arXiv subjects
Publications and source records attributed to Edi Halyo.
We argue that dilaton supersymmetry breaking in string derived supergravity requires an effective superpotential which is not separable as a function of the dilaton times a function of the moduli. We show that in a simple model with hidden sector matter condensation and a dilaton independent term one can easily obtain $|F_S| \not=0$. For a wide range of realistic model parameters $|F_S|>>|F_T|$ and supersymmetry is mainly broken in the dilaton direction.
We show that large string threshold corrections can reconcile the string and MSSM unification scales in fermionic strings. This requires at least three moduli with large VEVs which are different from each other and MSSM states arising in an unconventional manner from the string spectrum. The former is easily achieved by supersymmetry breaking by both hidden gaugino and matter condensation whereas the latter needs to be seen in explicit string models.
We investigate the effects of hidden matter condensation on supersymmetry breaking in supergravity models derived from free fermionic strings. We find that the minimum of the effective potential in the modulus direction depends strongly on only one parameter which is fixed by the hidden sector. For nonpositive values of the parameter the potential is unstable which constrains realistic models severely. For positive and decreasing values which correspond to more and/or lighter hidden matter, $T_R$ increases whereas $T_I$ is periodic and depends on the parameter very weakly. Supersymmetry can be broken in the matter direction with a stable vacuum only if the fields which give mass to the hidden matter are light and have modulus independent Kahler potentials. Then, for a wide range of model parameters, supersymmetry is mainly broken by hidden matter condensation in the matter direction rather than by hidden gaugino condensation in the modulus direction.
We investigate the dependence of the number and type of untwisted moduli on the boundary condition vectors of relistic free fermionic strings. The number of moduli is given by six minus the number of complex internal world--sheet fermions and the type of moduli is determined by the details of the world--sheet left--right asymmetry of the boundary conditions for the internal fermions. We give a geometrical description of our results in terms of the transformations of the compactified dimensions of $Z_2 \times Z_2$ orbifolds. We investigate all possible boundary conditions for the internal fermions and prove our results in general by showing that world--sheet supersymmetry eliminates those boundary conditions which violate our results.
We show that supersymmetry can be broken mainly by hidden matter condensates in the observable matter direction in generic superstring models. This happens only when the fields whose VEVs give masses to hidden matter do not decouple at the condensation scale. We find how the parameters of the string model and the vacuum determine whether supersymmetry is broken mainly by hidden matter or gaugino condensates and in the matter or moduli directions.
We examine the problem of supersymmetry breaking in realistic superstring standard--like models which are constructed in the free fermionic formulation. We impose a supersymmetric vacuum at the Planck scale by requiring vanishing F and D constraints at the cubic level of the superpotential. We then study possible scenarios for supersymmetry breaking by examining the role of nonrenormalizable terms and hidden sector gaugino and matter condensates. We argue that in some scenarios hierarchical supersymmetry breaking in the observable sector is possible.
We investigate a scenario in which the CKM matrix arises from leptoquark--down quark mixing in a particular standard--like superstring model. We find that for some choices of F and D flat directions realistic quark mixing can be obtained without any phenomenological problems. This scenario predicts a symmetric (in absolute value) CKM matrix.
We show that there can be TeV scale scalar and fermionic leptoquarks with very weak Yukawa couplings in a generic standard--like superstring model. Leptoquark--(down--like) quark mixing though present, is not large enough to violate the unitarity bounds on the CKM matrix. The constraints on leptoquark masses and couplings from FCNCs are easily satisfied whereas those from baryon number violation may cause problems. The leptoquarks of the model are compared to the ones in $E_6$ Calabi--Yau and flipped $SU(5) \times U(1)$ models.
We investigate the R symmetries of standard--like superstring models. At the level of the cubic superpotential there are three global $U(1)$ R symmetries. These are broken explicitly by $N>3$ terms in the superpotential and spontaneously by scalar VEVs necessary to preserve supersymmetry at $M_P$. A $Z_2$ discrete symmetry remains but is equivalent to fermion number modulo 2. These models possess an effective R parity which arises from the interplay between the gauged $U(1)_{B-L}$ and $U(1)_{r_{j+3}}$.
We examine the light quark masses in a standard--like superstring model in the four dimensional free fermionic formulation. We find that the supersymmetry constraints in the observable and hidden sectors eliminate all large contributions to $m_u$ and $m_d$ and force them to be much smaller than the other quark masses. The requirement for an acceptable Higgs doublet spectrum results in $m_u<<m_d$. In these models a realistic $m_d$ can always be obtained whereas $m_u$ is at most $10^{-5}~MeV$. For particular choices of flat directions or vacua $m_u$ can be as small as $10^{-7}~MeV$ but cannot vanish.
We find that there are three axions in standard--like superstring models in the four dimensional free fermionic formulation. These axions are either harmful or very heavy. Therefore, they cannot solve the strong CP problem. We show that this is a general result in superstring models with chiral generations from the $Z_2$ twisted sectors which use a $Z_4$ twist.
An effective Lagrangian for the technidilaton and its interactions with matter is constructed. Properties of the technidilaton are compared with those of the Higgs boson. Technidilaton decays and production channels are investigated. Main technidilaton decays are suppressed compared to the Higgs boson and the most important production mechanism is due to gluon fusion. Prospects for technidilaton production and detection at $e^+e^-$ colliders and the SSC are examined. LEP 1, LEP 2 and SSC can find or rule out a technidilaton with a mass up to $10~GeV$, $40~GeV$ and $230~GeV$ respectively.
We examine the problem of three generation quark flavor mixing in realistic, superstring derived standard--like models, constructed in the free fermionic formulation. We study the sources of family mixing in these models and discuss the necessary conditions to obtain a realistic Cabibbo--Kobayashi--Maskawa (CKM) mixing matrix. In a specific model, we estimate the mixing angles and discuss the weak CP violating phase. We argue that the superstring standard--like models can produce a realistic CKM mixing matrix. We discuss the possible textures of quark mass matrices that may be obtained in these models.
We propose a new scenario in a class of superstring derived standard--like models that explains the suppression of the left--handed neutrino masses. Due to nonrenormalizable terms and the breaking of the $U(1)_{Z^\prime}$ symmetry a generalized see--saw mechanism takes place. Contrary to the traditional see--saw mechanism in GUTs, the see--saw scale and the right--handed neutrino mass scale are suppressed relative to the $U(1)_{Z^\prime}$ breaking scale.
We examine the problem of generation mixing in realistic superstring derived standard--like models, constructed in the free fermionic formulation. We study the possible sources of family mixing in these models . In a specific model we estimate the Cabibbo angle. We argue that a Cabibbo angle of the correct order of magnitude can be obtained in these models.