Abstract
A first-order Electroweak Phase Transition (EWPT) could explain the observed baryon-antibaryon asymmetry and its dynamics could yield a detectable gravitational wave signature, while the underlying physics would be within the reach of colliders. The Standard Model, however, predicts a crossover transition. We therefore study the EWPT in the Standard Model Effective Field Theory (SMEFT) including dimension-six operators. A first-order EWPT has previously been shown to be possible in the SMEFT. Phenomenology studies have focused on scenarios with a tree-level barrier between minima, which requires a negative Higgs quartic coupling and a new physics scale low enough to raise questions about the validity of the EFT approach. In this work we stress that a first-order EWPT is also possible when the barrier between minima is generated radiatively, the quartic coupling is positive, the scale of new physics is higher, and there is good agreement with experimental bounds. Our calculation is done in a consistent, gauge-invariant way, and we carefully analyze the scaling of parameters necessary to generate a barrier in the potential. We perform a global fit in the relevant parameter space and explicitly find the points with a first-order transition that agree with experimental data. We also briefly discuss the prospects for probing the allowed parameter space using di-Higgs production in colliders.
Highlights
Given the significance of a possible first-order phase transition, it is somewhat disappointing that the SM does not allow one
In this work we have shown the importance of studying the region of the Standard Model Effective Field Theory (SMEFT) parameter space that leads to a first order electroweak transition by means of radiative corrections
JHEP10(2021)127 d) scale and in turn a more consistent use of effective field theory (EFT) compared to the negative λ case that has been often studied previously
Summary
The SM has had striking scientific success in explaining and reproducing experimental results, but it is a theory lacking answers to questions about a number of fundamental physical phenomena, such as the observed baryon asymmetry, the origin of neutrino masses or the nature of dark matter. In [30], all Wilson coefficients are defined to have mass dimension −2, or in other words, the cutoff scale Λ is not written explicitly. This is convenient as we do not have to assume any scale for new physics a priori. While all the dimension-six operators can in principle contribute to the calculations, the main actors will be those involving only Higgs and gauge fields. The field H above does not correspond to what we usually call the physical Higgs boson, because the derivatives in the operators Qφ and QφD in eq (2.5) give a contribution to the kinetic term. After linearizing in the Wilson coefficients, these are given by m2h
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