I will review the dispersive and data-driven calculations of the hadronic contributions to the Muon g-2, with emphasis on the hadronic vacuum polarization. I will discuss in detail the comparison with the lattice evaluation both of the total and of the intermediate window quantity, and the implications of the present discrepancy. I will conclude with an outlook on future developments.
The ratio 𝑅(𝐸) of the cross-sections for 𝑒+𝑒−→ hadrons and 𝑒+𝑒−→𝜇+𝜇− is a valuable energy-dependent probe of the hadronic sector of the Standard Model. Moreover, the experimental measurements of 𝑅(𝐸) are the inputs of the dispersive calculations of the leading hadronic vacuum polarization contribution to the muon 𝑔−2 and these are in significant tension with direct lattice calculations and...
A search for the electroweak production of pairs of charged sleptons decaying into two-lepton final states with missing transverse momentum is presented. A simplified model of 𝑅-parity-conserving supersymmetry is considered: direct pair-production of sleptons (ℓ̃ℓ̃), with each decaying into a charged lepton and a 𝜒̃01 neutralino. The lightest neutralino (𝜒̃01) is assumed to be the lightest...
I will give an overview of the RBC/UKQCD g-2 program including both the hadronic light-by-light as well as the hadronic vacuum polarization contribution.
The Muon g-2 Experiment at Fermi National Accelerator Laboratory was designed to measure the anomalous magnetic moment of the muon, $𝑎_𝜇$, with a target precision of 140 parts-per-billion (ppb); a four-fold improvement over the former measurement at Brookhaven National Laboratory. The experiment was motivated by the ~3.5 standard deviation between the BNL result and the Standard Model...
The error budget of the theory calculation of the muon 𝑔−2 is dominated by two hadronic contributions: the Hadronic Vacuum Polarization (HVP) and the Hadronic Light-by-Light (HLbL) scattering. Reducing the error on these contributions is essential to match the future experimental precision.
In this talk, we present a lattice calculation of the three light pseudoscalar meson ($\pi_0$, $\eta$...
By replacing continuous space–time with a Euclidean lattice, lattice gauge theories provide a way to capture the non-perturbative effects in the muon g-2. We present first results by the RC collaborations towards obtaining a precise estimate of these effects using a novel local description of lattice QCD and QED, based on C boundary conditions in space.
During the last 15 years the "Radio MontecarLow (“Radiative Corrections and Monte Carlo Generators for Low Energies”) Working Group, see www.lnf.infn.it/wg/sighad/, has been providing valuable support to the development of radiative corrections and Monte Carlo generators for low energy $e^+e^-$ data and tau-lepton decays. Its operation which started in 2006 proceeded until the last few years...
In this talk I will review the calculation of the short and intermediate window for g-2, based on our recent simulations performed int the Twisted Mass regularization of QCD, with physical pion mass and three different lattice spacings. Our results highlights that the tension with experimental measurement is concentrated in the intermediate energy region.
The muon anomalous magnetic moment is currently one of the most intriguing measurements, as it marks a 4.2 𝜎 deviation from the reference prediction of the Standard Model, and is expected to provide an even more stringent test in the next few years with the experimental error reducing by a factor of four. In parallel the theoretical error need to be reduced. It is dominated by the...
The Standard Model theoretical prediction of the muon anomalous magnetic moment, $𝑎_𝜇=(𝑔−2)_𝜇/2$, presents a discrepancy of $4.2~\sigma$ with respect to the combined Fermilab and BNL measurements.
The MUonE project is a recently proposed experiment at CERN that will help to shed light on this situation, by providing an independent determination of the leading order hadronic vacuum...
The muon anomaly, $𝑎_𝜇=\frac{(𝑔−2)}{2}$, is a low-energy observable which can be both measured and computed to high precision, making it a sensitive test of the Standard Model and a probe for new physics. The current discrepancy between the Standard Model calculation from the Muon $𝑔−2$ Theory Initiative [T. Aoyama et al. - Phys. Rept. 887 (2020), 1-166] and the experimental value is...
We present our previous and ongoing lattice QCD efforts to determine thehadron vacuum polarization contribution to the muon magnetic moment.
The Muon $g-2$ experiment measures the muon magnetic moment anomaly $a_\mu$ by relating the precession frequencies of muons inside a magnetic storage ring to the strength of the magnetic field that they experience. A series of NMR instruments map the primary magnetic field, but some short-lived transient magnetic fields require alternative approaches to measure with sufficient precision. The...
We show that the models that induce neutrino magnetic moments while maintaining their small masses naturally also predict observable shifts in the muon anomalous magnetic moment. This shift is of the right magnitude to be consistent with the Brookhaven measurement as well as the recent Fermilab measurement of the muon g−2. This points out the direct correlation between the magnetic moment of...
The LHCb collaboration has recently set a first limit on the radiative leptonic decay of the $B_s$-meson in the region of high momentum transfer, namely $\mathcal{B} (B_s^0 \to \mu^+ \mu^- \gamma) [q^2 > (4.9 \, \rm {GeV})^2] < 2.0 \times 10^{-9}$. From the theoretical point of view, several computations of the hadronic Form Factors (FFs) entering in this decay are available in the context of...
Several results in high energy physics experiments highlighted hints of new physics in semileptonic decays of B particles. Among the existing experiments, the LHCb detector plays a very important role in this sector. In fact, it is specifically designed for the study of particles containing b or c quarks. Some LHCb results suggested the violation of the lepton flavour universality stated in...
In this talk, we consider the rare decay channel $B_s\rightarrow\mu\mu\gamma$, the radiative counterpart of the very rare $B_s\rightarrow\mu\mu$ decay, from both theoretical and experimental perspectives. This decay is sensitive to possible new vector couplings in the $b\rightarrow s\mu\mu$ interaction vertex. Using different form factors parametrizations of the $B_s\rightarrow\gamma$...
We discuss a novel approach, based on spectral reconstruction techniques, which circumvents the well-known problem of the analytic continuation from Minkowskian to Euclidean time for hadronic processes above kinematical thresholds. The approach is discussed for the specific case of the radiative decays of pseudoscalar mesons $P\to \ell \nu_{\ell} \gamma^{}$, where $\gamma^{}$ is a virtual...
Since the observation of neutrino oscillations, lepton number conservation is known to be a non-exact symmetry of the Standard Model lagrangian: yet there is still no evidence of lepton flavour violating processes involving charged leptons (cLFV), such as $𝜇→e𝛾$, $𝜇→eee$ or $𝜇𝑁→eN$: according to minimal extensions of the Standard Model including neutrino masses, these processes are too rare to...
As the number of fermion fields is increased, gauge theories are expected to undergo a transition from a QCD-like phase, characterised by confinement and chiral symmetry breaking, to a conformal phase, where the theory becomes scale-invariant at large distances. In this paper, we discuss some properties of a third phase, where spontaneously broken conformal symmetry is characterised by its...
We discuss how a recently discovered non-perturbative field-theoretical mechanism giving mass to elementary fermions can be extended to generate a mass for the electro-weak bosons, when weak interactions are introduced, and can thus be used as a viable alternative to the Higgs scenario. We will show that this new scheme, successfully tested in extensive lattice simulations, offers a solution...
The Large Hadron Collider at CERN is currently our only tool for direct exploration of physics at the electroweak scale and above and the high-luminosity phase is planned to last until the late 2030s. Rare flavour-changing neutral current transitions $𝑏→𝑠𝜇^+𝜇^−$ probe higher energy scales than what is directly accessible at the LHC and therefore the presence of new physics in such transitions,...
The decreasing uncertainties in theoretical predictions and experimental measurements of several hadronic observables related to weak processes, which in many cases are now smaller than O(1%), require theoretical calculations to include subleading corrections that were neglected so far. Precise determinations of leptonic and semi-leptonic decay rates, including $\text{QED}$ and strong...
The main goal of the Fermilab Muon g-2 experiment is to determine the muon anomalous magnetic moment ($a_\mu$) to a 140 parts per billion (ppb) uncertainty, to compare it with the Standard Model prediction. The value of $a_\mu$ is determined by measuring two quantities: the anomalous spin precession frequency of positive muons circulating in a storage ring and the magnetic field experienced by...
The electromagnetic coupling constant, $\alpha$, is one of the fundamental parameters of the Standard Model (SM). Its value at the Z boson mass, $\alpha(M_Z)$, is of particular interest as it enters EW precision tests. When running $\alpha$ from low energies up to the Z mass, five orders of magnitude in precision are lost. This makes it one of the least well determined parameters of the SM at...
We explore the CP-violating (CPV) effects of heavy New Physics in the flavour-changing quark dipole transitions, within the framework of Standard Model Effective Field Theory (SMEFT). We connect the operators defined at the heavy scale $\Lambda$ with the low energy observable via the Renormalisation Group (RG) evolution of the appropriate Wilson coefficients. We investigate RG-induced...
Inspired by the various LHCb results of lepton flavour violation on $b\to s$ transition we will study the lepton flavour violating $\Sigma_b\to\Sigma l_1l_2$ decays in terms of transversity amplitudes in non-universal Z' model. These LFV processes are extremely suppressed in the Standard Model (SM) because the expected levels at the SM lie far below current experimental sensitivities. In...
In the Standard Model of particle physics, lepton flavour and lepton number are conserved quantities, although there is no fundamental symmetry associated with their conservation and lepton flavour violation has been already confirmed by the observation of neutrino oscillations.
Many lepton flavour violating (LFV) and lepton number violating (LNV) processes can be searched for in B meson...
Rare baryonic decays induced by flavour changing neutral current (FCNC) have been of immense interest in recent years because of their sensitivities towards new physics (NP) beyond the standard model (SM). The exploration had been triggered with the observation of $\Lambda_b\to\Lambda\mu^+\mu^−$ transition at the Fermilab [1] and the LHCb [2]. Theoretically these decays are also studied at...
The High-Intensity Muon Beams (HIMB) project aims to increase the rate of the intensity muon beamlines at Paul Scherrer Institute (PSI) by two orders of magnitude up to 10^10 µ+/s, with a significant impact on low-energy, high-precision muon-based experiments. This is done by improving the surface muon yield with a new target geometry and by increasing capture and transmission with...
The Standard Model (SM) of particle physics successfully predicts many fundamental properties and interactions, but it is still incomplete. Models like baryogenesis or leptogenesis for the matter-antimatter asymmetry lead to an additional CP violation beyond the SM. In this context, electric dipole moments (EDMs), which violate time-reversal and parity symmetry, and by virtue of the CPT...
The angular correlation distribution of electron-positron pairs from Internal Pair Conversion emitted by excited 8Be and 4He nucleus was measured by ATOMKI. Over the expected monotonically decreasing trend was measured a significant excess which can be interpreted as the production of a hypothetical particle (X17) whose mass is around 17 MeV.
The MEG-II experiment at the Paul Scherrer...
The study of non-perturbative properties characterizing Quantum Chromo-Dynamics (QCD) is of relevant theoretical and phenomenological interest. Indeed, the $\theta$-dependence of QCD is related to open issues such as the strong-$CP$ violation or to the Peccei-Quinn axion physical properties.
The lattice approach is a natural first-principle tool to investigate the non-perturbative properties...
I will overview the interplay between QCD axion properties and Lattice QCD inputs and discuss open questions in axion phenomenology and cosmology.
We consider a model involving a “visible” QCD axion with mass in the MeV range with flavour non-universal couplings to the Standard Model (SM) first generation fermions. Such a heavy axion must evade a variety of stringent constraints which precisely fix the couplings to the SM fields: the requirement of “pion-phobia” determines the Peccei-Quinn (PQ) charges of the light quarks to be 2/3 and...
High-statistics measurements in peripheral photon-induced scattering using relativistic heavy-ion beams provide a precise and unique opportunity to investigate extensions of the Standard Model. New measurements of exclusive dilepton production (electron, muon, and tau pairs) are discussed. In particular, the tau-pair production measurement is used to constrain tau lepton's anomalous magnetic...
We propose a new search for Axion-Like Particles (ALPs), targeting Vector Boson Scattering (VBS) processes at the LHC. We consider nonresonant ALP-mediated VBS, where the ALP participates as an off-shell mediator. This process occurs whenever the ALP is too light to be produced resonantly, and it takes advantage of the derivative nature of ALP interactions with the electroweak Standard Model...
Axion-like particle (ALP) is one of the promising candidates of dark matter (DM). It can emerge from the dark sector with global U(1) symmetry. It is often (implicitly) assumed that the dark sector has a CP symmetry. However, since CP is violated within the SM, the dark sector with CP violation is also an interesting possibility. In this talk, we propose a new renormalizable model for ALP with...
