Papers by George Leontaris
Phys Rev D, 2007
We discuss renormalization effects on neutrino masses and mixing angles in a supersymmetric strin... more We discuss renormalization effects on neutrino masses and mixing angles in a supersymmetric string-inspired SU(4)×SU(2)L×SU(2)R×U(1)X model, with matter in fundamental and antisymmetric tensor representations and singlet Higgs fields charged under the anomalous U(1)X family symmetry. The quark, lepton and neutrino Yukawa matrices are distinguished by different Clebsch-Gordan coefficients. The presence of a second U(1)X breaking singlet with fractional charge allows a more realistic, hierarchical light neutrino mass spectrum with bi-large mixing. By numerical investigation we find a region in the model parameter space where the neutrino mass-squared differences and mixing angles at low energy are consistent with experimental data.
Physics Letters B, 1988
In this letter, the problems of the up-quark and neutrmo mass matrix, as well as the lepton non-c... more In this letter, the problems of the up-quark and neutrmo mass matrix, as well as the lepton non-conservation are dlscussed wthm the N= 1 supersymmetric SU (5 ) x U ( 1) model derived from the four-dlmenslonal fermlomc superstrmg
Lepton number and lepton flavor violation in Susy models
AIP Conference Proceedings, 1986
We examine the consequences on lepton number and lepton flavor non-conservation of softly broken ... more We examine the consequences on lepton number and lepton flavor non-conservation of softly broken supersymmetric extensions of the standard model which arise in spontaneously broken supergravity theories.
MSSM from F-theory SU(5) with Klein monodromy
Physical Review D, 2016
Phys Lett B, 1987
One of the novel features of the superstring inspired models is the possible appearance of colour... more One of the novel features of the superstring inspired models is the possible appearance of colour triplet particles with diquark couplings. They can mediate hadronic decays of baryons and mesons. We investigate their contribution to the ΔI=1/2 rule through the operator product expansion.
The calculation of Yukawa couplings in F-theory GUTs is developed. The method is applied to the t... more The calculation of Yukawa couplings in F-theory GUTs is developed. The method is applied to the top and bottom Yukawa couplings in an SU(5) model of fermion masses based on family symmetries coming from the SU(5)_\perp factor in the underlying E(8) theory. The remaining Yukawa couplings involving the light quark generations are determined by the Froggatt Nielsen non-renormalisable terms generated by heavy messenger states. We extend the calculation of Yukawa couplings to include massive states and estimate the full up and down quark mass matrices in the SU(5) model. We discuss the new features of the resulting structure compared to what is usually assumed for Abelian family symmetry models and show how the model can give a realistic quark mass matrix structure. We extend the analysis to the neutrino sector masses and mixing where we find that tri-bi-maximal mixing is readily accommodated. Finally we discuss mechanisms for splitting the degeneracy between the charged leptons and the down quarks and the doublet triplet splitting in the Higgs sector.
We discuss the origin of both non-Abelian discrete family symmetry and Abelian continuous family ... more We discuss the origin of both non-Abelian discrete family symmetry and Abelian continuous family symmetry, as well as matter parity, from F-theory SUSY GUTs. We propose a minimal model based on the smallest GUT group $SU(5)$, together with the non-Abelian family symmetry $D_4$ plus an Abelian family symmetry, where fluxes are responsible for doublet-triplet splitting, leading to a realistic low energy spectrum with phenomenologically acceptable quark and lepton masses and mixing. We show how a $Z_2$ matter parity emerging from F-theory can suppress proton decay while allowing neutron-antineutron oscillations, providing a distinctive signature of the set-up.
Contribution of scalar diquarks to the ?I = 1/2 rule
Phys Lett B, 1987
Journal of Physics: Conference Series, 2015
While non-abelian groups are undoubtedly the cornerstone of Grand Unified Theories (GUTs), phenom... more While non-abelian groups are undoubtedly the cornerstone of Grand Unified Theories (GUTs), phenomenology shows that the role of abelian and discrete symmetries is equally important in model building. The latter are the appropriate tool to suppress undesired proton decay operators and various flavour violating interactions, to generate a hierarchical fermion mass spectrum, etc. In F-theory, GUT symmetries are linked to the singularities of the elliptically fibred K3 manifolds; they are of ADE type and have been extensively discussed in recent literature. In this context, abelian and discrete symmetries usually arise either as a subgroup of the non-abelian symmetry or from a non-trivial Mordell-Weil group associated to rational sections of the elliptic fibration. In this note we give a short overview of the current status and focus in models with rank-one Mordell-Weil group. arXiv:1501.06499v2 [hep-th]
Neutrinoless Double beta-Decay and Lepton Flavor Violation
We discuss the phenomenological implications of gauge theories on lepton number and lepton flavor... more We discuss the phenomenological implications of gauge theories on lepton number and lepton flavor non-conservation. In particular we compare neutrinoless double β-decay to muon violating processes.
In this paper we present solutions to the fermion mass hierarchy problem in the context of the mi... more In this paper we present solutions to the fermion mass hierarchy problem in the context of the minimal supersymmetric standard theory augmented by an anomalous family dependent U(1) X symmetry. The latter is spontaneously broken by non-zero vevs of a pair of singlet fields whose magnitude is determined through the D- and F-flatness conditions of the superpotential. We derive the general solutions to the anomaly cancellation conditions and show that they allow numerous choices for the U(1) X fermion charges which give several fermion mass textures in agreement with the observed fermion mass hierarchy and mixing. Solutions with U(1) X fermion charge assignments are found which forbid or substantially suppress the dangerous baryon and lepton number violating operators and the lepton-Higgs mixing coupling while a Higgs mixing mass parameter ( μ-term) can be fixed at the electroweak level. We give a general classification of the fermion mass textures with respect to the sum of the doublet-Higgs U(1) X charges and show that suppression of dimension-five operators naturally occurs for various charge assignments. We work out cases which retain a quartic term providing the left-handed neutrinos with Majorana masses in the absence of right-handed neutrino components and consistent with the experimental bounds. Although there exist solutions which naturally combine all the above features with rather natural U(1) X charges, the suppression of the μ-term occurs for particular assignments.
Phys Rev D, 1996
We give a classification of heavy Majorana neutrino mass matrices with up to three texture zeros,... more We give a classification of heavy Majorana neutrino mass matrices with up to three texture zeros, assuming the Dirac masses of the neutrinos to be of the same form as the ones of the up quarks in the five texture zero solutions for the quark matrices. This is the case for many unified and partially unified models. We find that it is possible to have solutions which account for the solar and atmospheric neutrino problems as well as the COBE observations simultaneously, and we motivate the existence of such solutions from symmetries.
Using conformal field theory methods we construct a metric that describes the distortion of space... more Using conformal field theory methods we construct a metric that describes the distortion of space-time surrounding a D(irichlet)-brane (solitonic) defect after being struck by another D-brane. By viewing our four-dimensional universe as such a struck brane, embedded in a five-dimensional space-time, we argue on the appearance of a band of massive Kaluza-Klein excitations for the bulk graviton which is localized in a region of the fifth dimension determined by the inverse size of the band. The band incorporates the massless mode (ordinary graviton) and its thickness is determined essentially by the width of the Gaussian distribution describing the (target-space) quantum fluctuations of the intersecting-brane configuration.
We discuss in brief the corrections to Newton's inverse square law due to possible existence of e... more We discuss in brief the corrections to Newton's inverse square law due to possible existence of extra decompactified dimensions. Experimental bounds on the parameters (compactification radius and the number of extra dimensions) are also given .
MSSM phenomenology in the large tan beta regime
Phys Lett B, 1996
We discuss aspects of the low energy phenomenology of the MSSM, in the large tan β regime. We exp... more We discuss aspects of the low energy phenomenology of the MSSM, in the large tan β regime. We explore the regions of the parameter space where the ht and hb Yukawa couplings exhibit a fixed point structure, using previous analytic solutions for these coupling. Expressions for the parameters At and Ab and the renormalised soft mass terms are also derived, making it possible to estimate analytically the sparticle loop - corrections to the bottom mass, which are important in this limit.
Phys Lett B, 1998
We derive the scalar mass matrices in effective supergravity models augmented by a $U(1)_F$ famil... more We derive the scalar mass matrices in effective supergravity models augmented by a $U(1)_F$ family symmetry. Simple relations between $U(1)_F$ charges and modular weights of the superfields are derived and used to express the matrices with a minimum number of parameters. The model predicts a branching ratio for the $\mu\to e\gamma$ process close to the present experimental limits.
European Physical Journal C, Nov 23, 1999
Motivated by the data from Super-Kamiokande and elsewhere indicating oscillations of atmospheric ... more Motivated by the data from Super-Kamiokande and elsewhere indicating oscillations of atmospheric and solar neutrinos, we study charged-lepton-flavour violation, in particular the radiative decays µ → eγ and τ → µγ, but also commenting on µ → 3e and τ → 3µ/e decays, as well as µ → e conversion on nuclei. We first show how the renormalization group may be used to calculate flavour-violating soft supersymmetrybreaking masses for charged sleptons and sneutrinos in models with universal input parameters. Subsequently, we classify possible patterns of lepton-flavour violation in the context of phenomenological neutrino mass textures that accommodate the Super-Kamiokande data, giving examples based on Abelian flavour symmetries. Then we calculate in these examples rates for µ → eγ and τ → µγ, which may be close to the present experimental upper limits, and show how they may distinguish between the different generic mixing patterns. The rates are promisingly large when the soft supersymmetry-breaking mass parameters are chosen to be consistent with the cosmological relic-density constraints. In addition, we discuss µ → e conversion on Titanium, which may also be accessible to future experiments.
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Papers by George Leontaris