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Georgi, Howard

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Georgi, Howard
Author's Publications: search.filters.isAuthorOfPublication.883dce0d-c2fe-4cbf-882b-680d6dd05080

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Now showing 1 - 10 of 30
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    Top-color jungle gym: An alternative to the seesaw mechanism
    (American Physical Society (APS), 2000) Georgi, Howard; Grant, Aaron K.
    We discuss an alternative to the topcolor seesaw mechanism. In our scheme, all the light quarks carry topcolor, and there are many composit e SU(2) doublets. This makes it possible to get the observed t quark mass and observed SU(2) × U(1) breaking in a way that is quite different from the classic seesaw mechanism. We discuss a model of this kind that arises naturally in the context of dynamically broken topcolor. There are many composite scalars in a theory of this kind. This has important effects on the Pagels-Stokar relation and the Higgs mass. We find mHiggs ∼< 330 GeV, lighter than in typical topcolor models. We also show that the electroweak singlet quarks in such a model can be lighter than the corresponding quarks in a seesaw model.
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    Phenomenology of a top quark seesaw model
    (American Physical Society (APS), 2000) Collins, Hael; Grant, Aaron; Georgi, Howard
    The top quark seesaw mechanism offers a method for constructing a composite Higgs field without the usual difficulties that accompany traditional technicolor or topcolor theories. The focus of this article is to study the phenomenology of the new physics required by this mechanism. After establishing a set of criteria for a plausible top quark seesaw theory, we develop two models, the first of which has a heavy weak singlet fermion with hypercharge 43 while the secon has, in addition, a heavy weak singlet hypercharge −23 fermion. At low energies, these theories contain one or two Higgs doublets respectively. We then derive the low energy effective Higgs potential in detail for the two-doublet theory as well as study the likely experimental signatures for both theories. A strong constraint on the one-doublet model is the measured value of the ρ parameter which permits the new heavy fermion to have a mass of about 5–7 TeV, when the Higgs has a mass greater than 300 GeV. In the two-doublet model, mixing of the new heavy Y = − 23 fermion and the b quark affects the prediction for R b. In order to agree with the current limits on R b, the mass of this fermion should be at least 12 TeV. The mass of the heavy Y = 43 fermion in the two-doublet model is not as sharply constrained by experiments and can be as light as 2 .5 TeV.
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    Fun with Higgsless theories
    (American Physical Society (APS), 2005) Georgi, Howard
    Motivated by recent works on “Higgsless theories,” I discuss an SU(2) 0 × SU(2) N × U(1) gauge theory with arbitrary bifundamental (or custodia l SU(2) preserving) symmetry breaking between the gauge subgroups and with ordinary matter transforming only under the U(1) and SU(2) 0. When the couplings, gj, of the other SU(2)s are very large, this reproduces the standard model at the tree level. I calculate the W and Z masses and other electroweak parameters in a perturbative expansion in 1/g 2j, and give physical interpretations of the results in a mechanical analog built out of masses and springs. In the mechanical analog, it is clear that even for arbitrary patterns of symmetry breaking, it is not possible (in the perturbative regime) to raise the Higgs mass by a large factor while keeping the S parameter small.
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    Electroweak symmetry breaking from dimensional deconstruction
    (Elsevier BV, 2001) Arkani-Hamed, Nima; Cohen, Andrew G.; Georgi, Howard
    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 light SU(2) doublet scalar.
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    (De)Constructing Dimensions
    (American Physical Society (APS), 2001) Arkani-Hamed, Nima; Cohen, Andrew G.; Georgi, Howard
    We construct renormalizable, asymptotically free, four dimensional gauge theories that dynamically generate a fifth dimension.
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    S3 and the L = 1 baryons in the quark model and the chiral quark model
    (American Physical Society (APS), 1999) Collins, Hael; Georgi, Howard
    The S 3 symmetry corresponding to permuting the positions of the quarks within a baryon allows us to study the 70-plet of L = 1 baryons without an explicit choice for the spatial part of the quark wave functions: given a set of operators with definite transformation properties under the spin-flavor group SU(3) × SU(2) and under this S 3, the masses of the baryons can be expressed in terms of a small number of unknown parameters which are fit to the observed L = 1 baryon mass spectrum. This approach is applied to study both the quark model and chiral constituent quark model. The latter theory leads to a set of mass perturbations which more satisfactorily fits the observed L = 1 baryon mass spectrum (though we can say nothing, within our approach, about the physical reasonableness of the parameters in the fit). Predictions for the mixing angles and the unobserved baryon masses are given for both models as well as a discussion of specific baryons.
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    Neutrinos on Earth and in the heavens
    (American Physical Society (APS), 2000) Georgi, Howard; Glashow, Sheldon
    Recent data lead us to a simple and intriguing form of the neutrino mass matrix. In particular, we find solar neutrino oscillations to be nearly maximal (and rule out the small-angle MSW explanation of solar neutrino observations) if relic neutrinos comprise at least one percent of the critical mass density of the universe.
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    Color fields on the light-shell
    (Springer Science + Business Media, 2016) Georgi, Howard; Kestin, Gregory; Sajjad, Aqil
    We study the classical color radiation from very high energy collisions that produce colored particles. In the extreme high energy limit, the classical color fields are confined to a light-shell expanding at c and are associated with a non-linear σ-model on the 2D light-shell with specific symmetry breaking terms. We argue that the quantum version of this picture exhibits asymptotic freedom and may be a useful starting point for an effective light-shell theory of the structure between the jets at a very high energy collider.
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    Brane couplings from bulk loops
    (Elsevier BV, 2001) Georgi, Howard; Grant, Aaron K.; Hailu, Girma
    We compute loop corrections to the effective action of a field theory on a fivedimensional S1/Z2 orbifold. We find that the quantum loop effects of interactions in the bulk produce infinite contributions that require renormalization by fourdimensional couplings on the orbifold fixed planes. Thus bulk couplings give rise to renormalization group running of brane couplings.
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    Soft superweak CP violation and the strong CP puzzle
    (Elsevier BV, 1999) Georgi, Howard; Glashow, Sheldon
    We discuss a class of models in which CP is violated softly in a heavy sector adjoined to the standard model. Heavy-sector loops produce the observed CP violation in kaon physics, yielding a tiny and probably undetectable value for ǫ′. All other CPviolating parameters in the effective low-energy standard model, including the area of the unitarity triangle and θ, are finite, calculable and can be made very small. The leading contribution to θ comes from a four-loop graph. These models offer a natural realization of superweak CP violation and can resolve the strong CP puzzle. In one realization of this idea, CP is violated in the mass matrix of heavy majorana neutrinos.