General Neutrino Interactions (GNI) are scalar, pseudoscalar, vector, axial vector or tensor interactions of neutrinos with fermions, and generalise the often studied neutrino Non-Standard ...Interactions (NSI). If GNI arise from heavy new physics, they should be embeddable into effective field theory operators that respect the Standard Model (SM) gauge symmetry. Therefore we consider a full basis of gauge-invariant dimension-six operators involving SM fermions and right-handed singlet neutrinos and map their Wilson coefficients onto GNI parameters. In this embedding we discuss correlations of and bounds on different GNI in the context of charged lepton flavour violation processes and neutrino-fermion scattering, as well as beta decay and coherent neutrino-nucleus scattering. We also study possible UV completions of the relevant dimension-six operators for GNI via leptoquarks that can be related to radiative neutrino masses and B physics anomalies. Details on the numbers of free GNI parameters for Dirac or Majorana neutrinos and for CP violation or conservation are also provided.
We propose a new parametrization for the quark and lepton mixing matrices: the two 12-mixing angles (the Cabibbo angle and the angle responsible for solar neutrino oscillations) are at zeroth order ...π/12 and π/5, respectively. The resulting 12-elements in the CKM and PMNS matrices, Vus and Ue2, are in this order irrational but simple algebraic numbers. We note that the cosine of π/5 is the golden ratio divided by two. The difference between π/5 and the observed best-fit value of solar neutrino mixing is of the same order as the difference between the observed value and the one for tri-bimaximal mixing. In order to reproduce the central values of current fits, corrections to the zeroth order expressions are necessary. They are small and of the same order and sign for quarks and leptons. We parametrize the perturbations to the CKM and PMNS matrices in a “triminimal” way, i.e., with three small rotations in an order corresponding to the order of the rotations in the PDG-description of mixing matrices.
Neutrinoless double-beta decay is a forbidden, lepton-number-violating nuclear transition whose observation would have fundamental implications for neutrino physics, theories beyond the Standard ...Model, and cosmology. In this review, we summarize the theoretical progress to understand this process, the expectations and implications under various particle physics models, and the nuclear physics challenges that affect the precise predictions of the decay half-life. We also provide a synopsis of the current and future large-scale experiments that aim to discover this process in physically well-motivated half-life ranges.
If light new physics with lepton-flavor-violating couplings exists, the prime discovery channel might not be ℓ→ℓ′γ but rather ℓ→ℓ′X, where the new boson X could be an axion, majoron, familon or Z′ ...gauge boson. The most conservative bound then comes from ℓ→ℓ′+inv, but if the on-shell X can decay back into leptons or photons, displaced-vertex searches could give much better limits. We show that only a narrow region in parameter space allows for displaced vertices in muon decays, μ→eX,X→γγ,ee, whereas tauon decays can have much more interesting signatures.
Neutrinoless double beta decay Päs, Heinrich; Rodejohann, Werner
New journal of physics,
11/2015, Letnik:
17, Številka:
11
Journal Article
Recenzirano
Odprti dostop
We review the potential to probe new physics with neutrinoless double beta decay Both the standard long-range light neutrino mechanism as well as non-standard long-range and short-range mechanisms ...mediated by heavy particles are discussed. We also stress aspects of the connection to lepton number violation at colliders and the implications for baryogenesis.
We study lepton flavor violating Higgs decays in two models, with the recently found hint for Higgs→μτ at CMS as a benchmark value for the branching ratio. The first model uses the discrete flavor ...symmetry group A4, broken at the electroweak scale, while the second is renormalizable and based on the Abelian gauge group Lμ−Lτ. Within the models we find characteristic predictions for other non-standard Higgs decay modes, charged lepton flavor violating decays and correlations of the branching ratios with neutrino oscillation parameters.
Motivated by recent hints in particle physics and cosmology, we study the realization of eV-scale sterile neutrinos within both the seesaw mechanism and flavor symmetry theories. We show that light ...sterile neutrinos can rather easily be accommodated in the popular
A
4
flavor symmetry models. The exact tri-bimaximal mixing pattern is perturbed due to active-sterile mixing, which we discuss in detail for one example. In addition, we find an interesting extension of the type I seesaw, which can provide a natural origin for eV-scale sterile neutrinos as well as visible admixtures between sterile and active neutrinos. We also show that the presence of sterile neutrinos would significantly change the observables in neutrino experiments, specifically the oscillation probabilities in short-baseline experiments and the effective mass in neutrino-less double beta decay. The latter can prove particularly helpful in strengthening the case for eV-scale sterile neutrinos.
A
bstract
The presence of right-handed neutrinos in the type I seesaw mechanism may lead to significant corrections to the RG evolution of the Higgs self-coupling. Compared to the Standard Model ...case, the Higgs mass window can become narrower, and the cutoff scale become lower. Naively, these effects decrease with decreasing right-handed neutrino mass. However, we point out that the unknown Dirac Yukawa matrix may impact the vacuum stability constraints even in the low scale seesaw case not far away from the electroweak scale, hence much below the canonical seesaw scale of 10
15
GeV. This includes situations in which production of right-handed neutrinos at colliders is possible. We illustrate this within a particular parametrization of the Dirac Yukawas and with explicit low scale seesaw models. We also note the effect of massive neutrinos on the top quark Yukawa coupling, whose high energy value can be increased with respect to the Standard Model case.
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