arXiv subjects

Max Ferré

Publications and source records attributed to Max Ferré.

4 recordsLinked to original sources

arXiv2026

Electromagnetic tails of $B$-meson light-cone distribution amplitudes

We investigate electromagnetic corrections to the $B$-meson decay constant and light-cone distribution amplitudes (LCDAs) within the framework of heavy-quark effective theory. The inclusion of QED effects extends the support of the LCDAs to negative values of the light-cone momentum. We clarify the relation between this region and QED-generalized decay constants sensitive to electromagnetic final-state radiation. We derive model-independent expressions for the asymptotic behavior in the large negative-momentum region of the QED-generalized LCDAs $\Phi_\pm(\omega,\mu)$ in terms of integrals over the two- and three-particle LCDAs defined in pure QCD. We show that our result for $\Phi_+$ is consistent with the renormalization-group equation satisfied by this object and study its evolution using the known one-loop anomalous dimension. Finally, we propose a phenomenological model consistent with these constraints

hep-ph↗

arXiv2026

QED Corrections to $B^-\to\tau^-\bar{\nu}_\tau$

Using a sequence of effective field theories (EFTs), we calculate the rate for the leptonic decay $B^-\to\tau^-\bar{\nu}_\tau(\gamma)$ including real and virtual QED corrections, with a cut $E_{\rm cut}\ll\Lambda_{\rm QCD}$ imposed on electromagnetic radiation in the $B$-meson rest frame. We establish a factorization theorem for the rate and evaluate it at $\mathcal{O}(\alpha)$, resumming the leading logarithmic corrections to all orders in perturbation theory. The large mass $m_\tau$ allows us to treat the tau lepton as a heavy fermion below $\mu\sim m_B\sim m_\tau$, leading to an EFT construction that is structurally different and noticeably simpler than that for the muon case. In particular, hadron-structure dependent QED corrections can be described in terms of QED-induced $B^-\to\tau^-$ form factors, which should be calculable on the lattice. Our analysis includes the leading $\Lambda_{\rm QCD}/m_\tau$ corrections as well as the leading corrections in $E_{\rm cut}/\Lambda_{\rm QCD}$. We show that contributions of the form $\Lambda_{\rm QCD}m_B/m_\tau^2$, which are naively sizable, cancel among each other. Contrary to the muon channel, structure-dependent corrections involving $BB^\ast\gamma$ transitions are numerically negligible for the tau case. The remaining logarithmic dependence on $E_\mathrm{cut}$ is mild. We estimate that the present uncertainty in the calculation of the structure-dependent QED corrections is about 0.5\% of the rate. As a byproduct, we present a state-of-the-art prediction for the lepton flavor universality ratio of the tau and muon channels.

hep-ph↗

arXiv2026

Three-particle di-light-cone distribution amplitudes of the $B$-meson in heavy-quark effective theory

We present a systematic study of the three-particle di-light-cone distribution amplitudes (DLCDAs) of the $B$-meson. They are defined through $B$-meson--to--vacuum matrix elements of trilocal HQET operators, in which the light antiquark and the gluon field-strength tensor are located on two back-to-back light rays. In this sense, the DLCDAs generalise the conventional $B$-meson light-cone distribution amplitudes to configurations where soft fields couple to collinear degrees of freedom in two distinct directions. As such, they parametrise the non-perturbative dynamics associated with non-factorisable soft-gluon contributions in rare and non-leptonic exclusive $B$-meson decays. We derive the complete Lorentz decomposition of the matrix elements of generic trilocal operators, identify eight independent DLCDAs, and organise them in a basis of definite twist. Using local operator identities and equations-of-motion constraints, we obtain tree-level relations for their normalisation integrals and first moments in terms of a minimal set of hadronic parameters. These relations allow us to construct simple momentum-space models for all independent DLCDAs. For the leading-twist distribution, we further incorporate the perturbative radiative tail at order $\alpha_s$ and discuss its impact on the resulting parametrisation.

hep-ph↗

arXiv2026

The Simplest B Decay, Precisely

We derive the QCD$\times$QED factorization theorem governing the leptonic decay $B^-\to\mu^-\bar\nu_\mu(\gamma)$ at all orders in $\alpha_s$ and $\alpha$. Electromagnetic corrections to this decay probe multiple scales, which we disentangle through a sequence of effective field theories (EFTs). The resulting state-of-the-art prediction for the photon-vetoed rate includes the complete structure-dependent component and is accurate at the percent level, establishing the theoretical framework required for future high-precision measurements of this channel, which will allow for a clean determination of $|V_{ub}|$ and powerful tests of new physics. Our work presents the first complete study of QED effects to an exclusive $B$-meson decay at next-to-leading power (NLP) in the heavy-quark expansion. Important milestones are (i) the construction of the complete NLP operator basis in soft-collinear effective theory (SCET); (ii) the proposal of a "SCET-friendly" reduction scheme for the Dirac structures of four-fermion operators in dimensional regularization, which avoids power-enhanced evanescent operators; (iii) the consistent refactorization of endpoint-divergent convolution integrals and the first complete resummation of "rapidity logarithms" arising at the boundary between the contributions involving soft and hard-collinear quarks; (iv) the systematic discussion of the EFT below the scale of QCD confinement and the non-perturbative matching of SCET onto this low-energy theory; (v) the decoupling of pseudoscalar mesons in the context of heavy-hadron chiral perturbation theory, so that they can be integrated out for processes in which they do not appear as external particles. We perform a phenomenological analysis of direct and indirect contributions to the decay rate and radiation-energy spectrum, highlighting the importance of the chiral anomaly.

hep-ph↗