arXiv subjects

C. E. M. Wagner

Publications and source records attributed to C. E. M. Wagner.

79 records · Page 5Linked to original sources

arXiv1993

Radiative Electroweak Symmetry Breaking and the Infrared Fixed Point of the Top Quark Mass

The infrared quasi fixed point solution for the top quark mass in the Minimal Supersymmetric Standard Model explains in a natural way large values of the top quark mass and appears as a prediction in many interesting theoretical schemes. Moreover, as has been recently pointed out, for moderate values of $\tanβ$, in order to achieve gauge and bottom-tau Yukawa coupling unification, the top quark mass must be within $10 \%$ of its fixed point value. In this work we show that the convergence of the top quark mass to its fixed point value has relevant consequences for the (assumed) universal soft supersymmetry breaking parameters at the grand unification scale. In particular, we show that the low energy parameters do not depend on $A_0$ and $B_0$ but on the combination $δ= B_0 - A_0/2$. Hence, there is a reduction in the number of independent parameters. Most interesting, the radiative $SU(2)_L \times U(1)_Y$ breaking condition implies strong correlations between the supersymmetric mass parameter $μ$ and the supersymmetry breaking parameters $δ$ and $M_{1/2}$ or $m_0$. These correlations, which become stronger for $\tanβ< 2$, may have some fundamental origin, which would imply the need of a reformulation of the naive fine tuning criteria.

hep-ph↗

arXiv1993

Infrared Fixed Point Solution for the Top Quark Mass and Unification of Couplings in the MSSM

We analyze the implications of the infrared quasi fixed point solution for the top quark mass in the Minimal Supersymmetric Standard Model. This solution could explain in a natural way the relatively large value of the top quark mass and, if confirmed experimentally, may be suggestive of the onset of nonperturbative physics at very high energy scales. In the framework of grand unification, the expected bottom quark - tau lepton Yukawa coupling unification is very sensitive to the fixed point structure of the top quark mass. For the presently allowed values of the electroweak parameters and the bottom quark mass, the Yukawa coupling unification implies that the top quark mass must be within ten percent of its fixed point values.

hep-ph↗

arXiv1993

The $τ$ neutrino as a Majorana particle

A Majorana mass term for the $τ$ neutrino would induce neutrino - antineutrino mixing and thereby a process which violates fermion number by two units. We study the possibility of distinguishing between a massive Majorana and a Dirac $τ$ neutrino, by measuring fermion number violating processes in a deep inelastic scattering experiment $νp \rightarrow τX$. We show that, if the neutrino beam is obtained from the decay of high energetic pions, the probability of obtaining "wrong sign" $τ$ leptons is suppressed by a factor ${\cal{O}}(m_{ν_τ}^2 θ^2/m_μ^2)$ instead of the naively expected suppression factor $θ^2 m_{ν_τ}^2/E_ν^2$, where $E_ν$ is the $τ$ neutrino energy, $m_{ν_τ}$ and $m_μ$ are the $τ$-neutrino and muon masses, respectively, and $θ$ is the $ν_μ$ - $ν_τ$ mixing angle. If $m_{ν_τ}$ is of the order of 10 MeV and $θ$ is of the order of $0.01 - 0.04$ (the present bounds are ($m_{ν_τ} < 35 MeV, θ< 0.04$) the next round of experiments may be able to distinguish between Majorana and Dirac $τ$-neutrinos.

hep-ph↗

arXiv1993

Light Gluinos and Unification of Couplings

We analyze the implications of the light gluino scenario for the unification of gauge and Yukawa couplings within the minimal supersymmetric standard model. Within this scheme all fermionic supersymmetric particles are naturally light, while the scalar partners of quarks and leptons, together with the heavy Higgs doublet may be heavy. This implies both a bound on $\tanβ< 2.3$, in order to fulfill the experimental constraints on the chargino masses, and a strong correlation between $\sin^2θ_W(M_Z)$ and $α_3(M_Z)$, due to the suppression of the supersymmetric threshold corrections to the low energy values of the gauge couplings. Assuming the scalar sparticles to be lighter than 10 TeV, the physical top quark mass is constrained to be 145 GeV $< M_T <$ 210 GeV for $\tanβ>1$, while the strong gauge coupling values, $0.122\leqα_3(M_Z) \leq 0.133$, are in good agreement with the measured LEP ones. We also show that a relaxation of some of the conventional assumptions is necessary in order to achieve radiative breaking of the electroweak symmetry within the grand unification scheme.

hep-ph↗

arXiv1993

Unification of Couplings and the Dynamical Breakdown of the Electroweak Symmetry

I discuss the properties of the minimal supersymmetric extension of the standard model, in the case in which there is a dynamical breakdown of the electroweak symmetry induced by the formation of condensates of the third generation of quarks and their supersymmetric partners. The top quark and Higgs mass predictions derived within this scheme are essentially equivalent to those ones obtained from the requirement of bottom-tau Yukawa coupling unification in a supersymmetric grand unified scenario, if the compositeness scale is identified with the grand unification scale. I give an explanation of this interesting result, for which the relevance of the infrared quasi fixed point on the top quark Yukawa coupling is emphasized.

hep-ph↗

arXiv1993

On the Unification of Couplings in the Minimal Supersymmetric Standard Model

The unification of gauge and Yukawa couplings within the minimal supersymmetric standard model is studied at the two loop level. We derive an expression for the effective scale, $T_{SUSY}$, which characterizes the supersymmetric particle threshold corrections to the gauge couplings, and demonstrate that $T_{SUSY}$ is only slightly dependent on the squark and slepton masses, and strongly dependent on the Higgsino masses as well as on the mass ratio of the gauginos of the strong and weak interactions. Moreover, the value of the top quark Yukawa coupling necessary to achieve the unification of bottom and tau Yukawa couplings is also governed by $T_{SUSY}$, and it yields predictions for the top quark mass which are close to the quasi infrared fixed point results associated with the triviality bounds on this quantity. From the requirement of perturbative consistency of the top quark Yukawa sector of the theory, we obtain constraints on the allowed splitting of the supersymmetric spectrum, which, for certain values of the running bottom quark mass, are stronger than those ones coming from the experimental constraints on the strong gauge coupling.

hep-ph↗

arXiv1992

On the Finite Temperature Effective Potential in Scalar QED with N Flavors

The effective potential of scalar quantum electrodynamics with N flavors of complex scalar fields is studied, by performing a self consistent 1/N expansion up to next to leading order in $1/N$. Starting from the broken phase at zero temperature, the theory exhibits a phase transition to the symmetric phase at some finite temperature $T_c$. We work in general covariant gauges and demonstrate the gauge invariance of both, the critical temperature $T_c$ and the minimization condition at any finite temperature T. Furthermore, the only minimum of the potential is at zero scalar vacuum expectation value for any temperature $T \geq T_c$ and varies continuously to nonzero values for temperatures below $T_c$, implying the existence of a second order phase transition.

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