Abstract
Multi-peaked spectra of the primordial gravitational waves are considered as a phenomenologically relevant source of information about the dynamics of sequential phase transitions in the early Universe. In particular, such signatures trace back to specific patterns of the first-order electroweak phase transition in the early Universe occurring in multiple steps. Such phenomena appear to be rather generic in multi-scalar extensions of the Standard Model. In a particularly simple extension of the Higgs sector, we have identified and studied the emergence of sequential long- and short-lasting transitions as well as their fundamental role in generation of multi-peaked structures in the primordial gravitational-wave spectrum. We discuss the potential detectability of these signatures by the proposed gravitational-wave interferometers.
Highlights
Measurements of the corresponding GWs signals may be considered as a gravitational probe for BSM scenarios complementary to collider searches
We investigate a possibility for probing the multi-scalar new physics models via their gravitational footprints that emerge due to specific sequential EWPT patterns and a nontrivial vacuum structure significantly extending our previous study of Ref. [24]
We notice that the GW spectra emerging in multi-step EWPTs in a combined pattern with, at least, one weak and one strong FOPTs occurring at well-separated temperatures in the early Universe naturally exhibits a multi-peaked shape
Summary
A typical new physics scenario incorporates several scalar fields in the potential that could be responsible for triggering the EWPTs. The resulting potential possesses an approximate discrete Z2 symmetry with respect to the following transformations H1 → −H1∗, H2 → −H2∗ and S → −S∗ which significantly simplify the vacuum structure of the model. Such transformation properties together with those in. The referred Z2 symmetry is explicitly broken by soft SUSY-breaking interactions and terms of the type a12sH1H2†S +h.c. can only be generated at one-loop level induced by Z2-violating and SU(3)F conserving trilinear couplings This means that, while a12s is technically allowed by the remnant U(1)F family symmetry, it can naturally be small in the SHUT model. The model under consideration, due to its apparent simplicity, could be viewed as an important benchmark model for future thorough studies of cosmological implications of multi-scalar new physics scenarios
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