Publications

Order by: publication date number of citations

• Search for lepton-flavour-violating decays of the $Z$ boson into a $\tau$-lepton and a light lepton with the ATLAS detector

  Wing Sheung Chan on behalf of the ATLAS collaboration

  SciPost Phys. Proc. 1, 048 (2019) · published 22 February 2019 | Toggle abstract · pdf

  Lepton flavour violation in the charged lepton sector is an unambiguous signal of physics beyond the Standard Model. Searches for lepton flavour violation in decays of the $Z$ boson with the ATLAS detector is reported, focusing on decays into an electron or muon and a hadronically decaying $\tau$-lepton, using $pp$ collisions data with a centre-of-mass energy of 13 TeV. Upper limits on the branching ratios of lepton-flavor-violating decays are set at the 95\% confidence level: $\mathcal{B}(Z\to e\tau) < 5.8\times10^{-5}$ and $\mathcal{B}(Z\to \mu\tau) < 2.4\times10^{-5}$. When combined with a previous ATLAS result based on $pp$ collisions data with a centre-of-mass energy of 8 TeV, an upper limit of $\mathcal{B}(Z\to \mu\tau) < 1.3\times10^{-5}$ is obtained.

• Charged lepton flavour violating processes

  Adrian Signer

  SciPost Phys. Proc. 1, 014 (2019) · published 19 February 2019 | Toggle abstract · pdf

  Charged lepton flavour violating processes are naturally present in many extensions of the Standard Model. After a brief overview on the experimental situation, an effective-field-theory framework is described that allows to interpret and compare the various experiments in a consistent way. The usefulness of this approach is then illustrated in the context of a specific model with a doubly charged scalar.

• Field-induced local Fermi-liquid states in the underscreened Kondo model for Eu compounds

  Shingo Kuniyoshi, Ryousuke Shiina

  SciPost Phys. Proc. 11, 015 (2023) · published 6 June 2023 | Toggle abstract · pdf

  We have studied an underscreened Kondo model for the impurity spin $S=7/2$ capturing the $4f$ characteristics of a nearly divalent Eu ion. By using the numerical renormalization group method, it is shown that an unusual heavy-fermion state is induced from the underscreened spin state when a weak crystal field is introduced. It is also found that the application of the magnetic field enhances the effective mass of the heavy fermions, reflecting the field-induced level crossing of the spin states. We will discuss the mechanism of these mass enhancements in terms of a realization of the two-stage Kondo effect.

• Petro-politics, Gender Violence and Human Trafficking in Nigeria’s Niger Delta Region

  Abosede Omowumi Babatunde

  Mig. Pol. 4, 003 (2025) · published 27 May 2025 | Toggle abstract · pdf

  In Nigeria’s Niger Delta, oil politics by global oil corporation, national government and local leaders perpetuate gender inequalities in the distribution of oil benefits to women in oil communities. Women also bear the greater cost of oil-induced environmental harms which adversely affect their traditional livelihood of farming and fishing. Scholarship on human trafficking in Nigeria focused scant attention on the structural conditions that influenced women experience of human trafficking in extractive contexts. This article examines how oil politics perpetuate gender violence and expose women to human trafficking for sexual exploitation and forced labour in the Niger Delta region. Based on feminist political ecology perspectives and field studies in selected oil communities, the study seeks to explain how oil politics perpetuate women’s socio-economic deprivation, in ways that expose them to human trafficking as victims and accomplice. Women exposure to human trafficking amplify their experience of gender violence and violate their rights and aspiration for emancipation and justice in Nigeria’s oil extractive region. International organizations and policy makers need to consider the global and local dynamics that magnified women’s experience of human trafficking in extractive communities and the wider implications for the global and local efforts to combat human trafficking.

• Knowledge-dependent optimal Gaussian strategies for phase estimation

  Ricard Ravell Rodríguez, Simon Morelli

  SciPost Phys. 18, 167 (2025) · published 27 May 2025 | Toggle abstract · pdf

  When estimating an unknown phase rotation of a continuous-variable system with homodyne detection, the optimal probe state strongly depends on the value of the estimated parameter. In this article, we identify the optimal pure single-mode Gaussian probe states depending on the knowledge of the estimated phase parameter before the measurement. We find that for a large prior uncertainty, the optimal probe states are close to coherent states, a result in line with findings from noisy parameter estimation. However, with increasingly precise estimates of the parameter, it becomes beneficial to put more of the available energy into the squeezing of the probe state. Surprisingly, there is a clear jump, where the optimal probe state changes abruptly to a squeezed vacuum state, which maximizes the Fisher information for this estimation task. We use our results to study repeated measurements and compare different methods to adapt the probe state based on the changing knowledge of the parameter according to the previous findings.

• NLO prediction for the decays $\tau \to \ell \ell'\ell' \nu \bar \nu$ and $\mu \to e e e \nu \bar\nu$

  Matteo Fael

  SciPost Phys. Proc. 1, 009 (2019) · published 18 February 2019 | Toggle abstract · pdf

  These proceedings present the differential decay rates and the branching ratios of the tau and muon decays $\tau \to \ell \ell' \ell' \nu \bar\nu$ (with $\ell,\ell'=\mu,e$) and $\mu \to e e e \nu \bar \nu$ in the Standard Model at NLO. These five-body leptonic decays are a tool to study the Lorentz structure of weak interactions and to test lepton flavour universality. They are also a source of SM background to searches for the lepton-flavour-violating decays $\mu \to e e e$ and $\tau \to \ell \ell' \ell'$. Even if the shift in the branching ratios induced by radiative corrections turns out to be small and of order 1% - mainly due to a running effect of the fine structure constant - locally in the phase space these corrections can reach the 5 - 10% level, depending on the applied cuts. We found for instance that in the phase space region where the neutrino energies are small, and the momenta of the three charged leptons have a similar signature as in $\mu \to eee$ and $\tau \to \ell \ell'\ell'$, the NLO corrections decrease the leading-order prediction by about 10 - 20%.

• Coherent deflection of atomic samples and positional mesoscopic superpositions

  Luis Felipe Alves da Silva, Leandro M. R. Rocha, Miled H. Y. Moussa

  SciPost Phys. 18, 169 (2025) · published 28 May 2025 | Toggle abstract · pdf

  We present a protocol based on the interplay between superradiance and superabsorption to achieve the coherent deflection of an atomic sample due to the momentum transfer from the atoms to a cavity field. The coherent character of this momentum transfer, causing the atomic sample to deflect as a whole, follows from the collective nature of the atomic superradiant pulse and its superabsorption by the cavity field. The protocol is then used for the construction of positional mesoscopic atomic superpositions in cavity quantum electrodynamics.

• Experimental input from $e^+e^-$ for $a_{\mu}$ light-by-light

  Yuping Guo on behalf of BESIII Collaboration

  SciPost Phys. Proc. 1, 054 (2019) · published 9 May 2019 | Toggle abstract · pdf

  The anomalous magnetic momentum of the muon, $a_{\mu}$, has been measured and calculated with a precision up to $~0.5$ ppm, but there is a 3 to 4 standard deviations between these two values. The uncertainty in the calculation is dominated by the hadronic part, including the hadronic vacuum polarization and the hadronic light-by-light. The meson transition form factors and the helicity amplitudes can be used as input or constraint to the calculation of the hadronic light-by-light contribution. Latest experimental studies of the transition form factors of $\pi^0$, $\eta$, and $\eta^{*}$ and the cross-section of $\gamma\gamma^*\to\pi^+\pi-$from $e^+e^-$ collider are presented.

• Classical weight-four L-value ratios as sums of Calabi-Yau invariants

  Philip Candelas, Xenia de la Ossa, Joseph McGovern

  SciPost Phys. 18, 181 (2025) · published 6 June 2025 | Toggle abstract · pdf

  We revisit the series solutions of the attractor equations of 4d $\mathcal{N}=2$ supergravities obtained by Calabi–Yau compactifications previously studied in [P. Candelas et al., J. High Energy Phys. 11, 032 (2021)]. While only convergent for a restricted set of black hole charges, we find that they are summable with Padé resummation providing a suitable method. By specialising these solutions to rank-two attractors, we obtain many conjectural identities of the type discovered in [P. Candelas et al., J. High Energy Phys. 11, 032 (2021)]. These equate ratios of weight-four special L-values with an infinite series whose summands are formed out of genus-0 Gromov–Witten invariants. We also present two new rank-two attractors which belong to moduli spaces each interesting in their own right. Each of these moduli spaces possess two points of maximal unipotent monodromy. One has already been studied by Hosono and Takagi, and we discuss issues stemming from the associated L-function having nonzero rank.

• Emergent dipole field theory in atomic ladders

  Hernan B. Xavier, Poetri Sonya Tarabunga, Marcello Dalmonte, Rodrigo G. Pereira

  SciPost Phys. 18, 184 (2025) · published 10 June 2025 | Toggle abstract · pdf

  We study the dynamics of hard-core bosons on ladders, in the presence of strong kinetic constrains akin to those of the Bariev model. We use a combination of analytical methods and numerical simulations to establish the phase diagram of the model. The model displays a paired Tomonaga-Luttinger liquid phase featuring an emergent dipole symmetry, which encodes the local pairing constraint into a global, nonlocal quantity. We scrutinize the effect of such emergent low-energy symmetry during quench dynamics including single-particle defects. We observe that, despite being approximate, the dipole symmetry still leads to very slow relaxation dynamics, which we model via an effective field theory. The model we discuss is amenable to realization in both cold atoms in optical lattices and Rydberg atom arrays with dynamics taking place solely in the Rydberg manifold. To observe the unusual dynamics of excitations in such experimental platforms, we propose a two-step protocol, which starts with the quasi-adiabatic preparation of low-energy states, followed by the local creation of defects and their study under quench dynamics.