Sofiane M. Boucenna

Non-abelian gauge extensions for B-decay anomalies

Abstract We study the generic features of minimal gauge extensions of the Standard Model in view of recent hints of lepton-flavor non-universality in semi-leptonic b → s l + l − and b → c l ν decays. We classify the possible models according to the symmetry-breaking pattern and the source of flavor non-universality. We find that in viable models the S U ( 2 ) L factor is embedded non-trivially in the extended gauge group, and that gauge couplings should be universal, hinting to the presence of new degrees of freedom sourcing non-universality. Finally, we provide an explicit model that can explain the B -decay anomalies in a coherent way and confront it with the relevant phenomenological constraints.

The low-scale approach to neutrino masses

In this short review we revisit the broad landscape of low-scale models of neutrino mass generation, with view on their phenomenological potential. This includes signatures associated to direct neutrino mass messenger production at the LHC, as well as messenger-induced lepton flavor violation processes. We also briefly comment on the presence of WIMP cold dark matter candidates.

Phenomenology of an

A bstractWe investigate a gauge extension of the Standard Model in light of the observed hints of lepton universality violation in b → cℓν and b → sℓ+ℓ− decays at BaBar, Belle and LHCb. The model consists of an extended gauge group SU(2)1 × SU(2)2 × U(1)Y which breaks spontaneously around the TeV scale to the electroweak gauge group. Fermion mixing effects with vector-like fermions give rise to potentially large new physics contributions in flavour transitions mediated by W′ and Z′ bosons. This model can ease tensions in B-physics data while satisfying stringent bounds from flavour physics, and electroweak precision data. Possible ways to test the proposed new physics scenario with upcoming experimental measurements are discussed. Among other predictions, the ratios RM = Γ(B → M μ+μ−)/Γ(B → Me+e−), with M = K*, ϕ, are found to be reduced with respect to the Standard Model expectation RM ≃ 1.

SU(2) \times SU(2) \times U(1)

A bstractWe investigate a gauge extension of the Standard Model in light of the observed hints of lepton universality violation in b → cℓν and b → sℓ+ℓ− decays at BaBar, Belle and LHCb. The model consists of an extended gauge group SU(2)1 × SU(2)2 × U(1)Y which breaks spontaneously around the TeV scale to the electroweak gauge group. Fermion mixing effects with vector-like fermions give rise to potentially large new physics contributions in flavour transitions mediated by W′ and Z′ bosons. This model can ease tensions in B-physics data while satisfying stringent bounds from flavour physics, and electroweak precision data. Possible ways to test the proposed new physics scenario with upcoming experimental measurements are discussed. Among other predictions, the ratios RM = Γ(B → M μ+μ−)/Γ(B → Me+e−), with M = K*, ϕ, are found to be reduced with respect to the Standard Model expectation RM ≃ 1.

model with lepton-flavour non-universality

Beyond the discovery of the Higgs boson [1, 2] no signs of genuine new physics have shown up so far at high energies. However, the existence of new physics has been established with the discovery of neutrino oscillations [3, 4], implying the existence of lepton flavor violation and nonzero neutrino masses. Unraveling the origin of the latter constitutes one of the main challenges of particle physics. While the prevailing view is that neutrino masses arise from physics associated with unification, they might as well signal novel TeV-scale physics leading to potentially large charged lepton flavor violating (LFV) rates and possibly also new phenomena testable at the LHC [5]. In this case it could well be that new physics may actually show up mainly in the form of lepton flavor violation, boosting the motivation to search for charged LFV phenomena such as the rare decay ! e . In fact, the current limit BR( ! e ) < 5:7 10 13 [6] puts severe constraints on models of new physics. Models based on the SU(3)C SU(3)L U(1)X gauge theory (3-3-1) constitute a minimal extension of the Standard Model (SM) that accounts for the existence of three families of fermions [7, 8]. They provide an economical scheme to generate tiny neutrino masses radiatively from TeV scale physics [9] and could lead to successful gauge coupling unification through neutrino masses and TeV scale physics [10]. Moreover, they naturally solve the strong CP problem by including in an elegant way the Peccei-Quinn symmetry [11, 12]. Here we focus on the phenomenology of lepton flavor violation in the SU(3)C SU(3)L U(1)X schemes. For definiteness we focus on a the simplest implementation of the inverse seesaw mechanism in the 3-3-1 model. We show that it oers striking flavor correlations between rare charged lepton flavor violating decays and the measured neutrino oscillations parameters. Such predictions result from the gauge theory structure itself without the need for imposing any specific flavor symmetry. We analyze the complementarity between charged LFV and neutrino oscillations, a feature which may render the 3-3-1 scenario strictly testable with the coming generation of LFV searches.

Phenomenology of an SU(2) × SU(2) × U(1) model with lepton-flavour non-universality

The physics responsible for gauge coupling unification may also induce small neutrino masses. We propose a novel gauge mediated radiative seesaw mechanism for calculable neutrino masses. These arise from quantum corrections mediated by new

Predicting charged lepton flavor violation from 3-3-1 gauge symmetry

SU(3)_c \times SU(2)_L \times U(1)_X

Small neutrino masses and gauge coupling unification

(3-3-1) gauge bosons and the physics driving gauge coupling unification. Gauge couplings unify for a 3-3-1 scale in the TeV range, making the model directly testable at the LHC.

Inflation and majoron dark matter in the neutrino seesaw mechanism

We propose that inflation and dark matter have a common origin, connected to the neutrino mass generation scheme. As a model we consider spontaneous breaking of global lepton number within the seesaw mechanism. We show that it provides an acceptable inflationary scenario consistent with the recent CMB B-mode observation by the BICEP2 experiment. The scheme may also account for the baryon asymmetry of the Universe through leptogenesis for reasonable parameter choices.

Are the B decay anomalies related to neutrino oscillations

Abstract Neutrino oscillations are solidly established, with a hint of CP violation just emerging. Similarly, there are hints of lepton universality violation in b → s transitions at the level of 2.6σ. By assuming that the unitary transformation between weak and mass charged leptons equals the leptonic mixing matrix measured in neutrino oscillation experiments, we predict several lepton flavor violating (LFV) B meson decays. We are led to the tantalizing possibility that some LFV branching ratios for B decays correlate with the leptonic CP phase δ characterizing neutrino oscillations. Moreover, we also consider implications for l i → l j l k l k decays.