580 research outputs found
Investigation of Quasi--Realistic Heterotic String Models with Reduced Higgs Spectrum
Quasi--realistic heterotic-string models in the free fermionic formulation
typically contain an anomalous U(1), which gives rise to a Fayet-Iliopolous
term that breaks supersymmetry at the one--loop level in string perturbation
theory. Supersymmetry is restored by imposing F- and D-flatness on the vacuum.
In Phys. Rev. D 78 (2008) 046009, we presented a three generation free
fermionic standard-like model which did not admit stringent F- and D-flat
directions, and argued that the all the moduli in the model are fixed. The
particular property of the model was the reduction of the untwisted Higgs
spectrum by a combination of symmetric and asymmetric boundary conditions with
respect to the internal fermions associated with the compactified dimensions.
In this paper we extend the analysis of free fermionic models with reduced
Higgs spectrum to the cases in which the SO(10) symmetry is left unbroken, or
is reduced to the flipped SU(5) subgroup. We show that all the models that we
study in this paper do admit stringent flat directions. The only examples of
models that do not admit stringent flat directions remain the strandard-like
models of reference Phys. Rev. D 78 (2008) 046009.Comment: 38 pages, 1 figur
Minimal Standard Heterotic String Models
Three generation heterotic-string vacua in the free fermionic formulation
gave rise to models with solely the MSSM states in the observable Standard
Model charged sector. The relation of these models to Z_2 x Z_2 orbifold
compactifications dictates that they produce three pairs of untwisted Higgs
multiplets. The reduction to one pair relies on the analysis of supersymmetric
flat directions, that give superheavy mass to the dispensable Higgs states. We
explore the removal of the extra Higgs representations by using the free
fermion boundary conditions and hence directly at the string level, rather than
in the effective low energy field theory. We present a general mechanism that
achieves this reduction by using asymmetric boundary conditions between the
left- and right-moving internal fermions. We incorporate this mechanism in
explicit string models containing three twisted generations and a single
untwisted Higgs doublet pair. We further demonstrate that an additional effect
of the asymmetric boundary conditions is to substantially reduce the
supersymmetric moduli space.Comment: 20 pages, LaTeX; added reference
Reply to Comment on "Duality of x and psi in Quantum Mechanics"
The content of the comment [hep-th/9712219] is the derivation of Eq.(13) in
Phys. Rev. Lett. 78 (1997) 163 by direct differential calculus: which is
precisely the same method we used to derive it (it is in fact difficult to
imagine any other possible derivation).Comment: 2 pages, LaTe
Spinor-Vector Duality in Heterotic String Orbifolds
The three generation heterotic-string models in the free fermionic
formulation are among the most realistic string vacua constructed to date,
which motivated their detailed investigation. The classification of free
fermion heterotic string vacua has revealed a duality under the exchange of
spinor and vector representations of the SO(10) GUT symmetry over the space of
models. We demonstrate the existence of the spinor-vector duality using
orbifold techniques, and elaborate on the relation of these vacua to free
fermionic models.Comment: 20 pages. v2 minor corrections. Version to appear on JHEP. v3
misprints correcte
The Relativistic Quantum Motions
Using the relativistic quantum stationary Hamilton-Jacobi equation within the
framework of the equivalence postulate, and grounding oneself on both
relativistic and quantum Lagrangians, we construct a Lagrangian of a
relativistic quantum system in one dimension and derive a third order equation
of motion representing a first integral of the relativistic quantum Newton's
law. Then, we plot the relativistic quantum trajectories of a particle moving
under the constant and the linear potentials. We establish the existence of
nodes and link them to the de Broglie's wavelength.Comment: Latex, 18 pages, 3 eps figure
Proton Stability and Light Inspired by String Derived Models
Proton stability is one of the most perplexing puzzles in particle physics.
While the renormalizable Standard Model forbids proton decay mediating
operators due to accidental global symmetries, many of its extensions introduce
such dimension four, five and six operators. Furthermore, it is, in general,
expected that quantum gravity only respects local gauge, or discreet,
symmetries. String theory provides the arena to study particle physics in a
consistent framework of perturbative quantum gravity. An appealing proposition,
in this context, is that the dangerous operators are suppressed by an Abelian
gauge symmetry, which is broken near the TeV scale. A viable U(1) symmetry
should also be anomaly free, be family universal, and allow the generation of
fermion masses via the Higgs mechanism. We discuss such U(1) symmetries that
arise in quasi--realistic free fermionic heterotic--string derived models.
Ensuring that the U(1) symmetry is anomaly free at the low scale requires that
the Standard Model spectrum is augmented by additional states that are
compatible with the charge assignments in the string models. We construct such
string--inspired models and discuss some of their phenomenological
implications.Comment: 22 Page
Proton Stability, Gauge Coupling Unification and a Light in Heterotic-string Models
We explore the phenomenological viability of a light Z' in heterotic-string
models, whose existence has been motivated by proton stability arguments. A
class of quasi-realistic string models that produce such a viable Z' are the
Left-Right Symmetric (LRS) heterotic-string models in the free fermionic
formulation. A key feature of these models is that the matter charges under
U(1)_Z' do not admit an E6 embedding. The light Z' in the LRS heterotic-string
models forbids baryon number violating operators, while allowing lepton number
violating operators, hence suppressing proton decay yet allowing for
sufficiently small neutrino masses via a seesaw mechanism. We show that the
constraints imposed by the gauge coupling data and heterotic-string coupling
unification nullify the viability of a light Z' in these models. We further
argue that agreement with the gauge coupling data necessitates that the U(1)_Z'
charges admit an E6 embedding. We discuss how viable string models with this
property may be constructed.Comment: 20 pages, 2 figures, references added, minor corrections -- accepted
for publication in PR
Self-duality and vacuum selection
I propose that self-duality in quantum phase-space provides the criteria for
the selection of the quantum gravity vacuum. The evidence for this assertion
arises from two independent considerations. The first is the phenomenological
success of the free fermionic heterotic-string models, which are constructed in
the vicinity of the self-dual point under T-duality. The relation between the
free fermionic models and the underlying Z2 X Z2 toroidal orbifolds is
discussed. Recent analysis revealed that the Z2 X Z2 free fermionic orbifolds
utilize an asymmetric shift in the reduction to three generations, which
indicates that the untwisted geometrical moduli are fixed near the self-dual
point. The second consideration arises from the recent formulation of quantum
mechanics from an equivalence postulate and its relation to phase-space
duality. In this context it is demonstrated that the trivial state, with
V(q)=E=0, is identified with the self-dual state under phase-space duality.
These observations suggest a more general mathematical principle in operation.
In physical systems that exhibit a duality structure, the self-dual states
under the given duality transformations correspond to critical points.Comment: 40 pages. Standard Latex. 1 figur
A Minimal Superstring Standard Model I: Flat Directions
Three family SU(3)_C x SU(2)_L x U(1)_Y string models in several
constructions generically possess two features: (i) an extra local anomalous
U(1)_A and (ii) numerous (often fractionally charged) exotic particles beyond
those in the minimal supersymmetric model (MSSM). Recently, we demonstrated
that the observable sector effective field theory of such a free fermionic
string model can reduce to that of the MSSM, with the standard observable gauge
group being just SU(3)_C x SU(2)_L x U(1)_Y and the SU(3)_C x SU(2)_L x
U(1)_Y-charged spectrum of the observable sector consisting solely of the MSSM
spectrum. An example of a model with this property was shown. We continue our
investigation of this model by presenting a large set of different flat
directions of the same model that all produce the MSSM spectrum. Our results
suggest that even after imposing the conditions for the decoupling of exotic
states, there may remain sufficient freedom to satisfy the remaining
phenomenological constraints imposed by the observed data.Comment: 64 pages. Latex. Revisions to match version in Int. J. Mod. Physics
On the Possibility of Optical Unification in Heterotic Strings
Recently J. Giedt discussed a mechanism, entitled optical unification,
whereby string scale unification is facilitated via exotic matter with
intermediate scale mass. This mechanism guarantees that a virtual MSSM
unification below the string scale is extrapolated from the running of gauge
couplings upward from M_Z^o when an intermediate scale desert is assumed. In
this letter we explore the possibility of optical unification within the
context of weakly coupled heterotic strings. In particular, we investigate this
for models of free fermionic construction containing the NAHE set of basis
vectors. This class is of particular interest for optical unification, because
it provides a standard hypercharge embedding within SO(10), giving the standard
k_Y = 5/3 hypercharge level, which was shown necessary for optical unification.
We present a NAHE model for which the set of exotic SU(3)_C
triplet/anti-triplet pairs, SU(2)_L doublets, and non-Abelian singlets with
hypercharge offers the possibility of optical unification. Whether this model
can realize optical unification is conditional upon these exotics not receiving
Fayet-Iliopoulos (FI) scale masses when a flat direction of scalar vacuum
expectation values is non-perturbatively chosen to cancel the FI D-term, xi,
generated by the anomalous U(1)-breaking Green-Schwarz-Dine-Seiberg-Wittten
mechanism. A study of perturbative flat directions and their phenomenological
implications for this model is underway.
This paper is a product of the NFS Research Experiences for Undergraduates
and the NSF High School Summer Science Research programs at Baylor University.Comment: 16 pages. Standard Late
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