Electroweak Baryogenesis and Higgs Physics

TL;DR

The paper assesses electroweak baryogenesis (EWB) and its testability, arguing that the Standard Model cannot realize a sufficiently strong first-order electroweak phase transition for realistic Higgs masses. It proposes the MSSM as a viable framework where a light stop and new CP-violating phases enable a strong transition (v(Tc)/Tc ≳ 1) and baryogenesis, while detailing constraints from color-breaking minima and Higgs-sector dynamics. It analyzes the finite-temperature Higgs potential, stop/Higgsino/gaugino sector CP-violation, and diffusion dynamics that generate the baryon asymmetry, quantifying parameter regions (e.g., m_h ≈ 70–100 GeV, m_A ≳ 150 GeV) compatible with EWB. The paper then outlines concrete experimental tests, including LEP2 Higgs searches, Tevatron stop searches, and flavor observables like BR(b → sγ), arguing that a discovery or exclusion in these channels will strongly test the EWB MSSM scenario and constrain its CP-violating parameters.

Abstract

Electroweak Baryogenesis is a particularly attractive theoretical scenario, since it relies on physics which can be tested at present high energy collider facilities. Within the Standard Model, it has been shown that the requirement of preserving the baryon number generated at the weak scale leads to strong bounds on the Higgs mass, which are already inconsistent with the present experimental limits. In the Minimal Supersymmetric extension of the Standard Model we demonstrate that light stop effects can render the electroweak phase transition sufficiently strongly first order, opening the possibility of electroweak baryogenesis for values of the Higgs mass at the LEP2 reach. The generation of the observed baryon asymmetry also requires small chargino masses and new CP-violating phases associated with the stop and Higgsino mass parameters. We discuss the direct experimental tests of this scenario and other relevant phenomenological issues related to it.

Figures (8)

• Figure 1: Bounds on the Higgs mass as a function of the top quark mass for different values of the scale $\Lambda$, at which new physics is expected to appear.
• Figure 2: $v(T_c)/T_c$ as a function of $m_{\tilde{t}}$ for $M_t$ = 175 GeV, $m_Q =$ 500 GeV, $\tilde{A}_t$ = 0 and $\tan\beta$ =2. The diamond [cross, star] denotes the value of $\tilde{m}_U$ for which the bound, Eq. (\ref{['boundmu']}) is saturated [ Eq. (\ref{['stability2']}), while using the total and gluon induced trilinear coefficients, $E_U$ and $E_U^g$]
• Figure 3: $v(T_c)/T_c$ as a function of $\tan\beta$ for $m_Q$ and $\tilde{A}_t$ as in Fig. 2 and $\widetilde{m}_U$ saturating Eq. (\ref{['boundmu']}) [solid] and Eq. (\ref{['stability2']}) [thick dashed line when considering the total trilinear coefficient and thin dashed line for the gluon-induced part only]. The additional thin lines are plots of $m_h$ in units of 65 GeV [solid] and $\tilde{m}_t/m_t$ [short-dashed line], corresponding to the values of $\tilde{m}_U$ associated with the solid line.
• Figure 4: The same as Fig. 3 but as a function on $\tilde{A}_t$ for $\tan \beta$ =1.7
• Figure 5: Contour plots of constant values of $v(T_c)/T_c$ (solid lines) and $m_h$ in GeV (dashed lines) in the plane $(m_A,\tan\beta)$. We have fixed $M_t=175$ GeV and the values of sypersymmetric parameters: $m_Q=500$ GeV, $\widetilde{m}_U= \widetilde{m}_U^{c}$ fixed by the charge and color breaking constraint, and $A_t=\mu^*/\tan\beta$.