arXiv subjects

Javier Virto

Publications and source records attributed to Javier Virto.

At least 19 recordsLinked to original sources

arXiv2026

Universal Two-Loop Current--Current Renormalization of Four-Fermion Operators

The complete one- and two-loop gauge and scalar current--current contributions to the running of arbitrary dimension-six four-fermion operators are reported. The results are obtained in a basis-independent and renormalization-scheme-agnostic fashion and are valid for arbitrary gauge groups. The complete gauge and scalar contributions, including the genuine one- and two-loop poles, counterterm insertions, wave-function renormalization, finite evanescent insertions, diagram multiplicities, and the associated color, charge and Yukawa factors are provided for the most general renormalizable Lagrangian with gauge and scalar interactions. The results enable the derivation of leading- and next-to-leading-order current--current anomalous-dimension matrices for arbitrary Effective Field Theories (EFTs) and constitute a significant step toward the complete two-loop renormalization of general EFTs.

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arXiv2026

Inclusive Charmless Non-Leptonic B Decays at NLO within and beyond the Standard Model

We calculate the full set of BSM contributions to the inclusive non-leptonic $B$-meson lifetime from charmless final states within the framework of the Weak Effective Theory up to next-to-leading order in QCD and to leading power in the heavy-quark expansion. We do so by computing cut diagrams and the corresponding phase space integrals. This involves calculating current-current, penguin-penguin, penguin-dipole and dipole-dipole diagrams with two-, three- and four-particle cuts. We describe the technical difficulties of the computation. We then discuss how our results can be used to constrain new physics scenarios related to the anomalies observed in semi-leptonic and charmless non-leptonic decays.

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arXiv2025

Two-Loop Anomalous Dimensions in the LEFT: Dimension-Six Four-Fermion Operators in NDR

We derive the complete set of two-loop anomalous dimensions describing the mixing of four-fermion operators in the Low Energy Effective Field Theory (LEFT). The calculation is performed in Naive Dimensional Regularization with anticommuting $\gamma_5$ (the NDR scheme), and the results are given in the "JMS basis" of dimension-six operators. The derivation relies on known results for UV poles in two-loop diagrams in QCD, which are then used to derive the two-loop Anomalous Dimension Matrix (ADM) for the full set of four-fermion operators including $O(\alpha_s^2)$, $O(\alpha_s\alpha)$ and $O(\alpha^2)$ corrections. The method employed is an extension of a common approach to deal with traces containing $\gamma_5$ in NDR. Our results have been implemented in the public code DsixTools. We also discuss and provide the results in the LEFT with 5, 4 and 3 active quark flavors.

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arXiv2024

Towards a Global Analysis of the $b\to c\bar{u} q$ Puzzle

We study the nonleptonic decays $\bar{B}_s^0 \to D_s^{(*)+} \pi^-$ and $\bar{B}^0 \to D^{(*)+} K^-$ within the Weak Effective Theory (WET) up to mass-dimension six. We revisit the calculation of the hadronic matrix elements within QCD Factorization including the full set of WET operators. We recalculate the two-particle contributions to the hard-scattering kernels at next-to-leading order in $\alpha_s$, confirming recent results in the literature. We also calculate the three-particle contributions at leading order in $\alpha_s$, clarifying the procedure, refining the SM results in the literature, and providing for the first time the complete set of contributions within the WET. We use these results to perform a global phenomenological study of the effective couplings, putting bounds on the size of the WET Wilson coefficients in four distinct fit models. The fits include constraints from the nonleptonic $B$-meson decay width, which we calculate at the leading order for the full set of WET operators for the first time. This study is the first one to account for simultaneous variation of up to six effective couplings. We identify two distinct modes in all fit models and discuss how future measurements can be used to distinguish between them.

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arXiv2024

Computing Tools for Effective Field Theories

In recent years, theoretical and phenomenological studies with effective field theories have become a trending and prolific line of research in the field of high-energy physics. In order to discuss present and future prospects concerning automated tools in this field, the SMEFT-Tools 2022 workshop was held at the University of Zurich from 14th-16th September 2022. The current document collects and summarizes the content of this workshop.

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arXiv2024

On the two-loop penguin contributions to the Anomalous Dimensions of four-quark operators

We revisit the Next-to-Leading Order (two-loop) contributions to the Anomalous Dimensions of $\Delta F = 1$ four-quark operators in QCD. We devise a test for anomalous dimensions, that we regard as of general interest, and by means of which we detect a problem in the results available in the literature. Deconstructing the steps leading to the available result, we identify the source of the problem, which is related to the operator known as $Q_{11}$. We show how to fix the problem and provide the corrected anomalous dimensions. With the insight of our findings, we propose an alternative approach to the one used in the literature which does not suffer from the identified disease, and which confirms our corrected results. We assess the numerical impact of our corrections, which happens to be in the ballpark of $5\%$ in certain entries of the evolution matrix. Our results are important for the correct resummation of Next-to-Leading Logarithms in analyses of physics beyond the Standard Model in $\Delta F = 1$ processes, such as the decays of Kaons and $B$-mesons.

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arXiv2023

Dark Matter Direct Detection in $t$-channel mediator models

We perform a comprehensive study of the Direct Detection phenomenology of singlet Dark Matter $t$-channel portal models. For that purpose, we present a complete one-loop matching onto a Heavy Dark-Matter Effective Field Theory, leading to a complete computation of the loop induced direct detection cross-section for both scalar and fermionic Dark Matter candidates. The results are compared with current and future bounds from Direct Detection experiments, as well as with the requirement of the correct Dark Matter relic density.

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arXiv2023

Dispersive Analysis of $B\to K^{(*)}$ and $B_s\to \phi$ Form Factors

We perform the first simultaneous dispersive analysis of the $B\to K$, $B\to K^*$, and $B_s\to \phi$ form factors. By means of an improved parametrization, we take into account the form factors' below-threshold branch cuts arising from on-shell $\bar{B}_s \pi^0$ and $\bar{B}_s \pi^0 \pi^0$ states, which so far have been ignored in the literature. In this way, we eliminate a source of hard-to-quantify systematic uncertainties. We provide machine-readable files to obtain the full set of the $\bar{B}\to \bar{K}^{(*)}$ and $\bar{B}_s\to \phi$ form factors in and beyond the entire semileptonic phase space.

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arXiv2023

Light-Cone Sum Rules for $S$-wave $B\to Kπ$ Form Factors

We derive a set of light-cone sum rules relating the $S$-wave $B\to K π$ hadronic form factors to the $B$-meson light-cone distribution amplitudes (LCDAs), taking into account the complete set of LCDAs up to and including twist four. These results complement the sum rules for the $P$-wave $B\to K π$ form factors obtained earlier. We then use the new sum rules to estimate the $S$-wave contributions to $B\to K π\ell\ell$ decays as a function of the $Kπ$ invariant mass. We pay particular attention to the fact that the $S$-wave $Kπ$ spectrum cannot be modelled by a sum of Breit-Wigner resonances, and employ a more consistent dispersive coupled-channel approach. We compare our predictions for branching ratios and angular observables with LHCb measurements in two different kinematic regions, around $K^*(892)$ and $K^*_0(1430)$. We observe an overall compatibility and discuss possible improvements of our model to obtain a better description of the $B\to Kπ$ form factors over a large kinematic range.

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arXiv2022

50 Years of Quantum Chromodynamics

This paper presents a comprehensive review of both the theory and experimental successes of Quantum Chromodynamics, starting with its emergence as a well defined theory in 1972-73 and following developments and results up to the present day. Topics include a review of the earliest theoretical and experimental foundations; the fundamental constants of QCD; an introductory discussion of lattice QCD, the only known method for obtaining exact predictions from QCD; methods for approximating QCD, with special focus on effective field theories; QCD under extreme conditions; measurements and predictions of meson and baryon states; a special discussion of the structure of the nucleon; techniques for study of QCD at high energy, including treatment of jets and showers; measurements at colliders; weak decays and quark mixing; and a section on the future, which discusses new experimental facilities or upgrades currently funded. The paper is intended to provide a broad background for Ph.D. students and postdocs starting their career. Some contributions include personal accounts of how the ideas or experiments were developed.

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arXiv2022

Improved Theory Predictions and Global Analysis of Exclusive $\boldsymbol{b\to sμ^+μ^-}$ Processes

We provide improved Standard Model theory predictions for the exclusive rare semimuonic processes $B\to K^{(*)}μ^+μ^-$ and $B_s\toϕμ^+μ^-$. Our results are based on a novel parametrization of the non-local form factors, which manifestly respects a recently developed dispersive bound. We critically compare our predictions to those obtained in the framework of QCD factorization. Our predictions provide, for the first time, parametric estimates of the systematic uncertainties due to non-local contributions. Comparing our predictions within the Standard Model to available experimental data, we find a large tension for $B\to Kμ^+μ^-$. A simple model-independent analysis of potential effects beyond the Standard Model yields results compatible with other approaches, albeit with larger uncertainties for the $B\to K^*μ^+μ^-$ and $B_s\to ϕμ^+μ^-$ decays. Our approach yields systematically improvable predictions, and we look forward to its application in further analyses beyond the Standard Model.

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arXiv2022

Next-to-Leading-Order QCD Matching for $ΔF=2$ Processes in Scalar Leptoquark Models

Leptoquarks provide viable solutions to the flavour anomalies, i.e. they can explain the tensions between the measurements and the Standard Model predictions of the anomalous magnetic moment of the muon as well as $b\to s\ell^+\ell^-$ and $b\to cτν$ processes. However, leptoquarks also contribute to other flavour observables, such as $ΔF=2$ processes, at the loop-level. In particular, $B_s-\bar B_s$ mixing provides a crucial bound in setups addressing $b\to cτν$ data, often excluding a big portion of the parameter space that could otherwise account for it. In this article, we first derive the complete leading order matching, including all five scalar LQ representations, for $D^0-\bar D^0$, $K^0-\bar K^0$ and $B_{s,d}-\bar B_{s,d}$ mixing (at the dimension-six level). We then calculate the next-to-leading order $α_s$ matching corrections to these $ΔF=2$ processes in generic scalar leptoquark models. We find that the two-loop corrections increase the effects in $ΔF=2$ processes by $\sim 5$-$10\%$ and significantly reduce the matching scale uncertainty.

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arXiv2021

EOS -- A Software for Flavor Physics Phenomenology

EOS is an open-source software for a variety of computational tasks in flavor physics. Its use cases include theory predictions within and beyond the Standard Model of particle physics, Bayesian inference of theory parameters from experimental and theoretical likelihoods, and simulation of pseudo events for a number of signal processes. EOS ensures high-performance computations through a C++ back-end and ease of usability through a Python front-end. To achieve this flexibility, EOS enables the user to select from a variety of implementations of the relevant decay processes and hadronic matrix elements at run time. In this article, we describe the general structure of the software framework and provide basic examples. Further details and in-depth interactive examples are provided as part of the EOS online documentation.

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arXiv2021

Non-local matrix elements in $B_{(s)}\to \{K^{(*)},ϕ\}\ell^+\ell^-$

We revisit the theoretical predictions and the parametrization of non-local matrix elements in rare $\bar{B}_{(s)}\to \lbrace \bar{K}^{(*)},ϕ\rbrace\ell^+\ell^-$ and $\bar{B}_{(s)}\to \lbrace \bar{K}^{*}, ϕ\rbrace γ$ decays. We improve upon the current state of these matrix elements in two ways. First, we recalculate the hadronic matrix elements needed at subleading power in the light-cone OPE using $B$-meson light-cone sum rules. Our analytical results supersede those in the literature. We discuss the origin of our improvements and provide numerical results for the processes under consideration. Second, we derive the first dispersive bound on the non-local matrix elements. It provides a parametric handle on the truncation error in extrapolations of the matrix elements to large timelike momentum transfer using the $z$ expansion. We illustrate the power of the dispersive bound at the hand of a simple phenomenological application. As a side result of our work, we also provide numerical results for the $B_s \to ϕ$ form factors from $B$-meson light-cone sum rules.

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arXiv2021

Anomalies in $b\to s \ell\ell$ transitions and Global Fits

We review the status of the anomalies in $b\to s \ell\ell$ transitions, and comment on the impact of the most recent measurements in 2019 and 2020 on the global fits. We also discuss a few developments in the theory calculation of local and non-local form factors.

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arXiv2020

DsixTools 2.0: The Effective Field Theory Toolkit

$\tt DsixTools$ is a Mathematica package for the handling of the Standard Model Effective Field Theory (SMEFT) and the Low-energy Effective Field Theory (LEFT) with operators up to dimension six, both at the algebraic and numerical level. $\tt DsixTools$ contains a visually accessible and operationally convenient repository of all operators and parameters of the SMEFT and the LEFT. This repository also provides information concerning symmetry categories and number of degrees of freedom, and routines that allow to implement this information on global expressions (such as decay amplitudes and cross-sections). $\tt DsixTools$ also performs weak basis transformations, and implements the full one-loop Renormalization Group Evolution in both EFTs (with SM beta functions up to five loops in QCD), and the full one-loop SMEFT-LEFT matching at the electroweak scale.

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arXiv2020

Three-Body Non-Leptonic Heavy-to-heavy $B$ Decays at NNLO in QCD

Exclusive non-leptonic two-body decays of $B$ mesons have been studied extensively in the past two decades within the framework of factorization. However, the exploration of the corresponding three-body case has only started recently, in part motivated by new data. We consider here the simplest non-leptonic three-body $B$ decays from the point of view of factorization, namely heavy-to-heavy transitions. We provide a careful derivation of the SCET/QCDF factorized amplitudes to NNLO in $α_s$, and discuss the numerical impact of NLO and NNLO corrections. We then study the narrow-width limit, showing that the three-body amplitude reproduces analytically the known quasi-two-body decay amplitudes, and compute finite-width corrections. Finally, we discuss certain observables that are sensitive to perturbative NLO and NNLO corrections and to higher Gegenbauer moments of the dimeson LCDAs. This is the first study of non-leptonic three-body $B$ decays to NNLO in QCD.

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arXiv2020

Emerging patterns of New Physics with and without Lepton Flavour Universal contributions

We perform a model-independent global fit to $b\to s\ell^+\ell^-$ observables to confirm existing New Physics (NP) patterns (or scenarios) and to identify new ones emerging from the inclusion of the updated LHCb and Belle measurements of $R_K$ and $R_{K^*}$, respectively. Our analysis, updating Refs. [1,2] and including these new data, suggests the presence of right-handed couplings encoded in the Wilson coefficients ${\cal C}_{9'μ}$ and ${\cal C}_{10'μ}$. It also strengthens our earlier observation that a lepton flavour universality violating (LFUV) left-handed lepton coupling (${\cal C}_{9μ}^{\rm V}=-{\cal C}_{10μ}^{\rm V}$), often preferred from the model building point of view, accommodates the data better if lepton-flavour universal (LFU) NP is allowed, in particular in ${\cal C}_{9}^{\rm U}$. Furthermore, this scenario with LFU NP provides a simple and model-independent connection to the $b\to cτν$ anomalies, showing a preference of $\approx 7\,σ$ with respect to the SM. It may also explain why fits to the whole set of $b\to s\ell^+\ell^-$ data or to the subset of LFUV data exhibit stronger preferences for different NP scenarios. Finally, motivated by $Z^\prime$ models with vector-like quarks, we propose four new scenarios with LFU and LFUV NP contributions that give a very good fit to data. We provide also an addendum collecting our updated results after including the data for the $B\to K^*μμ$ angular distribution released in 2020 by the LHCb collaboration.

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