arXiv subjects

A. Dedes

Publications and source records attributed to A. Dedes.

46 records · Page 3Linked to original sources

arXiv1999

Bounds on R-parity Violating Couplings at the Weak Scale and at the GUT Scale

We present an update of the most stringent experimental bounds on the trilinear R-parity violating couplings. We then analyse bounds on the R-parity violating couplings at the unification scale by renormalising the weak scale bounds. We derive unification scale upper bounds upon the couplings which are broadly independent of the fermion mass texture assumed. The R-parity violating couplings are factors of two to five more severely bounded at the unification scale than at the electroweak scale. In the presence of quark mixing, a few of the bounds are orders of magnitude stronger than their weak scale counterparts due to new R-parity violating operators being induced in the renormalisation between high and low scales. These induced bounds are fermion mass texture dependent. New bounds upon the weak scale couplings are obtained by the requirement of perturbativity between the weak and unification scales. A comprehensive set of the latest limits is included.

hep-ph↗

arXiv1999

Higgs production in association with squark pairs in the Minimal Supersymmetric Standard Model at future hadron colliders

We study neutral and charged Higgs boson production in association with stop and sbottom squarks at the Large Hadron Collider, within the Supergravity inspired Minimal Supersymmetric Standard Model. The phenomenological relevance of such reactions is twofold. Firstly, they constitute a novel production mechanism of Higgs particles, either through a decay of a heavier (anti)squark into a lighter one or via a Higgs bremsstrahlung process. Secondly, their production rates are extremely sensitive to the values assumed by the five input parameters of the model, this possibly allowing one to put stringent constraints on the latter. After an exhaustive scan of the parameter space, we find that the majority of such processes could be detectable at high luminosity, provided tan(beta) is large, tan(beta) > 30 (except in the case of \tilde{t}_1\tilde{t}_1^* h and \tilde{t}_1\tilde{t}_2^* h final states, whose detection is also possible for smaller values), that the universal soft Supersymmetric breaking masses are in the ranges M_0 < 500 GeV and M_{1/2} < 220 GeV, and that the trilinear couplings are negative, A_0 < 0. We also point out some sizable decay signatures and discuss their Standard Model (SM) backgrounds. Finally, we derive compact analytical formulae of the corresponding scattering matrix elements.

hep-ph↗

arXiv1999

2-Loop Supersymmetric Renormalisation Group Equations Including R-Parity Violation and Aspects of Unification

We present the complete 2-loop renormalisation group equations of the superpotential parameters for the supersymmetric standard model including the full set of R-parity violating couplings. We use these equations to do a study of (a) gauge coupling unification, (b) bottom-tau unification, (c) the fixed-point structure of the top quark Yukawa coupling, and (d) two-loop bounds from perturbative unification. For large values of the R-parity violating coupling, the value of α_S(M_Z) predicted from unification can be reduced by 5% with respect to the R-parity conserving case, bringing it to within 2σof the observed value. Bottom-tau Yukawa unification becomes potentially valid for any value of \tanβ\sim 2-50. The prediction of the top Yukawa coupling from the low \tanβ, infra-red quasi fixed point can be lowered by up to 10%, raising \tanβup to a maximum of 5 and relaxing experimental constraints upon the quasi-fixed point scenario. For heavy scalar fermion masses of order 1 Tev the limits on the higher family ΔL\not=0 operators from perturbative unification are competitive with the indirect laboratory bounds. We calculate the dependence of these bounds upon \tan β.

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arXiv1999

Pseudoscalar Higgs production in association with stop and sbottom pairs at the LHC in the MSSM

We study the processes `gluon gluon -> squark antisquark CP-odd Higgs' within the theoretical framework of the Supergravity (SUGRA) inspired Minimal Supersymmetric Standard Model (MSSM) at the leading order (LO) in perturbative Quantum Chromo-Dynamics (QCD). Other than constituting a novel production mechanism of the neutral, CP-odd Higgs particle, they also allow one to relate the size of the corresponding production rates to the ratio of the vacuum expectation values of the two Higgs fields tan(beta), to the trilinear couplings A_0 and to the sign of the Higgsino mass term sign(mu). This interplay is made easier by the absence of any mixing in the {tilde{q}}_1{tilde{q}}_2 A vertices, contrary to the case of all other Higgs bosons of the theory.

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arXiv1998

The Effective Weak Mixing Angle in the MSSM

The predictions of the MSSM are discussed in the light of recent LEP and SLD precision data. The full supersymmetric one loop corrections to the effective weak mixing angle, experimentally determined in LEP and SLD experiments, are considered. It is demonstrated, both analytically and numerically, that, potentially dangerous, large logarithmic sparticle corrections are cancelled. The relative difference factor Δk between the mixing angle defined as a ratio of couplings and the experimentally obtained angle is discussed. It is found that Δk is dominated by the oblique corrections, while the non-oblique overall supersymmetric EW and SQCD corrections are negligible. The comparison of the MSSM with radiative electroweak symmetry breaking to the LEP+SLD precision data indicates that rather large values of the soft breaking parameter M_{1/2} in the region greater than 500 GeV are preferred.

hep-ph↗

arXiv1998

Z-Observables and the Effective Weak Mixing Angle in the MSSM

We make a comparison of the predicted effective weak mixing angle, the Z-on resonance asymmetries and the W-boson mass to the LEP and SLD data at their present status. We find that the predicted MSSM values for the effective weak mixing angle are in agreement with the LEP+SLD average value for a ``heavy'' SUSY breaking scale while we observe an agreement with SLD data in the case of a ``light'' SUSY breaking scale. The resulting values for the W-boson mass and for the electron left-right asymmetries are compatible with CDF,UA2,DO and LEP data respectively. Unexpectedly we find that the supersymmetric QCD contributions to the Z-observables tend to vanish everywhere in the M1/2-M0 plane. Furthermore, values of M1/2 which are greater than 500 GeV are favoured by the MSSM if one considers the current experimental value for the strong coupling.

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arXiv1998

Radiative GUT Symmetry Breaking in a R-Symmetric Flipped SU(5) Model

We study the generation of the GUT scale through radiative corrections in the context of a R-symmetric "flipped" SU(5) X U(1)_X model. A negative mass squared term for the GUT Higgs fields develops due to radiative effects along a flat direction at a superheavy energy scale. The R-symmetry is essential in maintaining triplet-doublet splitting and F-flatness in the presence of non-renormalizable terms. The model displays radiative electroweak symmetry breaking and satisfies all relevant phenomenological constraints.

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arXiv1997

b-tau Unification and neutrino masses in SU(5) extensions of the MSSM with radiative electroweak symmetry breaking

We make a complete analysis of the Yukawa coupling unification in SU(5) extensions of the MSSM in the framework of the radiative symmetry breaking scenario. Both logarithmic and finite threshold corrections of sparticles have been included in the determination of the gauge and Yukawa couplings at M_Z. The effect of the heavy masses of each model in the renormalization group equations is also included. We find that in the minimal SU(5) model b-tau Yukawa unification can be achieved for too large a value of alpha_s. On the other hand the Peccei-Quinn version of the Missing Doublet model, with the effect of the right handed neutrino also included, exhibits b-tau unification in excellent agreement with all low energy experimental data. Unification of all Yukawa couplings is also discussed.

hep-ph↗

arXiv1996

Threshold effects and radiative electroweak symmetry breaking in $SU(5)$ extensions of the MSSM

We make a complete analysis of radiative symmetry breaking in the MSSM and its $SU(5)$ extensions including low- and high-energy threshold effects in the framework of the two-loop renormalization group. In particular, we consider minimal $SU(5)$, the ``missing-doublet'' $SU(5)$, a Peccei-Quinn invariant version of $SU(5)$ as well as a version with light adjoint remnants. We derive permitted ranges for the parameters of these models in relation to predicted $α_{s}$ and $M_G$ values within the present experimental accuracy. The parameter regions allowed under the constraints of radiative symmetry breaking, perturbativity and proton stability, include the experimentally designated domain for $α_s$. In the case of the minimal $SU(5)$, the values of $α_s$ obtained are somewhat large in comparison with the experimental average. The ``missing-doublet'' $SU(5)$, generally, predicts smaller values of $α_s$. In both versions of the ``missing-doublet'', the high energy threshold effects on $α_s$ operate in the opposite direction than in the case of the minimal model, leading to small values. In the case of the Peccei-Quinn version however the presence of an extra intermediate scale allows to achieve an excellent agreement with the experimental $α_s$ values. Finally, the last considered version, with light remnants, exhibits unification of couplings at string scale at the expense however of rather large $α_s$ values.

hep-ph↗

arXiv1995

Radiative Electroweak symmetry breaking in the MSSM and Low Energy Thresholds

We study Radiative Electroweak Symmetry Breaking in the Minimal Supersymmetric Standard Model (MSSM). We employ the 2-loop Renormalization Group equations for running masses and couplings taking into account sparticle threshold effects. The decoupling of each particle below its threshold is realized by a step function in all one-loop Renormalization Group equations (RGE). This program requires the calculation of all wavefunction, vertex and mass renormalizations for all particles involved. Adapting our numerical routines to take care of the succesive decoupling of each particle below its threshold, we compute the mass spectrum of sparticles and Higgses consistent with the existing experimental constraints. The effect of the threshold corrections is in general of the same order of magnitude as the two-loop contributions with the exception of the heavy Higgses and those neutralino and chargino states that are nearly

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