From the string partition function, we discuss the mass-shell and GSO projection conditions valid for Kaluza-Klein (KK) as well as massless states in the heterotic string theory compactified on a nonprime orbifold. Based on the obtained conditions we construct a 4D string standard model, which is embedded in a 6D SUSY GUT by including KK states above the compactification scale. We discuss the stringy threshold corrections to gauge couplings, including the Wilson line effects.
We discuss how to calculate Yukawa couplings in string-derived orbifold GUTs. As an application we investigate the quark mass hierarchies in these models. An interplay of different mechanisms derived from string theory leads to an interesting pattern. We discuss concrete examples in the context of heterotic orbifold compactifications.
The gauge coupling unification is one of main motivations in the split-SUSY scenario, and the existence of the grand unified theories (GUTs) is assumed. We examine how to realize split-SUSY mass spectrum in the context of GUTs and find that the construction of split-SUSY GUTs is by no means straightforward. With R-symmetry breaking sources in the GUT sector, GUT particles play a role of the messengers in the gauge mediation scenario and their contributions to gaugino masses can be sizable. We find the upper bound on soft scalar masses of O(10^{10}) GeV from consistency for constructing the spl…
Non-renormalizable operators both account for the failure of down quark and charged lepton Yukawa couplings to unify and reduce the proton decay rate via dimension-five operators in minimal SUSY SU(5) GUT. We extend the analysis to SUSY SO(10) GUT models.
The SUSY-GUT paradigm is the most promising scenario for the physics beyond the Standard Model. After the LHC run I, it is of interest to reanalyze the room still remaining for SUSY-GUT inspired models and to study the limits on the SUSY mass spectrum. Assuming one step unification of gauge couplings, under some natural requirements we have obtained the energy upper bound for the observation of SUSY phenomenology. We found that in the SUSY-GUT framework the mass of lightest gluino or Higgsino cannot be larger than about 20 TeV.
It is explained why excessive mu to e gamma can be a problem in SUSY GUT see-saw models of neutrino mass, and ways that this problem might be avoided are discussed.
In 5D SUSY GUTs, wave-function localization permits to reproduce flavour hierarchy. As this mechanism also acts on SUSY breaking parameters, it can potentially solve the SUSY flavour problem. We carry out an analysis of the Holographic Grand Unification framework, where we take properly into account effects of matrix anarchy. In this contribution, we focus on brane-localized SUSY breaking and its consequences.
While the observation of nucleon decay would be a smoking gun of Grand Unified Theories (GUTs) in general, the ratios between the decay rates of the various channels carry rich information about the specific GUT model realization. To investigate this fingerprint of GUT models in the context of supersymmetric (SUSY) GUTs, we present the software tool \texttt{SusyTCProton}, which is an extension of the module \texttt{SusyTC} to be used with the \texttt{REAP} package. It allows to calculate nucleon decay rates from the relevant dimension five GUT operators specified at the GUT scale, including th…
It is shown that a realistic SUSY SU(6) GUT can dynamically generate the GUT scale and solve at the same time the doublet-triplet splitting problem. The cosmological implications of such a model are briefly reviewed.
Constraints from flavour changing neutral currents are discussed in the context of predictive Grand Unified Supersymmetric Theories. Uncertainties in the estimation of their amplitudes are minimized by using a successful mass matrix ansatz which predicts the arbitrary parameters of the Standard Model. Furthermore, Renormalization Group Equations are used in order to express the sparticle masses involved, in terms of the gaugino mass $m_{1/2}$, the universal scalar mass $m_0$ and the trilinear coupling $A$ at the GUT scale. Modifications in the low energy expressions for the squark masses due t…
The neutrino flavor mixing may induce rich flavor and CP violating phenomena in the SUSY GUTs. In this paper we discuss the hadronic EDMs and the correlation among low-energy processes induced by the mixings between second and third generations in the SUSY SU(5) GUT with the right-handed neutrinos.
I discuss an evolution of SUSY GUT model building, starting with the construction of 4d GUTs, to orbifold GUTs and finally to orbifold GUTs within the heterotic string. This evolution is an attempt to obtain realistic string models, perhaps relevant for the LHC. This review is in memory of the sudden loss of Julius Wess, a leader in the field, who will be sorely missed.
In this paper we analyze Yukawa unification in a three family SO(10) SUSY GUT. We perform a global $χ^2$ analysis and show that SUSY effects do not decouple even though the universal scalar mass parameter at the GUT scale, $m_{16}$, is found to lie between 15 and 30 TeV with the best fit given for $m_{16} \approx 25$ TeV. Note, SUSY effects don't decouple since stops and bottoms have mass of order 5 TeV, due to RG running from $M_{GUT}$. The model has many testable predictions. Gauginos are the lightest sparticles and the light Higgs boson is very much Standard Model-like. The model is consist…
On the evaluation of $\tanβ$ is revisited by the method of the renormalization group with the criteria of the bottom-tau unification in the SUSY SU(5) GUT model. Among the conventional supersymmetric theories, an energy-scale constant $M_{SUSY}$ is introduced by-hand to decouple the lower energy-scale region from the effects of the supersymmetric particles. Provided that $M_{SUSY}$ really exists, only small $\tanβ \simeq 2$ is allowed theoretically. While, medium value as $\tanβ = 6 \sim 25$ is also supported if $M_{SUSY}$ is vanished away from the model.
The neutrino mass problem in $SU(4) \times SU(2)_{L} \times SU(2)_{R}$ SUSY GUT obtained from the compactification of $E_{8} \times E_{8}$ heterotic string is analyzed. The estimated values of the neutrino masses and mixing angles can explain the experimental data on solar neutrino flux.
We study soft SUSY breaking terms in heterotic M-theory. We show that both weakly and strongly coupled heterotic string models lead to the same relations of soft SUSY breaking terms, $A=-M$ and $m^2 = M^2/3$, up to $O((αT/S)^2)$.
We study the influence of messenger Yukawa couplings and top, bottom and $τ$ Yukawa couplings on the proton lifetime in SU(5) Supersymmetric GUT with dynamical supersymmetry breaking mechanism due to Dine and Nelson.
The idea of GUT implies that the universe went through a series of phase transitions during which topological defects are expected to form. We investigate here the genericity of cosmic strings formation in realistic SUSY GUTs models. We conclude that all acceptable symmetry breaking schemes produce cosmic strings after the last inflationary phase. Generically, as they form at the end of inflation, they have a mass of order of the GUT scale. Since cosmological data coming from CMB measurements do not show evidence for such strings, they constrain GUT scale physics.
The existing estimation of the Electric Dipole Moment(EDM) of the neutron in the SUSY SU(5) GUT model was quite smaller than one in the MSSM, despite of its increased degree of freedom. This paradoxical result can be resolved by appropriately estimating the CP-violation in the Higgs sector. As a result, the neutron EDM in this model is estimated lager than the existing one as expected.
Unification of GUT-scale t-b-τYukawa couplings is a significant feature of simple SO(10) SUSY GUTs. Here we present the results of a search that used the Markov Chain Monte Carlo technique to investigate regions of Yukawa unification and WMAP-compatible dark matter relic density in SO(10)-like MSSM parameter spaces. We mention the possible LHC signatures of Yukawa unified scenarios and discuss the consequences for dark matter.
In order to evade the proton decay which appears when the Zee model is embedded into a SUSY GUT scenario with R-parity violation, a new idea based on a discrete Z_2 symmetry is proposed. Under the symmetry Z_2, the quark and lepton mass matrices are tightly constrained. The admissible form of the radiatively-induced neutrino mass matrix is investigated.
Grand Unified Theories (GUTs) can feature predictions for the ratios of quark and lepton Yukawa couplings at high energy, which can be tested with the increasingly precise results for the fermion masses, given at low energies. To perform such tests, the renormalization group (RG) running has to be performed with sufficient accuracy. In supersymmetric (SUSY) theories, the one-loop threshold corrections (TC) are of particular importance and, since they affect the quark-lepton mass relations, link a given GUT flavour model to the sparticle spectrum. To accurately study such predictions, we extend…
We propose the Fritzsch-Branco-Silva-Marcos type fermion mass matrix, which is a typical texture in the nearest-neighbor interaction form, in SU(5) GUT. By evolution of the mass matrices with SU(5) GUT relations in the minimal SUSY standard model, we obtain predictions for the unitarity triangle of CP violation as well as the quark flavor mixing angles, which are consistent with experimental data, in the case of \tanβ\simeq 3.
We show that the Polonyi problem is solved in the minimum SUSY-GUT model in which a self-coupling strength for a heavy Higgs $Σ$, $λΣ^{3}$, is very small $λ\sim 10^{-6}$. It is stressed that with this small $λ$ the mass of the physical $Σ$ becomes $m_Σ \sim 10^{12}\GEV$ and the unification scale is raised up to the gravitational one, $M\simeq 2\times 10^{18}\GEV$. A potential problem, however, is also pointed out in this GUT model.
Grand Unified Theories (GUTs) are attractive candidates for more fundamental elementary particle theories. They can not only unify the Standard Model (SM) interactions but also different types of SM fermions, in particular quarks and leptons, in joint representations of the GUT gauge group. We discuss how comparing predictive supersymmetric GUT models with the experimental results for quark and charged lepton masses leads to constraints on the SUSY spectrum. We show an example from a recent analysis where the resulting superpartner masses where found just beyond the reach of LHC run 1, but ful…
The magic couple of SUSY and GUT still appears the most elegant and predictive physics concept beyond the Standard Model. Since up to now LHC found no evidence for supersymmetric particles it becomes of particular relevance to determine an upper bound of the energy scale they have to show up. In particular, we have analyzed a generic SUSY-GUT model assuming one step unification like in SU(5), and adopting naturalness principles, we have obtained general bounds on the mass spectrum of SUSY particles. We claim that if a SUSY gauge coupling unification takes place, the lightest gluino or Higgsino…
An analysis is made on bottom-tau Yukawa unification in supersymmetric (SUSY) SU(5) grand unified theory (GUT) in the framework of minimal supergravity, in which the parameter space is restricted by some experimental constraints including Br(b to s gamma) and muon g-2. The bottom-tau unification can be accommodated to the measured branching ratio Br(b to s gamma) if superparticle masses are relatively heavy and higgsino mass parameter μis negative. On the other hand, if we take the latest muon g-2 data to require positive SUSY contributions, then wrong-sign threshold corrections at SUSY scale …
By using the anomalous magnetic and electric dipole moments of the $τ$ lepton in an effective lagrangian approach to the new physics, we investigate the lepton flavor violation (LFV) decays, $l\to l'γ$, and $μ,τ$ anomalous magnetic and electric dipole moments in a lepton mass matrices ansatz which induced by SUSY GUT. We put very stringent constraints LFV decays and $τ$ anomalous magnetic and electric dipole moments.
We propose an $SO(10)$ supersymmetric grand unified theory (SUSY GUT), where the $SO(10)$ gauge symmetry breaks down to $SU(3)_c \times SU(2)_L \times U(1)_Y\times U(1)_{X}$ at the GUT scale and $U(1)_X$ is radiatively broken at the SUSY-braking scale. In order to achieve the observed Higgs mass around $126$ GeV and also to satisfy constraints on flavor- and/or CP-violating processes, we assume that the SUSY-breaking scale is $O(100)$ TeV, so that the $U(1)_X$ breaking scale is also $O(100)$ TeV. One big issue in the SO(10) GUTs is how to realize realistic Yukawa couplings. In our model, not o…
We investigate the effect of supersymmetric (SUSY) threshold corrections on the values of the running quark and charged lepton masses at the GUT scale within the large $\tanβ$ regime of the MSSM. In addition to the typically dominant SUSY QCD contributions for the quarks, we also include the electroweak contributions for quarks and leptons and show that they can have significant effects. We provide the GUT scale ranges of quark and charged lepton Yukawa couplings as well as of the ratios $m_μ/m_s$, $m_e/m_d$, $y_τ/y_b$ and $y_t/y_b$ for three example ranges of SUSY parameters. We discuss how t…
An SO(10) SUSY GUT model which leads to maximal atmospheric neutrino mixing and the LMA solar neutrino solution, developed in collaboration with S.M. Barr, is briefly described. Since the model is quantitatively predictive, it can be used to assess the need for a neutrino factory, as shown in collaboration with S. Geer.
We analyze finite supersymmetric SU(5) GUT taking into account the problem in the Higgs potential and threshold corrections to gauge and Yukawa couplings at GUT and SUSY scales which is important in case of large $\tan β$ model. We find that even with these finiteness conditions, which are very restrictive, there are parameter regions where low-energy experimental values are consistently reproduced and the Higgs potential actually realizes both constraints for large $\tan β$ and radiative electroweak symmetry breaking, provided that a free parameter is introduced in the boundary condition of t…
In the minimal SUSY SU(5) GUT with $O(1)$ TeV SUSY particles and $O(1)$ or below self-coupling for the GUT-breaking Higgs field, the width of the dimension-6 proton decay is suppressed below the reach of Hyper-Kamiokande. In this paper, we point out that a SUSY SO(10) GUT which adopts only ${\bf 45}_{\rm H}+{\bf 16}_{\rm H}+{\bf \overline{16}}_{\rm H}$ GUT-breaking Higgs fields leads to an enhanced dimension-6 proton decay width detectable at Hyper-Kamiokande. The enhancement is because the SU(5)-breaking VEV of ${\bf 45}_{\rm H}$ arises due to Planck-suppressed terms, $W\propto ({\bf 45}_{\rm…
The (B_{d}\longrightarrow ΦK_{s}) process is without tree level decay amplitude . Then the SUSY contributions may be significant . We calculate the neutralino and gluino penguin contributions to the CP violating phase in (SU(5) ) grand unified theory with right-handed neutrino (SU(5)_{RN}) . We find that the SUSY contribution may change the phase in (B_{d}\longrightarrow ΦK_{s} ).
I first emphasize the importance of searching for nucleon decay in the context of supersymmetric models. The status of minimal SUSY SU(5) model is reviewed, which can be definitively ruled out by a combination of superKamiokande and LEP-2 experiments. Non-minimal models may provide some suppression in the nucleon decay rates, but there is still a good chance for superKamiokande. I point out that the operators suppressed even by the Planck-scale are too large. We need a suppression mechanism for the operators at the level of $10^{-7}$, and the mechanism, I argue, may well be a flavor symmetry. …
Among three typical energy scales, a neutrino mass scale ($m_ν\sim$ 0.1 eV), a GUT scale ($M_{GUT}\sim 10^{16}$ GeV), and a TeV-scale ($M_{NP}\sim$ 1 TeV), there is a fascinating relation of $M_{NP}\simeq \sqrt{m_ν\cdot M_{GUT}}$.The TeV-scale, $M_{NP}$, is a new physics scale beyond the standard model which is regarded as "supersymmetry" (SUSY) in this letter. We investigate phenomenology of SUSY SU(5) GUT with neutrinophilic Higgs, which realizes the above relation dynamically as well as the suitable magnitude of Dirac mass, $m_ν$, through a tiny vacuum expectation value of neutrinophilic Hi…
We discuss the fermion mass problem in SUSY GUTs, including such ideas as texture zeroes, and Georgi-Jarlskog textures. We focus on a specific supersymmetric model based on the gauge group $SU(4)\otimes SU(2)_L \otimes SU(2)_R$. In this model the gauge group is broken to that of the standard model at $10^{16}$ GeV, and supersymmetry is broken at low-energy. The model may be regarded as a ``surrogate SUSY GUT'', and has several advantages over the $SU(5)$ and $SO(10)$ SUSY GUTs, such as the absence of the doublet-triplet splitting problem, and a simpler Higgs sector which does not involve any l…
We discuss how flavour GUT models in the context of supergravity can be completed with a simple SUSY breaking sector, such that the flavour-dependent (non-universal) soft breaking terms can be calculated. As an example, we discuss a model based on an SU(5) GUT symmetry and $A_4$ family symmetry, plus additional discrete "shaping symmetries" and a $\mathbb{Z}_4^\mathrm{R}$ symmetry. We calculate the soft terms and identify the relevant high scale input parameters, and investigate the resulting predictions for the low scale observables, such as flavour violating processes, the sparticle spectrum…
We propose a natural framework of SU(5) supersymmetric grand unified theory with the minimal particle contents, which does not contain dimension five proton decay operators. The suitable fermion mass hierarchy can be reproduced by higher dimensional operators of an adjoint Higgs field which breaks SU(5) gauge symmetry.
The ratio of the partial widths of some dimension-5 proton decay modes can be predicted without detailed knowledge of SUSY particle masses, and thus allows us to experimentally test various SUSY GUT models without discovering SUSY particles. In this paper, we study the ratio of the partial widths of the $p\to K^0μ^+$ and $p\to K^+\barν_μ$ decays in the minimal renormalizable SUSY $SO(10)$ GUT, under only a plausible assumption that the 1st and 2nd generation left-handed squarks are mass-degenerate. In the model, we expect that the Wilson coefficients of dimension-5 operators responsible for th…
In the minimal SU(5) SUSY GUT $d =5$ operators lead to $p\to K^+ ν$ decay with the proton life time of the order of $10^{28}$ years for the natural choice of the parameters of the theory. This value is in strong contradiction with experimental bound $τ_{p\to Kν} > 10^{32}$ years. $d=5$ operators are induced by colored Higgsino exchanges and are closely (through SU(5) and super symmetry) related to another wrong prediction of SU(5) SUSY GUT: $m_d /m_s = m_e /m_μ$. We demonstrate how in the model where reasonable pattern of quark and lepton masses and CKM mixing angles are obtained proton decay …
Using the freedom in SO(10) GUT's one can generalize the existing models without changing the mass spectrum of fermions to obtain a significant suppression of proton decay resulting from the baryon number violating operators of dimension 5. In some limiting cases, their contributions can be made negligible compared to the dimension 6 operators resulting from the heavy gauge bosons exchange.
Certain supersymmetric grand unified models predict that the coefficients of the quadratic terms in the MSSM Higgs potential should be degenerate at the GUT scale. We discuss some examples for such models, and we analyse the implications of this peculiar condition of a GUT-scale degenerate Higgs mass matrix for low-scale MSSM phenomenology. To this end we explore the parameter space which is consistent with existing experimental constraints by means of a Markov Chain Monte Carlo analysis.
Motivated by the recent measurements of the B_s-\bar{B}_s mass difference from the D0 and CDF collaborations, we probe new physics effects in the B_q-\bar{B}_q mixing within the context of the supersymmetric grand unified model (SUSY GUT). We find that new physics effects in B_{s(d)}-\bar{B}_{s(d)} mixing lead to the correlated information in the branching fractions of the lepton flavor violating decays, which may serve as a test of the SUSY GUT. We also discuss the implication of such new physics effects on the quark-lepton complementarity in the neutrino mixings.
Flavor changing neutral current and lepton flavor violating processes are studied in the SU(5) SUSY-GUT with right-handed neutrino supermultiplets. Using input parameters motivated by neutrino oscillation, it is shown that the time-dependent CP asymmetry of $b \to s γ$ can be as large as 20%. We also show that the $B_s$-$\bar{B}_s$ mixing can be significantly different from the standard model prediction.
It is recently announced by the {\bf Ut}{\it fit} collaboration that the CP phase of the $B_s$ mixing amplitude, $ϕ_{B_s}$, deviates more than $3 σ$ from the standard-model prediction. In this paper we discuss how large correction to $ϕ_{B_s}$ is possible in the supersymmetric SU(5) ground unified model (SUSY SU(5) GUT) with right-handed neutrinos. Here, we assume the supergravity-like boundary condition for the SUSY-breaking terms. We found that the 95% probability region derived by the {\bf Ut}{\it fit} collaboration is marginal in this model.
I consider the superfield derivation of the effective theory of softly broken supersymmetry below the GUT scale. I point out the role of supergauge invariance in determining the form of the result, which is rather restricted in interesting classes of models. As an example I discuss sfermion mass splittings for matter embedded in a single GUT multiplet. Interesting differences arise between the cases of $SU(5)$, $SO(10)$ and $E_6$.
In this work we re-examine the correlation between B(d,s)-anti-B(d,s) mixing and Lepton Flavour Violation in the light of recent experimental measurements in the $B_s$ system. We perform a generic SUSY analysis of the allowed down squark mass insertion parameter space. In the SUSY GUT scenario this parameter space is then used to make predictions for LFV branching ratios. We find that the recent measurement for the CP phase $ϕ_s$ excludes the lowest rates for tau --> mu + gamma and provides a lower bound of ~ 3E-9 for tan beta = 10. Future experimental improvements in the bound on tau --> mu +…
In the SUSY SU(5) GUT with the right-handed neutrinos, the neutrino Yukawa coupling induces the flavor-violating mass terms for the right-handed down squarks and left-handed sleptons, and they lead to imprint on the flavor physics in the hadronic and leptonic sectors. In this paper we study CP violation in $B_d^0$ and $B_s^0$, which is induced by the tau-neutrino Yukawa coupling. In particular, we notice the correlation of the CP asymmetries in $B_d^0\to ϕK_s$ ($S_{ϕK_s}$) and $B_s^0\to J/ψϕ$ ($S_{J/ψϕ}$) with other observables, such as $Br(τ\toμγ)$, the muon EDM ($d_μ$), and the mixing-induce…
We briefly review the GIFT (Goltstones instead of Fine Tuning) mechanism which provides a promising solution to the doublet-triplet splitting problem and some other puzzles of the supersymmetric grand unification as are the $μ$-problem, the fermion mass problem, etc. It can be naturally implemented by extending the minimal SUSY SU(5) model to the gauge SU(6) theory.
We show how approximate Minimal Flavour Violation (MFV) can emerge from an SU(5) Supersymmetric Grand Unified Theory (SUSY GUT) supplemented by an S4 x U(1) family symmetry, which provides a good description of all quark and lepton (including neutrino) masses, mixings and CP violation. Assuming a SUSY breaking mechanism which respects the family symmetry, we calculate in full explicit detail the low energy mass insertion parameters in the super-CKM basis, including the effects of canonical normalisation and renormalisation group running. We find that the very simple family symmetry S4 x U(1) i…
The horizontal symmetry $U(3)_H$ can greatly help in solving the flavor problems in the supersymmetric grand unification. We consider the $SU(5)\times U(3)_H$ model and show that it leads to the remarkable relations between the fermion mass matrices and the soft SUSY breaking terms. Dangerous supersymmetric contributions to the flavor-changing phenomena are naturally suppressed. The possible extensions to the $SO(10)\times U(3)_H$ model are also outlined.
In this paper, we calculate neutron and proton decay rates and branching ratios in a predictive SO(10) SUSY GUT which agrees well with low energy data. We show that the nucleon lifetimes are consistent with the experimental bounds. The nucleon decay rates are calculated using all one-loop chargino and gluino dressed diagrams regardless of their chiral structure. We show that the four-fermion operator $C_{jk} (u_R {d_j}_R)({d_k}_L {ν_τ}_L)$, commonly neglected in previous nucleon decay calculations, not only contributes significantly to nucleon decay, but, for many values of the initial GUT par…
We propose a model with $A_4$ flavor symmetry for leptons and quarks in the framework of supersymmetric SU(5) grand unified theory (GUT). The running masses of quarks and charged leptons at GUT scale ($\sim 10^{16}$ GeV) are realized by the adjoint 24-dimensional Higgs multiplet and additional gauge singlet scalar fields including flavons. In this paper, we focus on a result of the quark and charged lepton masses and quark mixing since our present model is known to reproduce recent experimental results of the neutrino mass and oscillation. Those results are showed numerically.
We analyse the complementarity between Lepton Flavour Violation (LFV) and LHC experiments in probing the Supersymmetric (SUSY) Grand Unified Theories (GUT) when neutrinos got a mass via the see--saw mechanism. Our analysis is performed in an SO(10) framework, where at least one neutrino Yukawa coupling is necessarily as large as the top Yukawa coupling. Our study thoroughly takes into account the whole RG running, including the GUT and the right handed neutrino mass scales, as well as the running of the observable neutrino spectrum. We find that the upcoming (MEG, SuperKEKB) and future (PRISM/…
Proton decay is one of the most important predictions of the grand unified theory (GUT). In the supersymmetric (SUSY) GUT, proton decays via the dimension-five operators need to be suppressed. In the $SO(10)$ model where ${\bf 10}+\overline{\bf 126}$ Higgs fields couple to fermions, neutrino oscillation parameters including the CP-violating Pontecorvo-Maki-Nakagawa-Sakata (PMNS) phase can be related to the Yukawa couplings to generate the dimension-five operators in the unified framework. We show how the suppressed proton decay depends on the PMNS phase, and stress the importance of the precis…
We examined the neutrino sector in E6 x SU(2)F SUSY GUT with spontaneous CP violation. At a glance, the discrete symmetry, which is introduced in order to solve the SUSY CP problem, constrains the allowed operators too strongly for the neutrino sector to be consistent with the experimental data, i.e., the mu neutrino becomes massless as commented in the previous paper. We showed that this issue can be solved if some operators are taken into account. And we saw that such operators do not play an important role in studying quark and charged lepton sectors. The predictions on the neutrino masses …
In supersymmetric (SUSY) models the misalignment between fermion and sfermion families introduces unsuppressed flavor-changing processes. Even if the mass parameters are chosen to give no flavor violation, family dependent radiative corrections make this adjustment not stable. In particular, due to the observed large neutrino mixings and potentially large neutrino Yukawa couplings, sizable lepton flavor violation (LFV) is expected. After introducing the basic concepts, the framework and the main assumptions, we report on a recent study of rare leptonic decays in a class of SUSY-GUT models with…
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.
