arXiv subjects

Zurab Tavartkiladze

Publications and source records attributed to Zurab Tavartkiladze.

66 records · Page 4Linked to original sources

arXiv1999

Bi-maximal Neutrino Mixings And Proton Decay In SO(10) With Anomalous Flavor ${\cal U}(1)$

By supplementing supersymmetric SO(10) with an anomalous ${\cal U}(1)$ flavor symmetry and additional `matter' superfields carrying suitable ${\cal U}(1)$ charges, we explain the charged fermion mass hierarchies, the magnitudes of the CKM matrix elements, as well as the solar and atmospheric neutrino data. We stress bi-maximal vacuum neutrino mixings, and indicate how the small or large mixing angle MSW solution can be incorporated. The ${\cal U}(1)$ symmetry also implies that $τ_{p\to Kν}[SO(10)]\sim (10-100)\cdot τ_{p\to Kν}[{\rm minimal}~SU(5)]$.

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arXiv1999

Proton Decay, Neutrino Oscillations And Other Consequences From Supersymmetric SU(6) With Pseudo-Goldstone Higgs

We suggest a new mechanism for naturally suppressing dimension five baryon number violating in supersymmetric SU(5+N) (N=0, 1,...) GUTs. The mechanism is realized through suppression of qqT type couplings, and is implemented by introducing new `matter' multiplets belonging to symmetric representations of SU(5+N). Together with the suppression of nucleon decay, these multiplets also enable one to avoid the unwanted asymptotic mass relations $m_s=m_μ$, $\frac{m_d}{m_s}=\frac{m_e}{m_μ}$. As an example, we consider a SU(6) model with pseudo-Goldstone Higgs. By supplementing the model with an anomalous ${\cal U}(1)$ flavor symmetry, we also obtain a simple `all-order' solution of the gauge hierarchy problem and natural explanation of charged fermion mass hierarchies and values of the CKM matrix elements. The proton life time $τ_p\sim 10^{2}τ_p^{SU(5)}$~yr. is compatible with experiments, with the dominant decay being $p\to Kν_{μ, τ}$. Thanks to the SU(6) symmetry, successful unification of the gauge couplings can be retained, and the value of the strong coupling $α_s(M_Z)$ can be reduced to $\simeq 0.12$. Finally, we show how to accommodate the solar and atmospheric neutrino data through the bi-maximal neutrino mixing scenario, with maximal vacuum $ν_e-ν_{μ, τ}$ and large angle $ν_μ-ν_τ$ oscillations.

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arXiv1999

R-Parity Violation: Origin of $μ$-Term and Other Consequences

We propose a new mechanism in which the generation of the supersymmetric $μ$-term as well charged lepton masses is closely tied to R-parity violation involving heavy vector-like families . A realistic example based on $SU(3)_c\times SU(2)_L\times U(1)_Y$, supplemented by the symmetry ${\cal R}\times {\cal U}(1)$, is presented, where ${\cal R}$ (${\cal U}(1)$) denotes a continuous $R$ (flavor) symmetry. In addition to the $μ$-term, the charged fermion mass hierarchies and mixings, as well as baryon number conservation are also nicely explained. Bilinear R-parity violating coupling involving the first generation gives rise to neutrino mass relevant for the small angle $ν_e-ν_s$ MSW oscillations, where $ν_s $ denotes a sterile state. The atmospheric neutrino puzzle is resolved via maximal mixing angle $ν_{μ}-ν_τ$ oscillations. The decay of the lightest neutralino (LSP) and leptogenesis are briefly discussed.

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arXiv1999

An Improved Supersymmetric SU(5)

By supplementing minimal supersymmetric SU(5) (MSSU(5)) with a flavor ${\cal U}(1)$ symmetry and two pairs of $\bar{15}+15$ `matter' supermultiplets, we present an improved model which explains the charged fermion mass hierarchies and the magnitudes of the CKM matrix elements, while avoiding the undesirable asymptotic mass relations $m_s=m_μ, m_d/m_s = m_e/m_μ$. The strong coupling $α_s (M_Z)$ is predicted to be approximately 0.115, and the proton lifetime is estimated to be about five times larger than the MSSU(5) value. The atmospheric and solar neutrino puzzles are respectively resolved via maximal $ν_μ-ν_τ$ and small mixing angle $ν_e-ν_s$ MSW oscillations, where $ν_s$ denotes a sterile neutrino. The ${\cal U}(1)$ symmetry ensures not only a light $ν_s$ but also automatic `matter' parity.

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arXiv1999

Phenomenology with Supersymmetric Flipped SU(6)

The supersymmetric flipped $SU(6)\times U(1)$ gauge symmetry can arise through compactification of the ten dimensional $E_8\times E_8$ superstring theory. We show how realistic phenomenology can emerge from this theory by supplementing it with the symmetry ${\cal R}\times {\cal U}(1)$, where ${\cal R}$ denotes a discrete `R'-symmetry. The well-known doublet-triplet splitting problem is resolved to `all orders' via the pseudo-Goldstone mechanism, and the GUT scale arises from an interplay of the Planck and supersymmetry breaking scales. The symmetry ${\cal R}\times {\cal U}(1)$ is also important for understanding the fermion mass hierarchies as well as the magnitudes of the CKM matrix elements. Furthermore, the well known MSSM parameter $\tan β$ is estimated to be of order unity, while the proton lifetime ($τ_p\sim 10^2τ_{pSU(5)}$) is consistent with observations. Depending on some parameters, $p\to Kμ^+ $ can be the dominant decay mode. Finally, the observed solar and atmospheric neutrino `anomalies' require us to introduce a `sterile' neutrino state. Remarkably, the ${\cal R}\times {\cal U}(1)$ symmetry protects it from becoming heavy, so that maximal angle $ν_μ$ oscillations into a sterile state can explain the atmospheric anomaly, while the solar neutrino puzzle is resolved via the small angle $ν_e-ν_τ$ MSW oscillations. The existence of some ($\sim 15 - 20% $ of critical energy density) neutrino hot dark matter is also predicted.

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arXiv1999

Neutrino Mixings and Fermion Masses in Supersymmetric SU(5)

We consider neutrino mixings in supersymmetric SU(5) supplemented by a U(1) flavor symmetry. In particular, we show how bi-maximal neutrino mixings can be realized. Two scenarios for implementing the small mixing angle MSW solution, with one involving a sterile state $ν_s$ and maximal $ν_μ-ν_s$ mixing to resolve the atmospheric anomaly, are also discussed. Finally, a new mechanism for eliminating the asymptotic relations $m^{(0)}_μ =m^{(0)}_s$ and $m^{(0)}_e=m^{(0)}_d$, while retaining $m^{(0)}_τ=m^{(0)}_b$, is presented. It employs `matter' multiplets in the $15+\bar{15}$ of SU(5), and is consistent with the various oscillation scenarios, as well as with the unification at $M_{GUT}$ of the three gauge couplings.

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arXiv1999

Atmospheric and Solar Neutrino Oscillations in \nuMSSM and Beyond

We show how a unified description of the various two-flavor neutrino oscillation solutions, allowed by the atmospheric and solar neutrino experiments, are naturally realized within the framework of $ν$MSSM (MSSM augmented with the seesaw mechanism) and beyond, especially grand unified theories. A general mechanism for achieving maximal mixing to resolve the atmospheric anomaly is discussed, and applied to the flipped SU(5) model. Except in the case of MSSM and SU(5), a light sterile neutrino is an inevitable consequence of our considerations. The bi-maximal neutrino mixing scenario is one of the options considered. Neutrino hot dark matter can arise in models with maximal $ν_μ-ν_s$ oscillations. A ${\cal U}(1)$ flavor symmetry, motivated by the charged fermion mass hierarchies and the magnitudes of the CKM matrix elements, plays a central role.

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arXiv1998

Neutrino Oscillations and Other Key Issues in Supersymmetric SU(4)_c \times SU(2)_L \times$ SU(2)_R

We try to gain an understanding of the recent Superkamiokande data on neutrino oscillations and several other important phenomenological issues within the framework of supersymmetric $SU(4)_c \times SU(2)_L \times SU(2)_R$ ($\equiv G_{422}$). By supplementing $G_{422}$ with a U(1)-${\cal R}$ symmetry, we can provide an explanation of the magnitude $M_G$ ($\sim 10^{16}$ GeV) of the $G_{422}$- symmetry breaking scale, resolve the MSSM $μ$ problem, and understand why proton decay has not been seen ($τ_p \gg 10^{34}$ yr). The family dependent ${\cal R}$ - symmetry also helps provide an explanation of the charged fermion mass hierarchies as well as the magnitudes of the CKM matrix elements. Several additional heavy states in the mass range $10^4-10^7$ GeV are predicted, and the MSSM parameter $\tan β$ turns out to be of order unity. The atmospheric neutrino problem is explained through $ν_μ-ν_τ$ mixing with $\sin^2 2θ_{μτ}\simeq 1$. The resolution of the solar neutrino puzzle is via the small angle MSW oscillations and necessarily requires a sterile neutrino $ν_s$ which, thanks to the ${\cal R}$ - symmetry, has a tiny mass.

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arXiv1998

Realistic GUT with Gauge Mediated Supersymmetry Breaking

We present an example of the gauge mediated SUSY breaking flipped SU(5) model. The messengers of the SUSY breaking are either only colour triplets which belong to the minimal content of the scalar supermultiplets or together with triplets as a messengers emerge the ordinary Higgs doublets. In both cases the model predicts light gauginos in respect of the squarks and sleptons, which could be tested in the nearest LEP experiments. In both cases ''all order`` solution of the doublet-triplet splitting problem is obtained, the $μ$-term of the order of 100 GeV is generated and the left handed neutrino masses are suppressed.

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arXiv1997

SUSY SU(6) GUT without Gauge Hierarchy Problem

A solution of the doublet-triplet splitting problem in the supersymmetric $SU(6)$ gauge theory is suggested. The `missing doublet' multiplet -- 175-plet of the $SU(6)$ group as well as the custodial $SU(2)_{cus}$ global symmetry play crucial role for achieving the doublet-triplet hierarchy. Two examples in which the doublet-triplet splitting occurs naturally are presented.

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arXiv1996

More missing VEV mechanism in supersymmetric SO(10) model

The anomalous gauge $U(1)_A$ symmetry which could emerge in the context of the string theories can be very useful ingredient towards builting the complete supersymmetric SO(10) model. We present an example of the $SO(10)\times U(1)_A$ model which provides the ``all order'' solution to the doublet-triplet splitting problem via the missing VEV mechanism -- the Planck scale corrections only can induce the mu-term naturally of order 1 TeV. An interesting feature of this model is that all relevant GUT scale VEVs are defined by the single dimensional parameter in the Higgs superpotential, so that the SO(10) symmetry breaks down to the MSSM practically at one step, without intermediate stages. The colour Higgsino mediated d=5 operators can be naturally suppressed. We also extend the model by implementing $U(1)_A$ as a horizontal symmetry for explaining the fermion mass and mixing pattern, and obtain a predictive texture for fermion masses. This model implies a moderate value of $\tanβ$ ($\sim 6-10$) and leads to five predictions for the low energy observables. It also leads to the neutrino masses and mixing pattern that could naturally explain both the atmospheric and solar neutrino problems. In addition, a remarkable interplay of the SO(10) and $U(1)_A$ symmetries guarantees an automatic R parity conservation at any order in $M_P^{-1}$, and also suppresses the Planck scale induced B and L violating d=5 operators to the needed level.

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arXiv1996

Anomalous U(1) symmetry and missing doublet SU(5) model

We present the supersymmetric $SU(5)$ models which provide a simple ``all order'' solution to the doublet-triplet splitting problem through the missing doublet mechanism. The crucial role is played by the anomalous $U(1)_A$ gauge symmetry and no additional discrete or global symmetries are needed. Remarkably, such models can be realized even if the 75-plet Higgs is replaced by the standard 24-plet. The same $U(1)_A$ symmetry can also guarantee an exact or approximate conservation of R parity, by suppressing the B and L violating operators to the needed level. The neutrino masses and the proton decay via $d=5$ operators are also examined. We also extend the model by incorporating $U(1)_A$ as a horizontal symmetry for explaining the fermion mass and mixing hierarchy. Interestingly, in this scheme the necessary mild violation of the troublesome $SU(5)$ degeneracy between the down quark and the charged lepton masses can be induced by certain R-parity violating operators.

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