Top Quark Seesaw, Vacuum Structure and Electroweak Precision Constraints

Abstract

We present a complete study of the vacuum structure of Top Quark Seesaw models of the Electroweak Symmetry Breaking, including bottom quark mass generation. Such models emerge naturally from extra dimensions. We perform a systematic gap equation analysis and develop an improved broken phase formulation for including exact seesaw mixings. The composite Higgs boson spectrum is studied in the large-N_c fermion-bubble approximation and an improved renormalization group approach. The theoretically allowed parameter space is restrictive, leading to well-defined predictions. We further analyze the electroweak precision constraints. Generically, a heavy composite Higgs boson with a mass of ~1TeV is predicted, yet fully compatible with the precision data.

Figures (18)

• Figure 1: Dirac fermion corresponding to constant $\phi$ has both chiral modes on all branes. The $\times$ symbols denote the $\phi$ couplings on each brane, and the links are the latticized fermion kinetic terms which become Wilson links when gauge fields are present.
• Figure 2: A chiral fermion occurs on brane $n$ where $\phi(x^5)$ swings rapidly through zero. The chiral fermion has kinetic term (Wilson links) connecting to adjoining branes.
• Figure 3: Pure top quark condensation by Topcolor is obtained in the limit of critical coupling on brane $n$ and decoupling to the nearest neighbors. Decoupling corresponds to taking the compactification mass scale large; the links are then denoted by dashed lines.
• Figure 4: Top Seesaw Model arises when the effects of nearest neighbor vector-like fermions are retained, i.e., when these heavier states are only partially decoupled. Keeping more links maintains the seesaw. Usually we denote $t_{Rn}\sim \chi_R$, $t_{Ln+1}\sim \chi_L$, $t_{Rn+1}\sim t_R$seesaw.
• Figure 5: The $68\%$ and $95\%$ C.L. $S$-$T$ contours (solid), superimposing the Standard Model curve for Higgs mass varying from $100$ GeV up to $1000$ GeV. The pre-1999 $95\%$ ellipse is shown with a dashed line. For the Top Seesaw model with a $1$ TeV composite Higgs, we show the $S$-$T$ contributions as a function of $\chi$ mass. The data is therefore consistent with a $\sim\!1$ TeV Higgs and $M_\chi \sim 4.0$ TeV. (The $S$-$T$ ellipses are taken from 1999 precision fit 99fit.)