Even if the concerns related to the naturalness of the electroweak scale are repressed, the Higgs mass and stability of the electroweak vacuum do not allow arbitrarily large supersymmetry breaking scale, $M_S$, in the minimal models with split or high-scale supersymmetry. We show that $M_S$ can be raised to the GUT scale if the theory below $M_S$ contains a Higgs doublet, a pair of TeV scale Higgsino and widely separated gauginos in addition to the Standard Model particles. The presence of wino and gluino below ${\cal O}(100)$ TeV leads to precision unification of the gauge couplings consistent with the current limits on the proton lifetime. Wino, at this scale, renders the Higgsino as pseudo-Dirac dark matter which in turn evades the existing constraints from the direct detection experiments. Bino mass scale is required to be $\gtrsim 10^{10}$ GeV to get the observed Higgs mass respecting the current limit on the charged Higgs mass. The framework predicts, $1 \lesssim \tanβ\lesssim 2.2$ and $τ[p\to e^+\, π^0] < 7 \times 10^{35}$ years, almost independent of values of the other parameters. The electroweak vacuum is found to be stable or metastable. The underlying framework provides an example of a viable sub-GUT scale theory of supersymmetric grand unified theory in which supersymmetry and unified gauge symmetry are broken at a common scale.
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.
We explore gauge coupling unification and dark matter in high scale supersymmetry where the scale of supersymmetry breaking is much above the weak scale. The gauge couplings unify as precisely as in low energy supersymmetry if the higgsinos, whose mass does not break supersymmetry, are much lighter than those obtaining masses from supersymmetry breaking. The dark matter of the universe can then be explained by the neutral higgsino or the gravitino. High scale supersymmetry with light higgsinos requires a large Higgs mixing parameter for electroweak symmetry breaking to take place. It is thus n…
We investigate a scenario in which supersymmetry is broken at scale $M_S \geq 10^{14}$ GeV leaving only a pair of Higgs doublets, their superpartners (Higgsinos) and a gauge singlet fermion (singlino) besides the standard model fermions and gauge bosons at low energy. The Higgsino-singlino mixing induces small splitting between the masses of electrically neutral components of Higgsinos which otherwise remain almost degenerate in GUT scale supersymmetry. The lightest combination of them provides a viable thermal dark matter if the Higgsino mass scale is close to $1$ TeV. The small mass splittin…
In the MSSM, the assumptions of a common sfermion mass parameter m_0 and a common gaugino mass parameter m_1/2, along with the requirements from radiative electroweak symmetry breaking, lead to relatively large values of the Higgs mixing parameter mu, and consequently to a gaugino-like lightest neutralino. Lifting the requirement that the Higgs mass parameters unify with the sfermion masses is known to allow for smaller mu. We show that a mu parameter sufficiently small to yield a Higgsino-like neutralino requires a precise adjustment of the Higgs mass parameter m_Hu. Consequently a gaugino-ty…
A wide variety of unified models predict asymptotic relations at $M_{GUT}$ between the b quark and $τ$ lepton Yukawa couplings. Within the framework of supersymmetric SU(4) $\times$ SU(2)$_L \times$ SU(2)$_R$, we explore regions of the parameter space that are compatible with b-$τ$ quasi-Yukawa unification and the higgsinos being the lightest supersymmetric particles ($\lesssim$ 1 TeV). Among the colored sparticles, the stop weighs more than 1.5 TeV or so, whereas the squarks of the first two families are signifcantly heavier, approaching 10 TeV in some cases. The gluino mass is estimated to l…
Grand-unified models with extra dimensions at the GUT scale will typically contain exotic states with Standard Model charges and GUT-scale masses. They can act as messengers for gauge-mediated supersymmetry breaking. If the number of messengers is sizeable, soft terms for the visible sector fields will be predominantly generated by gauge mediation, while gravity mediation can induce a small mu parameter. We illustrate this hybrid mediation pattern with two examples, in which the superpartner spectrum contains light and near-degenerate higgsinos with masses below 200 GeV. The typical masses of …
We examine the issue of fine tuning in the MSSM with GUT-scale boundary conditions. We identify specific unification patterns and mass relations that can lead to a significant lowering of the fine tuning due to gauginos, scalars, and the μ parameter, relative to the simplest unification conditions. We focus on a phenomenologically interesting region that is favored by the Higgs mass and the relic density where the dark matter is a nearly pure higgsino with mass given by μ~1 TeV while the scalars and gauginos have masses in the multi-TeV regime. There, we find that the fine tuning can be reduce…
It is shown, that the presently accepted value for b-quark mass can be obtained from the requirement of the exact b-$τ$ unification in the both non-SUSY and SUSY non-chiral extended GUTs.
We propose a unified model of elementary particles based on a supersymmetric SO(10)$_{GUT} \:\times$ SO(6)$_H$ gauge theory. This model completely achieves natural unification of the strong and electroweak interactions without any fine-tunings.
Unification of Gauge and Yukawa sectors of GUTs is obtained by searching for renormalization group invariant relations among the couplings of the both sectors which hold beyond the unification scale. This procedure singled out two supersymmetric GUTs, the finite and the minimal SU(5) models which, among others, were predicting successfully the top quark mass. The same procedure is currently extended in the soft supersymmetry-breaking sector of the theories, providing us with interesting, though preliminary, predictions on the Higgs and superpartner masses.
We show that in the framework of grand unified theory (GUT) with anomalous $U(1)_A$ gauge symmetry, the success of the gauge coupling unification in the minimal SU(5) GUT is naturally explained, even if the mass spectrum of superheavy fields does not respect SU(5) symmetry. Because the unification scale for most realizations of the theory becomes smaller than the usual GUT scale, it suggests that the present level of experiments is close to that sufficient to observe proton decay via dimension 6 operators, $p\to e+π$.
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 consider a new class of light vectorlike exotics with fractional electric charge which do not come in complete representations of a grand unified gauge group, and are nevertheless compatible with gauge coupling unification and other predictions from Grand Unified Theories. Such states naturally arise in orbifold constructions of the heterotic string. Some aspects of their phenomenology and the consequences for the LHC are explored.
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 explore the implications of third family ($t-b-τ$) quasi-Yukawa unification (QYU) for collider and dark matter (DM) searches within the framework of a supersymmetric $SU(4)_c \times SU(2)_L \times SU(2)_R$ model. The deviation from exact Yukawa unification is quantified through the relation $y_t : y_b : y_τ= |1+C|:|1-C|:|1+3C|$, with $C$ being a real parameter ($|C| \leq 0.2$). We allow for the breaking of left-right symmetry both by the soft scalar and gaugino mass parameters and obtain a variety of viable solutions that predict the sparticle mass spectrum including LSP DM (whose stability…
From the LZ Event to Grand Unification: Heavy Higgsinos and Proton Decay
Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交大李政道研究所）；School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）；Department of Physics, University of Tokyo（东京大学物理学系）；Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), University of Tokyo（东京大学宇宙物质起源科学中心）
We present GUT models based on an $SU(5)\times SU(5)$ GUT group. These models maintain the main successes of simple-group GUTs but permit simple solutions to the doublet-triplet splitting problem. Moreover, GUT breaking is triggered by supersymmetry breaking so that the GUT scale is naturally generated as a combination of the Planck scale and the supersymmetry breaking scale.
We consider field sets that do not form complete SU(5) multiplets, but exactly preserve the one-loop MSSM prediction for $α_3(M_Z)$ independently of the value of their mass. Such fields can raise the unification scale in different ways, through a delayed convergence of the gauge couplings, a fake unified running below the GUT scale, or a postponed unification after a hoax crossing at a lower scale. The $α_3(M_Z)$ prediction is independent of the mass of the new fields, while the GUT scale often is not, which allows to vary the GUT scale. Such "magic" fields represent a useful tool in GUT model…
The requirement of electroweak naturalness in simple supersymmetric models implies the existence of a cluster of four light higgsinos with mass $\sim 100-300$\,GeV, the lighter the better. While such light compressed spectra may be challenging to observe at LHC, the International Linear $e^+e^-$ Collider (ILC) with $\sqrt{s}>2m_{\rm higgsino}$ would serve as both a SUSY discovery machine and a precision microscope. We study higgsino pair production signatures at the ILC based on full, \texttt{Geant4-}based simulation of the ILD detector concept. We examine several benchmark scenarios that may …
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 …
The top-quark Yukawa infrared fixed-point solution of the renormalization group equations, with minimal supersymmetry and GUT unification, defines a low-energy spectrum of supersymmetric particle masses in terms of a few GUT-scale parameters assuming universal boundary conditions. We give predictions in this model for the inclusive $b\to sγ$ branching fraction and investigate the impact of non-universal scalar mass boundary conditions. We find our results do not depend significantly on the value of the GUT-scale trilinear coupling $A^G$. The small $\tan β$ region favors predictions for the inc…
We consider a supersymmetric type-I seesaw framework with non-universal scalar masses at the GUT scale to explain the long-standing discrepancy of the anomalous magnetic moment of the muon. We find that it is difficult to accommodate the muon g-2 while keeping charged-lepton flavor violating processes under control for the conventional SO(10)-based relation between the up sector and neutrino sector. However, such tension can be relaxed by adding a Georgi-Jarlskog factor for the Yukawa matrices, which requires a non-trivial GUT-based model. In this model, we find that both observables are compa…
We investigate gauge coupling unification in higher dimensional GUT models with split supersymmetry. We focus on 5d and 6d orbifold GUTs, which permit a simple solution to several problems of 4D GUTs as well as control over GUT scale threshold corrections. In orbifold GUTs, calculable threshold corrections can raise or lower the prediction for $α_s(M_Z)$ in a way that depends on the location of Higgs fields. On the other hand, split supersymmetry lowers the prediction for $α_s(M_Z)$. Consequently, split supersymmetry changes the preferred location of the Higgs fields in orbifold GUTs. In the s…
The logarithmic running of the gauge couplings alpha_1, alpha_2 and alpha_3, indicates that they may unify at some scale M_GUT ~ 10^16. This is often taken to imply that the standard model gauge group is embedded into some larger simple group in which quarks and leptons are placed in the same multiplet. These models have generic features, such as proton decay, and generic problems, namely the splitting of the Higgs doublet and triplet. Inspired by the recent discusion of dimensional deconstruction, we propose an interesting alternative: we postulate a strongly coupled SU(3)xSU(2)xU(1), which i…
Supersymmetric grand unified models based on SO(10) gauge symmetry have many desireable features, including the unification of Yukawa couplings. Using D-term contributions to scalar masses arising from the breakdown of SO(10), Yukawa coupling unification only to 30% can be achieved in models with a positive superpotential Higgs mass. The superparticle mass spectrum is highly constrained, and yields relatively light top squarks and charginos. Surprisingly, the pattern of GUT scale soft SUSY breaking masses are close to those found in the context of inverted hierarchy models. Our analysis suppor…
Motivated by the observation that the Higgs quartic coupling runs to zero at an intermediate scale, we propose a new framework for models of split supersymmetry, in which gauginos acquire intermediate scale Dirac masses of $\sim 10^{8-11}$ GeV. Scalar masses arise from one-loop finite contributions as well as direct gravity-mediated contributions. Like split supersymmetry, one Higgs doublet is fine-tuned to be light. The scale at which the Dirac gauginos are introduced to make the Higgs quartic zero is the same as is necessary for gauge coupling unification. Thus, gauge coupling unification pe…
We consider a 5-dimensional SU(5) model wherein the symmetry is broken to the 4-dimensional Standard Model by compactification of the 5th dimension on an S^1/(Z_2 \times Z^\prime_2) orbifold. We identify the members of all SU(5) representations upto 75 which have zero modes. We examine how these light scalars affect gauge coupling unification assuming a single intermediate scale and present several acceptable solutions. The 5-D compactification scale coincides with the unification scale of gauge couplings and is determined via this renormalization group analysis. When SO(10) is considered as t…
In a scenario with heavy supersymmetric sfermions and decoupled supersymmetric Higgs sector, a well tempered neutralino is the remaining candidate for thermal single-component sub-TeV dark matter. Well tempered neutralinos are studied in the context of supersymmetric grand unified theories with third family Yukawa coupling unification. A global chi^2 analysis is performed, including the observables MW, MZ, GF, alpha_em, alpha_s(MZ), Mt, mb(mb), Mtau, b -> s gamma, BR(Bs -> mu^+ mu^-), Mh and Omegah^2. Tensions in simultaneously fitting the Higgs and bottom quark masses while also avoiding glui…
The results for the running of the gauge couplings in the MSSM are up-dated by proper inclusion of all low scale effects. They are presented as predictions for the strong coupling constant in the scenario with only two parameters at the GUT scale ~ ($α_{U}$ ~and ~$M_{U}$) ~and as a mismatch of the couplings at the scales ~$\sim 3 \times 10^{16}$ GeV ~and ~$4\times10^{17}$ GeV, when all three couplings are taken as the experimental input.
We discuss the Yukawa coupling unification, a very interesting prediction of the grand unified theory, in the context of scenarios with more than one pair of Higgs doublet since the current LHC constraint has become a problem for the Yukawa unification scenarios with just one pair of Higgs doublet. More than one pair of Higgs doublets can easily arise in missing partner mechanism which solves the doublet-triplet splitting problem. In such a scenario, the Yukawa unification occurs at a medium $\tanβ$ value, e.g., $\sim$ 30, which corresponds to much smaller threshold corrections compared to usu…
We estimate the CKM matrix elements in the recently proposed minimal model, anti-SU(7) GUT for the family unification, $[\,3\,]+2\,[\,2\,]+8\,[\,\bar{1}\,]$+\,(singlets). It is shown that the real angles of the right-handed unitary matrix diagonalizing the mass matrix can be determined to fit the Particle Data Group data. However, the phase in the right-handed unitary matrix is not constrained very much. We also includes an argument about allocating the Jarlskog phase in the CKM matrix. Phenomenologically, there are three classes of possible parametrizations, $\delq=α,β,$ or $γ$ of the unitari…
An analytical formalism, including RG running at two loop order, is used to link the supersymmetric and GUT spectra in any GUT model in which the three gauge couplings unify. In each specific GUT model, one can then fully explore the interplay between the pattern of supersymmetry breaking and the prediction for the proton lifetime. With this formalism at hand, we study three concrete GUT models: (i) Minimal SU(5) SUSY GUT, (ii) Missing Partner SU(5) SUSY GUT, and (iii) an orbifold SU(5) SUSY GUT. In each case we derive interesting conclusions about the possible patterns of the supersymmetric s…
LZ-Motivated Pseudo-Dirac Higgsinos in the Supersymmetric 331 Model from the Supersymmetric \texorpdfstring{$SU(6)$}{SU(6)} GUT Model
Zhejiang Normal University（浙江师范大学）；Khazar University（阿塞拜疆哈萨克斯坦大学）；Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Kimyo International University in Tashkent（塔什干金约国际大学）；Harbin Institute of Technology（哈尔滨工业大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）
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…
We study grand unified theories based on an SU(5)xSU(5) gauge group in which the GUT scale, M_{GUT}, is the VEV of an exact or approximate modulus, and in which fast proton decay is avoided through a combination of a large triplet mass and small triplet couplings. These features are achieved by discrete symmetries. In many of our models, M_{GUT} is generated naturally by the balance of higher dimension terms that lift the GUT modulus potential, and soft supersymmetry breaking masses. The theories often lead to interesting patterns of quark and lepton masses. We also discuss some distinctions b…
Fermion pair production at $e^-e^+$ linear collider experiments with polarized $e^-$ and $e^+$ beams is examined in the GUT inspired $SO(5)\times U(1)\times SU(3)$ gauge-Higgs unification. There arises large parity violation in the couplings of leptons and quarks to Kaluza-Klein (KK) excited neutral vector bosons $Z'$s, which leads to distinctive polarization dependence in cross sections, forward-backward asymmetries, left-right asymmetries, and left-right forward-backward asymmetries in various processes. Those effects are detectable even for the KK mass scale up to about 15 TeV at future $e^…
We address the viability of exact Yukawa unification in the context of general SUSY GUTs with universal soft-breaking sfermion and gaugino mass terms at the GUT scale. We find that this possibility is challenged, unless the squark spectrum is pushed well above the limits allowed by naturalness. This conclusion is assessed through a global fit using electroweak observables and quark flavour-changing neutral current (FCNC) processes. The problem is mostly the impossibility of accommodating simultaneously the bottom mass and the BR(B --> Xs gamma), after the stringent CDF upper bound on the decay…
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…
With the recent experimental hint of new physics from flavor physics anomalies, combined with the evidence from neutrino mass and dark matter, we consider a minimal extension of SM with a scalar leptoquark and a fermion triplet. The scalar leptoquark with couplings to leptons and quarks can explain lepton flavor non-universality observables $R_K$, $R_{K^{(*)}}$, $R_{D^{(*)}}$ and $R_{J/ψ}$. Neutral component of fermion triplet provides current abundance of dark matter in the Universe. The interesting feature of the proposal is that the minimal addition of these phenomenologically rich particle…
The Weinberg angle is an important parameter in Grand Unified Theories (GUT) as its size is crucially influenced by the assumption of unification. In scenarios with different steps of symmetry breaking, in particular in models that involve gauge-Higgs unification, the connection of the ultraviolet theory and the TeV scale-relevant, effective Standard Model description is an important test of the models' validity. In this work, we consider a 6D gauge-Higgs unification GUT scenario and explore the TeV scale-GUT relation using a detailed RGE analysis in the 4D and 5D regimes of the theory, includ…
Gauge-Yukawa Unification (GYU) is a renormalization group invariant functional relation among gauge and Yukawa couplings which holds beyond the unification point in Grand Unified Theories (GUTs). Here, GYU is obtained by requiring finiteness and reduction of couplings to all orders in perturbation theory. We examine the consequences of GYU in various supersymmetric GUTs and in particular the predictions for the top quark mass. These predictions are such that they distinguish already GYU from ordinary GUTs. Moreover, when more accurate measurements of the top quark mass are available, it is exp…
We study $3$rd family Yukawa unification in the context of supersymmetric (SUSY) $\mathrm{SO}(10)$ GUTs and $\mathrm{SO}(10)$-motivated boundary conditions for the SUSY-breaking soft terms. We consider $μ<0$ such that the SUSY loop-threshold effects enable a good fit to all third family masses of the charged Standard Model (SM) fermions. We find that fitting the third family masses together with the mass of the SM-like Higgs particle, the scenario predicts the masses of the superpartner particles and of the extra Higgs states of the MSSM: while the sparticles are predicted to be comparatively …
$SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification model inspired by $SO(11)$ gauge-Higgs grand unification is constructed in the Randall-Sundrum warped space. The 4D Higgs boson is identified with the Aharonov-Bohm phase in the fifth dimension. Fermion multiplets are introduced in the bulk in the spinor, vector and singlet representations of $SO(5)$ such that they are implemented in the spinor and vector representations of $SO(11)$. The mass spectrum of quarks and leptons in three generations is reproduced except for the down quark mass. The small neutrino masses are explained by the ga…
We have studied the gauge unification with the recent electroweak data as a function of the higgsino mass. It was shown that if the strong coupling constant is small $\approx 0.11$, consistent picture of gauge unification is not possible in the minimal supersymmetric standard model.
The effective potential for the Aharonov-Bohm phase $θ_H$ in the fifth dimension in GUT inspired $SO(5)\times U(1) \times SU(3)$ gauge-Higgs unification is evaluated to show that dynamical electroweak symmetry breaking takes place with $θ_H \not= 0$, the 4D Higgs boson mass 125$\,$GeV being generated at the quantum level. The cubic and quartic self-couplings $(λ_3, λ_4)$ of the Higgs boson are found to satisfy universal relations, i.e. they are determined, to high accuracy, solely by $θ_H$, irrespective of values of other parameters in the model. For $θ_H=0.1$ ($0.15$), $λ_3$ and $λ_4$ are sma…
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 consider 5 dimensional E_6 and E_7 supersymmetric grand unified theories (GUTs) on an orbifold S^1/Z_2, in which the Higgs fields arise from the 5th components of the 5D gauge fields. We introduce matter fields in 5 dimensions, then the Yukawa interactions are induced from the gauge interactions among the 5th component of gauge fields and the bulk hyper-multiplets. The adjoint and fundamental representations of bulk matter fields can induce all Yukawa interactions of the standard model in E_6 GUT. Furthermore, realistic fermion mass hierarchies and flavor mixings with the CP violating phase…
We study the low-energy consequences of the mass and mixing angle relations in grand unified theories (GUT), which follow from an assumption that some quarks and leptons are placed in the same GUT multiplets. This assumption is a simple extension of that for the well-known bottom/tau mass ratio, which is one of the most successful predictions of grand unification of matter multiplets. We show that imposing the GUT relations leads naturally to a limited parameter space from the large lepton mixing between the second and third generations.
A constraint on masses of superheavy gauge and Higgs multiplets at the grand unification (GUT) scale is obtained from the gauge coupling unification in the case of high-scale supersymmetry. We found that all of the particles may lie around a scale of 10^16 GeV so that the threshold corrections to the gauge coupling constants at the GUT scale are smaller than those in the case of the low-energy supersymmetry. In addition, the GUT scale tends to be slightly lower when the gauginos are heavier and, thus, the proton decay rate via the X-boson exchange process is expected to be enhanced.
No-scale structure of the Kahler potential is obtained in many types of supersymmetric models. In this paper, phenomenological aspects of these models are investigated with special attention to the current Higgs mass bound at LEP and b \to s γresult at the CLEO. When the boundary condition is given at the GUT scale and gaugino masses are universal at this scale, very narrow parameter region is allowed only for positive Higgsino mass region if R-parity is conserved. The negative Higgsino mass case is entirely excluded. On the other hand, relatively large parameter region is allowed when the bou…
Gauge and Yukawa (for the third family) coupling unification seem to be the best predictions of the grand-unified theories (GUTs). In supersymmetric GUTs, one also expects that the sparticle masses unify at the GUT scale (for sparticles embedded in the same GUT multiplet). I show under what circumstances GUTs do not lead to sparticle mass unification. In particular, I give examples of SU(5) and SO(10) SUSY GUTs in which squarks and sleptons of a family have different tree-level masses at the unification scale. The models have interesting relations between Yukawa couplings. For example, I prese…
Grand Unified Theories predict relationships between the GUT-scale quark and lepton masses. Using new data in the context of the MSSM, we update the values and uncertainties of the masses and mixing angles for the three generations at the GUT scale. We also update fits to hierarchical patterns in the GUT-scale Yukawa matrices. The new data shows not all the classic GUT-scale mass relationships remain in quantitative agreement at small to moderate tan beta. However, at large tan beta, these discrepancies can be eliminated by finite, tan beta-enhanced, radiative, threshold corrections if the glu…
We observe that in SUSY models with non-universal GUT scale gaugino mass parameters, raising the GUT scale SU(2) gaugino mass |M_2| from its unified value results in a smaller value of -m_{H_u}^2 at the weak scale. By the electroweak symmetry breaking conditions, this implies a reduced value of μ^2 {\it vis à vis} models with gaugino mass unification. The lightest neutralino can then be mixed Higgsino dark matter with a relic density in agreement with the measured abundance of cold dark matter (DM). We explore the phenomenology of this high |M_2| DM model. The spectrum is characterized by a ve…
Nucleon lifetimes for various decay modes via dimension 6 operators are calculated in the anomalous $U(1)_A$ GUT scenario, in which the unification scale $Λ_u$ becomes smaller than the usual supersymmetric (SUSY) unification scale $Λ_G=2\times 10^{16}$ GeV in general. Since the predicted lifetime $τ(p\rightarrow π^0+e^c)$ becomes around the experimental lower bound though it is strongly dependent on the explicit models, the discovery of the nucleon decay in near future can be expected. We explain why the two ratios $R_1\equiv\frac{Γ_{n \rightarrow π^0 + ν^c}}{Γ_{p \rightarrow π^0 + e^c}}$ and …
In this paper we examine gauge coupling unification of the the non-SUSY SO(10) grand unified theory proposed by Babu and Mohapatra at the two loop level. This theory breaks down to the standard model in a single step and has the distinguishing feature of TeV non-standard model scalars. This leads to a plethora of interesting new physics at the TeV scale and the discovery of new particles at the LHC. This model gives rise to testable proton decay, neutron-antineutron oscillations, provides a mechanism for baryogenesis, and contains potential dark matter candidates. In this paper, we compute the…
In gauge-Higgs unification (GHU), the 4D Higgs boson appears as a part of the fifth dimensional component of 5D gauge field. Recently, an $SO(11)$ GUT inspired $SO(5)\times U(1)\times SU(3)$ GHU model has been proposed. In the GHU, Kaluza-Klein (KK) excited states of neutral vector bosons, photon, $Z$ boson and $Z_R$ boson, appear as neutral massive vector bosons $Z'$s. The $Z'$ bosons in the GHU couple to quarks and leptons with large parity violation, which leads to distinctive polarization dependence in, e.g., cross sections and forward-backward asymmetries in $e^-e^+\toμ^-μ^+,q\bar{q}$ pro…
