Reconciling ALP Dark Matter and Electroweak Baryogenesis through First-Order Electroweak Phase Transition

TL;DR

The paper proposes that an axionlike particle (ALP) can act as both dark matter and a driver of electroweak baryogenesis when a first-order electroweak phase transition is triggered by a real singlet. A set of higher-dimensional U(1) breaking operators transiently enhances the ALP mass during the FOEWPT, producing a burst of ALP velocity that enables baryogenesis through the electroweak anomaly, while the ALP oscillations after the transition account for dark matter via recurrent misalignment. The framework jointly predicts a stochastic gravitational-wave background from the FOEWPT, offering a complementary observational handle. By decoupling the ALP mass from its decay constant, the model broadens the viable ALP DM parameter space and ties the DM phenomenology to BAU and GW signals in a testable way.

Abstract

We show that an axionlike particle (ALP) can simultaneously generate the baryon asymmetry and constitute dark matter through dynamics triggered by a first-order electroweak phase transition (EWPT). In our proposal, the transition briefly reshapes the ALP potential via a temperature-dependent vacuum expectation value of a scalar field $S$, responsible for making the EWPT of first order, inducing a transient mass enhancement of ALP via higher-dimensional $U(1)$-breaking operator(s). This sudden kick generates a large ALP velocity near the onset of EWPT enabling the broadening of relic satisfied parameter space and predict a complementary stochastic gravitational-wave signal from the underlying first-order transition. We further show that the same ALP dynamics can naturally fuel electroweak baryogenesis through its coupling to electroweak anomaly.

Figures (7)

• Figure 1: Regions in the $m_{a0}-f_a$ plane showing whether ALP oscillations begin above (blue) or below (orange) the temperature $T_s$.
• Figure 2: ALP dark matter parameter space in $m_a-f_a$ plane satisfying the correct relic abundance for Case-A. The cyan coloured star indicates the benchmark BP-I in Table \ref{['tab:Two BP-baryonasymmetry-DM relic']}, consistent with both the observed BAU and the correct relic density. Here, the colorbar indicates the variation of the cut-off scale, $\Lambda$.
• Figure 3: Variation of $f_a^2/(T_{\rm osc}^A)^3$ with $f_a$ for fixed choices of $m_{a0}$.
• Figure 4: Excluded regions of the ALP parameter space (in $m_a-g_{a\gamma\gamma}$ plane) from various constraints, together with the relic-density-allowed region for Case-A, adapted from Fig. \ref{['fig:ALP-ps-A']}. All the experimental, observational and cosmological bounds are taken from the online repository AxionLimitsOhare2020-gy.
• Figure 5: ALP dark matter parameter space in $m_a-f_a$ plane satisfying the correct relic abundance for Case-B. The cyan coloured star indicates the benchmark BP-II in Table \ref{['tab:Two BP-baryonasymmetry-DM relic']}, satisfying both the observed BAU and the correct relic abundance. The colorbar signifies the variation of the cut-off scale, $\Lambda$.