arXiv subjects
Publications and source records attributed to Zurab Tavartkiladze.
Within a democratic approach based on discrete symmetries, we show how the charged lepton mass hierarchies and bilarge neutrino mixings can be realized. For the third mixing angle we find $\te_{13}\sim \sq{\fr{\De m_{\rm sol}^2}{\De m_{\rm atm}^2}}\sim 0.1-0.2$.
We present a five dimensional supersymmetric SO(10) model compactified on an orbifold $S^{(1)}/Z_2\tm Z_2'$. The gauge symmetry $G_{422}\equiv SU(4)_c\tm SU(2)_L\tm SU(2)_R$, realized on one of the fixed points (branes), is spontaneously broken to the MSSM via the higgs mechanism. Employing a flavor ${\cal U}(1)$ symmetry and suitably extending the 'matter' sector enables us to understand large mixings in the neutrino sector via a democratic approach, versus the small CKM mixings. A residual ${\cal R}$-symmetry on $G_{422}$ brane helps eliminate the troublesome dimension five nucleon decay, while the ${\cal U}(1)$ symmetry plays an essential role in suppressing dimension six decay. For rare leptonic decays we expect ${\rm BR}(μ\to e\ga)\sim {\rm BR}(τ\to μ\ga)\sim {\rm BR}(τ\to e\ga)$.
The possibility of appearance of GUT precursors near the TeV scale (suggested by Dienes-Dudas-Gherghetta) is addressed within 5D GUTs compactified on an $S^{(1)}/Z_2\tm Z_2'$ orbifold. For a low compactification scale (large radius), there is a significant non universal logarithmic contribution in the relative running of gauge couplings. This within 5D SU(5), with the minimal field content, gives wrong prediction for $\al_3(M_Z)$ unless one goes beyond the minimal setting. The realization of the light precursors' idea thus requires some specific extensions. As a scenario alternative to SU(5) we also consider an SU(6) orbifold GUT, whose minimal non SUSY version gives natural unification. In all the presented unification scenarios with light precursors, various GUT scales are realized. This allows the model to be naturally embedded in either heterotic or Type ${\rm I}$ string theories.
We discuss the variation of gauge couplings in time in the framework of orbifold constructions, due to a change of the extra compact dimension's size. Models with gauge coupling unification allow to estimate the variation of the strong coupling constant $\al_3$ and to relate it to a variation of $α_{em}$. The extra-dimensional construction turns out to be crucial for the model to be compatible with data. Within the presented 5D scenarios, the tower of KK states significantly affects gauge coupling running, leads to low scale unification, and provides a suppression of the $\al_3(M_Z)$ variation.
Working with a ${\cal U}(1)$ flavor symmetry, we show how the hierarchical structure in the charged fermion sector and a democratic approach for neutrinos that yields large solar and atmospheric neutrino mixings can be simultaneously realized in the MSSM framework. However, in SU(5) due to the unified multiplets we encounter difficulties. Namely, democracy for the neutrinos leads to a wrong hierarchical pattern for charged fermion masses and mixings. We discuss how this is overcome in flipped SU(5).
We study gauge coupling unification and various phenomenological issues, such as baryon number conservation, the $μ$ problem and neutrino anomalies, within SUSY 5D orbifold models. The 5D MSSM on an $S^{(1)}/Z_2$ orbifold with 'minimal' field content does not lead to low scale unification, while some of its extensions can give unification near the multi TeV scale. Within the orbifold SU(5) GUT, low scale unification can not be realized due to full SU(5) multiplets participating in the renormalization above the compactification scale. As alternative examples, we construct 5D N=1 SUSY Pati-Salam $SU(4)_c\tm SU(2)_L\tm SU(2)_R\equiv G_{422}$ and flipped $SU(5)\tm U(1)\equiv G_{51}$ GUTs [both maximal subgroups of SO(10)] on an $S^{(1)}/Z_2\tm Z_2'$ orbifold. New examples of low scale unifications within $G_{422}$ are presented. For $G_{51}$ the unification scale is shown to be necessarily close to $\sim 10^{16}$ GeV. The possible influence of brane couplings on the gauge coupling unification is also outlined. For the resolution of the various phenomenological problems extensions with a discrete ${\cal Z}$ symmetry turn out to be very effective.
We investigate supersymmetric $SU(4)_c\times SU(4)_{L+R}$ theory in 5 dimensions whose compactification on a $S^{(1)}/Z_2$ orbifold yields N=1 supersymmetric $SU(4)_c\times SU(2)_L\times SU(2)_R$ supplemented by a $\tl{U}(1)$ gauge symmetry. We discuss how the $μ$ problem is resolved, a realistic Yukawa sector achieved, and a stable proton realized. Neutrino masses and oscillations are also briefly discussed.
The explanation of various observed phenomena such as large angle neutrino oscillations, hierarchies of charged fermion masses and CKM mixings, and apparent baryon number conservation may have a common origin. We show how this could occur in 5D SUSY SU(5) supplemented by a ${\cal U}(1)$ flavor symmetry and additional matter supermultiplets called 'copies'. In addition, the proton decays into $p\to Kν$, with an estimated lifetime of order $10^{33}-10^{36}$ yrs. Other decay channels include $Ke$ and $Kμ$ with comparable rates. We also expect that BR$(μ\to eγ)\sim $BR$(τ\to μγ)$.
We construct a 5D SUSY SU(6) GUT on an $S^{(1)}/Z_2\tm Z_2'$ orbifold. The first stage of gauge symmetry breaking occurs through compactification and a specific selection of boundary conditions. Additional symmetries play a crucial role for the generation of $μ$ and $Bμ$ terms of appropriate values: with a $SU(2)_{cus}$ custodial symmetry the Higgs doublets naturally emerge as massless pseudo-Goldstone bosons in the unbroken SUSY limit. After SUSY breaking they get masses of the order of the weak scale. If instead of $SU(2)_{cus}$ a discrete $Z_5$ symmetry is applied the Higgs doublet's masses are still adequately suppressed, but they are not pseudo-Goldstones. The $Z_5$ discrete symmetry also can be very important for GUT scale generation and an all order hierarchy. Fermion masses are naturally generated and nicely blend with additional symmetries. In the considered scenario unification of the three gauge couplings occurs near $10^{16}$ GeV.
We discuss how an anomalous U(1) symmetry when appended to MSSM and SUSY GUTs [e.g. SU(5)] can help overcome a variety of puzzles related to charged fermion masses and mixings, flavor changing processes, proton decay and neutrino oscillations. Proton lifetime for SU(5) GUT, in particular, is predicted in a range accessible to the ongoing or planned searches.
We consider a 5D SUSY $SU(3)_c\times SU(2)_L\times U(1)_Y\times {\cal U}(1)$ model compactified on an $S^{(1)}/Z_2$ orbifold. To cancel anomalies arising from the presence of ${\cal U}(1)$, we employ a Chern-Simons term and also chiral fields which could reside on the brane or in the bulk depending on the model. The presence of ${\cal U}(1)$ symmetry leads to baryon number conservation, gives rise to matter parity, and permits satisfactory neutrino masses and mixings even for a low fundamental scale. The brane Fayet-Iliopoulos D-terms naturally break ${\cal U}(1)$, leaving N=1 SUSY unbroken in 4 dimensions.
Within low scale theories traditional see-saw and scalar triplet mechanisms, for neutrino mass suppression, do not work out anymore and for realistic model building some new ideas are needed. In this paper we suggest mechanism, different from existing ones, which provides natural suppression of the neutrino masses. The mechanism is realized through extended scalars of 4, 5 or 6 dimensional $SU(2)_L$ multiplets. Scenario, with fundamental mass scale $M_f$ in a $\sim 10^{3}$ TeV range, requires 4-plets guaranteeing neutrino masses $\stackrel{<}{\sim}1$ eV. For theories with $M_f= few \cdot 10$ TeV 5-plets should be involved, while in scenarios with $M_f=$ few TeV, 6-plets could be efficient. The considered mechanism could be successfully applied also for supersymmetric theories, building scenarios with various values of low $M_f$. Within considered models we also address the question of gauge coupling unification. For low scale unification, existence of compact extra dimensions turns out to be crucial. Due to additional scalar multiplets, some new examples of unification are found for both - non SUSY and SUSY cases. Within non SUSY scenarios introduced $SU(2)_L$ scalars take advantage and are important for successful unification.
Mechanism for generation of suppressed neutrino masses, within low scale theories, is considered. The mechanism do not have extradimensional nature and is realized through extended $SU(2)_L$ scalar multiplets. Latters, in some cases, are also crucial for successful low scale unification.
We present an example of SUSY SU(6) GUT, which predicts an excellent value for $\al_s(M_Z)(\simeq 0.119)$, in comparison with the value $\al_s^0(M_Z)\simeq 0.126$ of minimal SUSY SU(5). A crucial role is played by the vectorlike multiplets from the matter sector, whose masses lie below the GUT scale. For a realistic pattern of fermion masses, the adjoint scalar of SU(6) has VEV along the $SU(4)\times SU(2)\times U(1)$ direction. This also offers a natural resolution of the doublet-triplet (DT) splitting through the pseudo Goldstone Boson mechanism.
We discuss how a three-brane with an associated non-factorizable (warped) geometry can emerge from a five dimensional theory of gravity coupled to a complex scalar field. The system possesses a discrete $Z_2$ symmetry, whose spontaneous breaking yields an 'axionic' three-brane and a warped metric. Analytic solutions for the wall profile and warp factor are presented. The Kaluza-Klein decomposition and some related issues are also discussed.
We describe how bi-maximal neutrino mixing can be realized in realistic models based on MSSM and SUSY GUTs such as SU(5) and SO(10). A crucial role is played by an anomalous ${\cal U}(1)$ flavor symmetry, which also helps understand the observed charged fermion mass hierarchies and the magnitudes of the CKM matrix elements. While in MSSM a variety of solutions for the solar neutrino puzzle are possible, SUSY SU(5) and SO(10) only permit the large mixing angle MSW solution. Models in which the ${\cal U}(1)$ symmetry also mediates SUSY breaking allow both the large mixing angle and the low MSW solutions. We also present renormalization group studies for the neutrino mass matrix, generated through the ${\cal U}(1)$ flavor symmetry. Our analysis shows that renormalization does not change the desirable picture of bi-maximal mixing.
We present a scenario which naturally provides bi-maximal neutrino mixings for a simultaneous explanation of the recent atmospheric and solar neutrino data. A crucial role is played by an anomalous flavor ${\cal U}(1)$ symmetry, which is also important for a natural understanding of charged fermion mass hierarchies and magnitudes of the CKM matrix elements. Within MSSM the solar neutrino problem can be resolved either through vacuum oscillations or the large mixing angle MSW solution. In supersymmetric GUTs such as SU(5) and SO(10) the MSW solution is realized. If the flavor ${\cal U}(1)$ also mediates supersymmetry breaking, the vacuum solution in MSSM is eliminated, and only the large mixing angle MSW solution survives.
We discuss how realistic supersymmetric models can be constructed by employing an anomalous ${\cal U}(1)$ flavor symmetry which also mediates supersymmetry breaking. A judicious choice of ${\cal U}(1)$ charges enables the first two squark families to be sufficiently heavy ($\stackrel{>}{_\sim}10$ TeV), so that flavor changing neutral currents as well as dimension five nucleon decay are adequately suppressed. Using the SU(5) example, the charged fermion mass hierarchies, magnitudes of the CKM matrix elements, as well as the observed neutrino oscillations are simultaneously accommodated. We estimate the proton lifetime to be $τ_p\sim 10^3\cdot τ_p[{\rm minimal} SU(5)]$, with the decay mode $p\to Kμ$ being comparable to $p\to Kν_{μ, τ}$.