arXiv subjects
Publications and source records attributed to K. Tamvakis.
We reconsider the Next to Minimal Supersymmetric Standard Model (NMSSM) as a natural solution to the $μ$-problem and show that both the stability and the cosmological domain wall problems are eliminated if we impose a ${\cal {Z}}_2$ $R$-symmetry on the non-renormalizable operators.
We discuss dimension-5 operators in supersymmetric models containing extra hypercharge 1/3 color-triplets. We derive a general formula relating dimension-5 operator to the color-triplet mass matrix. We show that certain zeros in the triplet mass-matrix together with some triplet coupling selection rules can lead to elimination of dimension-5 operators. In particular we focus on SU(5) models and show that (a) Dimension-5 operators can be eliminated in the standard SU(5) model by the introduction of an extra pair of 5+5b Higgses with specific couplings (b) Flipped SU(5) models with extra 10+10b Higgses are free of dimension-5 operators (c) Flipped SU(5) models with extra 5+5b and/or extra 10+10b Higgses can be made free of dimension-5 operators for a textured form of the triplet mass-matrix accompanied by constraints on the 5-plet couplings to matter. Our analysis is motivated by the recently put forward M-theory phenomenological framework that requires a strong string coupling and reintroduces the problem of eliminating dimension-5 operators.
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.
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.
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.
We construct and analyze an $SU(6)\times SU(2)$ GUT. The model is k=1 string embedable in the sense that we employ only chiral representations allowed at the k=1 level of the associated Kač-Moody Algebra. Both cases $SU(6)\times SU(2)_{L}$ and $SU(6)\times SU(2)_{R}$ are realized. The model is characterized by the $SU(6)\times SU(2) \to SU(4)\times SU(2)\times SU(2)$ breaking scale $M_X$, and the $SU(4)\times SU(2)\times SU(2) \to SU(3)_{C}\times SU(2)_{L}\times U(1)_{Y}$ breaking scale $M_{R}$ . The spectrum bellow $M_R$ includes an extra pair of charge-1/3 colour-triplets of mass $M_{I}\leq M_{R}$ that does not couple to matter fields and, possibly, an extra pair of isodoublets. Above $M_{X}$ the SU(6) and SU(2) gauge couplings always unify at a scale which can be taken to be the string unification scale $M_{s}\sim 5\times 10^{17} GeV$. The model has Yukawa coupling unification since quarks and leptons obtain their masses from a single Yukawa coupling. Neutrinos obtain acceptably small masses through a see-saw mechanism. Coloured triplets that couple to matter fields are naturally split from the coexisting isodoublets without the need of any numerical fine tuning.
We consider a class of supersymmetric SU(3)\times SU(2)\times U(1) multihiggs models in which R-parity is violated through bilinear Higgs-lepton interactions. The required, due to R-parity violation, higgs-lepton rotations introduce an alternative way to generate the phenomenologically desirable fermion mass matrix structures independently of the equality of Yukawas, possibly imposed by superstring or other unification.
We demonstrate linear stability of the dilatonic Black Holes appearing in a string-inspired higher-derivative gravity theory with a Gauss- Bonnet curvature-squared term. The proof is accomplished by mapping the system to a one-dimensional Schrodinger problem which admits no bound states. This result is important in that it constitutes a linearly stable example of a black hole that bypasses the `no-hair conjecture'. However, the dilaton hair is `secondary'in the sense that it is not accompanied by any new quantum number for the black hole solution.
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.
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.
We consider the combined Yang Mills-Dilaton-Gravity system in the presence of a Gauss-Bonnet term as it appears in the $4D$ Effective Superstring Action. We give analytical arguments and demonstrate numerically the existence of black hole solutions with non-trivial dilaton and Yang Mills hair for the particular case of SU(2) gauge fields. The thermodynamical properties of the solutions are also discussed.
We study $R$-parity violation in the framework of GUTs, focusing on the case that $R$-parity is broken exclusively through $ΔB=1$, $ΔL=0$ effective interactions. We construct two such models, an $SU(5)$ and an $SU(5)\times U(1)_{X}$ model, in which $R$-parity breaking is induced through interactions with extra supermassive fields. The presence of only the Baryon Number violating operators ${d^c}{d^c}{u^c}$ requires an asymmetry between quarks and leptons, which is achieved either by virtue of the Higgs representations used or by modifications in the matter multiplets. The latter possibility is realized in the second of the above models, where the left-handed leptons have been removed from the representation in which they normaly cohabit with the right-handed up quarks and enter as a combination of the isodoublets in $(\bf {\overline{5},-3})$ and $(\bf {5,-2})$ representations. In both models the particle content below the GUT scale is unaffected by the introduced $R$-parity breaking sector.
We address the question whether it is possible in GUTs to obtain R-parity violation with a large ${ΔL{/}ΔB}$ hierarchy of strengths so that the proton is stable while phenomenologically interesting $L$-violation is present. We consider versions of SU(5) with a built-in Peccei-Quinn symmetry spontaneously broken at an intermediate scale. The P-Q symmetry and the field content guarantee a large suppression of the effective $B$-violating terms by a factor $Λ^3_{PQ}/M_PM^2_X $ while the effective $L$-violating terms stay large.
We analyse the high temperature behaviour of softly broken supersymmetric theories taking into account the role played by effective non-renormalizable terms generated by the decoupling of superheavy degrees of freedom or the Planck scale physics. It turns out that discrete or continuous symmetries, spontaneously broken at intermediate scales, may never be restored, at least up to temperatures of the cutoff scale. There are a few interesting differences from the usual non-restoration in non-supersymmetric theories case where one needs at least two Higgs fields and non-restoration takes place for a range of parameters only. We show that with non-renormalizable interactions taken into account the non-restoration can occur for any nonzero range of parameters even for a single Higgs field. We show that such theories in general solve the cosmological domain wall problem, since the thermal production of the dangerous domain walls is enormously suppressed.
We give analytical arguments and demonstrate numerically the existence of black hole solutions of the $4D$ Effective Superstring Action in the presence of Gauss-Bonnet quadratic curvature terms. The solutions possess non-trivial dilaton hair. The hair, however, is of ``secondary" type", in the sense that the dilaton charge is expressed in terms of the black hole mass. Our solutions are not covered by the assumptions of existing proofs of the ``no-hair" theorem. We also find some alternative solutions with singular metric behaviour, but finite energy. The absence of naked singularities in this system is pointed out.
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.
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
We extend existing treatments of black hole solutions in String Gravity to include moduli fields. We compute the external moduli and dilaton hair, as well as of their associated axions,to $O(α')$ in the framework of the loop corrected superstring effective action for a Kerr-Newman black hole background.