0^-$ resonance, $π^\prime$, can contribute. The interference between the $a_1$ and $π^\prime$ resonances can lead to enhanced CP-violating asymmetries whose magnitudes depend crucially on the $π^\prime$ decay constant, $f_{π^\prime}$. We make an estimate of $f_{π^\prime}$ with a simplified chiral Lagrangian coupled to a massive pseudoscalar field, and we compare the estimates from the non-relativistic quark model and from the QCD sum rule with the estimate from the `mock' meson model. We then estimate quantitatively the size of CP-violating effects in a multi-Higgs-doublet model and scalar-leptoquark models. We find that, while CP-violating effects in the scalar-leptoquark models may require more than $10^{10}$ $τ$ leptons, CP-violating effects from the multi-Higgs-doublet model can be seen at the $2σ$ level with about $10^7$ $τ$ leptons using the chiral Lagrangian estimate of $f_{π^\prime}=(1\sim 5)\times 10^{-3}$ GeV.