arXiv subjects
Publications and source records attributed to Christopher T. Hill.
We review a class of dynamical models in which top condensation occurs at the weak scale, giving rise to the large top quark mass and other phenomena. This typically requires a color embedding, $SU(3)_c \rightarrow SU(3)_1\times SU(3)_2$. These models imply many signatures addressable in near term experiments at colliders and in fixed target mode.
Very recently, a possible clustering of a subset of observed ultrahigh energy cosmic rays above about 40EeV (4x10^19eV) in pairs near the supergalactic plane was reported. We show that a confirmation of this effect would provide information on origin and nature of these events and, in case of charged primaries, imply interesting constraints on the extragalactic magnetic field. The observed time correlation would most likely rule out an association of these events with cosmological gamma ray bursts. If no prominent astrophysical source candidates such as powerful radiogalaxies can be found, the existence of a mechanism involving new fundamental physics would be favored.
A condensate, $\overline{t}t$, arising from $O(TeV)$ scale ``topcolor,'' in addition to technicolor (and ETC) may naturally explain the gauge hierarchy, the large top quark mass, and contains a rich system of testable consequences. A triplet of strongly coupled pseudo--Nambu--Goldstone bosons, ``top-pions,'' near the top mass scale is a generic prediction of the models. A new class of technicolor schemes and associated phenomenology is suggested in this approach.
In models of dynamical electroweak symmetry breaking which sensitively involve the third generation, such as top quark condensation, the effects of the new dynamics can show up experimentally in Z->b\bar{b}. We compare the sensitivity of Z->b\bar{b} and top quark production at the Tevatron to models of the new physics. Z->b\bar{b} is a relatively more sensitive probe to new strongly coupled U(1) gauge bosons, while it is generally less sensitive a probe to new physics involving color octet gauge bosons as is top quark production itself. Nonetheless, to accomodate a significant excess in Z->b\bar{b} requires choosing model parameters that may be ruled out within run I(b) at the Tevatron.
The production cross--section and distributions of the top quark are sensitive to new physics, e.g., the $t\overline{t}$ system can be a probe of new resonances or gauge bosons that are strongly coupled to the top quark, in analogy to Drell--Yan production. The existence of such new physics is expected in dynamical electroweak symmetry breaking schemes, and associated with the large mass of the top quark. The total top production cross--section can be more than doubled, and distributions significantly distorted with a chosen scale of new physics of $\sim 1 $ TeV in the vector color singlet or octet $s$--channel. New resonance physics is most readily discernible in the high--$p_T$ distributions of the single top quark and of the $W$ boson.
The possibility of exploring the systematics of the spectroscopy, strong dynamics, and the weak and rare decay modes of b--quark systems at hadron colliders such as Fermilab, LHC and SSC, is discussed. A copious yield of $10^{10}$ detected $B$--mesons is readily accessible in a dedicated Fermilab program, and implies a vast array of accessible decay modes, including second order weak processes and $CP$--violation, which will be unavailable elsewhere until the commissioning of LHC or SSC. Kinematic and flavor tagging, utilizing the ``daughter pions'' from resonances, is expected to play a major role in semileptonic weak decay studies and the search for $CP$--violation. Plenary talk, Workshop on $B$ Physics at Hadron Accelerators, Snowmass, Colorado, June 25, 1993; Invited Lecture, TASI, Boulder, Colorado, June 18, 1993.
Orbitally excited heavy-light mesons are potentially important as tools for tagging the flavors and momenta of ground-state pseudoscalars detected through weak decays. We use heavy-quark symmetry supplemented by insights gleaned from potential models to estimate masses and widths of $p$-wave $B$, $B_s$, and $D_s$ mesons. We generalize these results to higher excitations.
We study a solvable QCD--like toy theory, a generalization of the Nambu--Jona-Lasinio model, which implements chiral symmetries of light quarks and heavy quark symmetry. The chiral symmetric and chiral broken phases can be dynamically tuned. This implies a parity doubled heavy--light meson system, corresponding to a $(0^-,1^-)$ multiplet and a $(0^+,1^+)$ heavy spin multiplet. Consequently the mass difference of the two multiplets is given by a Goldberger--Treiman relation and $g_A$ is found to be small. The Isgur--Wise function, $ξ(w)$, the decay constant, $f_B$, and other observables are studied.
We propose spontaneously breaking technicolor, thus liberating techniquarks and suppressing large resonance contributions to the electroweak $S$ parameter. The dynamics is modeled by a fermion bubble approximation to a single massive techni--gluon exchange potential. This contains a Nambu--Jona-Lasinio model with additional interactions. ``Virtual'' vector mesons occur and contribute to $S$, and their effects are studied. Models of broken technicolor are discussed.