Cutoff Scales in the Type-I 2HDM with Strongly First-Order Electroweak Phase Transitions: One-Step versus Multistep
Abstract
We investigate the UV viability of strongly first-order electroweak phase transitions (SFOEWPTs) in the Type-I two-Higgs-doublet model (2HDM), considering both the Normal and Inverted Scenarios (NS and IS). For each scenario, we scan 5×106 physical parameter points and determine the cutoff scale Λc through a two-loop renormalization-group analysis, where Λc is set by the first violation of perturbativity, tree-level unitarity, or vacuum stability. For one-step transitions, the SFOEWPT strength and high-scale UV validity exhibit a pronounced tension: the maximal transition strength ξp decreases with increasing Λc. Requiring Λc>10 TeV limits the transition strength to ξp≲2.7 in the NS and ξp≲1.8 in the IS, while requiring ξp>1 restricts the cutoff scale to Λc≲ O(106) GeV in both scenarios. Multistep transitions exhibit qualitatively different behavior. Two-step SFOEWPTs, found in appreciable numbers only in the IS, can remain theoretically consistent up to Λc∼ O(1015) GeV while reaching ξp≃7, without exhibiting the pronounced ξp-Λc anticorrelation characteristic of one-step transitions. Imposing UV validity also sharpens the phenomenologically viable parameter space. In particular, increasing the minimum allowed cutoff scale for two-step SFOEWPTs in the IS favors a light scalar spectrum and moderate tanβ, providing a promising target for current and future collider searches.
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BibTeX
@misc{cho2026cutoff,
title = {{Cutoff Scales in the Type-I 2HDM with Strongly First-Order Electroweak Phase Transitions: One-Step versus Multistep}},
author = {Jin-Hwan Cho and Dongjoo Kim and Jinheung Kim and Jeonghyeon Song},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.09444},
eprint = {2609.09444},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.09444},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Cutoff Scales in the Type-I 2HDM with Strongly First-Order Electroweak Phase Transitions: One-Step versus Multistep
AU - Jin-Hwan Cho
AU - Dongjoo Kim
AU - Jinheung Kim
AU - Jeonghyeon Song
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2609.09444
UR - https://arxiv.org/abs/2609.09444
AB - We investigate the UV viability of strongly first-order electroweak phase transitions (SFOEWPTs) in the Type-I two-Higgs-doublet model (2HDM), considering both the Normal and Inverted Scenarios (NS and IS). For each scenario, we scan 5×10^6 physical parameter points and determine the cutoff scale Λ_c through a two-loop renormalization-group analysis, where Λ_c is set by the first violation of perturbativity, tree-level unitarity, or vacuum stability. For one-step transitions, the SFOEWPT strength and high-scale UV validity exhibit a pronounced tension: the maximal transition strength ξ_p decreases with increasing Λ_c. Requiring Λ_c>10 TeV limits the transition strength to ξ_p≲2.7 in the NS and ξ_p≲1.8 in the IS, while requiring ξ_p>1 restricts the cutoff scale to Λ_c≲ O(10^6) GeV in both scenarios. Multistep transitions exhibit qualitatively different behavior. Two-step SFOEWPTs, found in appreciable numbers only in the IS, can remain theoretically consistent up to Λ_c∼ O(10^15) GeV while reaching ξ_p≃7, without exhibiting the pronounced ξ_p-Λ_c anticorrelation characteristic of one-step transitions. Imposing UV validity also sharpens the phenomenologically viable parameter space. In particular, increasing the minimum allowed cutoff scale for two-step SFOEWPTs in the IS favors a light scalar spectrum and moderate tanβ, providing a promising target for current and future collider searches.
ER -