CP violation and circular polarisation in neutrino radiative decay

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The CP violation in the neutrino transition electromagnetic dipole moment is discussed in the context of the Standard Model with an arbitrary number of right-handed singlet neutrinos. A full one-loop calculation of the neutrino electromagnetic form factors is performed in the Feynman gauge. A non-zero CP asymmetry is generated by a required threshold condition for the neutrino masses along with non-vanishing CP violating phases in the lepton flavour mixing matrix. We follow the paradiagm of CP violation in neutrino oscillations to parametrise the flavour mixing contribution into a series of Jarlskog-like parameters. This formalism is then applied to a minimal seesaw model with two heavy right-handed neutrinos denoted N1 and N2. We observe that the CP asymmetries for decays into light neutrinos N → νγ are extremely suppressed, maximally around 10−17. However the CP asymmetry for N2→ N1γ can reach of order unity. Even if the Dirac CP phase δ is the only source of CP violation, a large CP asymmetry around 10−5–10−3 is comfortably achieved.

Section: Cp Violating Form Factors Induced By Charged-current Interacmentioning

confidence: 81%

“…We refer to our former paper ref. [38] for the detailed derivation. Discussions in section 2.1 assumes neutrinos are Dirac particles.…”

Section: Neutrino Electromagnetic Dipole Moment With Cp Violationmentioning

confidence: 99%

“…fi and the chiral projection operators are defined as P L,R = 1 2 (1 ∓ γ 5 ) [38]. The amplitudes M(ν i → ν f γ ± ) are directly correlated with the coefficients as [38]…”

Section: Form Factors For Dirac Neutrinomentioning

confidence: 99%

“…In [38], we have defined a set of CP asymmetries between neutrino radiative decay and antineutrino radiative decay. In terms of ratios specifying photon polarisations, we may write…”

Section: Form Factors For Dirac Neutrinomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

CP violation in neutral lepton transition dipole moment

Balaji

Ramirez-Quezada

Zhou

2020

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Leptonic CP violation from a vector-like lepton

Cherchiglia

Conto

Nishi

2022

Leptonic CP violation is yet to be confirmed as an additional source of CP violation in fundamental interactions. We study the case where leptonic CP violation is spontaneous and is induced by the mixing with a heavy charged vector-like lepton (VLL). We show that the non-decoupling of this VLL is linked with the presence of CP violation and its coupling with the SM leptons are partly fixed from the SM Yukawas. Due to the large leptonic mixing angles, these couplings are typically of the same order and there is no flavor preference. Strong but not definitive constraints come from charged lepton flavor violating processes because the VLL can decouple from one or two leptonic flavors in very special points of parameter space. These special points are very sensitive to the neutrino Majorana phases.

Asymmetry in flavour changing electromagnetic transitions of vector-like quarks

Balaji

2022

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Vector-like quarks have been of interest for a plethora of experimentally motivated reasons and have come under increased investigation recently due to their inclusion to the Standard Model (SM) appreciably improving global fits to several flavour physics and precision electroweak measurements. The addition of vector-like quark singlets breaks the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix and enables tree-level flavour changing neutral (FCN) vertices. The resulting radiative flavour changing decays of these particles through the electromagnetic transition dipole moment are a key means to study their properties and search for them at experiments like the Large Hadron Collider (LHC). Despite these radiative decays providing such a clean experimental signature, an explicit analytical study of the branching ratios and CP violation resulting from these loop level processes has thus far evaded attention. We provide the formulation for the decay rates and CP asymmetry resulting from a combination of the imaginary components of the loop integrals and complex phases in the quark mixing matrix. We then apply our analytical results to study phenomenology of these states for several global fits pertaining to vector-like isosinglets t′ and b′. We find that clean collider signatures and polarisation observables can be generated for both t′ and b′.