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.     

Approximating the radiatively corrected Higgs mass in the minimal supersymmetric model

To obtain the most accurate predictions for the Higgs masses in the minimal supersymmetric model (MSSM), one should compute the full set of one-loop radiative corrections, resum the large logarithms to all orders, and add the dominant two-loop effects. A complete computation following this procedure yields a complex set of formulae which must be analyzed numerically. We discuss a very simple approximation scheme which includes the most important terms from each of the three components mentioned above. We estimate that the Higgs masses computed using our scheme lie within 2 GeV of their theoretically predicted values over a very large fraction of MSSM parameter space.     

On the hidden supersymmetry of Fokker-Planck equations with potential forces

It is shown that the Martin-Siggie-Rose generating functional dissipative dynamics in the field of potential forces can be rewritten in the form of a functional integral for an euclidean supersymmetric field theory. The existence of a non-equilibrium steady state is equivalent to spontaneous supersymmetry breaking. A supersymmetric diagram technique, which is a convenient covariant form of the conventional dynamic diagram technique is derived.     

Discovering the Higgs bosons of minimal supersymmetry with muons and a bottom quark

We investigate the prospects for the discovery at the CERN Large Hadron Collider (LHC) of a neutral Higgs boson produced with one bottom quark followed by Higgs decay into a muon pair. We work within the framework of the minimal supersymmetric model. The dominant physics background from the production of b mu(+)mu(-), j mu(+)mu(-), j=g,u,d,s,c, and bbW+W- is calculated with realistic acceptance cuts. Promising results are found for the CP-odd pseudoscalar (A0) and the heavier CP-even scalar (H0) Higgs bosons with masses up to 600 GeV. This discovery channel with one energetic bottom quark greatly improves the discovery potential of the LHC beyond the inclusive channel pp-->phi(0)-->mu(+)mu(-)+X.     

An exact solution of the renormalization-group equations for the mean field theory of stable and metastable states

An exact solution of the renormalization-group equations corresponding to the mean field theory of stable and metastable states is given which yields the correct free energies for these states. An unusual feature of this solution is that the renormalized Hamiltonian in the two-phase region becomes a multivalued function of the order parameter for all values of the length rescaling parameter beyond a certain critical value. This is closely related to the multivaluedness of the free energy as a function of magnetic field which characterizes the classical theory of metastable and unstable states. As a consequence of this multivaluedness, the trajectory flow in the space of coupling constants exhibits unusual bifurcation. This leads to difficulties in evaluating the metastable and unstable free energies by a trajectory integral of the spin-independent term, which can be resolved by an extension of the standard formalism.This work was supported by NSF grant #550-346-01 (JDG) and a U.S.-Japan Cooperative Science grant (KK and JDG).     

Combined fit of low energy constraints to minimal supersymmetry and discovery potential at LEP II

Within the Constrained Minimal Supersymmetric Standard Model (CMSSM) it is possible to predict the low energy gauge couplings and masses of the 3. generation particles from a few parameters at the GUT scale. In addition the MSSM predicts electroweak symmetry breaking due to large radiative corrections from Yukawa couplings, thus relating theZ ⁰ boson mass to the top quark mass. From ax ² analysis, in which these constraints can be considered simultaneously, one can calculate the probability for each point in the MSGUT parameter space. The recently measured top quark mass prefers two solutions for the mixing angle in the Higgs sector: tanβ in the range between 1 and 3 or alternatively tanβ≈25?50. For both cases we find a uniquex ² minimum in the parameter space. From the corresponding most probable parameters at the GUT scale, the masses of all predicted particles can be calculated at low energies using the RGE, albeit with rather large errors due to the logarithmic nature of the running of the masses and coupling constants. Our fits include full second order corrections for the gauge and Yukawa couplings, low energy threshold effects, contributions of all (s)particles to the Higgs potential and corrections tom _b from gluinos and higgsinos, which exclude (in our notation) positive values of the mixing parameterμ in the Higgs potential for the large tanβ region. Further constraints can be derived from the branching ratio for the radiative (penguin) decay of theb-quark intosγ and the lower limit on the lifetime of the universe, which requires the dark matter density due to the Lightest Super-symmetric Particle (LSP) not to overclose the universe. For the low tanβ solution these additional constraints can be fulfilled simultaneously for quite a large region of the parameter space. In contrast, for the high tanβ solution the correct value for theb→sγ rate is obtained only for small values of the gaugino scale and electroweak symmetry breaking is difficult, unless one assumes the minimal SU(5) to be a subgroup of a larger symmetry group, which is broken between the Planck scale and the unification scale. In this case small splittings in the Yukawa couplings are expected at the unification scale and electroweak symmetry breaking is easily obtained, provided the Yukawa coupling for the top quark is slightly above the one for the bottom quark, as expected e.g. if the larger symmetry group would be SO(10). For particles, which are most likely to have masses in the LEP II energy range, the cross sections are given for the various energy scenarios at LEP II. For low tanβ the production of the lightest Higgs boson, which is expected to have a mass below 103 GeV, is the most promising channel, while for large tanβ the production of charginos and/or neutralinos covers the preferred parameter space.