arXiv subjects

Christopher D. Carone

Publications and source records attributed to Christopher D. Carone.

At least 109 records · Page 6Linked to original sources

arXiv1997

Supersymmetric model of quasi-degenerate neutrinos

We present a supersymmetric model of fermion masses, based on a non-Abelian family symmetry and the Froggatt-Nielsen mechanism, that can account for the solar and atmospheric neutrino problems via quasi-degenerate neutrinos. The model predicts that the ratio of neutrino mass squared splittings Δm^2_{12} / Δm^2_{23} is of order m_s^2/m_b^2, and the angles θ_{12} \sim m_d/m_s and θ_{23} \sim 1, which are of the desired orders of magnitude. We discuss the implications of the flavor structure of the neutrino sector on superparticle masses and mixing angles.

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arXiv1997

New Mechanism of Flavor Symmetry Breaking from Supersymmetric Strong Dynamics

We present a class of supersymmetric models in which flavor symmetries are broken dynamically, by a set of composite flavon fields. The strong dynamics that is responsible for confinement in the flavor sector also drives flavor symmetry breaking vacuum expectation values, as a consequence of a quantum-deformed moduli space. Yukawa couplings result as a power series in the ratio of the confinement to Planck scale, and the fermion mass hierarchy depends on the differing number of preons in different flavor symmetry-breaking operators. We present viable non-Abelian and Abelian flavor models that incorporate this mechanism.

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arXiv1997

Neutrino physics from a U(2) flavor symmetry

We consider the neutrino physics of models with a sequentially broken U(2) flavor symmetry. Such theories yield the observed pattern of quark and lepton masses, while maintaining sufficient degeneracies between superparticles of the first two generations to solve the supersymmetric flavor problem. Neutrino mass ratios and mixing angles in these models may differ significantly from those of the charged leptons, even though the neutrinos and charged leptons transform identically under the flavor group. A wide class of well-motivated U(2) theories yield order one $ν_μ- ν_τ$ mixing, without a fine-tuning of parameters. These models provide a natural solution to the atmospheric neutrino deficit, and also have distinctive signatures at long-baseline neutrino oscillation experiments.

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arXiv1996

TeV Right-handed Neutrinos and the Flavor-symmetry-improved Seesaw Mechanism

Horizontal flavor symmetries can drastically suppress Dirac neutrino masses well below those of the corresponding charged leptons. We show that models can be constructed where the light neutrino mass eigenvalues are small enough to give the MSW solution to the solar neutrino problem, with a right-handed neutrino scale no larger than a TeV. We present a model of this type where the right-handed neutrino scale is generated by the spontaneous breakdown of gauged U(1)$_{B-L}$, in a radiative breaking scenario driven by the right-handed neutrino Yukawa couplings. The model allows for a solution to the $μ$ problem, and predicts the existence of a $Z'$ boson within the reach of the LHC or the Tevatron.

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arXiv1996

(S_3)^3 Theories of Flavor

I present a supersymmetric theory of flavor based on the discrete flavor group $(S_3)^3$. The model can account for the masses and mixing angles of the standard model, while maintaining sufficient sfermion degeneracy to evade the supersymmetric flavor problem. I demonstrate that the model has a viable phenomenology and makes one very striking prediction: the nucleon decays predominantly to $K l$ where $l$ is a {\em first} generation lepton. I show that the modes $n \rightarrow K^0 \barν_e$, $p\rightarrow K^+ \barν_e$, and $p\rightarrow K^0 e^+$ occur at comparable rates, and could well be discovered simultaneously at the SuperKamiokande experiment.

hep-ph↗

arXiv1996

Supersymmetric Framework for a Dynamical Fermion Mass Hierarchy

We propose a new framework for constructing supersymmetric theories of flavor, in which flavor symmetry breaking is triggered by the dynamical breakdown of supersymmetry at low energies. All mass scales in our scheme are generated from the supersymmetry breaking scale $Λ_{SSB} \approx 10^7$ GeV through radiative corrections. We assume a spontaneously broken flavor symmetry and the Froggatt-Nielsen mechanism for generating the fermion Yukawa couplings. Supersymmetry breaking radiatively induces a vacuum expectation value for a scalar field, which generates invariant masses for the Froggatt-Nielsen fields at $M_F \approx 10^4$ GeV. `Flavon' fields $φ$, which spontaneously break the flavor symmetry, naturally acquire negative squared masses due to two-loop diagrams involving the Froggatt-Nielsen fields, and acquire vacuum expectation values of order $\langle φ\rangle \approx M_F/16π^2$. The fermion mass hierarchy arises in our framework as a power series in the ratio $\langle φ\rangle / M_F \approx 1/16π^2$.

hep-ph↗

arXiv1996

A Supersymmetric Theory of Flavor and R Parity

We construct a renormalizable, supersymmetric theory of flavor and $R$ parity based on the discrete flavor group $(S_3)^3$. The model can account for all the masses and mixing angles of the Standard Model, while maintaining sufficient squark degeneracy to circumvent the supersymmetric flavor problem. By starting with a simpler set of flavor symmetry breaking fields than we have suggested previously, we construct an economical Froggatt-Nielsen sector that generates the desired elements of the fermion Yukawa matrices. With the particle content above the flavor scale completely specified, we show that all renormalizable $R$-parity-violating interactions involving the ordinary matter fields are forbidden by the flavor symmetry. Thus, $R$ parity arises as an accidental symmetry in our model. Planck-suppressed operators that violate $R$ parity, if present, can be rendered harmless by taking the flavor scale to be $\lesssim 8 \times 10^{10}$ GeV.

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arXiv1995

$(S_3)^3$ flavor symmetry and $p\to K^0 e^+$

We show how to incorporate the lepton sector in a supersymmetric theory of flavor based on the discrete flavor group $(S_3)^3$. Assuming that all possible nonrenormalizable operators are generated at the Planck scale, we show that the transformation properties of the leptons and of the flavor-symmetry breaking fields are uniquely determined. We then demonstrate that the model has a viable phenomenology and makes one very striking prediction: the nucleon decays predominantly to $K l$ where $l$ is a {\em first} generation lepton. We show that the modes $n \rightarrow K^0 \barν_e$, $p\rightarrow K^+ \barν_e$, and $p\rightarrow K^0 e^+$ occur at comparable rates, and could well be discovered simultaneously at the SuperKamiokande experiment.

hep-ph↗

arXiv1995

Phenomenology of Minimal SU(5) Unification with Dynamical Supersymmetry Breaking

We consider the constraints from proton decay and $b$-$τ$ unification in the minimal supersymmetric SU(5) grand unified theory with a `visible' dynamical supersymmetry breaking sector. We show how the presence of vector-like messenger fields and the constrained superparticle mass spectrum affect the phenomenology of the model. We include the messenger fields in our renormalization group analysis between the messenger scale ($\sim 100$ TeV) and the GUT scale. We show that the simplest model of this type, a minimal SU(5) GUT with an additional {\bf 5}+\bfbar{5} of messenger fields is excluded by the constraints from proton decay and $b$-$τ$ unification.

hep-ph↗

arXiv1995

Light U(1) Gauge Boson Coupled to Baryon Number

We discuss the phenomenology of a light U(1) gauge boson, $γ_B$, that couples only to baryon number. Gauging baryon number at high energies can prevent dangerous baryon-number violating operators that may be generated by Planck scale physics. However, we assume at low energies that the new U(1) gauge symmetry is spontaneously broken and that the $γ_B$ mass $m_B$ is smaller than $m_Z$. We show for $m_Υ<m_B<m_Z$ that the $γ_B$ coupling $α_B$ can be as large as $\sim 0.1$ without conflicting with the current experimental constraints. We argue that $α_B\sim 0.1$ is large enough to produce visible collider signatures and that evidence for the $γ_B$ could be hidden in existing LEP data. We show that there are realistic models in which mixing between the $γ_B$ and the electroweak gauge bosons occurs only as a radiative effect and does not lead to conflict with precision electroweak measurements. Such mixing may nevertheless provide a leptonic signal for models of this type at an upgraded Tevatron.

hep-ph↗

arXiv1995

Third family flavor physics in an SU(3)^3 \times SU(2)_L \times U(1)_Y model

We consider a model in which each family transforms under a different SU(3) color group. The low-energy effective theory is an extension of the Standard Model, with additional color octet gauge bosons $G_H$ with mass $M$ that couple preferentially to the third family quarks. We show that there are two distinct regions of the model's parameter space in which we can simultaneously evade all the current experimental constraints, one with $M \approx 250$ GeV and the other with $M \gtrsim 600$ GeV. Within each allowed region, we can obtain a correction to the $Zb\overline{b}$ vertex that is consistent with the slightly high value of $R_b$ observed at LEP. We show that there are $ΔB = 1$ operators in our model that can suppress the $B$-meson semileptonic branching ratio $B_{SL}$ and the charm multiplicity per decay $n_c$ by enough to reconcile the spectator parton model predictions with the experimental data. In the non-supersymmetric version of our model, we can only obtain the desired corrections to $R_b$, $B_{SL}$ and $n_c$ in different regions of the allowed parameter space, while in the supersymmetric version, we can obtain all three corrections simultaneously. We also discuss a strong-coupling limit of our model in which the third-family quarks become composite.

hep-ph↗

arXiv1995

REALISTIC MODELS WITH A LIGHT U(1) GAUGE BOSON COUPLED TO BARYON NUMBER

We recently showed that a new gauge boson $γ_B$ coupling only to baryon number is phenomenologically allowed, even if $m_B<m_Z$ and $α_B \approx 0.2$. In our previous work we assumed that kinetic mixing between the baryon number and hypercharge gauge bosons (via an $F^{μν}_B F_{μν}^Y$ term) was small enough to evade constraints from precision electroweak measurements. In this paper we propose a class of models in which this term is naturally absent above the electroweak scale. We show that the generation of a mixing term through radiative corrections in the low-energy effective theory does not lead to conflict with precision electroweak measurements and may provide a leptonic signal for models of this type at an upgraded Tevatron.

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arXiv1994

b \rightarrow s γAND Z \rightarrow b \overline{b} IN TECHNICOLOR WITH SCALARS

We consider the radiative decay $b\rightarrow s γ$, and the correction to the $Zb\overline{b}$ vertex in technicolor models with scalars. In these models, the scalar develops a vacuum expectation value when the technifermions condense, and the ordinary fermions develop masses via Yukawa couplings. Since the symmetry breaking sector involves both a fundamental scalar doublet and an isotriplet of composite scalars (the technipions), the phenomenology associated with the charged scalars is similar to that found in a type-I two-Higgs doublet model. We show that the correction to the $Zb\overline{b}$ vertex is small over the allowed parameter space of the model in the two limits that we consider, and that there can be large, potentially observable, contributions to the $b\rightarrow s γ$ branching fraction.

hep-ph↗

arXiv1994

Possible Light U(1) Gauge Boson Coupled to Baryon Number

We discuss the phenomenology of a light U(1) gauge boson, $γ_B$, that couples only to baryon number. We assume that the new U(1) gauge symmetry is spontaneously broken and that the $γ_B$ mass is smaller than $m_Z$. Nevertheless, we show that the model survives the current experimental constraints. In addition, we argue that evidence for the existence of such a particle could be hidden in existing LEP and Tevatron data. We determine the allowed regions of the $m_B$-$α_B$ plane, where $m_B$ is the $γ_B$ mass, and where $4 πα_B$ is the squared gauge coupling. We point out that in some parts of the allowed parameter space our model can account for rapidity gap events in proton-antiproton scattering seen at the Fermilab Tevatron.

hep-ph↗

arXiv1994

Decays of $\ell=1$ Baryons --- Quark Model versus Large-$N_c$

We study nonleptonic decays of the orbitally excited, \su6 \rep{70}-plet baryons in order to test the hypothesis that the successes of the nonrelativistic quark model have a natural explanation in the large-$N_c$ limit of QCD. By working in a Hartree approximation, we isolate a specific set of operators that contribute to the observed s- and d-wave decays in leading order in $1/N_c$. We fit our results to the current experimental decay data, and make predictions for a number of allowed but unobserved modes. Our tentative conclusion is that there is more to the nonrelativistic quark model of baryons than large-$N_c$.

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arXiv1993

Detecting the Technirho in Technicolor Models with Scalars

We consider the detection of the technirho in technicolor models that include a weak scalar doublet. In these models, the scalar develops a vacuum expectation value when the technifermions condense, and fermion masses are generated through Yukawa couplings, as in the standard model. Unlike ordinary technicolor models, the technicolor scale is generally smaller than the electroweak scale, and the entire technicolor spectrum is shifted to lower energies. In addition, the technifermions can develop large `current' masses from the scalar's vev, so that the technicolor spectrum does not necessarily look like a scaled-up version of ordinary QCD. We discuss the collider signatures for the technirho in these models in the limit that the technirho is light. Although we focus mostly on the production and detection of the technirho in hadron colliders, we also discuss a peculiar limit in which the technirho may be light enough to be seen at LEP II.

hep-ph↗

arXiv1993

Technicolor with a Massless Scalar Doublet

We consider a minimal technicolor model in which the ordinary and technicolor sectors are coupled by a {\it massless} scalar doublet. When technicolor interactions become strong, the resulting technicolor condensate not only breaks the electroweak symmetry, but also causes the scalar to develop a vacuum expectation value. With the appropriate choice of the scalar's Yukawa couplings, fermion masses are generated, giving us the conventional pattern of flavor symmetry breaking. Although no explicit scalar mass term appears in the full lagrangian of the model, the pseudoscalar states that remain in the low-energy effective theory gain sufficient mass through technicolor interactions to evade detection. We show that this model does not generate unacceptably large flavor changing neutral currents, and is consistent with the experimental constraints on oblique electroweak radiative corrections. We determine the experimentally allowed region of the model's parameter space, and discuss the significance of a phenomenologically viable model that has no arbitrary dimensionful parameters. In terms of parameter counting, our model is the simplest possible extension of the standard model.

hep-ph↗

arXiv1993

Double Beta Decay with Vector Majorons

We consider the possibility that neutrinoless double beta decay may occur in models with unbroken lepton number via the emission of a massive gauge boson with electron lepton number $-2$. We determine the shape of the $β\,β$ sum energy spectrum as a function of the gauge coupling, independent of model-specific details. We discuss our results in light of the persistent experimental claims that excess events are observed near but below the spectrum endpoint of several elements.

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