Abstract
We present a complementarity study of gravitational waves and double Higgs production in the 4b channel, exploring the gauge singlet scalar extension of the SM. This new physics extension serves as a simplified benchmark model that realizes a strongly first-order electroweak phase transition necessary to generate the observed baryon asymmetry in the universe. In calculating the signal-to-noise ratio of the gravitational waves, we incorporate the effect of the recently discovered significant suppression of the gravitational wave signals from sound waves for strong phase transitions, make sure that supercooled phase transitions do complete and adopt a bubble wall velocity that is consistent with a successful electroweak baryogenesis by solving the velocity profiles of the plasma. The high-luminosity LHC sensitivity to the singlet scalar extension of the SM is estimated using a shape-based analysis of the invariant 4b mass distribution. We find that while the region of parameter space giving detectable gravitational waves is shrunk due to the new gravitational wave simulations, the qualitative complementary role of gravitational waves and collider searches remain unchanged.
Highlights
Background fullGFxSM fullGFxSM resonant GFSM Events/GeV 10−1800 1000 1200 1400 mhh [GeV]Figure 4. mhh distribution for the Gluon Fusion (GF) components: SM, xSM resonant, and xSM full that accounts for the resonant and non-resonant contributions
We present a complementarity study of gravitational waves and double Higgs production in the 4b channel, exploring the gauge singlet scalar extension of the SM
In calculating the signal-to-noise ratio of the gravitational waves, we incorporate the effect of the recently discovered significant suppression of the gravitational wave signals from sound waves for strong phase transitions, make sure that supercooled phase transitions do complete and adopt a bubble wall velocity that is consistent with a successful electroweak baryogenesis by solving the velocity profiles of the plasma
Summary
The xSM model is defined by adding a gauge singlet real scalar to the SM with the following scalar sector potential [6, 7, 9]: V (H, S). √ Here HT = (G+, (vEW + h + iG0)/ 2) is the SM Higgs doublet and S = vs + s is the additional singlet scalar The parameters in this potential are all real. Higgs signal strength measurement [19] constrains the mixing angle θ: | sin θ| < 0.33 at 95% CL [19] Another set of constraints comes from EW precision measurements such as the oblique S, T, U parameters [20, 21] and correction to the the W boson mass mW [22]. We further note that a successful EWBG needs additional CPviolation, to fulfill one other Sakharov condition It is typically very constrained by the stringent EDM limits so that it tends to have a minor effect on the EWPT. For larger CP-violation, which is less constrained by the EDM constraints and negligibly affect the EWPT, see, e.g., ref. [24]
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