GUT Symmetry Research Articles

Viable models with non-universal gaugino mediated supersymmetry breaking

Recently, extra dimensional SUSY GUT models have been proposed in which compactification of the extra dimension(s) leads to a breakdown of the gauge symmetry and/or supersymmetry. We examine a particular class of higher-dimensional models exhibiting supersymmetry and SU(5) or SO(10) GUT symmetry. SUSY breaking occurs on a hidden brane, and is communicated to the visible brane via gaugino mediation. Non-universal gaugino masses are developed at the compactification scale as a consequence of a restricted gauge symmetry on the hidden brane. In this case, the compactification scale is at or slightly below the GUT scale. We examine the parameter space of such models where gaugino masses are related due to a Pati-Salam symmetry on the hidden brane. We find limited but significant regions of model parameter space where a viable spectra of SUSY matter is generated. Our results are extended to the more general case of three independent gaugino masses; here we find that large parameter space regions open up for large values of the U(1) gaugino mass M_1. We also find the relic density of neutralinos for these models to be generally below expectations from cosmological observations, thus leaving room for hidden sector states to make up the bulk of cold dark matter. Finally, we evaluate the branching fraction BF(b -> s gamma) and muon anomalous magnetic moment a_\mu.

Stable superstring relics and ultrahigh energy cosmic rays

One of the most intriguing experimental results of recent years is the observation of Ultrahigh Energy Cosmic Rays (UHECRs) above the GZK cutoff. Plausible candidates for the UHECR primaries are the decay products of a meta-stable matter state with mass of order O(10 12–15 GeV), which simultaneously is a good cold dark matter candidate. We study possible meta-stable matter states that arise from Wilson line breaking of GUT symmetries in semi-realistic heterotic string models. In the models that we study the exotic matter states can be classified according to patterns of SO(10) symmetry breaking. We show that cryptons, which are states that carry fractional electric charge ±1/2, and are confined by a hidden gauge group cannot produce viable dark matter. This is due to the fact that, in addition to the lightest neutral bound state, cryptons give rise to meta-stable charged bound states. However, these states may still account for the UHECR events. We argue that the uniton, which is an exotic Standard Model quark but carries “fractional” U(1) Z′ charge, as well as the singleton, which is a Standard Model singlet with “fractional” U(1) Z′ charge, do provide viable dark matter candidates and can at the same time explain the observed UHECR events.

Lepton number violation in supersymmetric grand unified theories

We argue that the nature of the global conservation laws in Supersymmetric Grand Unified Theories is determined by the basic vacuum configuration in the model rather than its Lagrangian. It is shown that the suppression of baryon number violation in a general ( R-parity violating) superpotential can naturally appear in some extended SU( N) SUSY GUTs which, among other degenerate symmetry-breaking vacua, have a missing VEV vacuum configuration giving a solution to the doublet-triplet splitting problem. We construct SU(7) and SU(8) GUTs where the effective lepton number violating couplings immediately evolve, while the baryon number non-conserving ones are safely projected out as the GUT symmetry breaks down to that of the MSSM. However at the next stage, when SUSY breaks, the radiative corrections shift the missing VEV components to some nonzero values of order M SUSY, thereby inducing the ordinary Higgs doublet mass, on the one hand, and tiny baryon number violation, on the other. So, a missing VEV solution to the gauge hierarchy problem leads at the same time to a similar hierarchy of baryon vs lepton number violation.

The Dispersal of the Lesbian, or Re-Patriating the Lesbian in British Writing

ABSTRACT Based on an analysis of Kay Summerscale's (1997) biography The Queen of Whale Cay, Jeanette Winterson's (1997) novel Gut Symmetries and Patricia Duncker's novel Hallucinating Foucault (1996), I argue that the emergence of postmodernism and queer has led to a re-positioning of ‘the lesbian’ in a number of contemporary texts whereby the once taken-for-granted notions of women and their relation to each other have become subsumed under an interrogation not so much of gender, the queer term, but of textuality, the postmodern turn. The result is a dispersal and simultaneously a re-patriation of ‘the les-bian’1 which obliterates her within the in/difference of the text.

R-CHARGE KILLS MONOPOLES

Large charge density, unlike high temperature, may lead to nonrestoration of global and gauge symmetries. Supersymmetric GUTs with the appealing scenario of unification scale being generated dynamically naturally contain global continuous R-symmetries. We point out that the presence of a large R-charge in the early universe can lead to GUT symmetry nonrestoration. This provides a simple way out of the monopole problem and, at the same time, solves the well-known cosmological problem of the theory being caught permanently in the wrong vacuum with the GUT gauge group unbroken.

Models of supersymmetric U(2)× U(1) flavor symmetry

We use a U(2)× U(1) horizontal symmetry in order to construct supersymmetric models where the flavor structure of both quarks and leptons is induced naturally. The supersymmetric flavor changing neutral currents problem is solved by the degeneracy between sfermions induced by the U(2) symmetry. The additional U(1) enables the generation of mass ratios that cannot be generated by U(2) alone. The resulting phenomenology differs from that of models with either abelian or U(2)× GUT symmetries. Our models give rise to interesting neutrino spectra, which can incorporate the Super-Kamiokande results regarding atmospheric neutrinos.

Problem of flavour in SUSY GUT and horizontal symmetry

The concept of non-abelian horizontal symmetry $SU(3)_H$ can greatly help in understanding the fermion and sfermion flavour structures in supersymmetric grand unification. For the sake of demonstration the $SU(5)\times SU(3)_H$ model, suggested earlier in ref. \cite{PLB85}, is revisited. We show that under very simple and natural assumption it links the sfermion mass pattern to those of fermions in a remarkable way. All dangerous supersymmetric flavour-changing contributions are naturally suppressed in a general case, independently of the concrete texture for fermion mass matrices. Nevertheless, within this framework we present an example of predictive model for fermion masses and mixing, which leads to 7 consistent predictions for the low energy observables. [Based on talks given at Int. Workshop {\em `SUSY 96'}, Univ. of Maryland, 29 May - 1 June 1996 (to appear on Proceedings), and II US-Polish Workshop {\em `Physics from Planck Scale to Electroweak Scale'}, Warsaw, 28-30 March 1996.]

Some aspects of thermal inflation: The finite temperature potential and topological defects.

Currently favoured extensions of the Standard Model typically contain `flaton fields' defined as fields with large vacuum expectation values (vevs) and almost flat potentials. If a flaton field is trapped at the origin in the early universe, one expects `thermal inflation' to take place before it rolls away to the true vacuum, because the finite-temperature correction to the potential will hold it at the origin until the temperature falls below $1\TeV$ or so. In the first part of the paper, that expectation is confirmed by an estimate of the finite temperature corrections and of the tunneling rate to the true vacuum, paying careful attention to the validity of the approximations that are used. The second part of the paper considers topological defects which may be produced at the end of an era of thermal inflation. If the flaton fields associated with the era are GUT higgs fields, then its end corresponds to the GUT phase transition. In that case monopoles (as well as GUT higgs particles) will have to be diluted by a second era of thermal inflation. Such an era will not affect the cosmology of GUT strings, for which the crucial parameter is the string mass per unit length. Because of the flat Higgs potential, the GUT symmetry breaking scale required for the strings to be a candidate for the origin of large scale structure and the cmb anisotropy is about three times bigger than usual, but given the uncertainties it is still compatible with the one required by the unification of the Standard Model gauge couplings. The cosmology of textures and of global monopoles is unaffected by the flatness of the potential.

Light colour-triplet Higgs is compatible with proton stability: An alternative approach to the doublet-triplet splitting problem

It is usually assumed that the proton stability requires the coloured triplet partner of the electroweak Higgs doublet to be superheavy (with a mass ∼ M GUT). We show that this is a very model-dependent statement and that the colour triplet can be as light as the weak doublet without leading to the proton decay problem. This implies an alternative approach to the doublet-triplet splitting problem: instead of using the mass difference the splitting can occur between the doublet and triplet Yukawa coupling constants so that the light Higgs triplet can appear decoupled from the quarks and leptons and cannot lead to the proton decay. In this scenario the GUT symmetry breaking automatically induces an extremely strong suppression ∼ M W M GUT of the coloured Higgs effective Yukawa coupling; this happens without any fine-tuning, just because of the Clebsch factors. Conceptual differences of the above picture are: (1) an essentially stable proton: both d = 5 and d = 6 proton decay mediating operators are suppressed by the same factors ∼ ( M w M GUT ) 2 ; (2) the possibility of solving the μ problem by the light gauge singlet field (this fact would lead to the destabilization of the hierarchy in the standard case); (3) the existence of the long-lived, light, coloured and charged supermultiplet in the 100 GeV to 1 TeV mass region, which can be the subject of an experimental search. We construct two explicit SO(10) examples with the above properties, with superpotentials most general under the symmetries.

Nonabelian Duality and Higgs Multiplets in Supersymmetric Grand Unified Theories

We consider strongly interacting supersymmetric gauge theories which break dynamically the GUT symmetry and produce the light Higgs doublets naturally. Two models we proposed in the previous articles are reanalyzed as two phases of one theory and are shown to have desired features. Furthermore, employing nonabelian duality proposed recently by Seiberg, we study the dual theory of the above one and show that the low-energy physics of the original and dual models are the same as expected. We note that the Higgs multiplets in the original model are regarded as composite states of the elementary hyperquarks in its dual theory. Theories with other hypercolors and similar matter contents are also analyzed in the same way.

Construction of minimal supersymmetric Z orbifold GUT models

Taking into account modular invariance and absence of target space duality anomalies as well as chiral gauge anomalies, we found that the Z 3 orbifold compactification with two Wilson lines gives a unique flipped SO(10) minimal supersymmetric grand unified model, where the hidden sector gauge group is also uniquely determined by the duality-anomaly-free condition as SU(5). We propose a dynamical mechanism of GUT symmetry breaking which may generate two hierarchical mass scales as M GUT ≈ ( g st 2 4π ) M st .

Why is the Higgs doublet light?

We consider a possible mechanism for the explanation of the doublet-triplet mass hierarchy in the grand unified theories. The Higgs doublet is automatically light since it is related by a certain “custodial” SU(2) C symmetry to another doublet which after GUT symmetry breaking becomes an unphysical Higgs. Custodial symmetry may or may not be a part of GUT symmetry. An explicit example of SUSY GUT is constructed.

TOWARD THE REALISTIC THREE-GENERATION MODEL IN THE (2, 0) HETEROTIC STRING COMPACTIFICATION

In the three-generation models with SUSY SO(10) or SU(5) GUTs derived from the (2, 0) compactification of E8×E′8 heterotic string, the massless matter field spectra at the GUT scale Mx and the breaking directions of GUT symmetries are discussed. A pseudo-left-right symmetric Pati-Salam model is naturally deduced in the SUSY SO(10) GUT and shown to have an interesting property, Mx≃MP1, MR≃1010 GeV and Ms (the scale of superpartner masses) ≃104 GeV, as a result of the renormalization group equation analysis using the new precise LEP data.

Can the “doublet-triplet splitting” problem be solved without doublet-triplet splitting?

We consider a new possible mechanism for the natural solution of the doublet-triplet splitting problem in SUSY GUTs. In contrast to the usually discussed scenarios, in our case the GUT symmetry breaking does not provide any splitting between the Higgs doublet and the triplet masses. The weak doublet and its colour triplet partner both remain light, but the triplet automatically occurs decoupled from the quark and lepton superfields and cannot induce proton decay. The advantage of the above scenario is the absence at the GUT scale of the baryon number violating the tree level d = 5 and d = 6 operators via the colour triplet exchange. It is shown that in flipped SU(5) GUT they do not appear at any scale. In the SO(10) model, such operators can be induced after SUSY breaking but are strongly suppressed.

Color breaking and X-, Y- and W- boson condensation on the cosmic string

The GUT symmetry breaking pattern can be changed in the core of the cosmic string. This can lead to the accumulation of the X-, Y-, W ±-gauge boson condensates on the phase boundary around the vortex. A similar condensation of the gauge bosons, which may take place during different phase transitions in the early Universe, can play some role in the generation of the baryon asymmetry.

Dynamical electroweak, GUT and family symmetry breaking in an E 8 SUSY sigma model

The electroweak symmetry may be broken dynamically by a mechanism similar to the one of the Nambu-Jona-Lasinio Model. We show that scale-invariant supersymmetric sigma models can provide the required four-fermi interactions and solve the associated hierarchy problem. A model based on E 8/SO(10)×SU(3) is discussed in detail; the SU(3) family group is broken together with the GUT group SO(10) and a hierarchy of quark and lepton masses follows automatically due to an extended Higgs sector and radiative corrections.

Horizontal interaction and their symmetries in GUTs

Using very general assumptions we find and discuss a large class of unified models with horizontal symmetries. We classify them and show on the basis of renormalisation group equations that the typical horizontal mass scale must be at least 109–1013 GeV, depending on the model. A class of nonsupersymmetric theories with horizontal symmetries is discovered which predicts a proton lifetimeτp≧1033 and sin2θw≃0.23. It is also argued that supersymmetric unified models involving horizontal symmetries are unlikely to meet present experimental and theoretical requirements—contrary to ordinary supersymmetric theories without horizontal sector.

Horizontal interactions and their symmetries in GUTs

Horizontal interactions and their symmetries in GUTs

Chaotic inflation and cold baryosynthesis in a supersymmetric gut

We consider chaotic inflation followed by Affleck-Dine cold baryosynthesis in a recently proposed flipped SU(5)×(1) GUT derived from the superstring. We show that the presence of a “quasi-flat” direction λΨ QF 4 in the scalar potential with λ=| λ e| 2∼10 −11 leads naturally to density perturbations ϖϱ ϱ ∼10 −4−10 −5 . We also show that the decay of an Affleck-Dine-like direction Ψ AD leads naturally to n B s ≈10 −6−10 −10 taking account of the large increase in entropy Δ∼10 8 produced by the subsequent decay of the “flaton” field Ψ responsible for GUT symmetry breaking.

Monopole abundance from first‐order GUT phase transition of the early Universe

AbstractMonopole annihilation and pair creation are investigated in a first order GUT symmetry breaking phase transition without inflation. It is found that even with complete initial monopole suppression, some monopoles are inevitably produced during the transition. According to this, some constraints are obtained for initial and equilibrium monopole densities in order to be compatible with the present observational limits even without inflation.