Phenomenology ofSO(10) unified superstring models with intermediate scaleSU R(2) breaking

Electroweak breaking and the supersymmetric particle spectrum are discussed in superstring theories where the gauge group after compactification isSO(10)×E _s ^′ , and where the gauge symmetry after flux breaking isSU(3)×SU(2)×SU(2)×U(1).     

Dynamical supersymmetry breaking and gauge anomalies

Some aspects of supersymmetric gauge theories and discussed. It is shown that dynamical supersymmetry breaking does not occur in supersymmetric QED in higher dimensions. The cancellation of both local (perturbative) and global (non-perturbative) gauge anomalies are also discussed in supersymmetric gauge theories. We argue that there is no dynamical supersymmetry breaking in higher dimensions in any supersymmetric gauge theories free of gauge anomalies. It is also shown that for supersymmetric gauge theories in higher dimensions with a compact connected simple gauge group, when the local anomaly-free condition is satisfied, there can be at most a possibleZ ₂ global gauge anomaly in extended supersymmetricSO(10) (or spin (10)) gauge theories inD=10 dimensions containing additional Weyl fermions in a spinor representation ofSO(10) (or spin (10)). In four dimensions with local anomaly-free condition satisfied, the only possible global gauge anomalies in supersymmetric gauge theories areZ ₂ global gauge anomalies for extended supersymmetricSP(2N) (N=rank) gauge theories containing additional Weyl fermions in a representation ofSP(2N) with an odd 2nd-order Dynkin index.     

Superalgebras in N = 1 gauge theories

N = 1 supersymmetric gauge theories with global flavor symmetries contain a gauge invariant W-superalgebra which acts on its moduli space of gauge invariants. With adjoint matter, this superalgebra reduces to a graded Lie algebra. When the gauge group is SO(n_c), with vector matter, it is a W-algebra, and the primary invariants form one of its representation. The same superalgebra exists in the dual theory, but its construction in terms of the dual fields suggests that duality may be understood in terms of a charge conjugation within the algebra. We extend the analysis to the gauge group E₆.     

Chiral anomalies and constraints on the gauge group in higher-dimensional supersymmetric Yang-Mills theories

Chiral anomalies for gauge theories in any even dimension are computed and the results applied to supersymmetric theories in D = 6, 8 and 10. For D = 8 there is an anomalous chiral U(1) invariance, just as in D = 4, except for certain special groups. For D = 6 and D = 10 there is no anomalous chiral U(1) symmetry, but the gauge current is anomalous except for certain “anomaly-free” groups. For D = 6 the group is thereby constrained to be one of {SU(2), SU(3), exceptional}, while for D = 10 it is constrained to be one of {SU(n) n ≤ 5, USp(4), E₈}.     

Asymmetric orbifolds and higher level models

I introduce a class of string constructions based on asymmetric orbifolds leading to level two models. In particular, I derive in detail various models with gauge groups E₆ and SO(10), including a four generation E₆ model with two adjoint representations. The occurrence of multiple adjoint representations is a generic feature of the construction. In the course of describing this approach, I will address the problem of twist phases in higher twisted sectors of asymmetric orbifolds.     

Fermion spectra from superstrings

Some compactifications of the ten-dimensional anomaly-free E₈ × E₈ and SO(32) theories that correspond to superstrings are studied. Compactification is achieved by setting the classical gauge field equal to the spin connection. The resulting chiral fermion spectra are obtained for any six-dimensional manifold, under the condition Tr F² = 30 Tr R², plus a quantization condition for U(1) charges. For E₈ × E₈ these conditions lead to potentially realistic models for any irreducible six-dimensional manifold and any embedding of the holonomy group. Apart from a few more exotic examples, the four-dimensional models we obtain are more or less standard SU(5), SO(10), SU(4) × SU(2) × SU(2) or E₆ models.     

The fate of primordial magnetic monopoles

Unified gauge theories, in which the SU (2)_L and U (1)_Y subgroups do not have non-trivial intersections, possess an in-built mechanism for a complete extinction of the primordial magnetic monopoles. The potential conflict with the standard hot big bang cosmology is therefore avoided in such theories. The usual gauge theories, based on SU (5), SO (10) and E₆ do not have this property.     

Renormalization of scalar quartic and Yukawa couplings in unified gauge theories based onE 6

Renormalization group equations for scalar and Yukawa couplings in gauge theories based on the exceptional groupE ₆ are analyzed. Asymptotic freedom is possible only for a limited set of scalar fields, and then only if several fermion generations are present. The infrared behavior of the scalar quartic coupling constants is striking: they are necessarily driven out of the region of positivity of the classical potential. Some useful group theoretic relations inE ₆ are given in an Appendix.     

Seiberg-Witten geometry with various matter contents

We obtain the Seiberg-Witten geometry for four-dimensional N = 2 gauge theory with gauge group SO(2N_c) (N_c ⩽ 5) with massive spinor and vector hypermultiplets by considering the gauge symmetry breaking in the N = 2 E₆ theory with massive fundamental hypermultiplets. In a similar way the Seiberg-Witten geometry is determined for N = 2 SU(N_c) (N_c ⩽ 6) gauge theory with massive antisymmetric and fundamental hypermultiplets. Whenever possible we compare our results expressed in the form of ALE fibrations with those obtained by geometric engineering and brane dynamics, and find a remarkable agreement. We also show that these results are reproduced by using N = 1 confining phase superpotentials.     

Superconformal Indices of $${{\mathcal N}=4}$$ SYM Field Theories

Superconformal indices (SCIs) of 4d N = 4{{\mathcal N} = 4} SYM theories with simple gauge groups are described in terms of elliptic hypergeometric integrals. For F ₄, E ₆, E ₇, E ₈ gauge groups this yields first examples of integrals of such type. S-duality transformation for G ₂ and F ₄ SCIs is equivalent to a change of integration variables. Equality of SCIs for SP(2N) and SO(2N + 1) group theories is proved in several important special cases. Reduction of SCIs to partition functions of 3d N=2{{\mathcal N}=2} SYM theories with one matter field in the adjoint representation is investigated, corresponding 3d dual partners are found, and some new related hyperbolic beta integrals are conjectured.     

Gauge group breaking by Wilson loops

We examine the breaking of gauge symmetries by Wilson loops in the Hosotani-Toms model by determining the background gauge field which minimises the one-loop effective potential for massless Dirac fermions. For anti-periodic fermions, all gauge groups remain unbroken. For periodic fermions, the groups G₂, F₄ and E₈ are broken by quantum corrections due to fermions in any irreducible representation, whereas E₆, E₇ and the classical groups only break if the fermion representation is in the same congruency class as the adjoint.     

Symmetry-breaking scenarios of Wilson-loop broken E6

In superstring theories formulated on a multiply-connected manifold, E₆ gauge symmetry can be broken at the Planck scale to an extended standard model via an effective Higgs adjoint. It is possible to arrange for the coloured components of a Higgs 27 to gain a large mass via this Wilson-Loop breaking while leaving some colour singlet components massless. The remaining light Higgs representations can then be applied to break the extended electroweak symmetry at a lower scale. We investigate some of the symmetry-breaking scenarios for a rank-six extended group. We find that the Higgs multiplets left light after Wilson-loop breaking are not sufficient to break the extended electroweak symmetry to U₁^em     

Fermion mass relations from a superstring inspired model

It is assumed that theE ₈ gauge group of theE ₈×E ₈ heterotic superstring can be broken intoSO(10). A model to give the mass relationm _u /m _d =m _c /m _s =m _t /m _b is presented and Kobayashi-Maskawa mixing is discussed.     

Supernova neutrino energy spectra and the MSW effect

The distortions in the thermal energy spectra for neutrinos produced in a supernova when a resonant oscillation, MSW effect, occurs are determined. In order to show this effect for some relevant and representative examples of unified gauge models, we have chosen SO(10), and SU(5)_SUSY, SO(10)_SUSY with a particular scheme for fermion masses (DHR model). The analysis has been performed for two choices of neutrinos parameters, predicted by the above models, and capable to explain the solar neutrino problem. In both cases one observes a strong distortion in the electron neutrino energy spectrum. This effect, computed for a wide range of SO(10)_SUSY models has produced the same results of the previous supersymmetric ones.     

Coset space dimensional reduction and Wilson flux breaking of ten-dimensional $\mathcal{N}=1$ , E8 gauge theory

We consider a supersymmetric E ₈ gauge theory, defined in ten dimensions and we determine all four-dimensional gauge theories resulting from the generalized dimensional reduction à la Forgacs–Manton over coset spaces, followed by a subsequent application of the Wilson flux spontaneous symmetry-breaking mechanism. Our investigation is constrained only by the requirements that (i) the dimensional reduction leads to the potentially phenomenologically interesting, anomaly-free, four-dimensional E ₆, SO₁₀ and SU₅ GUTs and (ii) the Wilson flux mechanism makes use only of the freely acting discrete symmetries of all possible six-dimensional coset spaces. Supported by the EPEAEK II programme IRAKLEITOS. Partially supported by the NTUA programme for basic research “Karatheodoris” and the European Union’s RTN programme under contract MRTN-CT-2006-035505.     

Geometry of multidimensional universes

LetG be a compact group of transformation (global symmetry group) of a manifoldE (multidimensional universe) with all orbits of the same type (one stratum). We studyG invariant metrics onE and show that there is one-to-one correspondence between those metrics and triples (g _μv,A _μ ^ä ,h _αβ), whereg _μv is a (pseudo-) Riemannian metric on the space of orbits (space-time),A _μ ^ä is a Yang-Mills field for the gauge groupN|H, whereN is the normalizer of the isotropy groupH inG, andh _αβ are certain scalar fields characterizing geometry of the orbits (internal spaces). The scalar curvature ofE is expressed in terms of the component fields onM. Examples and model building recipes are also given. The results generalize those of non-abelian Kaluza-Klein theories to the case where internal spaces are not necessarily group manifolds.     

The Dirac Equation in Six-dimensional <Emphasis Type="Italic">SO</Emphasis>(3,3) Symmetry Group and a Non-chiral “Electroweak” Theory

We propose a model of electroweak interactions without chirality in a six-dimensional spacetime with 3 time-like and 3 space-like coordinates, which allows a geometrical meaning for gauge symmetries. The spacetime interval ds ²=dx _μ dx ^μ is left invariant under the symmetry group SO(3,3). We obtain the six-dimensional version of the Dirac gamma matrices, Γ _μ , and write down a Dirac-like Lagrangian density, \(\mathcal{L}=i\bar{\psi}\Gamma ^{\mu }\nabla _{\mu }\psi\). The spinor ψ can be decomposed into two Dirac spinors, ψ ₁ and ψ ₂, interpreted as the electron and neutrino fields, respectively. In six-dimensional spacetime the electron and neutrino fields appear as parts of the same entity in a natural manner. The SO(3,3) Lorentz symmetry group is locally broken to the observable SO(1,3) Lorentz group, with only one observable time component, t _z . The t _z -axis may not be the same at all points of the spacetime, and the effect of breaking the SO(3,3) spacetime symmetry group locally to an SO(1,3) Lorentz group, is perceived by the observers as the existence of the gauge fields. We interpret the origin of mass and gauge interactions as a consequence of extra time dimensions, without the need of introducing the so-called Higgs mechanism for the generation of mass. Further, in our ‘toy’ model, we are able to give a geometric meaning to the electromagnetic and non-Abelian gauge symmetries.     

Superconformal deformation,zero-norm states and space-time symmetries of the superstring theories

We present a formalism to study type II and Heterotic superstrings with massless and massive background fields in the bosonic sector. This formalism is appropriate to study high energy symmetries of the superstring. As an example, we explicitly relate all massless symmetries to the massless zero-norm states in the spectrum. This includes theE ₈ ?E ₈ andSO (32) gauge symmetries in the ten-dimensional Heterotic string. The first (evenG-parity) massive level is briefly described. We then argue the existence of new symmetries for the massive Yang-Mills-like gauge bosons and tensor fields at each fixed mass level. These enlarged stringy symmetries correspond to the decoupling of massive zero-norm states in the spectrum.     

On thermodynamic properties of the chromoplasma

We calculate the contributions of electric and magnetic modes to some thermodynamic functions in SU(2)-gauge theory on the lattice 4×12³. It is shown that the behaviour of the chromoelectric part of the energy E_E can be interpreted within the Ising-type model in agreement with the universality hypothesis. At the same time the behaviour of the magnetic parts of the internal energy and pressure (i.e. E_M and P_M) differs drastically from that of E_E and P_M. The character of the temperature dependence of E_M and P_M exhibited here testifies to the presence of highly nonidentical properties of electric and magnetic excitation modes of chromoplasma and may shed light on the role of unstable modes in gauge theories.     

Non-perturbative aspects in supersymmetric gauge theories

We review our present understanding of those non-perturbative features of supersymmetric gauge theories that are believed to determine the properties of their ground states (vacua). A wide variety of theories is discussed in detail: pure Yang-Mills, theories with massive or massless real matter fields, theories with chiral matter, both for SU(N) and for the case of a general compact gauge group (as for instance E₈). Depending on some general features of the theory under consideration, various (perhaps) unexpected phenomena are shown to occur. Among these the breakdown of the (perturbatively established) non-renormalization theorem, the occurrence of runaway vacua in certain limits, the spontaneous dynamical breaking of supersymmetry itself in some chiral theories. Throughout the report we restrict ourselves to the confining picture instanton method, occasionally complementing it with the information coming from chiral and supersymmetric Ward-Takahashi identities. We compare our results with the ones suggested earlier by effective Lagrangian methods and, only briefly, with those obtained by other groups in the Higgs picture.