Generic SO(10) GUT models suffer from the problem that Planck scale induced non-renormalizable proton decay operators require extreme suppression of their couplings to be compatible with present experimental upper limits. One way to resolve this problem is to supplement SO(10) by simple gauged discrete symmetries which can also simultaneously suppress the renormalizable R-parity violating ones when they occur and make the theory "more natural". Here we discuss the phenomenological viability of such models. We first show that for both classes of models, e.g the ones that use ${\bf 16}_H$ or ${\bf 126}_H$ to break B-L symmetry, the minimal Higgs content which is sufficient for proton decay suppression is inadequate for explaining fermion masses despite the presence of all apparently needed couplings. We then present an extended ${\bf 16}_H$ model, with three {\bf 10} and three {\bf 45}-Higgs, where is free of this problem. We propose this as a realistic and "natural" model for fermion unification and discuss the phenomenology of this model e.g. its predictions for neutrino mixings and lepton flavor violation.
We show that gauge couplings unify more precisely in the region of SUSY parameter space already preferred by Yukawa unification. While proton decay due to dimension 5 operators is maximally suppressed in this region, the contribution from dimension 6 operators is enhanced as a consequence of lower unification scale.
We consider explicit unified models based on the flipped ${SU(5)\times U(1)}$ and $SU(6)\times SU(2)$ gauge groups in which gauge mediated proton decay operators are suppressed at leading order due to the special placement of matter fields in unified multiplets. We discuss both the theoretical structure and phenomenological implications of these models. For the latter, we examine the viability of the physical spectrum in each scenario and focus on the possible presence of other operators that could also contribute significantly to the proton decay rate.
The infra-red attractive force of the bulk gauge interactions is applied to soften the supersymmetric flavor problem in the orbifold SU(5) GUT of Kawamura. Then this force aligns in the infra-red regime the soft supersymmetry breaking terms out of their anarchical disorder at a fundamental scale, in such a way that flavor-changing neutral currents as well as dangerous CP-violating phases are suppressed at low energies. It is found that this dynamical alignment is sufficiently good compared with the current experimental bounds, as long as the diagonalization matrices of the Yukawa couplings are…
We calculate the high and low scale threshold corrections to the D=6 proton decay mode in supersymmetric SU(5) grand unified theories with higher-dimensional representation Higgs multiplets. In particular, we focus on a missing-partner model in which the grand unified group is spontaneously broken by the 75-dimensional Higgs multiplet and the doublet-triplet splitting problem is solved. We find that in the missing-partner model the D=6 proton decay rate gets suppressed by about 60%, mainly due to the threshold effect at the GUT scale, while the SUSY-scale threshold corrections are found to be …
The doublet-triplet splitting problem can be simply solved in product-group GUT models, using a global symmetry that distinguishes the doublets from the triplets. Apart from giving the required mass hierarchy, this ``triplet symmetry'' can also forbid some of the triplet couplings to matter. We point out that, since this symmetry is typically generation-dependent, it gives rise to non-trivial flavor structure. Furthermore, because flavor symmetries cannot be exact, the triplet-matter couplings are not forbidden then but only suppressed. We construct models in which the triplet symmetry gives a…
We reconsider dimension-five proton decay operators, making semi-quantitative remarks which apply to a large class of supersymmetric GUTs in which the short-distance operators are correlated with the fermion Yukawa couplings. In these GUTs, which include minimal SU(5), the operators $(u^cd_i^c)^\dagger(d_jν_τ)$, induced by charged Higgsino dressing, completely dominate for moderate to large $\tanbeta$. The rate for $p \rarr (K^+,π^+) \barν_τ$ grows rapidly, as $\tanbeta^4$, and the K^+ to π^+ branching ratio can often be precisely predicted. At small $\tanbeta$ the operators $(u d_i)(d_j ν)$ a…
In this paper we study flavor violation in supersymmetric models with gauged flavor symmetries. There are several sources of flavor violation in these theories. The dominant flavor violation is the tree-level $D$-term contribution to scalar masses generated by flavor symmetry breaking. We present a new approach for suppressing this phenomenologically dangerous effects by separating the flavor-breaking sector from supersymmetry-breaking one. The separation can be achieved in geometrical setups or in a dynamical way. We also point out that radiative corrections from the gauginos of gauged flavor…
Cruz et al. recently showed that the CMB cold spot can be explained by a GUT-scale texture. But following Turok's argument that gauged configurations always relax quickly, they posit a global symmetry, without obvious relation to GUTs. An observation by Nambu invalidates Turok's argument when the broken symmetry group has commuting generators. This is demonstrated explicitly in the standard model of electroweak interactions and holds generally for intermediate SSB stages in GUTs. The cold spot could therefore be due to a GUT texture, and electroweak Higgs gradients may evolve indefinitely.
We study the coupling of MSSM fields to heavy modes through cubic superpotential interactions in F-theory SU(5) GUTs. The couplings are calculated by integrating the overlap of two massless and one massive wavefunctions. The overlap integral receives contributions from only a small patch around a point of symmetry enhancement thereby allowing the wavefunctions to be determined locally on flat space, drastically simplifying the calculation. The cubic coupling between two MSSM fields and one of the massive coloured Higgs triplets present in SU(5) GUTs is calculated using a local eight-dimensiona…
We discuss the proton decay problem in theories with low gravity and/or GUT scales. We pointed out that the gravity induced proton decay can be indeed suppressed up to a desired level, while the GUT origin of the proton instability is rather problematic. To solve this problem we suggest the GUT model where the proton is stable in all orders of perturbation theory. This can be simply achieved by the replication of quark-lepton families with ordinary quarks and leptons residing in different GUT representations and by an appropriate dimensional reduction. The model predicts extra mirror states wh…
Supersymmetric GUTs are the most natural extension of the Standard model unifying electroweak and strong forces. Despite their indubitable virtues, among these the gauge coupling unification and the quantization of the electric charge, one of their shortcomings is the large number of parameters used to describe the high energy thresholds (HET), which are hard to handle. We present a new method according to which the effects of the HET, in any GUT model, can be described by fewer parameters that are randomly produced from the original set of the parameters of the model. In this way, regions fav…
In supersymmetry, there are gauge invariant dimension 5 proton decay operators which must be suppressed by a mass scale much larger than the Planck mass. It is natural to expect that this suppression should be explained by a mechanism that explains the hierarchical structure of the fermion mass matrices. We apply this argument to the case where wave functions of chiral multiplets are localized under a kink background along an extra spatial dimension and the Yukawa couplings as well as the coefficients of the proton decay operators are determined by the overlap of the relevant wave functions. A…
The nature of R-parity violating interactions in two classes of string inspired supersymmetric grand unified theories (SISUSY GUT), based on the gauge groups $SO(10)$ (and its subgroup $SU(2)_L\times SU(2)_R\times SU(4)_c\equiv G_{224}$) as well as $[SU(3)]^3$, are discussed and their strengths are related to the ratio of symmetry breaking scales present in the model. We first argue that for the R-parity violating couplings $λ_{R\!\!\!/}$ to be suppressed to the desired level, the $B-L$ local symmetry must break at an intermediate scale $M_{B-L}$ since $λ_{R\!\!\!/} =M_{B-L}/M_{GUT}$. We then …
A mechanism for the enhancement for proton lifetime in supersymmetric/supergravity (SUSY/SUGRA) grand unified theories (GUTs) and in string theory models is discussed where Higgsino mediated proton decay arising from color triplets (anti-triplets) with charges $Q=-1/3(1/3)$ and $Q=-4/3(4/3)$ is suppressed by an internal cancellation due to contributions from different sources. We exhibit the mechanism for an SU(5) model with $45_H+\bar{45}_H$ Higgs multiplets in addition to the usual Higgs structure of the minimal model. This model contains both $Q=-1/3(1/3)$ and $Q=-4/3(4/3)$ Higgs color trip…
We construct a novel flavor-dependent gauged lepton number $U(1)_\ell$ model for the hierarchical charged lepton masses and the observed $(g-2)_{e,μ}$. Only tau participates in the tree-level Standard Model ( SM ) Yukawa interaction. At the same time, the masses of electron and muon are light due to radiative generation and(or) the heavy-mediator-suppressed Yukawa coupling to the SM Higgs. Not only can the measured anomalous magnetic dipole moment of the muon, $\triangle a_μ$, be explained, but the positive (or negative) $\triangle a_e$ can also be accommodated in this model. Without additiona…
Fermion Multiplicities at the GUT Scale: A Statistical Study of Unification and Proton Decay
ICRR, The University of Tokyo（东京大学宇宙射线研究所）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo（东京大学前沿研究机构 Kavli宇宙物理数学研究所）
We consider $b$-$τ$ unification in supersymmetric $SU(5)$ grand unified theories (GUTs) with extra matters. The renormalization group runnings of $b$ and $τ$ Yukawa coupling constants may be significantly affected by the existence of extra matters. If the extra matters interact with the standard model particles (and their superpartners) only through gauge interaction, the ratio of the $b$ to $τ$ Yukawa coupling constants at the GUT scale becomes suppressed compared to the case without extra matters. This is mainly due to the change of the renormalization group running of the $SU(3)_C$ gauge co…
We propose a gauged two-Higgs-doublet model (2HDM) featuring an anomalous Peccei-Quinn symmetry, $U(1)_{PQ}$. Dangerous tree-level flavour-changing neutral currents, common in 2HDMs, are forbidden by the extra gauge symmetry, $U(1)_X$. In our construction, the solutions to the important issues of neutrino masses, dark matter and the strong CP problem are interrelated. Neutrino masses are generated via a Dirac seesaw mechanism and are suppressed by the ratio of the $U(1)_X$ and the $U(1)_{PQ}$ breaking scales. Naturally small neutrino masses suggest that the breaking of $U(1)_X$ occurs at a rel…
Recently, a simple prescription to embed the global Peccei-Quinn (PQ) symmetry into a gauged $U(1)$ symmetry has been proposed. There, explicit breaking of the global PQ symmetry expected in quantum gravity are highly suppressed due to the gauged PQ symmetry. In this paper, we apply the gauged PQ mechanism to models where the global PQ symmetry and supersymmetry (SUSY) are simultaneously broken at around $\mathcal{O}(10^{11-12})$\,GeV. Such scenario is motivated by an intriguing coincidence between the supersymmetry breaking scale which explains the observed Higgs boson mass by the gravity med…
A pseudo-Nambu-Goldstone boson (pNGB) is an attractive candidate for dark matter since the current severe limits of dark matter direct detection experiments are naturally evaded by its nature. We construct a model with pNGB dark matter based on a {\it gauged} $U(1)_{B-L}$ symmetry, where no ad-hoc global symmetry is assumed. The model keeps natural suppression mechanism for the dark matter direct detection cross section. On the other hand, the pNGB can decay through the new high scale suppressed operators. We show that the pNGB has long enough lifetime to be a dark matter in the wide range of …
The concept of chirality is extended to the Minimal Supersymmetric Standard Model (MSSM) and the mu term is forbidden by a gauged U(1)' symmetry. R-parity automatically emerges after symmetry breaking, suppressing proton decay and protecting the LSP. Exotics charged under the SM pose a challenge to traditional SU(5) unification, but unification is still implemented in deconstructed GUTs. Because of the multitude of additional states to the MSSM, the Z' has a large width, and the SM background, neglected in previous theoretical studies, becomes important for Z' discovery. As a result, the LHC r…
Gauging the global $B-L$ (Baryon number minus Lepton number) symmetry in the Standard Model (SM) is well-motivated since anomaly cancellations require the introduction of three right-handed neutrinos (RHNs) which play an essential role in naturally generating tiny SM neutrino masses through the seesaw mechanism. In the context of the $B-L$ extended SM, we propose a pseudo-Goldstone boson dark matter (DM) scenario in which the imaginary component of a complex $B-L$ Higgs field serves as the DM in the universe. The DM relic density is determined by the SM Higgs boson mediated process, but its el…
Triplet-mediated proton decay in Grand Unified Theories (GUTs) is usually suppressed by arranging a large triplet mass. Here we explore instead a mechanism for suppressing the couplings of the triplets to the first and second generations compared to the Yukawa couplings, so that the triplets' mass can be below the GUT scale. This mechanism is based on a ``triplet symmetry'' in the context of product-group GUTs. We study two possibilities. One, which requires the top Yukawa to arise from a non-renormalizable operator at the GUT scale, is that all triplet couplings to matter are negligible, so t…
We point out that in non supersymmetric GUTs, in which the SU(5) gauge symmetry is broken down to the Standard Model gauge group by a $\mathbf{24}$ Higgs multiplet the Appelquist-Carazzone decoupling is violated. This is because the $SU(2)_L$ Higgs triplet contained in the $\mathbf{24}$ acquires a dimensionfull coupling to the $SU(2)_L$ Higgs doublets which is proportional to the GUT breaking vacuum expectation value (VEV) $V$. As a result, at one loop heavy gauge and Higgs fields contribution to tadpoles generate a VEV of the triplet which is not suppressed for $V\to\infty$ and violates the c…
The proton decay in supersymmetric (SUSY) Grand Unified Theories (GUTs), where the special mechanism provides the natural suppression of the dimension 5 ($d=5$) operators, was studied. Due to this mechanism, $d=5$ operator induced proton decay takes place only through the mixing of light generation fermions with those from third generation and crucially depends on the structure of fermion mass matrices. We show that in general proton decay is strongly suppressed relative to the standard SUSY GUT situation and for wide class of fermion mass matrices the SUSY parameter space practically has no r…
Small instantons can play an important role in Yang-Mills theories whose gauge couplings are sizeable at small distances. An interesting class of theories where this could occur is in weakly-gauged holographic models (dual to Yang-Mills theories interacting with strongly-coupled CFTs), since gauge couplings are indeed enhanced towards the UV boundary of the 5D AdS space. However, contrary to expectations, we show that small instantons in these non-asymptotically-free models are highly suppressed and ineffective. This is due to the conservation of topological charge that forbids instantons to b…
A mechanism to generate realistic fermion mass hierarchies based on supersymmetric gauged $U(1)_F$ symmetry in flat five-dimensional (5D) spacetime is proposed. The fifth dimension is compactified on $S^1/Z_2$ orbifold. The standard model fermions charged under the extra abelian symmetry along with their superpartners live in the 5D bulk. Bulk masses of fermions are generated by the vacuum expectation value of $N=2$ superpartner of $U(1)_F$ gauge field, and they are proportional to $U(1)_F$ charges of respective fermions. This decides localization of fermions in the extra dimension, which in t…
We propose simpler Higgs sectors in $E_6$ grand unified theory with anomalous $U(1)_A$ gauge symmetry than the previous model in Ref.1). As in the previous model, the doublet-triplet splitting can be realized in a natural way, while proton decay via dimension 5 operators is suppressed and gauge coupling unification is also realized without fine-tuning. Combining the matter sector, simple complete GUTs can be obtained. Since the Higgs sector is simpler, the gauge coupling constant at the cutoff scale can be in perturbative region, and therefore, the estimated value of the lifetime of a nucleon …
In this thesis, we study the hidden symmetries in the SM and also use discrete gauge symmetries as model building tools to solve various problems in the SM as well as the MSSM, such as R-parity, mu-term, stabilizing the axion solutions, etc. The flavor independent non-supersymmetric SM at the renormalizable level has a discrete Z_3 gauge symmetry known as baryon parity. It is anomaly free at the discrete level as a result of the existence of three generations. The symmetry can effectively act as the Baryon number up to the ΔB=3 mod 3 level which is also consistent with the prediction from non-…
We discuss the first string theory examples of three generation non-supersymmetric SU(5) and {\em flipped} SU(5) GUTS, which break to the Standard model at low energy, without extra matter and/or gauge group factors. Our GUT examples are based on IIA $Z_3$ orientifolds with D6-branes intersecting at non-trivial angles. These theories necessarily satisfy RR tadpoles and are free of NSNS tadpoles as the complex structure moduli are frozen (even though a dilaton tadpole remains) to discrete values. We identify appropriately the bifundamental Higgses responsible for electroweak symmetry breaking. …
Sichuan University（四川大学）；Nanjing Normal University（南京师范大学）；The Hong Kong University of Science and Technology（香港科技大学）；Tokyo University of Science（东京科学大学）
The absolute stability of a dark matter (DM) particle is not a binding requirement. Here we suggest a few scenarios where the DM particle is liable to decay via extremely feeble interactions. This can happen via inexplicably small Yukawa couplings in the simplest conjectures. After setting down such a model, we go beyond it, thus treading onto scenarios where the spontaneous breakdown of some gauged $U(1)$ symmetry may lead to intermediate scales, and suitably suppressed effective operators which allow the DM particle to decay slowly. The constraints from particle physics as well as cosmology …
In this work, we address two paradoxes. The first is that the measured dark-matter relic density can be satisfied with new physics at O(100 GeV - 1 TeV), while the null results from direct-detection experiments place lower bounds of O(10 TeV) on a new-physics scale. The second puzzle is that the severe suppression of lepton-flavor-violating processes involving electrons, e.g. mu->3e, tau->e mu mu, etc., implies that generic new-physics contributions to lepton interactions cannot exist below O(10 - 100 TeV), whereas the 3.6sigma deviation of the muon g-2 from the standard model can be explained…
We show how the SUSY flavour and CP problems can be solved using gauged SU(3) family symmetry previously introduced to describe quark and lepton masses and mixings, in particular neutrino tri-bimaximal mixing via constrained sequential dominance. The Yukawa and soft trilinear and scalar mass squared matrices and kinetic terms are expanded in powers of the flavons used to spontaneously break the SU(3) family symmetry, and the canonically normalized versions of these matrices are constructed. The soft mass matrices are then expressed in the Super-CKM basis, and the leading order mass insertion p…
We propose a gauged $U(1)_{H}$ horizontal symmetry around TeV scale that is a subgroup of a $SU(3)_{H}$ horizontal gauge symmetry broken at ${\cal O}(10^{14}) \GeV$. The breaking generates right-handed Majorana neutrino masses through a $SU(3)_H$ sextet scalar. A particular Majorana right-handed neutrino mass matrix explicitly determines the remnant $U(1)_{H}$ at low energy which only couples to $b-s$ and $μ-τ$ in the gauge eigenstate. The dangerous $K-\bar{K}$, $D-\bar{D}$ mixing and $B_s \rightarrow μ^+ μ^-$ are kept to be safe because the relevant couplings are suppressed through high power…
We propose a model for Dirac leptogenesis based on a non-anomalous $U(1)^{\prime}$ gauged family symmetry. The anomaly cancellation conditions are satisfied with no new chiral fermions other than the three right-handed neutrinos, giving rise to stringent constraints among the charges. Realistic masses and mixing angles are obtained for all fermions. The model predicts neutrinos of the Dirac type with naturally suppressed masses. Dirac leptogenesis is achieved through the decay of the flavon fields. The cascade decays of the vector-like heavy fermions in the Froggatt-Nielsen mechanism play a cr…
For explaining the AMS-02 cosmic positron excess, which was recently reported, we consider a scenario of thermally produced and decaying dark matter (DM) into the standard model (SM) leptons with an extremely small decay rate, Γ_{DM} \sim 10^{-26} sec.^{-1}. Since the needed DM mass is relatively heavy (700 GeV < m_{DM} < 3000 GeV), we introduce another DM component apart from the lightest supersymmetric particle ("LSP"). For its (meta-) stability and annihilation into other particles, the new DM should be accompanied with another Z_2 symmetry apart from the R-parity. Sizable renormalizable co…
We present a UV complete model with a gauged flavor symmetry which approximately realizes holomorphic Minimal Flavor Violation (MFV) in R-parity violating (RPV) supersymmetry. Previous work has shown that imposing MFV as an ansatz easily evades direct constraints and has interesting collider phenomenology. The model in this work spontaneously breaks the flavor symmetry and features the minimum "exotic" field content needed to cancel anomalies. The flavor gauge bosons exhibit an inverted hierarchy so that those associated with the third generation are the lightest. This allows low energy flavor…
Several experiments reported hints for the violation of lepton flavor or lepton flavor universality in processes involving muons. Most prominently, there is the hint for a non-zero rate of the flavor violating Higgs decay $h \to τμ$ at the LHC, as well as the hint for lepton flavor universality violation in rare $B$ meson decays at LHCb. In addition, also the long standing discrepancy in the anomalous magnetic moment of the muon motivates new physics connected to muons. A symmetry which violates lepton flavor universality, is $L_μ-L_τ$: the difference of muon-number and tau-number. We show tha…
Higgs sector of the Standard model (SM) is replaced by quantum flavor dynamics (QFD), the gauged flavor $SU(3)_f$ symmetry with scale $Λ$. Anomaly freedom requires addition of three $ν_R$. The approximate QFD Schwinger-Dyson equation for the Euclidean infrared fermion self-energies $Σ_f(p^2)$ has the spontaneous-chiral-symmetry-breaking solutions ideal for seesaw: (1) $Σ_f(p^2)=M_{fR}^2/p$ where three Majorana masses $M_{fR}$ of $ν_{fR}$ are of order $Λ$. (2) $Σ_f(p^2)=m_f^2/p$ where three Dirac masses $m_f=m_{(0)}1+m_{(3)}λ_3+m_{(8)}λ_8$ of SM fermions are {\it exponentially suppressed w.r.t.…
Supersymmetry breaking close to the scale of grand unification can explain cosmic inflation. As we demonstrate in this paper, this can be achieved in strongly coupled supersymmetric gauge theories, such that the energy scales of inflation and supersymmetry breaking are generated dynamically. As a consequence, both scales are related to each other and exponentially suppressed compared to the Planck scale. As an example, we consider a dynamical model in which gauging a global flavor symmetry in the supersymmetry-breaking sector gives rise to a Fayet-Iliopoulos D term. This results in successful …
We study Gauge-Higgs unification model on the orbifold $S^{1}/Z_{2}$ based on the extended SM gauge group $G_{SM}^{ex}=SU(2)_{L} \times U(1)_{Y} \times SO(3)_{F}$. The group $SO(3)_{F}$ is treated as a chiral gauged flavour symmetry. Electroweak-, flavour- and Higgs interactions are unified in one single gauge group SU(7) which is broken again down to $G_{SM}^{ex}$ by orbifolding and imposing additional boundary conditions. The compactification scale is O(1) TeV. The orbifold $S^{1}/Z_{2}$ is put on a lattice. This setting gives a staring point for RG-transformations. As a result the bulk is i…
Extensions of the standard model with a $U(1)$ gauge symmetry contain gauge invariant kinetic mixing, $\sinχ$, and gauge non-invariant mass mixing, $δM^2$, between the hypercharge and the new gauge boson $Z'$. These represent a priori incalculable but phenomenologically important parameters of the theory. They become calculable if there exist spontaneously or softly broken symmetries which forbid them at tree level but allow their generation at the loop level. We discuss various symmetries falling in this category in the context of the gauged $L_μ-L_τ$ models and their interplay with lepton mi…
