abstract

Recently, the exciting new Fermilab (FNAL) Muon \(g-2\) measurement impressively confirmed the final Brookhaven (BNL) result from 2004 and, with a result four times more precise, has launched a new serious attack on the Standard Model (SM). On the theoretical side, ab-initio lattice QCD (LQCD) calculations of hadronic vacuum polarization have made remarkable progress. They are now the new standard for studying the leading non-perturbative contributions, which have previously hindered matching with the precision required for full exploitation of the experimental results. The lattice results affected both leading hadronic contributions — the hadronic vacuum polarization (HVP) and the hadronic light-by-light (HLbL) contributions — by increasing the previously generally accepted \(e^+e^- \to \) hadrons based dispersion relation results. The shifts reduced the discrepancy between theory and experiment to “nothing missing.” One of the most prominent signs of “beyond the Standard Model” (BSM) physics has disappeared: the SM appears validated more than ever, in agreement with what also searches at the Large Hadron Collider (LHC) at CERN tell us! A triumph of the SM, in spite of the fact that the SM cannot explain known cosmological puzzles such as dark matter or baryogenesis and why neutrino masses are so tiny, the absence of strong CP violation, for example. I also argue that the discrepancy between the data-driven dispersive result and the lattice QCD results for the hadronic vacuum polarization can be largely explained by correcting the \(\epm \) data for \(\rho ^0\)–\(\gamma \) mixing effects.

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In this paper, we briefly present the Monte Carlo event generators BHLUMI and BHWIDE for small- and large-angle Bhabha scattering, respectively, and discuss possible ways of their improvements in order to satisfy precision needs of future electron–positron colliders.

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The possible anomalous New Physics contributions to magnetic and electric dipole moments of the \(\tau \) lepton have brought renewed interest in studying \(\tau \) pair production at energies of the LHC and future colliders. We discuss effects of electromagnetic and weak dipole moment contributions to the \(\tau \)-lepton polarization and \(\tau \tau \) spin correlations in the \(\gamma \gamma \to \tau ^-\tau ^+\) and \(q \bar {q} \to \tau ^- \tau ^+\) processes. Such processes have been observed in the \(pp\) and PbPb collisions in the LHC experiments. Extensions of the Standard Model amplitudes for \(\gamma \gamma \to \tau ^-\tau ^+\) and \(q \bar {q} \to \tau ^- \tau ^+\) processes, which include dipole moments of the \(\tau \) lepton, are implemented in the TauSpinner Monte Carlo program. A few examples of signatures of \(\tau \tau \) spin correlations and \(\tau \)-lepton dipole moments in observables are presented.

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Precise QED radiative corrections for low- and high-energy electron–positron colliders are essential for accurate simulations of luminosity processes and precision tests of the Standard Model. We review the historical formulation and the recent developments of the BabaYaga@NLO event generator, which implements a QED Parton Shower (PS) matched with fixed-order calculations. We discuss the theoretical formulation of the code, as well as the assessment of its theoretical accuracy. Applications at low- and high-energy \(e^+e^-\) colliders are presented, including the latest result, together with the perspectives for future improvements, in view of the demanding precision requirements of future machines at the intensity frontier.

abstract

I cover usually omitted essentials from more than 43 years of my own experience in the domain of precision Monte Carlo programs development. I was not working alone, my work was a continuation of earlier efforts. For example, Stanisław Jadach’s achievements before 1981 were essential. I was working with him and B.F.L. Ward over most of these years. Also, monumental projects of Bryan Lynn, Robin Stuart, Dima Bardin, and Wolfgang Hollik in the domain of precision physics need to be mentioned, because they affected my work. This is a challenging call for me! Usually, we were publishing our own projects, and the following incomplete lists of methodology domains and projects were left aside in references, appendices, and private notes: (i) phase space: symmetries, (ii) matrix element preparation \(\to \) factorizations, (iii) program and development process design, (iv) testing strategies, (v) user interaction, (vi) software tools, (vii) partners and competitors. The work started on the basis of previous efforts which can be listed following names of the programs: (i) FOWL, (ii) GENRAP, (iii) Mustraal, (iv) Koralb, (v) Lesko, (vi) TAUOLA, (vii) KORALZ, (viii) LUMLOG, (ix) OLDBAB, (x) BHLUMI, (xi) BHWIDE, and (xii) KKMC. I will focus on some of these points. Others, hopefully, are sufficiently well covered in other papers. In particular, I do not need to cover exponentiation, see contribution to the proceedings by W. Placzek and talk of B.F.L. Ward. Developments took years and did not follow a straight line; that is why there are inevitable simplifications and biases in my presentation. Also, a review of the essential literature could not be completed.

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Beyond leading order, perturbative QCD calculations require the choice of a factorisation scheme to define the coefficient functions and parton distribution functions. Through the years, a number of different schemes were proposed, with different motivations and purposes. We present the first-ever comparison of these factorisation schemes on a common basis. We compare their features, both at the analytical and numerical level, and assess the impact of this choice on phenomenology at the LHC.

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In this contribution, we present the extension of the CoLoRFulNNLO subtraction scheme to the production of color-singlet final states in hadronic collisions. We also showcase the NNLOCAL code, a publicly available proof-of-concept implementation of the method, and report on the current directions of code development.

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The conic hulls/triangulation method is extended to the analytic computation of multiple Mellin–Barnes having polygamma functions of arbitrary order in their integrand. This computational approach is automatized in the MBConicHulls.wl Mathematica package, which we give a brief description of the new corresponding functionalities, basing our discussion on the example of a simple two-loop sunset integral.

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In this article, I discuss recent advancements made by the Wrocław Neutrino Group in neutrino–nucleus interaction modeling, focusing on the implementation of an exclusive model for meson-exchange current-driven interactions in the NuWro Monte Carlo event generator and on NuWro’s performance against recent MINER\({\nu }\)A CC1\(p\)0\(\pi \) measurements. I also briefly describe the fine-tuning of final-state interactions in NuWro. These improvements have a significant impact on exclusive observables.

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In this proceedings contribution, I summarize recent developments of the spectral function approach implemented in the NuWro Monte Carlo event generator. The modified framework provides a consistent treatment of multinucleon final states in quasielastic scattering. The model is first validated using inclusive electron–carbon scattering data and then applied to the exclusive MicroBooNE measurements. I demonstrate that the implemented improvements play a crucial role in reproducing both the shapes and normalizations of the experimental data.

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Hyper-Kamiokande is a next-generation water Cherenkov detector that will detect neutrinos from terrestrial and astrophysical sources in addition to probing nucleon decay. The accelerator beam neutrino program with the 258 kiloton Hyper-K as the far detector will provide high sensitivity to the unknown parameters of 3-flavour neutrino oscillation physics, especially the leptonic CP phase, \(\delta _{\mathrm {CP}}\). Hyper-K will also detect atmospheric neutrinos that experience Earth matter effects and has sensitivity to neutrino mass hierarchy. The expected sensitivities to \(\Delta {m^2_{32}}\), \(\sin ^2\theta _{23}\), \(\delta _{\mathrm {CP}}\), and neutrino mass hierarchy from accelerator and atmospheric neutrino programs at Hyper-K are discussed here. Hyper-K is currently under construction and the data-taking is expected to commence in 2028.

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The NA61/SHINE strong interaction program is dedicated to exploring the properties of strongly interacting matter under extreme conditions. Its central objectives are the search for the critical point in the QCD phase diagram and the study of the properties of the onset of deconfinement. This contribution summarizes selected recent achievements of the NA61/SHINE Collaboration, including results on hadron production, fluctuations, and correlations, and outlines future prospects for the experiment.

abstract

Sterile neutrinos are promising candidates for dark matter, particularly in addressing small-scale challenges of the \({\mit \Lambda }\)CDM model. These particles are radiatively unstable, decaying into active neutrinos and photons, thereby injecting energy into the intergalactic medium (IGM) during the cosmic dawn. The energy injection can alter the temperature and ionization history of IGM, impacting the global 21 cm absorption signal predicted by standard cosmological models. Using the observed 21 cm signal from the EDGES Collaboration, we derive constraints on the sterile neutrino lifetime and their mixing angle with active neutrinos. Our bounds, obtained without assuming non-standard cooling mechanisms or additional radio backgrounds, are compared with the existing astrophysical limits, such as those from X-ray observations. For sterile neutrino masses between 2 keV and 50 keV, the lifetime is constrained to be greater than \(8.3 \times 10^{27}\) s to \(9.4 \times 10^{25}\) s for a 21 cm brightness temperature of \( -150 \) mK at \( z=17.2\). These results provide model-independent probes of sterile neutrino parameters relevant to dark-matter phenomenology.

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In this work, we take the Grimus–Neufeld model, which extends the Standard Model by adding a sterile neutrino and a second Higgs doublet. We calculate the decay rates for the heaviest neutrino, and by that the life-time, in the tiny seesaw scenario. The tree-level decay is mediated by the \(Z\) boson and the neutral Higgs bosons. The loop-level decay into a neutrino and a photon can dominate in some parameter regions.

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In this contribution, we explore the physics potential of the ESSnuSBplus setup to study beam- and non-beam-based physics scenarios in both standard and New Physics cases. The ESSnuSBplus setup consists of three neutrino sources: the main ESS linac, a low-energy monitored neutrino beam, and a low-energy nuSTORM facility and three detectors: the main far detector and two near detectors. The goal of this facility is to measure the leptonic CP phase with extremely high precision and the neutrino–nucleus cross section in the few-hundred-MeV region.

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When the Higgs doublets in the three-Higgs-doublet model (3HDM) transform as a flavor triplet under the \(A_4\) group, the resulting lepton mass matrices reproduce the experimentally observed neutrino mixing angles with arbitrary precision, while simultaneously maintaining the correct mass ordering of both charged and neutral leptons, where the latter are Dirac neutrinos with a normal mass hierarchy. Imposing the \(A_4\) symmetry also allows for agreement between the calculated and observed lepton masses for Higgs vacuum configurations that differ from those required to fit \(U_{\mathrm {PMNS}}\). Among all discrete groups of order less than or equal to 600, no contraction other than the one associated with \(A_4\) leads to a better agreement with experimental data, and the solution structure presented here is unique within the set of groups investigated.

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We present the ingredients of a computation needed for a semi-classical treatment for estimating the amount of baryogenesis via leptogenesis. Our main focus is on the computation of the finite temperature CP-asymmetry factor originating from Majorana fermion decays into a lepton and a scalar particle at next-to-leading order in perturbation theory. Such decays emerge naturally in U(1) extensions of the Standard Model, such as the superweak extension (SWSM). We emphasize the importance of all cuts in the one-loop corrections in order to obtain physically meaningful expressions and present benchmark predictions for the CP-asymmetry factor as a function of temperature in the SWSM.

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Leptogenesis is an attractive explanation for the observed baryon asymmetry of our Universe. In these proceedings, we study a framework where thermal leptogenesis occurs during a period of a first-order phase transition (FOPT). Right-handed neutrinos (RHNs) remain massless until bubble nucleation. Their abrupt mass generation leads to rapid decoupling and modifies the usual washout dynamics. Compared to standard thermal leptogenesis, where successful asymmetry requires masses above a certain scale, we find that bubble dynamics can dramatically reduce this scale and also study associated gravitational wave signals observable at terrestrial interferometers.

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In these proceedings, we report on a secluding mechanism for dark matter from quantum scale symmetry: in the presence of an asymptotically safe ultraviolet fixed point at trans-Planckian scales, the renormalization group flow of the gauge–Yukawa couplings can control dark matter decays, without the need for discrete or global symmetries. We show explicitly how the mechanism works for an SU(6) model and indirectly constrain physical mass scales of the theory.

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Despite the remarkable success of the Standard Model in describing fundamental interactions, unresolved phenomena such as dark matter, dark energy, and matter–antimatter asymmetry strongly suggest the existence of physics beyond the Standard Model. The absence of new particle discoveries at the LHC indicates that such New Physics may be significantly heavier than the electroweak scale. In this context, Effective Field Theories offer a powerful framework for studying the indirect effects of heavy New Physics. This contribution reviews some of the recent advancements, computational tools, and phenomenology of Effective Field Theories, with a particular focus on the Standard Model Effective Field Theory.

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The discovery of gravitational lensing marked a significant milestone in observational astronomy. Massive galaxy surveys, combined with dedicated search strategies, have resulted in hundreds of known strong lensing systems. Consequently, this phenomenon is increasingly seen as a crucial tool in cosmology and fundamental physics. This article reviews selected developments in this field.

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High-energy colliders, such as the Large Hadron Collider (LHC) at CERN, are genuine quantum machines, so, in line with Richard Feynman’s original motivation for Quantum Computing, the scattering processes that take place there are natural candidates to be simulated on a quantum system. Potential applications range from quantum machine learning methods for collider data analysis, to faster and more precise evaluations of intricate multiloop Feynman diagrams, more efficient jet clustering, improved simulations of parton showers, and many other tasks. In this work, the focus will be on two specific applications: first, the identification of the causal structure of multiloop vacuum amplitudes, a key ingredient of the Loop–Tree Duality and an area with deep connections to graph theory; and second, the integration and sampling of high-dimensional functions. The latter constitutes the first step toward the realization of a fully fledged quantum event generator operating at high perturbative orders.

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We briefly review false-vacuum decay and examine a recent proposal by Frampton to model the origin of the first single-celled organism (SCO) as a phase transition between no-life and life vacua. In his calculation, the exponent \(n\) entering the probability \(P_{\mathrm {SCO}}\sim 10^{-n}\) has dimensions of inverse time: it is an energy barrier divided by the Planck constant, rather than a dimensionless tunnelling action. The resulting probability is mathematically ill-defined and does not determine a tunnelling rate. Apart from this dimensional issue, the assumed initial configuration, a toroidal structure made of long molecules, and its treatment in empty space are inconsistent with soft-matter physics and with the hot, collisional environment expected for prebiotic chemistry. Consequently, the claimed exponential suppression of biogenesis, and the inference that extraterrestrial life is likely absent, are not supported.