The fate of $$\mathbf{V}_\mathbf{1}$$ vector leptoquarks: the impact of future flavour data

Motivated by the recent experimental progress on the B-meson decay anomalies (in particular the angular observables in $$B\rightarrow K^*\mu \mu $$ B → K ∗ μ μ ), we rely on a simplified-model approach to study the prospects of vector leptoquarks in what concerns numerous flavour observables, identifying several promising decay modes which would allow to (indirectly) probe such an extension. Our findings suggest that the confirmation of the B-meson decay anomalies, in parallel with positive signals (at Belle II or LHCb) for $$\tau \rightarrow \phi \mu $$ τ → ϕ μ , $$B_{(s)}$$ B ( s ) -meson decays to $$\tau ^+ \tau ^-$$ τ + τ - and $$\tau ^+ \mu ^-$$ τ + μ - ($$\tau ^+ e^-$$ τ + e - ) final states, as well as an observation of certain charged lepton flavour violation decays (at COMET or Mu2e), would contribute to strengthen the case for this scenario. We also illustrate how the evolution of the experimental determination of $$R_{D^{(*)}}$$ R D ( ∗ ) could be instrumental in falsifying an explanation of the anomalous B-meson decay data via a vector $$V_1$$ V 1 leptoquark.

Charming ALPs

Axion-like particles (ALPs) are ubiquitous in models of new physics explaining some of the most pressing puzzles of the Standard Model. However, until relatively recently, little attention has been paid to its interplay with flavour. In this work, we study in detail the phenomenology of ALPs that exclusively interact with up-type quarks at the tree-level, which arise in some well-motivated ultra-violet completions such as QCD-like dark sectors or Froggatt-Nielsen type models of flavour. Our study is performed in the low-energy effective theory to highlight the key features of these scenarios in a model independent way. We derive all the existing constraints on these models and demonstrate how upcoming experiments at fixed-target facilities and the LHC can probe regions of the parameter space which are currently not excluded by cosmological and astrophysical bounds. We also emphasize how a future measurement of the currently unavailable meson decay D → π + invisible could complement these upcoming searches.

Lowering the scale of Pati-Salam breaking through seesaw mixing

We analyse the experimental limits on the breaking scale of Pati-Salam extensions of the Standard Model. These arise from the experimental limits on rare-meson decay processes mediated at tree-level by the vector leptoquark in the model. This leptoquark ordinarily couples to both left- and right-handed SM fermions and therefore the meson decays do not experience a helicity suppression. We find that the current limits vary from $$ \mathcal{O} $$ O (80–2500) TeV depending on the choice of matrix structure appearing in the relevant three-generational charged-current interactions. We extensively analyse scenarios where additional fermionic degrees of freedom are introduced, transforming as complete Pati-Salam multiplets. These can lower the scales of Pati-Salam breaking through mass-mixing within the charged-lepton and down-quark sectors, leading to a helicity suppression of the meson decay widths which constrain Pati-Salam breaking. We find four multiplets with varying degrees of viability for this purpose: an SU(2)L/R bidoublet, a pair of SU(4) decuplets and either an SU(2)L or SU(2)R triplet all of which contain heavy exotic versions of the SM charged leptons. We find that the Pati-Salam limits can be as low as $$ \mathcal{O} $$ O (5–150) TeV with the addition of these four multiplets. We also identify an interesting possible connection between the smallness of the neutrino masses and a helicity suppression of the Pati-Salam limits for three of the four multiplets.

Precision calculations of the double radiative bottom-meson decays in soft-collinear effective theory

Employing the systematic framework of soft-collinear effective theory (SCET) we perform an improved calculation of the leading-power contributions to the double radiative Bd,s-meson decay amplitudes in the heavy quark expansion by including the perturbative resummation of enhanced logarithms of mb/ΛQCD at the next-to-leading-logarithmic accuracy. We then construct the QCD factorization formulae for the subleading power contributions arising from the energetic photon radiation off the constituent light-flavour quark of the bottom meson at tree level. Furthermore, we explore the factorization properties of the subleading power correction from the effective SCET current "Image missing" at $$ \mathcal{O}\left({\alpha}_s^0\right) $$ O α s 0 by virtue of the operator identities due to the classical equations of motion. The higher-twist contributions to the Bd,s→ γγ helicity form factors from the two-particle and three-particle bottom-meson distribution amplitudes are evaluated with the perturbative factorization technique, up to the twist-six accuracy. In addition, the subleading power weak-annihilation contributions from both the current-current and QCD penguin operators are taken into account at the one-loop accuracy. We proceed to apply the operator-production-expansion-controlled dispersion relation for estimating the power-suppressed soft contributions to the double radiative Bd,s-meson decay form factors, which cannot be factorized into the light-cone distribution amplitudes of the heavy-meson and the resolved photon as well as the hard-scattering kernel calculable in perturbation theory canonically. Phenomenological explorations of the radiative Bd,s→ γγ decay observables in the presence of the neutral-meson mixing, including the CP-averaged branching fractions, the polarization fractions and the time-dependent CP asymmetries, are carried out subsequently with an emphasis on the numerical impacts of the newly computed ingredients together with the theory uncertainties from the shape parameters of the HQET bottom-meson distribution amplitudes.

Thermal properties of $$\pi $$ and $$\rho $$ meson

We computed the pole masses and decay constants of $$\pi $$ π and $$\rho $$ ρ meson at finite temperature in the framework of Dyson–Schwinger equations and Bethe–Salpeter equations approach. Below transition temperature, pion pole mass increases monotonously, while $$\rho $$ ρ meson seems to be temperature independent. Above transition temperature, pion mass approaches the free field limit of screening mass $$\sim 2\pi T$$ ∼ 2 π T , whereas $$\rho $$ ρ meson is about twice as large as that limit. Pion and the longitudinal projection of $$\rho $$ ρ meson decay constants have similar behaviour as the order parameter of chiral symmetry, whereas the transverse projection of $$\rho $$ ρ meson decay constant rises monotonously as temperature increases. The inflection point of decay constant and the chiral susceptibility get the same phase transition temperature. Though there is no access to the thermal width of mesons within this scheme, it is discussed by analyzing the Gell-Mann-Oakes-Renner (GMOR) relation in medium. These thermal properties of hadron observables will help us understand the QCD phases at finite temperature and can be employed to improve the experimental data analysis and heavy ion collision simulations.

Branching ratio and CP violation in Bs0 → K∗0K̄∗0 decay in the framework of QCD factorization

We present an analytic calculation of Branching Ratio (BR) and Charge-Parity (CP) violating asymmetries of the [Formula: see text] meson decay into the two light vectors [Formula: see text] by calculating the helicity amplitude in the framework of quantum chromodynamics (QCD) factorization approach. We find the BR of [Formula: see text] which is in full agreement with the recent theoretical predictions and experimental measurements. We also calculate the direct CP violation, CP violation in mixing and CP violation due to interference which are [Formula: see text], [Formula: see text], and [Formula: see text], respectively.