Multistep strong first-order electroweak phase transitions in the inverted type-I 2HDM: Parameter space, gravitational waves, and collider phenomenology
Year: 2025
Type: article
Abstract: We investigate the electroweak phase transition (EWPT) within the inverted type-I two-Higgs-doublet model, where the observed 125 GeV Higgs boson is identified as the heavier C P -even scalar H . Through a comprehensive parameter-space scan consistent with current theoretical and experimental constraints, we identify regions supporting strong first-order EWPTs (SFOEWPTs), including multistep transitions. We find that two-step SFOEWPTs occur as frequently as one-step transitions, while three-step transitions can occur, albeit rarely. Crucially, the parameter spaces inducing one-step and two-step transitions are partially yet significantly separated: one-step transitions restrict the charged Higgs mass and tan β to m H ± ∈ [ 295 , 441 ] GeV and tan β ∈ [ 4.2 , 8.8 ] , whereas two-step transitions allow m H ± ∈ [ 100 , 350 ] GeV and tan β ∈ [ 2.5 , 45.4 ] . Notably, negative values of sin ( β − α ) arise almost exclusively in one-step scenarios. We present the calculation of gravitational wave (GW) signal-to-noise ratios (SNRs) at Laser Interferometer Space Antenna for multistep EWPTs, finding that detectable GW signals ( SNR > 10 ) predominantly emerge from two-step transitions. Furthermore, we demonstrate that the previously established correlation between the vacuum uplifting measure Δ F 0 and EWPT strength ξ c persists only in one-step transitions and breaks down in multistep cases. Finally, we perform a dedicated collider analysis for representative SFOEWPT parameter points at the 1.5 TeV Compact Linear Collider, identifying e + e − → H + H − → W + W − h h as a promising discovery channel. Enhanced h → γ γ branching ratios for negative sin ( β − α ) motivate two complementary golden final states, W + W − b b ¯ τ + τ − and W + W − b b ¯ γ γ , which demonstrate high discovery potential due to negligible Standard Model backgrounds.
DOI: 10.1103/cbgr-w9cb
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
Awards: G365257732, G8345484963
OpenAlex ID: W4414468269