Precise determination of the neutral Higgs boson masses in the MSSM

We present the implementation of the radiative corrections of the Higgs sector in three public computer codes for the evaluation of the particle spectrum in the Minimal Supersymmetric Standard Model, Softsusy, Spheno and SuSpect. We incorporate the full one-loop corrections to the Higgs boson masses and the electroweak symmetry breaking conditions, as well as the two-loop corrections controlled by the strong gauge coupling and the Yukawa couplings of the third generation fermions. We include also the corrections controlled by the tau Yukawa coupling that we derived for completeness. The computation is consistently performed in the DRbar renormalisation scheme. In a selected number of MSSM scenarios, we study the effect of these corrections and analyse the impact of some higher order effects. By considering the renormalisation scheme and scale dependence, and the effect of the approximation of zero external momentum in the two-loop corrections, we estimate the theoretical uncertainty on the lighter Higgs boson mass to be 3 to 5 GeV. The uncertainty on Mh due to the experimental error in the measurement of the SM input parameters is approximately of the same size. Finally, we discuss the phenomenological consequences, using the latest value of the top quark mass. We find, in particular, that the most conservative upper bound on the lighter Higgs boson mass in the general MSSM is Mh < 152 GeV and that there is no lower bound on the parameter tan(beta) from non-observation of the MSSM Higgs bosons at LEP2

TRILINEAR COUPLINGS AMONG THE ELECTROWEAK VECTOR BOSONS AND THEIR DETERMINATION AT LEP2

BILENKY M, KNEUR JL, RENARD FM, Schildknecht D. TRILINEAR COUPLINGS AMONG THE ELECTROWEAK VECTOR BOSONS AND THEIR DETERMINATION AT LEP2. NUCLEAR PHYSICS B. 1993;409(1):22-68.We present a detailed investigation of the potential of LEP2 to measure the (trilinear) couplings of the vector bosons, Z0W+ W- and gammaW+ W-, among one another. The restrictions imposed on non-standard trilinear couplings by symmetry requirements, thus excluding violent boson-loop divergences and a violent growth of tree amplitudes for vector-boson scattering, are discussed in detail. We elaborate on how to extract the W+/- spin-density matrix and the W+, W- spin correlations from future data. Various theoretically motivated fits to artificial ''data'' on e+ e- --> W+W- are carried out in order to evaluate the potential of LEP2 for, the measurement of trilinear vector boson couplings. We stress that a direct measurement of the couplings of the vector bosons with one another is indispensable for a verification of the basic SU(2)L X U(1)Y structure of the present electroweak theory. Such measurements at LEP2 improve indirect LEP1 bounds by factors which occasionally reach a full order of magnitude

STRONGLY COUPLED SU(2)NU BOSON AND LEP1 VERSUS LEP2

BILENKY M, KNEUR JL, RENARD FM, Schildknecht D. STRONGLY COUPLED SU(2)NU BOSON AND LEP1 VERSUS LEP2. PHYSICS LETTERS B. 1993;316(2-3):345-354.If new strong interactions exist in the electroweak bosonic sector (e.g., strong Higgs sector, dynamical electroweak breaking, etc. ), it is natural to expect new resonances, with potentially strong couplings. We consider an additional vector-boson triplet, V+/-, V0, associated with an SU(2)V local symmetry under the specific (but rather natural) assumption that ordinary fermions are SU(2)v singlets. Mixing of the V triplet with the W+/- Z0 bosons effectively leads to an SU(2)L X U(1)Y violating vector-boson-fermion interaction which is strongly bounded by LEP1 data. In contrast, the potentially large deviation of the Z0W+W-coupling from its SU(2)L X U(1)Y value is hardly constrained by LEP1 data, Results from experiments with direct access to the trilinear Z0W+W- coupling (LEP200, NLC) are urgently needed

THE POTENTIAL OF A NEW LINEAR COLLIDER FOR THE MEASUREMENT OF THE TRILINEAR COUPLINGS AMONG THE ELECTROWEAK VECTOR BOSONS

BILENKY M, KNEUR JL, RENARD FM, Schildknecht D. THE POTENTIAL OF A NEW LINEAR COLLIDER FOR THE MEASUREMENT OF THE TRILINEAR COUPLINGS AMONG THE ELECTROWEAK VECTOR BOSONS. NUCLEAR PHYSICS B. 1994;419(2):240-253.We study the accuracy to be obtained in measuring trilinear Z0W+W- and gammaW+W-couplings in the reaction e+e- --> W+W- at ''New Linear Collider'' (NLC) energies of 500 GeV to 1000 GeV. We derive simple scaling laws for the sensitivity in the measurement of these couplings. For most couplings the sensitivity increases as square-root L.s, where L denotes the integrated luminosity and square-root s denotes the e+e- center-of-mass energy. Detailed investigations based on various fits confirm these scaling laws and show that an accuracy of the order of the standard radiative corrections can be reached at the NLC for the design values of the luminosity

ONE-LOOP IMPROVED BORN APPROXIMATION FOR E+E--]W+W-

Fleischer J, KNEUR JL, KOLODZIEJ K, KURODA M, Schildknecht D. ONE-LOOP IMPROVED BORN APPROXIMATION FOR E+E--]W+W-. NUCLEAR PHYSICS B. 1992;378(3):443-467.The one-loop-corrected helicity amplitudes and the cross section for e+e- --> W+W- are represented in terms of invariant amplitudes related to corrections to Born-level gauge couplings as well as magnetic dipole, electric quadrupole, anapole, t-channel-exchange and contact interactions. Neglecting all but the (three) ultraviolet and infrared sensitive corrections to the gauge couplings yields an improved Born approximation which is sufficiently accurate for most practical purposes

SUSY particle physics summary

A review of the activity of the European Network "Physics at Colliders" in the area of SUSY particle physics is presented