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S. M. Barr

Publications and source records attributed to S. M. Barr.

At least 19 recordsLinked to original sources
arXiv2017

Families from Supergroups and Predictions for Leptonic CP Violation

As was shown in 1984 by Caneschi, Farrar, and Schwimmer, decomposing representations of the supergroup SU(M|N), can give interesting anomaly-free sets of fermion representations of SU(M) x SU(N) x U(1). It is shown here that such groups can be used to construct realistic grand unified models with non-abelian gauged family symmetries. A particularly simple three-family example based on SU(5) x SU(2) x U(1) is studied. The forms of the mass matrices, including that of the right-handed neutrinos, are determined in terms of SU(2) Clebsch coefficients; and the model is able to fit the lepton sector and predict the Dirac CP-violating phase of the neutrinos.. Models of this type would have a rich phenomenology if part of the family symmetry is broken near the electroweak scale.

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arXiv2016

Cogenerating and Pre-annihilating Dark Matter by a New Gauge Interaction in a Unified Model

Grand unified theories based on large groups (with rank greater or equal to 6 are a natural context for dark matter models. They contain Standard-Model-singlet fermions that could be dark matter candidates, and can contain new non-abelian interactions whose sphalerons convert baryons, leptons, and dark matter into each other, "cogenerating" a dark matter asymmetry comparable to the baryon asymmetry. In this paper it is shown that the same non-abelian interactions can "pre-annihilate" the symmetric component of heavy dark matter particles, which then decay late into light stable dark matter particles that inherit their asymmetry. It is shown that such decays can come from d=5 operators that are Planck or GUT suppressed. We derive constraints on such models and present a simple realization based on the group SU(7).

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arXiv2015

A Model of Quark and Lepton Mixing and Mass Hierarchy

It is shown that an idea proposed in 1996 that relates in a qualitatively correct way the inter-family mass hierarchies of the up quarks, down quarks, charged leptons, and neutrinos, can be combined with a predictive scheme recently proposed for relating quark mixing and neutrino mixing. In the resulting model, the entire flavor structure of the quarks and leptons is expressible in terms of two "master matrices": a diagonal matrix that gives the inter-family mass ratios, and an off-diagonal matrix that controls all flavor mixing.

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arXiv2015

Infinite Classes of Cases with Non-trivial Anomaly Cancellation

It is pointed out that there are infinite classes of cases based on gauge groups of the form SU(p)xSU(q)xU(1) in which gauge anomalies cancel non-trivially for small sets of fermion multiplets that include symmetric tensor representations. These cancellations are non-trivial in the sense that no group-theoretic explanation in terms of embedding in a larger simple group is apparent. The cases presented here could be useful for model building and lead to models with extra leptons and an extra U(1) gauge interaction under which the Standard Model fermions have distinctive charges. In many cases the SU(q)xU(1) groups act as family symmetries.

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arXiv2014

New confining force solution of QCD axion domain wall problem

The serious cosmological problems created by the axion-string/axion-domain-wall system in standard axion models are alleviated by positing the existence of a new confining force. The instantons of this force can generate an axion potential that erases the axion strings long before QCD effects become important, thus preventing QCD-generated axion walls from ever appearing. Axion walls generated by the new confining force would decay so early as not to contribute significantly to the energy in axion dark matter.

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arXiv2014

Absolutely Stable Proton and Lowering the Gauge Unification Scale

A unified model is constructed, based on flipped $SU(5)$ in which the proton is absolutely stable. The model requires the existence of new leptons with masses of order the weak scale. The possibility that the unification scale could be extremely low is discussed.

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arXiv2013

Cogeneration of Dark Matter and Baryons by Non-Standard-Model Sphalerons in Unified Models

Sphalerons of a new gauge interaction can convert a primordial asymmetry in B or L into a dark matter asymmetry. From the equilibrium conditions for the sphalerons of both the electroweak and the new interactions, one can compute the ratios of B, L, and X, where X is the dark matter number, thus determining the mass of the dark matter particle fairly precisely. Such a scenario can arise naturally in the context of unification with larger groups. An illustrative model embeddable in $SU(6) \times SU(2) \subset E_6$ is described as well as an equally simple model based on SU(7).

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arXiv2013

Rotating Away Proton Decay in Flipped Unification

It is shown that by a simple extension of the fermion sector of flipped SU(5) models and other flipped models proton decay coming from dimension-6 operators can be suppressed by fermion mixing angles by an arbitrary amount in a natural way.

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arXiv2012

A Simple Grand Unified Relation between Neutrino Mixing and Quark Mixing

It is proposed that all flavor mixing is caused by the mixing of the three quark and lepton families with vectorlike fermions in 5 + 5-bar multiplets of SU(5). This simple assumption implies that both V_{CKM} and U_{MNS} are generated by a single matrix. The entire 3-by-3 complex mass matrix of the neutrinos M_{nu} is then found to have a simple expression in terms of two complex parameters and an overall scale. Thus, all the presently unknown neutrino parameters are predicted. The best fits are for theta_{atm} less than or approximately 40 degrees. The leptonic Dirac CP phase is found to be somewhat greater than pi radians.

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arXiv2011

A Classification and Analysis of Higgs-flavor Models

A classification is given of Higgs-flavor models. In these models, there are several Higgs doublets in an irreducible multiplet R_{Phi} of a non-abelian symmetry G_{Phi}, under which the quarks and leptons do not transform (thus giving minimal flavor-changing for the fermions). It is found that different G_{Phi} and R_{Phi} lead to very distinctive spectra of the extra Higgs doublets, including different numbers of "sequential Higgs" and of "inert Higgs" that could play the role of dark matter, different mass relations, and different patterns of SU(2)_L-breaking splittings within the Higgs doublets.

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arXiv2011

The Unification and Cogeneration of Dark Matter and Baryonic Matter

In grand unified theories with gauge groups larger than SU(5), the multiplets that contain the known quarks and leptons also contain fermions that are singlets under the Standard Model gauge group. Some of these could be the dark matter of the universe. Grand unified theories can also have accidental U(1) global symmetries (analogous to B-L in minimal SU(5)) that can stabilize dark matter. These ideas are illustrated in an SU(6) model.

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arXiv2011

Higgs-Flavor Groups, Naturalness, and Dark Matter

In the absence of low-energy supersymmetry, a multiplicity of weak-scale Higgs doublets would require additional fine-tunings unless they formed an irreducible multiplet of a non-abelian symmetry. Remnants of such symmetry typically render some Higgs fields stable, giving several dark matter particles of various masses. The non-abelian symmetry also typically gives simple, testable mass relations.

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arXiv2011

Higgs Multiplets of the Quark-Lepton Family Group

It is shown that realistic models can be constructed in which the Standard Model Higgs field is in a non-trivial multiplet of a non-abelian family group of the quarks and leptons. It is shown that the observed quark and lepton masses and mixing angles can be fit, while the coefficients of flavor-changing four-fermion operators mediated by the extra Higgs doublets are determined in terms of only a few unknown parameters.

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arXiv2008

A Realistic Radiative Fermion Mass Hierarchy in Non-supersymmetric SO(10)

A non-supersymmetric grand unified theory can exhibit a "radiative fermion mass hierarchy", in which the heavier quarks and leptons get mass at tree level and the lighter ones get mass from loop diagrams. Recently the first predictive model of this type was proposed. Here it is analyzed numerically and it is shown to give an excellent fit to the quark and lepton masses and mixings, including the CP phase violating phase $δ_{CKM}$. A relation between the neutrino angle $θ_{13}$ and the atmospheric neutrino angle is obtained

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arXiv2008

Doubly Lopsided Mass Matrices from Supersymmetric SU(N) Unification

It is shown that in supersymmetric SU(N) models with N>5 the so-called doubly lopsided mass matrix structure can emerge in a natural way. The non-trivial flavor structure is entirely accounted for by the SU(N) gauge symmetry and supersymmetry, without any flavor symmetry. The hierarchy among the families results directly from a hierarchy of scales in the chain of breaking from SU(N)to the Standard Model group. A simple SU(7) example is presented.

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arXiv2008

Doubly Lopsided Mass Matrices from Unitary Unification

It is shown that the stratified or "doubly lopsided" mass matrix structure that is known to reproduce well the qualitative features of the quark and lepton masses and mixings can arise quite naturally in the context of grand unification based on the groups SU(N) with N > 5. An SU(8) example is constructed with the minimal anomaly-free, three-family set of fermions, in which a realistic flavor structure results without flavor symmetry.

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arXiv2007

Family Unification with SO(10)

Unification based on the group SO(10)^3 \times S_3 is studied. Each family has its own SO(10) group, and the S_3 permutes the three families and SO(10) factors. This is the maximal local symmetry for the known fermions. Family unification is achieved in the sense that all known fermions are in a single irreducible multiplet of the symmetry. The symmetry suppresses SUSY flavor changing effects by making all squarks and sleptons degenerate in the symmetry limit. Doublet-triplet splitting can arise simply, and non-trivial structure of the quark and lepton masses emerges from the gauge symmetry, including the "doubly lopsided" form.

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