arXiv subjects

G. K. Leontaris

Publications and source records attributed to G. K. Leontaris.

84 records · Page 5Linked to original sources

arXiv1994

Neutrino Masses from Gauge Symmetries

A very simple extension of the standard model to include an Abelian family symmetry is able to describe the hierarchy of quark and lepton masses and their mixing angles together with the unification of gauge couplings. We consider the implications of this model for neutrino masses and mixing angles and show that they are determined up to a discrete ambiguity corresponding to the representation content of the Higgs sector responsible for the Majorana mass matrix.

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arXiv1994

Large Top and Bottom Yukawa Couplings in Minimal Supersymmetry

We present analytic expressions for the top and bottom Yukawa couplings in the context of the minimal supersymmetric standard model when both couplings $h_{t,0},h_{b,0}$ are large at the unification scale. For sufficiently large $h_{t,0},h_{b,0}$, i.e. within $\sim (20-25)\% $ close to their fixed point values, using as input the central value of the bottom mass $m_b(m_b)=4.25GeV$, we find that the top mass lies in the range $m_t \approx (174-178)GeV$, while $tanβ\approx (55-58)$. Implications on the evolution of the scalar masses and the radiative symmetry breaking scenario are discussed. %

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arXiv1994

A New Treatment of Neutrino Oscillations in Medium

A new more rigorous and accurate method for treating neutrino oscillations in the context of the MSW effect in a medium is proposed. This leads to a new type of resonance condition which for small mixing angles puts rather stringent conditions on $E_ν/δ{m^2}$. The implications on the solar neutrino problem are discussed.

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arXiv1994

Implications of a Heavy Top in Supersymmetric Theories

In the context of the radiative electroweak symmetry breaking scenario, we investigate the implications of a heavy top quark mass, close to its infrared fixed point, on the low energy parameters of the minimal supersymmetric standard model. We use analytic expressions to calculate the Higgs masses as well as the supersymmetric masses of the third generation. We further assume bottom-tau unification at the GUT scale and examine the constraints put by this condition on the parameter space ($\tanβ$,$α_3$), using the renormalization group procedure at the two-loop level. We find only a small fraction of the parameter space where the above conditions can be satisfied, namely $1\le \tanβ\le 2$, while $0.111\leα_3(M_Z) \le 0.118$. We further analyse the case where all three Yukawa couplings reach the perturbative limit just after the unification scale. In this latter case, the situation turns out to be very strict demanding $\tanβ\sim 63$.

hep-ph↗

arXiv1994

Neutrino Properties in a GUT Analysis for Fermion Masses

In practically all extentions of the standard model, the neutrinos naturally acquire a mass. The neutrino mass matrix, however, contains many parameters which can neither be predicted by the prevailing models nor can be fitted to the data. We propose a fermion mass matrix ansatz in the context of Grand Unified Supersymmetric Theories (GUTs) at the GUT scale and use the renormalization group equations for the gauge and Yukawa couplings to predict the 13 arbitrary parameters of the Standard model. The constraints imposed by the charged fermion data are used to make predictions in the neutrino sector. The neutrino mass matrix is worked out in the case of the flipped SU(5) model and the predictions are compared with the available experimental data.

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arXiv1993

Lepton Flavor Non-Conservation

In the present work we review the most prominent lepton flavor violating processes ($μ\ra eγ$, $μ\ra 3e$, $(μ, e)$ conversion, $M-\bar M$ oscillations etc), in the context of unified gauge theories. Many currently fashionable extensions of the standard model are considered, such as: {\it i)} extensions of the fermion sector (right-handed neutrino); {\it ii)} minimal extensions involving additional Higgs scalars (more than one isodoublets, singly and doubly charged isosinglets, isotriplets with doubly charged members etc.); {\it iii)} supersymmetric or superstring inspired unified models emphasizing the implications of the renormalization group equations in the leptonic sector. Special attention is given to the experimentaly most interesting $(μ- e)$ conversion in the presence of nuclei. The relevant nuclear aspects of the amplitudes are discussed in a number of fashionable nuclear models. The main features of the relevant experiments are also discussed, and detailed predictions of the above models are compared to the present experimental limits.

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arXiv1993

FCNCs in SUSY GUTs (flavor changing neutral currents in predictive SUSY-GUTS)

Constraints from flavour changing neutral currents are discussed in the context of predictive Grand Unified Supersymmetric Theories. Uncertainties in the estimation of their amplitudes are minimized by using a successful mass matrix ansatz which predicts the arbitrary parameters of the Standard Model. Furthermore, Renormalization Group Equations are used in order to express the sparticle masses involved, in terms of the gaugino mass $m_{1/2}$, the universal scalar mass $m_0$ and the trilinear coupling $A$ at the GUT scale. Modifications in the low energy expressions for the squark masses due to a large top Yukawa coupling are also considered. The above results, reconciled with experimental limits are used to put lower bounds on the parameters $m_{1/2}$, $m_0$ and the low energy scalar masses.

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arXiv1993

Radiative Symmetry Breaking and the Top Quark Mass in Local Supersymmetry

Exact low energy expressions are derived for the top-squark and higgs masses, taking into account radiative contributions due to a heavy top quark. Their masses are expressed as analytic functions of $m_{1/2}$, $m_{3/2}$, $m_t$ and $sinβ$. Constraints from the radiative symmetry breaking mechanism are used then, to put lower bounds on the top-quark mass $m_t$. In particular, when $m_{3/2}\gg m_{1/2}$, we obtain the bound $m_t \ge 150sinβGeV$, while in the case of $m_{3/2}\equiv 0$, we obtain $m_t \ge 80sinβGeV$.

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arXiv1993

A Fermion Mass Matrix Ansatz for the Fipped SU(5) Model

A fermion mass matrix ansatz is proposed in the context of Grand Unified Supersymmetric Theories (GUTs). The fermion mass matrices are evolved down to the electroweak scale by solving the renormalization group equations for the gauge and Yukawa couplings. Eight inputs are introduced at the GUT scale to predict the 13 arbitrary parameters of the Standard model. The constraints imposed by the charged fermion data are used to make predictions in the neutrino sector. In particular, the neutrino mass matrix is worked out in the case of the flipped SU(5) model and it is found that the {\it generalized } see-saw mechanism which occurs naturally in this model can provide a solution to the solar neutrino puzzle and give a sufficiently large $ν_τ$ mass to contribute as a hot dark matter component as indicated by the recent COBE data.

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arXiv1993

Neutrino Masses in Flipped SU(5)

We analyse the fermion masses and mixings in the flipped SU(5) model. The fermion mass matrices are evolved from the GUT scale down to $m_W$ by solving the renormalization group equations for the Yukawa couplings. The constraints imposed by the charged fermion data are then utilised to make predictions about the neutrino properties . It is found that the {\it generalized } see-saw mechanism which occurs naturally in this model can provide {\it i})a solution to the solar neutrino problem via the MSW mechanism and {\it ii})a sufficiently large $ν_{τ}$ mass to contribute as a hot dark matter component as indicated by the recent COBE data.

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arXiv1992

Predictive Ansatz for Fermion Masses in SUSY GUTS

We reexamine a succesful fermion mass Ansatz proposed by Giudice for a wide range of the ratio $tanβ=\frac {<\bar h>}{ }$ (where ${\bar h},h$ are the two standard higgs fields), in the context of supersymmetric grand unified theories. We find that the 7 predictions of the ansatz, $V_{us}, V_{cb}, V_{ub}, m_u, m_d, m_s$ and $m_b$ are in good agreement with the experiment when either {\it i) } $tanβ\simeq 1$ or {\it ii)} $tanβ\geq 30$. A correct prediction for the bottom mass gives a lower limit on $m_t\geq 125$ for case {\it (i)}, in agreement with the previous analysis, while in case {\it (ii)} $m_t\geq 145$.

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arXiv1992

Ansatz for Quark, Charged Lepton, and Neutrino Masses in SUSY GUTS

We extend a fermion mass matrix Ansatz by Giuduce to include neutrino masses. The previous predictions are maintained. With two additional parameters, a large Majorana neutrino mass and a hierarchy factor, we have seven {\it further} low energy predictions: the masses of the neutrinos, the mixing angles and the phase in the leptonic sector. We choose a reasonable hierarchy of Majorana masses and fit the overall mass scale according to a solution of the solar neutrino problem via the MSW mechanism, which is in agreement with the $^{37}Cl$, Kamiokande, and GALLEX data. We then also obtain a cosmologically interesting tau-neutrino mass.

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