Howard Georgi

Softly Broken Supersymmetry and SU(5)

We construct an explicit realistic SU(5) model in which softly broken supersymmetry is used to protect the Higgs doublets from quadratic mass renormalization. The model requires one natural but incredibly accurate adjustment of parameters. We argue that such an adjustment will be required in any supersymmetric GUT in which baryon number is not conserved.

Chiral quarks and the non-relativistic quark model☆

Abstract We study some of the consequences of an effective lagrangian for quarks, gluons and goldstone bosons in the region between the chiral symmetry breaking and confinement scales. This provides an understanding of many of the successes of the non-relativistic quark model. It also suggests a resolution to the puzzle of the hyperon non-leptonic decays.

Electroweak symmetry breaking from dimensional deconstruction

We propose a new class of four-dimensional theories for natural electroweak symmetry breaking, relying neither on supersymmetry nor on strong dynamics at the TeV scale. The new TeV physics is perturbative, and radiative corrections to the Higgs mass are finite. The softening of this mass occurs because the Higgs is an extended object in theory space, resulting in an accidental symmetry. A novel Higgs potential emerges naturally, requiring a second lightSU(2)doublet scalar. 2001 Published by Elsevier Science B.V.

An Effective Field Theory for Heavy Quarks at Low-energies

I construct a Lorentz invariant effective field theory description of QCD in the presence of heavy quarks at energies large compared to the QCD scale and small compared to the heavy quark mass, formalizing the ideas of Isgur and Wise and of Eichten and Hill. The theory is built by “integrating in” degrees of freedom to implement a superselection rule for the velocity of the heavy quark.

De)Constructing Dimensions

We construct renormalizable, asymptotically free, four-dimensional gauge theories that dynamically generate a fifth dimension.

Effective field theory for massive gravitons and gravity in theory space

Abstract We introduce a technique for restoring general coordinate invariance into theories where it is explicitly broken. This is the analog for gravity of the Callan–Coleman–Wess–Zumino formalism for gauge theories. We use this to elucidate the properties of interacting massless and massive gravitons. For a single graviton with a Planck scale M Pl and a mass m g , we find that there is a sensible effective field theory which is valid up to a high-energy cutoff Λ parametrically above m g . Our methods allow for a transparent understanding of the many peculiarities associated with massive gravitons, among them the need for the Fierz–Pauli form of the Lagrangian, the presence or absence of the van Dam–Veltman–Zakharov discontinuity in general backgrounds, and the onset of non-linear effects and the breakdown of the effective theory at large distances from heavy sources. The natural sizes of all non-linear corrections beyond the Fierz–Pauli term are easily determined. The cutoff scales as Λ ∼( m g 4 M Pl ) 1/5 for the Fierz–Pauli theory, but can be raised to Λ ∼( m g 2 M Pl ) 1/3 in certain non-linear extensions. Having established that these models make sense as effective theories, there are a number of new avenues for exploration, including model building with gravity in theory space and constructing gravitational dimensions.

SU(2) × U(1) breaking by vacuum misalignment

Currently two scenarios exist which explain SU(2) × U(1) breaking: the Higgs mechanism, and standard hypercolor schemes. In this paper, a third scenario called “oblique hypercolor” is proposed. A hyperquark condensate is formed which, although kinematically allowed to point in an SU(2) × U(1) preserving direction, is forced by Yukawa interactions of the hyperquarks to misalign by a small angle, breaking SU(2) × U(1). The low energy spectrum involves normal fermions with correct masses, a partially composite Higgs boson, and physical charged scalars.

A New Lepton - Quark Mass Relation in a Unified Theory

Abstract We argue that the observed quark and lepton masses are related at momenta larger than 1015 GeV as follows: mb = mτ, mμ = 3ms and me = md/3. We construct a model in which these factors of three arise naturally — because quarks come in three colors.

Composite Higgs Scalars

We construct models in which the Higgs doublet whose vacuum expectation breaks SU(2) × U(10 is a bound state of massive strongly interacting fermions. The couplings of the composite Higgs to ordinary fermions are induced by heavy gauge boson exchange in the manner of extended technicolor. Other heavy gauge bosons generate a negative mass term for the Higgs.

Composite-technicolor standard model

Abstract We characterize a class of composite models in which the quarks and leptons and technifermions are built from fermions (preons) bound by strong gauge interactions. We argue that if the preon dynamics has as [SU(3) × U(1)]5 flavor symmetry that is explicitly broken only by preon mass terms proportional to the quark and lepton mass matrices, then the composite-tech-nicolor theory has a GIM mechanism that suppresses dangerous flavor changing neutral current effects. We show that the compositeness scale must be between ≈1 TeV and ≈2.5 TeV, giving rise to observable deviations from the standard electroweak interactions, and that B B mixing and CP violation in K mesons can differ significantly from the standard model predictions. The lepton flavor symmetries may be observable in the near future in the comparison of the compositeness effects in e+e− → μ+μ− with those in e+e− → e+e−.