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Article
Report number	hep-ph/9303291 ; CERN-TH-6835-93 ; IEM-FT-70-93 ; CERN-TH-6835-93 ; IEM-FT-70
Title	One-loop analysis of the electroweak breaking in supersymmetric models and the fine-tuning problem
Author(s)	de Carlos, B. (Madrid, Inst. Estructura Materia) ; Casas, J.A. (CERN ; Madrid, Inst. Estructura Materia)
Affiliation	(Inst. Estruct. Mat. Madrid) ; (CERN)
Publication	1993
Imprint	Mar 1993
Number of pages	16
In:	Phys. Lett. B 309 (1993) 320-328
DOI	10.1016/0370-2693(93)90940-J
Subject category	Particle Physics - Phenomenology ; Particle Physics - Theory
Abstract	We examine the electroweak breaking mechanism in the minimal supersymmetric standard model (MSSM) using the {\em complete} one-loop effective potential $V_1$. First, we study what is the region of the whole MSSM parameter space (i.e. $M_{1/2},m_o,\mu,...$) that leads to a succesful $SU(2)\times U(1)$ breaking with an acceptable top quark mass. In doing this it is observed that all the one-loop corrections to $V_1$ (even the apparently small ones) must be taken into account in order to get reliable results. We find that the allowed region of parameters is considerably enhanced with respect to former "improved" tree level results. Next, we study the fine-tuning problem associated with the high sensitivity of $M_Z$ to $h_t$ (the top Yukawa coupling). Again, we find that this fine-tuning is appreciably smaller once the one-loop effects are considered than in previous tree level calculations. Finally, we explore the ambiguities and limitations of the ordinary criterion to estimate the degree of fine-tuning. As a result of all this, the upper bounds on the MSSM parameters, and hence on the supersymmetric masses, are substantially raised, thus increasing the consistency between supersymmetry and observation.
Copyright/License	Copyright @ unknown. Published by Elsevier B.V.

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