Search results for "Global symmetries"
showing 6 items of 6 documents
Odd-intrinsic-parity processes within the Resonance Effective Theory of QCD
2003
19 páginas, 4 figuras.-- arXiv:hep-ph/0306157v1
Observable flavor violation from spontaneous lepton number breaking
2022
We propose a simple model of spontaneous lepton number violation with potentially large flavor violating decays, including the possibility that majoron emitting decays, such as $\mu \to e \, J$, saturate the experimental bounds. In this model the majoron is a singlet-doublet admixture. It generates a type-I seesaw for neutrino masses and contains also a vector-like lepton. As a by-product, the model can explain the anomalous $(g-2)_{\mu}$ in parts of its parameter space, where one expects that the branching ratio of the Higgs to muons is changed with respect to Standard Model expectations. However, the explanation of the muon $g-2$ anomaly would lead to tension with recent astrophysical bou…
On the strength of the U A (1) anomaly at the chiral phase transition in N f = 2 QCD
2016
We study the thermal transition of QCD with two degenerate light flavours by lattice simulations using $O(a)$-improved Wilson quarks. Temperature scans are performed at a fixed value of $N_t = (aT)^{-1}=16$, where $a$ is the lattice spacing and $T$ the temperature, at three fixed zero-temperature pion masses between 200 MeV and 540 MeV. In this range we find that the transition is consistent with a broad crossover. As a probe of the restoration of chiral symmetry, we study the static screening spectrum. We observe a degeneracy between the transverse isovector vector and axial-vector channels starting from the transition temperature. Particularly striking is the strong reduction of the split…
Searches for violation of lepton flavour and baryon number in tau lepton decays at LHCb
2013
Searches for the lepton flavour violating decay tau(-) -> mu(-)mu(+)mu(-) and the lepton flavour and baryon number violating decays tau(-) -> (p) over bar mu(+)mu(-) and tau(-) -> p mu(-)mu(-) have been carried out using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb(-1), taken by the LHCb experiment at root s = 7 TeV. No evidence has been found for any signal, and limits have been set at 90% confidence level on the branching fractions: B(tau(-) -> mu(-)mu(+)mu(-) mu(+)mu(-)) p mu(-)mu(-)) (p) over bar mu(+)mu(-) and tau(-) -> p mu(-)mu(-) decay modes represent the first direct experimental limits on these channels.
The Inverse Seesaw Family: Dirac And Majorana
2021
After developing a general criterion for deciding which neutrino mass models belong to the category of inverse seesaw models, we apply it to obtain the Dirac analogue of the canonical Majorana inverse seesaw model. We then generalize the inverse seesaw model and obtain a class of inverse seesaw mechanisms both for Majorana and Dirac neutrinos. We further show that many of the models have double or multiple suppressions coming from tiny symmetry breaking "$\mu$-terms". These models can be tested both in colliders and with the observation of lepton flavour violating processes.
Stimulated transitions in resonant atom Majorana mixing
2018
Massive neutrinos demand to ask whether they are Dirac or Majorana particles. Majorana neutrinos are an irrefutable proof of physics beyond the Standard Model. Neutrinoless double electron capture is not a process but a virtual $\Delta L = 2$ mixing between a parent $^AZ$ atom and a daughter $^A(Z-2)$ excited atom with two electron holes. As a mixing between two neutral atoms and the observable signal in terms of emitted two-hole X-rays, the strategy, experimental signature and background are different from neutrinoless double beta decay. The mixing is resonantly enhanced for almost degeneracy and, under these conditions, there is no irreducible background from the standard two-neutrino cha…