From Higgs Phenomenology to the Unification of Fundamental Interactions

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Vacuum structure of the Z(2) symmetric Georgi-Machacek model

Publication . Azevedo, Duarte; Ferreira, Pedro Miguel; Logan, Heather E.; Santos, Rui

We discuss the vacuum structure of a version of the Georgi-Machecek model with an exact Z(2) symmetry acting on the triplet fields. Besides the usual custodial-symmetric model, with rho = 1 at tree-level, a model with a dark matter candidate is also viable. The other phases of the model lead to electric charge breaking, a wrong pattern of electroweak symmetry breaking or to rho not equal 1 at tree-level. We derive conditions to have an absolute minimum in each of the two viable phases, the custodial and the dark matter phases.

2021-03-23Journal article

Open access

Ultralight bosons for strong gravity applications from simple Standard Model extensions

Publication . Freitas, Felipe F.; Herdeiro, Carlos A. R.; Morais, António P.; Onofre, Antonio; Pasechnik, Roman; Radu, Eugen; Sanchis-Gual, Nicolas; Santos, Rui

We construct families, and concrete examples, of simple extensions of the Standard Model that can yield ultralight real or complex vectors or scalars with potential astrophysical relevance. Specifically, the mass range for these putative fundamental bosons (∼ 10−10 − 10−20 eV) would lead dynamically to both new non-black hole compact objects (bosonic stars) and new non-Kerr black holes, with masses of ∼ M to ∼ 1010M, corresponding to the mass range of astrophysical black hole candidates (from stellar mass to supermassive). For each model, we study the properties of the mass spectrum and interactions after spontaneous symmetry breaking, discuss its theoretical viability and caveats, as well as some of its potential and most relevant phenomenological implications linking them to the physics of compact objects.

2021-12Journal article

Restricted access

ScannerS: parameter scans in extended scalar sectors

Publication . Mühlleitner, Margarete; Sampaio, Marco O. P.; Santos, Rui; Wittbrodt, Jonas

We present the public code ScannerS–2 that performs parameter scans and checks parameter points in theories beyond the Standard Model (BSM) with extended scalar sectors. ScannerS incorporates theoretical and experimental constraints from many different sources in order to judge whether a parameter point is allowed or excluded at approximately 95% {CL}95% {CL}. The BSM models implemented in ScannerS include many popular BSM models such as singlet extensions, different versions of the Two-Higgs-Doublet Model, or the different phases of the Next-to Two-Higgs-Doublet Model. The ScannerS framework allows straightforward extensions by additional constraints and BSM models.

2022-03Journal article

Open access

Impact of SM parameters and of the vacua of the Higgs potential in gravitational waves detection

Publication . Freitas, Felipe F.; Lourenço, Gabriel; Morais, António P.; Nunes, André; Olívia, João; Pasechnik, Roman; Santos, Rui; Viana, João

In this work we discuss two different phases of a complex singlet extension of the Standard Model (SM) together with an extension that also includes new fermion fields, in particular, a Majoron model equipped with an inverse seesaw mechanism. All considered scenarios contain a global U(1) symmetry and allow for first-order phase transitions while only two of them are strong enough to favour the detection of primordial gravitational waves (GWs) in planned experiments such as LISA. In particular, this is shown to be possible in the singlet extension with a non vanishing real VEV at zero temperature and also in the model with extra fermions. In the singlet extension with no additional fermions, the detection of GWs strongly depends on the U(1) symmetry breaking pattern of the scalar potential at zero temperature. We study for the first time the impact of the precision in the determination of the SM parameters on the strength of the GWs spectrum. It turns out that the variation of the SM parameters such as the Higgs boson mass and top quark Yukawa coupling in their allowed experimental ranges has a notable impact on GWs detectability prospect

2022-03Journal article

Open access

Direct detection of pseudo-Nambu-Goldstone dark matter in a two Higgs doublet plus singlet extension of the SM

Publication . Biekötter, Thomas; Gabriel, Pedro; Romacho, María Olalla Olea; Santos, Rui

We calculate the leading radiative corrections to the dark-matter-nucleon scattering in the pseudo-Nambu-Goldstone dark matter model augmented with a second Higgs doublet (S2HDM). In this model, the cross sections for the scattering of the darkmatter on nuclei vanishes at tree-level in the limit of zero momentum-transfer due to a U(1) symmetry. However, this symmetry is softly broken in order to give a mass to the dark-matter particle. As a consequence, non-vanishing scattering cross sections arise at the loop level. We find that the current cross-section limits from dark-matter direct-detection experiments can hardly constrain the parameter space of the S2HDM. However, the loop-corrected predictions for the scattering cross sections can be well within the reach of future direct-detection experiments. As a consequence, future phenomenological analyses of the S2HDM should take into account cross-section predictions beyond tree-level and the experimental constraints from dark-matter direct-detection experiments.

2022-10Journal article

Open access