A
bstract
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
′.
The Sun emits copious amounts of photons and neutrinos in an approximately spatially isotropic distribution. Diffuse γ-rays and ultra-high energy (UHE) neutrinos from extragalactic sources may ...subsequently interact and annihilate with the emitted solar photons and neutrinos respectively. This will in turn induce an anisotropy in the cosmic ray (CR) background due to attenuation of the γ-ray and UHE neutrino flux by the solar radiation. Measuring this reduction, therefore, presents a simple and powerful astrophysical probe of electroweak interactions. In this letter we compute such anisotropies, which at the Earth (Sun) can be at least ≃5×10−3(1)% and ≃1×10−16(2×10−14)% for TeV scale γ-rays and PeV scale UHE neutrinos respectively. We briefly discuss observational prospects for experiments such as the Fermi Gamma-Ray Space Telescope Large Area Telescope (Fermi LAT), High-Altitude Water Cherenkov (HAWC) detector, The Large High Altitude Air Shower Observatory (LHAASO), Cherenkov Telescope Array (CTA) and IceCube. The potential for measuring γ-ray attenuation at orbital locations of other active satellites such as the Parker Solar Probe and James Webb Space Telescope (JWST) is also explored.
A
bstract
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
N
1
and
N
2
. 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
N
2
→ N
1
γ
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.
A
bstract
The radiative decay of neutral fermions has been studied for decades but
CP
violation induced within such a paradigm has evaded attention.
CP
violation in these processes can produce an ...asymmetry between circularly polarised directions of the radiated photons and produces an important source of net circular polarisation in particle and astroparticle physics observables. The results presented in this work outlines the general connection between
CP
violation and circular polarisation for both Dirac and Majorana fermions and can be used for any class of models that produce such radiative decays. The total
CP
violation is calculated based on a widely studied Yukawa interaction considered in both active and sterile neutrino radiative decay scenarios as well as searches for dark matter via direct detection and collider signatures. Finally, the phenomenological implications of the formalism on keV sterile neutrino decay, leptogenesis-induced right-handed neutrino radiative decay and IceCube-driven heavy dark matter decay are discussed.
Abstract We study sub-GeV dark matter (DM) particles that may annihilate or decay into Standard Model particles producing an exotic injection component in the Milky Way that leaves an imprint in both ...photon and cosmic-ray (CR) fluxes. Specifically, the DM particles may annihilate or decay into e + e − , μ + μ − , or π + π − and may radiate photons through their e ± products. The resulting e ± products can be directly observed in probes such as Voyager 1. Alternatively, the e ± products may produce bremsstrahlung radiation and upscatter the low-energy Galactic photon fields via the inverse Compton process, generating a broad emission from X-ray to γ -ray energies observable in experiments such as XMM-Newton. We find that we get a significant improvement in the DM annihilation and decay constraints from XMM-Newton (excluding thermally averaged cross sections of 10 −31 cm 3 s −1 ≲ 〈 σ v 〉 ≲ 10 −26 cm 3 s −1 and decay lifetimes of 10 26 s ≲ τ ≲ 10 28 s, respectively) by including best-fit CR propagation and diffusion parameters. This yields the strongest astrophysical constraints for this mass range of DM of 1 MeV to a few GeV and even surpasses cosmological bounds across a wide range of masses as well.
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