Heavy neutral leptons are motivated by several extensions of the Standard
Model and their presence induces modifications in the lepton mixing matrix,
including new Dirac and Majorana CP violating ...phases. It has been recently
shown that these phases play an important role in lepton number and lepton
flavour violating decays and transitions, with a striking impact for the
predicted rates of certain observables. In this work, we now consider the
potential role of the heavy neutral fermions and of the new CP violating phases
in Higgs and $Z$-boson lepton flavour violating decays $H,Z\to
\ell_\alpha^\pm\ell_\beta^\mp$, as well as in the corresponding CP asymmetries.
In order to allow for a thorough analysis, we derive the full analytical
expressions of the latter observables, taking into account the effect of the
(final state) charged lepton masses. A comprehensive exploration of lepton
flavour violating $Z$ and Higgs decays confirms that these are very sensitive
to the presence of the additional heavy neutral leptons. Moreover, the new CPV
phases have a clear impact on the decay rates, leading to both destructive and
constructive interferences. Interestingly, in the $\mu\tau$ sector, the $Z\to
\ell_\alpha^\pm\ell_\beta^\mp$ rates are within reach of FCC-ee, with
associated CP asymmetries that can potentially reach up to $20\% - 30\%$.
Extensions of the Standard Model featuring light vector bosons have been explored with the goal of resolving certain tensions between theory and experiment, among them the discrepancy in the ...anomalous magnetic moment of the muon, \(\Delta a_{\mu}\). In particular, this is the case of a minimal construction including a leptophilic, strictly flavour violating, vector boson \(Z^\prime\). These new vector bosons are also well-motivated dark matter portals, with non-trivial couplings to stable, weakly interacting states which can account for the correct dark matter density. Here we study the prospects of a Standard Model extension (via a vector boson and a fermionic dark matter candidate) concerning signatures at the LHC, and at future lepton and hadron colliders.We discuss the cross-sections of several processes leading to same- and opposite-sign muon-tau lepton pairs in the final state, as well as final states with missing energy (in the form of neutrinos and/or dark matter). Our findings suggest that a future muon collider offers the best prospects to probe this model (together with searches for dilepton pairs and missing energy signatures at the FCC-ee running at the \(Z\)-pole); moreover, the complementarity of the different future high-energy colliders is also paramount to probing distinct \(Z^\prime\) mass regimes.
The apparent tensions emerging from the comparison of experimental data of the anomalous magnetic moments of the muon and electron to the Standard Model predictions (\(\Delta a_{\mu,e}\)) could be ...interpreted as a potential signal of New Physics. Models encompassing a light vector boson have been known to offer a satisfactory explanation to \(\Delta a_{\mu}\), albeit subject to stringent experimental constraints. Here we explore a minimal extension of the Standard Model via a leptophilic vector boson \(Z^\prime\), under the hypothesis of strictly flavour-violating couplings of the latter to leptons. The most constraining observables to this ad-hoc construction emerge from lepton flavour universality violation (in \(Z\) and \(\tau\) decays) and from rare charged lepton flavour violating transitions. Once these are accommodated, one can saturate the tensions in \(\Delta a_{\mu}\), but \(\Delta a_{e}\) is predicted to be Standard Model-like. We infer prospects for several observables, including leptonic \(Z\) decays and several charged lepton flavour violating processes. We also discuss potential signatures of the considered \(Z^\prime\) at a future muon collider, emphasising the role of the \(\mu^+\mu^- \to\tau^+\tau^- \) forward-backward asymmetry as a key probe of the model.
Standard Model extensions via heavy neutral leptons lead to modifications in the lepton mixing matrix, including new Dirac and Majorana CP violating phases. Here we consider the role of the Majorana ...fermions and of new CP violating phases in Higgs and \(Z\)-boson lepton flavour violating decays, as well as in the corresponding CP-asymmetries. We confirm that these decays are sensitive to the presence of additional sterile states and show that the new CP violating phases may lead to both destructive and constructive interferences in the decay rates. Interestingly the \(Z\to \mu^\pm\tau^\mp\) rates are within FCC-ee reach, with associated CP-asymmetries that can potentially reach up to 30%.
The Snowmass report on rare processes and precision measurements recommended Mu2e-II and a next generation muon facility at Fermilab (Advanced Muon Facility) as priorities for the frontier. The ...Workshop on a future muon program at FNAL was held in March 2023 to discuss design studies for Mu2e-II, organizing efforts for the next generation muon facility, and identify synergies with other efforts (e.g., muon collider). Topics included high-power targetry, status of R&D for Mu2e-II, development of compressor rings, FFA and concepts for muon experiments (conversion, decays, muonium and other opportunities) at AMF. This document summarizes the workshop discussions with a focus on future R&D tasks needed to realize these concepts.
Heavy neutral leptons are motivated by several extensions of the Standard Model and their presence induces modifications in the lepton mixing matrix, including new Dirac and Majorana CP violating ...phases. It has been recently shown that these phases play an important role in lepton number and lepton flavour violating decays and transitions, with a striking impact for the predicted rates of certain observables. In this work, we now consider the potential role of the heavy neutral fermions and of the new CP violating phases in Higgs and \(Z\)-boson lepton flavour violating decays \(H,Z\to \ell_\alpha^\pm\ell_\beta^\mp\), as well as in the corresponding CP asymmetries. In order to allow for a thorough analysis, we derive the full analytical expressions of the latter observables, taking into account the effect of the (final state) charged lepton masses. A comprehensive exploration of lepton flavour violating \(Z\) and Higgs decays confirms that these are very sensitive to the presence of the additional heavy neutral leptons. Moreover, the new CPV phases have a clear impact on the decay rates, leading to both destructive and constructive interferences. Interestingly, in the \(\mu\tau\) sector, the \(Z\to \ell_\alpha^\pm\ell_\beta^\mp\) rates are within reach of FCC-ee, with associated CP asymmetries that can potentially reach up to \(20\% - 30\%\).
Dual-frequency fiber lasers (DFFL) are shown to provide high purity beat notes for microwave signal generation and distribution. We study the stabilization of the beat from DFB DFFLs by using optical ...frequency-shifted feedback loop containing an electro-optic modulator (EOM). As a proof-of-principle of the method efficiency, a stabilized beat note with a phase noise level of -104 dBc/Hz at 1 kHz from a 1 GHz carrier, and of -90 dBc/Hz at 1 kHz from a 10 GHz carrier, is demonstrated when the EOM is driven by a synthesizer. Furthermore, the scheme is extended to a self-referenced scheme: a hybrid opto-electronic oscillator is obtained when the delayed DFFL beat note itself drives the EOM. Low-frequency phase noise is reduced by about 20 dB. Applications are discussed.
Behavioral, cognitive and functional particularities in autism differ according to autism subgroups and might be associated with domain-specific cognitive strengths. It is unknown whether structural ...changes support this specialization. We investigated the link between cortical folding, its maturation and cognitive strengths in autism subgroups presenting verbal or visuo-spatial peaks of abilities.
We measured gyrification, a structural index related to function, in 55 autistic participants with (AS-SOD, N = 27) or without (AS-NoSOD, N = 28) a speech onset delay (SOD) with similar symptom severity but respectively perceptual and verbal cognitive strengths, and 37 typical adolescents and young adults matched for intelligence and age. We calculated the local Gyrification Index (lGI) throughout an occipito-temporal region of interest and independently modeled age and peak of ability effects for each group.
Unique gyrification features in both autistic groups were detected in localized clusters. When comparing the three groups, gyrification was found lower in AS-SOD in a fusiform visual area, whereas it was higher in AS-NoSOD in a temporal language-related region. These particular areas presented age-related gyrification differences reflecting contrasting local maturation pathways in AS. As expected, peaks of ability were found in a verbal subtest for the AS-NoSOD group and in the Block Design IQ subtest for the AS-SOD group.
Irrespective of their direction, regional gyrification differences in visual and language processing areas respectively reflect AS-SOD perceptual and AS-NoSOD language-oriented peaks. Unique regional maturation trajectories in the autistic brain may underline specific cognitive strengths, which are key variables for understanding heterogeneity in autism.
•Subgrouping the autism spectrum (AS) partly accounts for its heterogeneity.•AS individuals with a speech onset delay (SOD) show perceptual cognitive strengths.•AS individuals without a SOD show language-related cognitive strengths.•AS subgroups show unique gyrification patterns in areas related to their strengths.•Cortical structural maturation may be related to domain-specific strengths in AS.
We report the design and performance of a single frequency all-fiber distributed feedback (DFB) laser sources employing fiber Bragg gratings (FBGs) emitting in the 2-<inline-formula><tex-math ...notation="LaTeX">\mu</tex-math></inline-formula>m region. Output powers up to 65 mW CW and optical signal-to-noise ratios of <inline-formula><tex-math notation="LaTeX">></tex-math></inline-formula>65 dB/0.05 nm are obtained. The emission wavelength of the DFB-FBG laser can be fine-tuned with picometer accuracy over a range of 0.6 nm by controlling the pump power and laser temperature. The single frequency source is amplified with polarization-maintaining Ho- or Tm-doped fiber amplifiers to an output power of 1 W CW at 2051 nm or 0.7 W CW at 2039 nm. Heterodyne measurements yield instantaneous laser linewidths of 5 kHz FWHM for both native and amplified signals.
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