arXiv subjects

Alon E. Faraggi

Publications and source records attributed to Alon E. Faraggi.

At least 109 records · Page 6Linked to original sources

arXiv2002

Phenomenological aspects of M-theory

The Standard Model data suggests the realization of grand unification structures in nature, in particular that of SO(10). A class of string vacua that preserve the SO(10) embedding, are the three generation free fermion heterotic-string models, that are related to Z2xZ2 orbifold compactification. Attempts to use the M-theory framework to explore further this class of models are discussed. Wilson line breaking of the SO(10) GUT symmetry results in super-heavy meta-stable states, which produce several exotic dark matter and UHECR candidates, with differing phenomenological characteristics. Attempts to develop the tools to study the properties of these states in forthcoming UHECR experiments are discussed. It is proposed that quantum mechanics arises from an equivalence postulate, that may lay the foundations for the rigorous formulation of quantum gravity.

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arXiv2002

CP violation in realistic String Models with family universal anomalous U(1)

The characteristic property of the Z2XZ2 orbifold compactification is the cyclic permutation symmetry between the three twisted sectors. We discuss how this property, which is retained in a class of realistic free fermionic string models, may be instrumental in enabling fermion mass hierarchy while ensuring sfermion mass degeneracy, irrespective of the dominant source of supersymmetry breaking. The cyclic symmetry is reflected in some models in the existence of a family universal anomalous U(1)_A. We analyze the FCNC and CP violation effects in a model with a dominant U(1)_A SUSY breaking. In this theories, new sources of FC are always suppressed with respect to the average sfermion masses. We make a phenomenological analysis of these effects and find that in most of the cases they are in qualitative agreement with the phenomenological limits. The most sensitive low-energy observables to these new FC sources are the $ε_K$ parameter, measuring indirect CP violation in neutral kaon mixing and EDMs. These observables set important constraints on the structure of the sfermion mass matrices, but do not require a large fine-tuning of the initial parameters and can be satisfied in most realistic constructions.

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arXiv2002

Nonperturbative flipped SU(5) vacua in heterotic M-theory

The evidence for neutrino masses in atmospheric and solar neutrino experiments provides further support for the embedding of the Standard Model fermions in the chiral 16 SO(10) representation. Such an embedding is afforded by the realistic free fermionic heterotic-string models. In this paper we advance the study of these string models toward a non-perturbative analysis by generalizing the work of Donagi, Pantev, Ovrut and Waldram from the case of G=SU(2n+1) to G=SU(2n) stable holomorphic vector bundles on elliptically fibered Calabi-Yau manifolds with fundamental group Z2. We demonstrate existence of G=SU(4) solutions with three generations and SO(10) observable gauge group over Hirzebruch base surface, whereas we show that certain classes of del Pezzo base surface do not admit such solutions. The SO(10) symmetry is broken to SU(5)XU(1) by Wilson line. The overlap with the realistic free fermionic heterotic-string models is discussed.

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arXiv2002

Partition functions of NAHE-based free fermionic string models

The heterotic string free fermionic formulation produced a large class of three generation models, with an underlying SO(10) GUT symmetry which is broken directly at the string level by Wilson lines. A common subset of boundary condition basis vectors in these models is the NAHE set, which corresponds to Z2 X Z2 orbifold of an SO(12) Narain lattice, with (h11,h21)=(27,3). Alternatively, a manifold with the same data is obtained by starting with a Z2 X Z2 orbifold at a generic point on the lattice, with (h11,h21)=(51,3), and adding a freely acting Z2 involution. The equivalence of the two constructions is proven by examining the relevant partition functions. The explicit realization of the shift that reproduces the compactification at the free fermionic point is found. It is shown that other closely related shifts reproduce the same massless spectrum, but different massive spectrum, thus demonstrating the utility of extracting information from the full partition function. A freely acting involution of the type discussed here, enables the use of Wilson lines to break the GUT symmetry and can be utilized in non-perturbative studies of the free fermionic models.

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arXiv2002

Flat Directions in Left-Right Symmetric String Derived Models

The only string models known to reproduce the Minimal Supersymmetric Standard Model in the low energy effective field theory are those constructed in the free fermionic formulation. We demonstrate the existence of quasi-realistic free fermionic heterotic-string models in which supersymmetric singlet flat directions do not exist. This raises the possibility that supersymmetry is broken perturbatively in such models by the one-loop Fayet-Iliopoulos term. We show, however, that supersymmetric flat directions that utilize VEVs of some non-Abelian fields in the massless string spectrum do exist in the model. We argue that hidden sector condensates lift the flat directions and break supersymmetry hierarchically.

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arXiv2002

Seeking experimental probes of string unification

A general prediction of string unification is the existence of exotic states with fractional charges under the free unbroken Abelian generators of the underlying GUT symmetry. Such states may be long-lived due to the existence of weakly broken gauge, or local discrete, symmetries, and may serve as experimental probes of string theory in forthcoming cosmic ray and dark matter experiments.

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arXiv2002

Susy QCD and High Energy Cosmic Rays 1. Fragmentation functions of Susy QCD

The supersymmetric evolution of the fragmentation functions (or timelike evolution) within N=1 $QCD$ is discussed and predictions for the fragmentation functions of the theory (into final protons) are given. We use a backward running of the supersymmetric DGLAP equations, using a method developed in previous works. We start from the usual QCD parameterizations at low energy and run the DGLAP back, up to an intermediate scale -assumed to be supersymmetric- where we switch-on supersymmetry. From there on we assume the applicability of an N=1 supersymmetric evolution (ESAP). We elaborate on possible application of these results to High Energy Cosmic Rays near the GZK cutoff.

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arXiv2001

String Inspired Z' Model With Stable Proton and Light Neutrino Masses

Grand unification, and its incarnation in the form of heterotic-string unification, are the only extensions of the Standard Model that are rooted in the structure of the Standard Model itself. In this context, it was proposed that the exclusiveness of proton stability and suppression of neutrino masses necessitates the existence of an additional U(1)_Z' symmetry, which is of non-GUT origin and remains unbroken down to intermediate, or low, energies. Realistic string models frequently give rise to non-GUT U(1) symmetries, which arise from the flavor symmetries in the models. In this paper we demonstrate in a string-inspired toy model that such a stringy Z' can indeed guarantee proton longevity and viable phenomenology in the neutrino sector, as well as in the quark and charged lepton sectors.

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arXiv2001

Doublet-Triplet Splitting in Realistic Heterotic String Derived models

There has been recently a surge of interest in Grand Unified Theories on orbifolds of higher dimensional spaces. In particular, the higher dimensional doublet-triplet splitting mechanism has been of much interest. I revisit the superstring doublet-triplet splitting mechanism in which the color triplets are projected out by the GSO projections, while leaving the electroweak doublets in the physical spectrum. The connection with the higher dimensional theories is elucidated. It is shown that the doublet-triplet splitting depends crucially on the assignment of boundary conditions in the compactified directions.

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arXiv2001

SUSY Scaling Violations and UHECR

Advancing QCD toward astroparticle applications generates new challenges for perturbation theory, such as the presence of large evolution scales with sizeable scaling violations involving both the initial and the final state of a collision. Possible applications in the context of Ultra High Energy Cosmic Rays (UHECR) of these effects are discussed.

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arXiv2001

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 $\pm1/2$, 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.

hep-ph↗

arXiv2000

Proton Stability and Superstring Z'

Recently it was argued that proton lifetime limits impose that the scale of quantum gravity must be above 10^{16} GeV. By studying the proton stability in the context of realistic heterotic-string models, I propose that proton longevity necessitates the existence of an additional U(1)_{Z'} symmetry, which is of non-GUT origin and remains unbroken down to intermediate, or low, energies. It is shown that the realistic string models frequently give rise to U(1) symmetries, which suppress the proton decay mediating operators, with, or without, the possibility of R-parity violation. By studying the F- and D-flat directions, I examine whether the required symmetries remain unbroken in the supersymmetric vacuum and show that in some examples they can, whereas in others they cannot. The proton decay rate is proportional to the U(1)_{Z'} symmetry breaking scale. Imposing the proton lifetime limits I estimate the U(1)_{Z'} breaking scale and show that if substantial R-parity violation is present the associated Z' is within reach of forthcoming collider experiments

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arXiv2000

Left-Right Symmetric Heterotic-String Derived Models

Recently it was demonstrated that free fermionic heterotic-strings can produce models with solely the Minimal Supersymmetric Standard Model states in the low energy spectrum. This unprecedented result provides further strong evidence for the possibility that the true string vacuum shares some of the properties of the free fermionic models. Past free fermionic models have focused on several possible unbroken observable SO(10) subgroups at the string scale, which include the flipped SU(5) (FSU5), the Pati-Salam (PS) string models, and the string Standard-like Models (SLM). We extend this study to include the case in which the SO(10) symmetry is broken to the Left-Right Symmetric (LRS) gauge group, SO(10) -> SU(3)_C X U(1)_{B-L} X SU(2)_L X SU(2)_R. We present several models of this type and discuss their phenomenological features. The most striking new outcome of the LRS string models, in contrast to the case of the FSU5, the PS, and the SLM string models, is that they can produce effective field theories that are free of Abelian anomalies. We discuss the distinction between the two types of free fermionic models which result in the presence, or absence, of an anomalous U(1). As a counter example we also present a LRS model that does contain an anomalous U(1). Additionally, we discuss how in string models the Standard Model spectrum may arise from the three $\mbf 16$ representations of SO(10), while the weak-hypercharge does not have the canonical SO(10) embedding.

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arXiv2000

Self-Interacting Dark Matter from the Hidden Heterotic-String Sector

It has been suggested recently that self-interacting dark matter fits better the observational characteristics of galaxy dynamics. We propose that the self-interacting dark matter is composed from the glueballs of the hidden sector non-Abelian gauge group, while the hidden matter states exist in vector-like representation and decouple from the light spectrum. It is shown that these glueballs are semi-stable with the life-time larger than the present age of the Universe, if their mass is 1 GeV or less. The constraint on their abundance today suggests that the energy was stored in the hidden sector soon after inflation. This imposes an upper limit on the reheating temperature. We further study the naturalness of this scenario in the context of the free-fermionic string models and point out a class of such models where the self-interacting dark matter from the hidden sector is indeed plausible.

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arXiv2000

Equivalence Principle, Higher Dimensional Moebius Group and the Hidden Antisymmetric Tensor of Quantum Mechanics

We show that the recently formulated Equivalence Principle (EP) implies a basic cocycle condition both in Euclidean and Minkowski spaces, which holds in any dimension. This condition, that in one-dimension is sufficient to fix the Schwarzian equation [6], implies a fundamental higher dimensional Moebius invariance which in turn univocally fixes the quantum version of the Hamilton-Jacobi equation. This holds also in the relativistic case, so that we obtain both the time-dependent Schroedinger equation and the Klein-Gordon equation in any dimension. We then show that the EP implies that masses are related by maps induced by the coordinate transformations connecting different physical systems. Furthermore, we show that the minimal coupling prescription, and therefore gauge invariance, arises quite naturally in implementing the EP. Finally, we show that there is an antisymmetric two-tensor which underlies Quantum Mechanics and sheds new light on the nature of the Quantum Hamilton-Jacobi equation.

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arXiv2000

Duality, Equivalence, Mass and The Quest For The Vacuum

I contemplate the possibility that the mismatch between the maximally symmetric point (the free fermionic point) and the strictly self-dual point in the Narain moduli space plays a role in the string vacuum selection. The role of self-duality in the recent formulation of quantum mechanics from an equivalence postulate, and the new perspective that it offers on the foundations of quantum gravity and the origin of mass, are discussed.

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arXiv1999

Superstring Phenomenology - A Personal Perspective

In the first part of this paper I review the construction of the realistic free fermionic models, as well as current attempts to study aspects of these models in the nonperturbative framework of M- and F-theories. I discuss the recent demonstration of a Minimal Superstring Standard Model, which contains in the observable sector, below the string scale, solely the MSSM charged spectrum, and provides further support to the assertion that the true string vacuum is connected to the Z_2 X Z_2 orbifold in the vicinity of the free fermionic point in the Narain moduli space. In the second part I review the recent formulation of quantum mechanics from an equivalence postulate, which offers a new perspective on the synthesis of gravity and quantum mechanics, and contemplate possible relations with string theory and beyond.

hep-th↗

arXiv1999

Probing the Desert with Ultra--Energetic Neutrinos from the Sun and the Earth

Realistic superstring models generically give rise to exotic matter states, which arise due to the ``Wilson-line'' breaking of the non-Abelian unifying gauge symmetry. Often such states are protected by a gauge or local discrete symmetry and therefore may be stable or meta-stable. We study the possibility of a flux of high energy neutrinos coming from the sun and the earth due to the annihilation of such exotic string states. We also discuss the expected flux for other heavy stable particles -- like the gluino LSP. We comment that the detection of ultra-energetic neutrinos from the sun and the earth imposes model independent constraints on the high energy cutoff, as for example in the recently entertained TeV scale Kaluza-Klein theories. We therefore propose that improved experimental resolution of the energy of the muons in neutrino detectors together with their correlation with neutrinos from the sun and the center of the earth will serve as a probe of the desert in Gravity Unified Theories.

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