Ref HAL: hal-00836881_v1
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Résumé:

We investigate grand unified theories (GUTs) in scenarios where electroweak (EW) symmetry breaking is triggered by a light composite Higgs, arising as a Nambu-Goldstone boson from a strongly interacting sector. The evolution of the standard model (SM) gauge couplings can be predicted at leading order, if the global symmetry of the composite sector is a simple group G that contains the SM gauge group. It was noticed that, if the right-handed top quark is also composite, precision gauge unification can be achieved. We build minimal consistent models for a composite sector with these properties, thus demonstrating how composite GUTs may represent an alternative to supersymmetric GUTs. Taking into account the new contributions to the EW precision parameters, we compute the Higgs effective potential and prove that it realizes consistently EW symmetry breaking with little fine-tuning. The G group structure and the requirement of proton stability determine the nature of the light composite states accompanying the Higgs and the top quark: a coloured triplet scalar and several vector-like fermions with exotic quantum numbers. We analyse the signatures of these composite partners at hadron colliders: distinctive final states contain multiple top and bottom quarks, either alone or accompanied by a heavy stable charged particle, or by missing transverse energy.

Ref HAL: hal-00631072_v1
Ref Arxiv: 1107.4564
DOI: 10.1103/PhysRevX.1.021026
WoS: 000310508700002
Ref. & Cit.: NASA ADS
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58 Citations
Résumé:

Pseudo Nambu-Goldstone bosons (pNGBs) are naturally light spin-zero particles, which can be interesting dark matter (DM) candidates. We study the phenomenology of a pNGB theta associated with an approximate symmetry of the neutrino seesaw sector. A small coupling of theta to the Higgs boson is induced radiatively by the neutrino Yukawa couplings. By virtue of this Higgs portal interaction (i) the pNGB acquires a mass m_theta proportional to the electroweak scale, and (ii) the observed DM relic density can be generated by the freeze-in of theta-particles with mass m_theta ~ 3 MeV. Alternatively, the coupling of theta to heavy sterile neutrinos can account for the DM relic density, in the 1 keV-3 MeV window. The decays of theta into light fermions are suppressed by the seesaw scale, making such pNGB sufficiently stable to play the role of DM.

Commentaires: 29 pages, 4 figures

Ref HAL: hal-00579768_v1
Ref Arxiv: 1103.2997
DOI: 10.1007/JHEP06(2011)029
WoS: 000293136500029
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
30 Citations
Résumé:

We investigate grand unified theories (GUTs) in scenarios where electroweak (EW) symmetry breaking is triggered by a light composite Higgs, arising as a Nambu-Goldstone boson from a strongly interacting sector. The evolution of the standard model (SM) gauge couplings can be predicted at leading order, if the global symmetry of the composite sector is a simple group G that contains the SM gauge group. It was noticed that, if the right-handed top quark is also composite, precision gauge unification can be achieved. We build minimal consistent models for a composite sector with these properties, thus demonstrating how composite GUTs may represent an alternative to supersymmetric GUTs. Taking into account the new contributions to the EW precision parameters, we compute the Higgs effective potential and prove that it realizes consistently EW symmetry breaking with little fine-tuning. The G group structure and the requirement of proton stability determine the nature of the light composite states accompanying the Higgs and the top quark: a coloured triplet scalar and several vector-like fermions with exotic quantum numbers. We analyse the signatures of these composite partners at hadron colliders: distinctive final states contain multiple top and bottom quarks, either alone or accompanied by a heavy stable charged particle, or by missing transverse energy.

Commentaires: 54 pages, 13 figures

Ref HAL: hal-00807559_v1
Ref Arxiv: 0912.1545
DOI: 10.1103/PhysRevD.81.075002
WoS: 000277201900062
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
54 Citations
Résumé:

In the absence of low energy supersymmetry, we show that (a) the dark matter particle alone at the TeV scale can improve gauge coupling unification, raising the unification scale up to the lower bound imposed by proton decay, and (b) the dark matter stability can automatically follow from the grand unification symmetry. Within reasonably simple unified models, a unique candidate satisfying these two properties is singled out: a fermion isotriplet with zero hypercharge, member of a 45 (or larger) representation of SO(10). We discuss the phenomenological signatures of this TeV scale fermion, which can be tested in direct and indirect future dark matter searches. The proton decay rate into e^+ \pi^0 is predicted close to the present bound.

Commentaires: 14 pages; several comments and references added; version published in PRD Journal: Phys.Rev.D81:075002,2010

Ref HAL: hal-00807557_v1
Ref Arxiv: 0910.0377
DOI: 10.1088/1126-6708/2009/12/057
WoS: 000273598500057
Ref. & Cit.: NASA ADS
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21 Citations
Résumé:

We study flavour violation in a supersymmetric SO(10) implementation of the type II seesaw mechanism, which provides a predictive realization of triplet leptogenesis. The experimental upper bounds on lepton flavour violating processes have a significant impact on the leptogenesis dynamics, in particular they exclude the strong washout regime. Requiring successful leptogenesis then constrains the otherwise largely unknown overall size of flavour-violating observables, thus yielding testable predictions. In particular, the branching ratio for mu -> e gamma lies within the reach of the MEG experiment if the superpartner spectrum is accessible at the LHC, and the supersymmetric contribution to epsilon_K can account for a significant part of the experimental value. We show that this scenario can be realized in a consistent SO(10) model achieving gauge symmetry breaking and doublet-triplet splitting in agreement with the proton decay bounds, improving on the MSSM prediction for alpha_3(m_Z), and reproducing the measured quark and lepton masses.

Commentaires: 40 pages, 10 figures. Accepted for publication in JHEP Journal: JHEP 0912:057,2009

Ref HAL: hal-00807553_v1
DOI: 10.1016/j.nuclphysb.2008.07.015
WoS: 000260352300004
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22 Citations
Résumé:

We point out that, in a class of SO(10) models with matter fields in 16 and 10 representations and type II realization of the seesaw mechanism, the light neutrino masses and the CP asymmetry needed for leptogenesis are controlled by one and the same set of couplings. The generated baryon asymmetry then directly depends on the low-energy neutrino parameters, with no unknown seesaw-scale flavour parameters involved/ in particular, the necessary CP violation is provided by the CP-violating phases of the lepton mixing matrix. We compute the CP asymmetry in triplet decays for this scenario and show that it can lead to successful leptogenesis.

Ref HAL: hal-00805211_v1
DOI: 10.1103/PhysRevD.78.116018
WoS: 000262252200096
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94 Citations
Résumé:

We study the flavor sector in models where the three families of matter are unified in a (16, 3) representation of the SO(10)×A4 group. The necessary ingredients to realize tribimaximal mixing in the lepton sector are identified systematically. The nonrenormalizable operators contributing to the fermion mass matrices play an important role. We also present a mechanism to explain the interfamily mass hierarchy of quarks and charged leptons, which relies on a “universal seesaw” mechanism and is compatible with tribimaximal mixing.