New constraints on parameters in the minimal supersymmetric model

New constraints on parameters are found to avoid charge- and/or color-breaking minima and instability of the scalar potential in the minimal low energy supergravity model. They eliminate a wide region of parameters. As a result, m_t is tightly bounded in the no-scale model. They are also applicable to the superstring inspired model with no extra U(1).     

Enhancement of “CP-odd” Higgs boson production in the minimal supersymmetric Standard Model with explicit CP-violation

We calculate the production cross section of the “CP-odd” Higgs boson via gluon fusion in the minimal supersymmetric Standard Model with explicit CP-violation in the stop sector. We show that there is a parameter region in which the cross section is enhanced by a factor of about 1000, as compared to the case without CP-violation in the stop sector. In the parameter region where the “CP-odd” Higgs boson can decay into a stop pair, the stop pair events will be the important signature of the enhanced “CP-odd” Higgs boson production. In the case where the “CP-odd” Higgs boson cannot decay into any superparticles, the γγ and ττ decay channels could become important for discovering the “CP-odd” Higgs boson. We also discuss the constraints from electric dipole moments of electron, neutron and mercury on the viable parameter space mentioned above.     

Neutralino mass matrix in the nonminimal supersymmetric Standard Model

We study in detail the neutralino mass matrix in the minimal extension of the minimal supersymmetric Standard Model. The model contains a Higgs singlet besides the two Higgs doublets of the minimal model. A number of limiting cases are considered wherein the neutralino mass spectrum can be analytically obtained. Based on these analytical results several useful approximation formulas for the neutralino masses are obtained. Using the constraints from the renormalization group analysis of the model, we obtain the spectrum numerically and study the dependence of the neutralino masses on the parameters of the model. We compare the results of the approximation formulas with the numerical results, and thereby establish the applicability of the these formulae in the different regions of the parameter space.     

Gauge coupling unification in the exceptional supersymmetric Standard Model

We consider the renormalisation group flow of gauge couplings within the so-called exceptional supersymmetric Standard Model (E₆SSM) based on the low-energy matter content of 27-dimensional representations of the gauge group E₆$E_6$, together with two additional non-Higgs doublets. The two-loop beta functions are computed, and the threshold corrections are studied in the E₆SSM. Our results show that gauge coupling unification in the E₆SSM can be achieved for phenomenologically acceptable values of α₃(MZ)${\alpha }_3(M_Z)$, consistent with the central measured low-energy value, unlike in the minimal supersymmetric Standard Model (MSSM) which, ignoring the effects of high energy threshold corrections, requires significantly higher values of α₃(MZ)${\alpha }_3(M_Z)$, well above the experimentally measured central value.     

Casimir effect at finite temperature for pure-photon sector of the minimal Standard Model Extension

Dynamics between particles is governed by Lorentz and CPT symmetry. There is a violation of Parity (P) and CP symmetry at low levels. The unified theory, that includes particle physics and quantum gravity, may be expected to be covariant with Lorentz and CPT symmetry. At high enough energies, will the unified theory display violation of any symmetry? The Standard Model Extension (SME), with Lorentz and CPT violating terms, has been suggested to include particle dynamics. The minimal SME in the pure photon sector is considered in order to calculate the Casimir effect at finite temperature.     

Higgs boson properties in the Standard Model and its supersymmetric extensions

We review the realization of the Brout–Englert–Higgs mechanism in the electroweak theory and describe the experimental and theoretical constraints on the mass of the single Higgs boson expected in the minimal Standard Model. We also discuss the couplings of this Higgs boson and its possible decay modes as functions of its unknown mass. We then review the structure of the Higgs sector in the minimal supersymmetric extension of the Standard Model (MSSM), noting the importance of loop corrections to the masses of its five physical Higgs bosons. Finally, we discuss some non-minimal models. To cite this article: J. Ellis et al., C. R. Physique 8 (2007).     

Ramond sector of the supersymmetric minimal models

A Coulomb gas representation for the Ramond sectors of the N = 1 supersymmetric models is constructed. The fusion rules and the 4-point functions for the Ramond fields are calculated explicitly by this method and used to describe the Z₂ odd sectors of the tricritical Ising model and of the critical Kosterlitz-Thouless XY model.     

Gauge-invariant inflaton in the minimal supersymmetric standard model

We argue that all the necessary ingredients for successful inflation are present in the flat directions of the Minimally Supersymmetric Standard Model. We show that out of many gauge-invariant combinations of squarks, sleptons, and Higgs bosons, there are two directions, LLe and udd, which are promising candidates for the inflaton. The model predicts more than 10(3) e-foldings, with an inflationary scale of H(inf) approximately O(1-10) GeV, provides a tilted spectrum with an amplitude of delta(H) approximately 10(-5) and a negligible tensor perturbation. The temperature of the thermalized plasma could be as low as T(rh) approximately O(1-10) TeV. Parts of the inflaton potential can be determined independently of cosmology by future particle physics experiments.     

Analytic expressions for threshold corrections to the finite-temperature higgs potential in the minimal supersymmetric standard model

Within the minimal supersymmwtric standard model (MSSM) featuring an explicit CP violation, one-loop corrections to the parameters of the effective two-doublet potential are calculated at finite temperature for various scales of the mass parameters in the sector of soft supersymmetry breaking. It is shown that the splitting of scalar-quark masses has a strong effect on the effective parameters of the potential and that, in the limiting case where all mass parameters of the squark sector are degenerate and where the temperature is zero, the potential parameters reduce to the results obtained previously.     

Radiative corrections to the scalar Higgs masses in a non-minimal supersymmetric Standard Model

We calculate the dominant one-loop radiative corrections arising from quark-squark loops to the mass squared matrix of theCP-even Higgs bosons in a non-minimal supersymmetric Standard Model containing two Higgs doublets and a Higgs singlet chiral superfield using one-loop effective potential approximation. We use this result to evaluate upper and lower bounds on the radiatively corrected masses of all the scalar Higgs bosons as a function of the parameters of the model. We find that the one-loop radiative corrections are substantial only for the lightest Higgs boson of the model and can push its mass beyond the reach of LEP. We also calculate an absolute upper bound on the mass of the radiatively corrected lightest Higgs boson and compare it with the corresponding bound in the minimal supersymmetric Standard Model.     

Charged current universality in the minimal supersymmetric standard model

We compute the complete one-loop contributions to low-energy charged current weak interaction observables in the minimal supersymmetric standard model (MSSM). We obtain the constraints on the MSSM parameter space which arise when precision low-energy charged current data are analyzed in tandem with measurements of the muon anomaly. While the data allow the presence of at least one light neutralino, they also imply a pattern of mass splittings among first and second generation sleptons and squarks which contradicts predictions of widely used models for supersymmetry-breaking mediation.     

Neutrino charge radius in the minimal supersymmetric standard model

As recently suggested by Degrassi, Marciano, and Sirlin, the electromagnetic form factor of the neutrino extracted from low energy elastic scattering cross sections ofv e and can be used to define the neutrino charge radius in the Standard Model in a gauge-invariant way. The complete one-loop contributions to the form factor consist not only the induced vertex but also the Z vertex corrections and theW andZ propagators arise from the counterterm diagrams, and theWW andZZ box diagrams. We show that the neutrino charge radius is a finite and gauge independent quantity in the Minimal Supersymmetric Standard Model. We consider only the oblique corrections to the neutrino charge radius in our numerical work, because the vertex and box contributions are small. The dependence of the oblique corrections on the supersymmetric parameters in each of the three sectors: Higgs, scalar matter and gaugino sectors are studied by taking into account of the current experimental bounds from LEP.     

Mechanisms of supersymmetry breaking in the minimal supersymmetric standard model

We provide a bird’s eyeview of current ideas on supersymmetry breaking mechanisms in the MSSM. The essentials of gauge, gravity, anomaly and gaugino/higgsino mediation mechanisms are covered briefly and the phenomenology of the associated models is touched upon. A few statement are also made on braneworld supersymmetry breaking.