Higgs and supersymmetric particle signals at the infrared fixed point of the top quark mass

Abstract

We study the properties of the Higgs and Supersymmetric particle spectrum, associated with the infrared fixed point solution of the top quark mass in the Minimal Supersymmetric Standard Model. We concentrate on the possible detection of these particles, analysing the deviations from the Standard Model predictions for the leptonic and hadronic variables measured at LEP and for the b → sγ decay rate. We consider the low and moderate tan β regime, imposing the constraints derived from a proper radiative SU (2) L ×U (1) Y symmetry breaking and we study both, the cases of universal and non-universal soft supersymmetry breaking parameters at high energies. In the first case, for any given value of the top quark mass, the Higgs and supersymmetric particle spectrum is completely determined as a function of only two soft supersymmetry breaking parameters, implying very definite experimental signatures. In the case of non-universal mass parameters at M GU T , instead, the strong correlations between the sparticle masses are relaxed, allowing a richer structure for the precision data variables. We show, however, that the requirement that the low energy theory proceeds from a grand unified theory with a local symmetry group including SU (5) strongly constrains the set of possible indirect experimental signatures. As a general feature, whenever a significant deviation from the Standard Model value of the precision data parameters is predicted, a light sparticle, visible at LEP2, appears in the model.

Naturalness upper bounds on gauge-mediated soft terms

“…Neglecting all couplings except the gauge and the top Yukawa ones, the solutions to the one loop RGEs between the messenger mass M U and M Z may be written in terms of analytic functions and 5 We are interested in the case where φ > ∼ T , so that the fermions coupled to φ receive large masses that prevent its decay. only one function, λ max t (E), calculable only numerically [9].…”

“…In specific models that try to understand the origin of the soft terms, specific relations hold between the sfermion masses and the Higgs soft terms, allowing to place specific naturalness bounds on sparticle masses. The case of supergravity mediated soft terms [1] has been extensively studied under the assumptions of universal boundary conditions [2,3,4] or with relations suggested by unification theories [5,6]. In this paper we will study the case of gauge-mediated soft terms [7].…”

Status of Precision Tests of the Standard Model

“…Concerning the Higgs it is interesting to recall that the large value of m t has important implications on m H both in the minimal SM [96]{ [98] and in its minimal supersymmetric extension [99], [100] . I will now discuss the restrictions on m H that follow from the CDF value of m t .…”

“…However, radiative corrections [102] increase the h mass by a term proportional to m 4 t and logarithmically dependent on the stop mass. Once the radiative corrections are taken into account the h mass still remains rather small: for m t = 174 GeV one nds the limit (for all values of tan ) m h < 130 GeV [100] . Actually there are reasons to expect that m h is well below the bound.…”

The Higgs mass in the MSSM infrared fixed point scenario

“…The classic example of the scenario just described is the quasi-infrared fixed point (IFP) prediction for the top-quark Yukawa coupling [4,5,6,7,8,9,10,11,12,13,14,15] 1 . As 1 The quasi-infrared fixed point differs from the infrared fixed point of Pendleton and Ross (PR) [16].…”