arXiv subjects

Alon E. Faraggi

Publications and source records attributed to Alon E. Faraggi.

158 records · Page 9Linked to original sources

arXiv1994

Deriving The Standard Model From Superstring Theory

I outline a program to derive the Standard Model directly from superstring theory. I present a class of three generation superstring standard--like models in the free fermionic formulation. I discuss some phenomenological properties of these models. In particular these models suggest an explanation for the top quark mass hierarchy. A numerical estimate yielded $m_t\sim175-180~GeV$. The general texture of fermion mass matrices was obtained from analysis of nonrenormalizable terms up to order $N=8$.I argue that the realistic features of these models are due to the underlying $Z_2\times Z_2$ orbifold, with standard embedding, at the free fermionic point in toroidal compactification space.

hep-ph↗

arXiv1994

Proton stability in superstring derived models

I discuss the problem of proton decay, from dimension four, five and six operators, in superstring derived standard--like models. I classify the sectors that produce color triplet superfields which may generate proton decay from dimension five and six operators. I show that for two of these sectors there exist a unique superstring doublet--triplet splitting mechanism that projects out the color triplets by means of the GSO projection, while leaving the electroweak doublets in the physical spectrum. I investigate possible proton decay due to additional color triplets in the massless spectrum and due to nonrenormalizable terms. I show that there exist models in which the dimension four, five and six operators, that lead to proton decay, are forbidden by the symmetries of the string models, to all orders of nonrenormalizable terms.

hep-ph↗

arXiv1993

Light Threshold Effects in Supersymmetric Grand Unified Theories

Supersymmetric Grand Unified Theories have a rich spectrum of particles barely heavier than the intermediate vector bosons. As their non-supersymmetric counterparts, they lead to many relations among low energy observables. But the precise form of the predictions is modified by the extended spectrum. If the masses of these new particles are comparable to $M_Z$, the standard computation of their effect becomes inaccurate. We present a detail discussion of the correct procedure, and carry out the relevant computations to one loop order. The procedure we propose has the advantage over other existing methods that two-loop running of gauge couplings can be incorporated readily and consistently. Attention is paid to the special treatment that the top and Higgs particles must receive. The size of the effect is explored for a range of parameters in the minimal supersymmetric $SU(5)$ grand-unified theory with radiative breaking. It is found that the naive (leading-log) computation can be fairly inaccurate.

hep-ph↗

arXiv1993

Light Fermion Masses in Superstring Derived Standard--like Models

I discuss the suppression of the lightest generation fermion mass terms in realistic superstring standard--like models in the free fermionic formulation. The suppression of the mass terms is a consequence of horizontal symmetries that arise due to the $Z_2\times Z_2$ orbifold compactification. In a specific model I investigate the possibility of resolving the strong CP puzzle by a highly suppressed up quark mass. In some scenarios the up quark mass may be as small as $10^{-8}MeV$. I show that in the specific model the suppression of the up quark mass is incompatible with the requirement of a nonvanishing electron mass. I discuss how this situation may be remedied.

hep-ph↗

arXiv1993

Z_2\times Z_2$ orbifold compactification as the origin of realistic free fermionic models

I discuss the correspondence between realistic four dimensional free fermionic models and $Z_2\times Z_2$ orbifold compactification. %I illustrate this correspondence for one particular example. I discuss the properties of the $Z_2\times Z_2$ orbifold that are reflected in the realistic free fermionic models. I argue that the properties of the realistic free fermionic models arise due to the underlying $Z_2\times Z_2$ orbifold compactification with nontrivial background fields. I suggest that three generation is a natural outcome of $Z_2\times Z_2$ orbifold compactification with ``standard embedding'' and at the point in compactification space that corresponds to the free fermionic formulation. I discuss how quark flavor mixing is related to the compactification.

hep-ph↗

arXiv1993

Cabibbo--Kobayashi--Maskawa Mixing in Superstring Derived Standard--like Models

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.

hep-ph↗

arXiv1993

Neutrino Masses in Superstring Derived Standard--like 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.

hep-th↗

arXiv1993

Gauge Coupling Unification in Superstring Derived Standard--like Models

I discuss gauge coupling unification in a class of superstring standard--like models, which are derived in the free fermionic formulation. Recent calculations indicate that the superstring unification scale is at $O(10^{18}GeV)$ while the minimal supersymmetric standard model is consistent with LEP data if the unification scale is at $O(10^{16})GeV$. A generic feature of the superstring standard--like models is the appearance of extra color triplets $(D,{\bar D})$, and electroweak doublets $(\ell,{\bar\ell})$, in vector--like representations, beyond the minimal supersymmetric standard model. I show that gauge coupling unification at $O(10^{18}GeV)$ in the superstring standard--like models can be consistent with LEP data. I present an explicit standard--like model that can realize superstring gauge coupling unification.

hep-ph↗

arXiv1993

Cabibbo Mixing in Superstring Derived Standard--like Models

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.

hep-ph↗

arXiv1993

Construction of Realistic superstring Standard--like Models

I discuss the construction of realistic superstring standard--like models in the four dimensional free fermionic formulation. I discuss proton lifetime constraints on superstring models. I discuss the massless spectrum of the superstring standard--like models, the texture of fermion mass matrices in these models and argue that the realistic features of these models are due to the underlying $Z_2\times Z_2$ orbifold compactification. (talk presented at the TEXAS\\PASCHOS conference, Berkeley CA, December 13--18 1992)

hep-ph↗

arXiv1992

Generation Mass Hierarchy in Superstring Derived Models

I discuss the problem of generation mass hierarchy in the context of realistic superstring models which are constructed in the free fermionic formulation. These models correspond to models which are compactified on $Z_2\times Z_2$ orbifold. I suggest that the hierarchy among the generations results from horizontal symmetries, which arise from the compactification. In particular, I show that in a class of free fermionic standard--like models, the suppression of the mass terms for the lightest generation is a general, and unambiguous, characteristic of these models. I show that the mixing between the generations is suppressed due to the horizontal symmetries. I conclude that these models may potentially explain the generation mass hierarchy.

hep-ph↗

arXiv1992

Comment On ``Grand Unification and Supersymmetric Threshold"

Barbieri and Hall have argued that threshold effects at the scale of grand-unification wipe out predictions on the SUSY scale, M_S. Using triviality arguments we give upper bounds on ultraheavy particles, while proton stability gives lower bounds on the mass of the higgs color-triplet. We find no useful lower bound on the $Σ$ supermultiplet, but if the strong coupling constant is as large as recent experiments suggest, unification in the minimal SUSY SU(5) model requires that the $Sigma$ masses be $\sim 10^{-7}M_V$ and that the color octet and weak triplet be split in mass by a factor of $\sim$100.

hep-ph↗

arXiv1992

Construction of Realistic Standard--like Models in the Free Fermionic Superstring Formulation

I discuss in detail the construction of realistic superstring standard--like models in the four dimensional free fermionic formulation. The analysis results in a restricted class of models with unique characteristics: (i) Three and only three generations of chiral fermions with their superpartners and the correct Standard Model quantum numbers. (ii) Proton decay from dimension four and dimension five operators is suppressed due to gauged $U(1)$ symmetries. (iii) There exist Higgs doublets from two distinct sectors, which can generate realistic symmetry breaking. (iv) These models explain the top--bottom mass hierarchy. At the trilinear level of the superpotential only the top quark gets a non vanishing mass term. The bottom quark and the lighter quarks and leptons get their mass terms from non renormalizable terms. This result is correlated with the requirement of a supersymmetric vacuum at the Planck scale. (v) The models predict the existence of small hidden gauge groups, like $SU(3)$, with matter spectrum in vector representations.

hep-th↗

arXiv1992

Aspects of Nonrenormalizable Terms in a Superstring Derived Standard--like Model

I investigate the role of nonrenormalizable terms, up to order N=8, in a superstring derived standard--like model. I argue that nonrenormalizable terms restrict the gauge symmetry, at the Planck scale, to be $SU(3)\times SU(2)\times U(1)_{B-L}\times U(1)_{T_{3_R}}$ rather than $SU(3)\times SU(2)\times U(1)_Y$. I show that breaking the gauge symmetry directly to the Standard Model leads to breaking of supersymmetry at the Planck scale, or to dimension four, baryon and lepton violating, operators. I show that if the gauge symmetry is broken directly to the Standard Model the cubic level solution to the F and D flatness constraints is violated by higher order terms, while if $U(1)_{Z^\prime}$ remains unbroken at the Planck scale, the cubic level solution is valid to all orders of nonrenormalizable terms. I discuss the Higgs and fermion mass spectrum. I demonstrate that realistic, hierarchical, fermion mass spectrum can be generated in this model.

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