[LPTh-Ji 10/004]{}

[***Electroweak Phase Transition in the U(1)’-MSSM***]{}

**Amine Ahriche**${}^{1}$ and **Salah Nasri**${}^{2}$

*${}^{1}$ Laboratory of Theoretical Physics, Department of Physics, University of Jijel, PB 98 Ouled Aissa, DZ-18000 Jijel, Algeria.*

*${}^{2}$ Department of Physics, UAE University, P.O. Box 17551, Al-Ain, United Arab Emirates.*

*Emails: ahriche@univ-jijel.dz, snasri@uaeu.ac.ae.*

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In this work, we have investigated the nature of the electroweak phase transition in the $U(1)$ extended minimal supersymmetric standard model without introducing any exotic fields. The effective potential has been estimated exactly at finite temperature taking into account the whole particle spectrum. For reasonable values of the lightest Higgs and neutralino, we found that the electroweak phase transition could be strongly first-order due to: (1) the interactions of the singlet with the doublets in the effective potential, and (2) the evolution of the wrong vacuum, that delays the transition.

**Keywords**: baryogenesis, electroweak phase transition, extra singlet, extra gauge boson.

**PACS**: 12.60.-i, 12.60.Jv, 14.80.Cp, 12.15.-y.

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Introduction
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The matter-antimatter asymmetry in the Universe is observed to be $%
n_{b}/n_{\gamma }\sim 10^{-10}$ [@wmap]. If this asymmetry is to be explained by microphysics rather than initial conditions, then there must be processes occurring in the early Universe that violate baryon number and CP 