In this paper we study the bounds that can be inferred on New Physics couplings to heavy sterile neutrinos from the recent measurements performed by the Belle collaboration of the angular analysis of $$ B\to {D}^{\ast}\ell {\overline{\nu}}_{\ell } $$ decays, with = , . Indeed, a sterile neutrino may lead to competing $$ B\to {D}^{\ast}\ell \overline{N} $$ decays and Belle might have measured an incoherent sum of these two independent channels. After reviewing the theoretical formalism required to describe this phenomenon in full generality, we first perform a bump hunt in the $$ {M}_{\textrm{miss}}^2 $$ Belle distribution to search for evidences of an additional massive neutrino. We found in such a way a small hint at $$ {M}_{\textrm{miss}}^2 $$ ∼ (354 MeV) . However, the Belle angular analysis is sensitive to masses up to $$ \mathcal{O} $$ (50 MeV), preventing us to further inspect this hint. Nevertheless, we study the potential impact of this additional channel in the allowed mass range on the measured angular distributions and extract model-independent bounds on the new-physics couplings which could mediate such an interaction. In particular, in the mass window here inspected, we obtain the most stringent bounds for vector and left-handed scalar operators to date.

Germany

Florian Bernlochner

Spain

Marco Fedele

Tim Kretz

Ulrich Nierste

Markus Prim

Model independent bounds on heavy sterile neutrinos from the angular distribution of B → D

The prospects are presented for precise measurements of the branching ratios of the purely leptonic  $$B_c^+ \rightarrow \tau ^+ \nu _\tau $$  <math> <mrow> <msubsup> <mi>B</mi> <mi>c</mi> <mo>+</mo> </msubsup> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msub> <mi>ν</mi> <mi>τ</mi> </msub> </mrow> </math>   and  $$B^+ \rightarrow \tau ^+ \nu _\tau $$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msub> <mi>ν</mi> <mi>τ</mi> </msub> </mrow> </math>   decays at the Future Circular Collider (FCC). This work is focused on the hadronic  $$\tau ^{+} \rightarrow \pi ^+ \pi ^+ \pi ^- {\bar{\nu }}_\tau $$  <math> <mrow> <msup> <mi>τ</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>π</mi> <mo>+</mo> </msup> <msup> <mi>π</mi> <mo>+</mo> </msup> <msup> <mi>π</mi> <mo>-</mo> </msup> <msub> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> <mi>τ</mi> </msub> </mrow> </math>   decay in both  $$B_c^+ \rightarrow \tau ^+ \nu _\tau $$  <math> <mrow> <msubsup> <mi>B</mi> <mi>c</mi> <mo>+</mo> </msubsup> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msub> <mi>ν</mi> <mi>τ</mi> </msub> </mrow> </math>   and  $$B^+ \rightarrow \tau ^+ \nu _\tau $$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msub> <mi>ν</mi> <mi>τ</mi> </msub> </mrow> </math>   processes. Events are selected with two Boosted Decision Tree algorithms to optimise the separation between the two signal processes as well as the generic hadronic Z decay backgrounds. The range of the expected precision for both signals are evaluated in different scenarios of non-ideal background modelling. This paper demonstrates, for the first time, that the  $$B^+ \rightarrow \tau ^+ \nu _\tau $$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msub> <mi>ν</mi> <mi>τ</mi> </msub> </mrow> </math>   decay can be well separated from both  $$B_c^+ \rightarrow \tau ^+ \nu _\tau $$  <math> <mrow> <msubsup> <mi>B</mi> <mi>c</mi> <mo>+</mo> </msubsup> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msub> <mi>ν</mi> <mi>τ</mi> </msub> </mrow> </math>   and generic  $$Z\rightarrow b{\bar{b}}$$  <math> <mrow> <mi>Z</mi> <mo>→</mo> <mi>b</mi> <mover> <mrow> <mi>b</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   processes in the FCC-ee collision environment and proposes the corresponding branching ratio measurement as a novel way to determine the CKM matrix element  $$|V_{ub}|$$  <math> <mrow> <mrow> <mo>|</mo> </mrow> <msub> <mi>V</mi> <mrow> <mi>ub</mi> </mrow> </msub> <mrow> <mo>|</mo> </mrow> </mrow> </math>  . The theoretical impacts of both  $$B^+ \rightarrow \tau ^+ \nu _\tau $$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msub> <mi>ν</mi> <mi>τ</mi> </msub> </mrow> </math>   and  $$B_c^+ \rightarrow \tau ^+ \nu _\tau $$  <math> <mrow> <msubsup> <mi>B</mi> <mi>c</mi> <mo>+</mo> </msubsup> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msub> <mi>ν</mi> <mi>τ</mi> </msub> </mrow> </math>   measurements on New Physics cases are discussed for interpretations in the generic Two-Higgs-doublet model and leptoquark models.

Xunwu Zuo

CERN

Switzerland

Clément Helsens

Donal Hill

Syuhei Iguro

Markus Klute

Prospects for  $$B_c^+$$  <math> <msubsup> <mi>B</mi> <mi>c</mi> <mo>+</mo> </msubsup> </math>   and  $$B^+\rightarrow \tau ^+ \nu _\tau $$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>τ</mi> <mo>+</mo> </msup> <msub> <mi>ν</mi> <mi>τ</mi> </msub> </mrow> </math>   at FCC-ee

Leptoquarks with masses between 2 TeV and 50 TeV are commonly invoked to explain deviations between data and Standard-Model (SM) predictions of several observables in the decays   <math> <mi>b</mi> <mo>→</mo> <mi>cτ</mi> <mover> <mi>ν</mi> <mo>¯</mo> </mover> </math>  $$ b\to c\tau \overline{\nu} $$  and b → sℓ + ℓ  −  with ℓ = e, μ. While Leptoquarks appear in theories unifying quarks and leptons, the corresponding unification scale M QLU is typically many orders of magnitude above this mass range. We study the case that the mass gap between the electroweak scale and M QLU is only populated by scalar Leptoquarks and SM particles, restricting ourselves to scenarios addressing the mentioned flavour anomalies, and determine the renormalisation-group evolution of Leptoquark couplings to fermions below M QLU. In the most general case, we consider three SU(2) triplet Leptoquarks   <math> <msubsup> <mi>S</mi> <mn>3</mn> <mi>ℓ</mi> </msubsup> </math>  $$ {S}_3^{\ell } $$ , ℓ = e, μ, τ, which couple quark doublets to the lepton doublet (ν  ℓ , ℓ  − ) to address the b → sℓ + ℓ  −  anomalies. In this case, we find a scenario in which the Leptoquark couplings to electrons and muons are driven to the same infrared fixed point, so that lepton flavour universality emerges dynamically. However, the corresponding fixed point for the couplings to taus is necessarily opposite in sign, leading to a unique signature in b → sτ + τ  − . For   <math> <mi>b</mi> <mo>→</mo> <mi>cτ</mi> <mover> <mi>ν</mi> <mo>¯</mo> </mover> </math>  $$ b\to c\tau \overline{\nu} $$  we complement these with either an SU(2) singlet   <math> <msubsup> <mi>S</mi> <mn>1</mn> <mi>τ</mi> </msubsup> </math>  $$ {S}_1^{\tau } $$  or doublet   <math> <msubsup> <mi>R</mi> <mn>2</mn> <mi>τ</mi> </msubsup> </math>  $$ {R}_2^{\tau } $$  and study further the cases that also these Leptoquarks come in three replicas. The fixed point solutions for the   <math> <msubsup> <mi>S</mi> <mn>3</mn> <mi>ℓ</mi> </msubsup> </math>  $$ {S}_3^{\ell } $$  couplings explain the b → sℓ + ℓ  −  data for   <math> <msubsup> <mi>S</mi> <mn>3</mn> <mrow> <mi>e</mi> <mo>,</mo> <mi>μ</mi> </mrow> </msubsup> </math>  $$ {S}_3^{e,\mu } $$  masses between 14 and 15 TeV, according to the scenario.   <math> <mi>b</mi> <mo>→</mo> <mi>cτ</mi> <mover> <mi>ν</mi> <mo>¯</mo> </mover> </math>  $$ b\to c\tau \overline{\nu} $$  data can only be fully explained by couplings exceeding their fixed-point values and evolving into Landau poles at high energies, so that one can place an upper bound on M QLU between 108 and 1011 GeV.

Felix Wuest

Renormalisation group analysis of scalar Leptoquark couplings addressing flavour anomalies: emergence of lepton-flavour universality

Form factors are a crucial theory input in order to extract <math><mo>|</mo><msub><mi>V</mi><mrow><mi>c</mi><mi>b</mi></mrow></msub><mo>|</mo></math> from <math><mi>B</mi><mo>→</mo><msup><mi>D</mi><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mo>ℓ</mo><mi>ν</mi></math> decays, to calculate the Standard Model prediction for <math><mi>R</mi><mo>(</mo><msup><mi>D</mi><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mo>)</mo></math> and to assess the impact of new physics. In this context, the dispersive matrix approach, a first-principle calculation of the form factors, using no experimental data but rather only lattice QCD results as input, was recently applied to <math><mi>B</mi><mo>→</mo><msup><mi>D</mi><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mo>ℓ</mo><mi>ν</mi></math>. It predicts (within the Standard Model) a much milder tension with the <math><mi>R</mi><mo>(</mo><msup><mi>D</mi><mo>*</mo></msup><mo>)</mo></math> measurements than the other form factor approaches, while at the same time giving a value of <math><mo>|</mo><msub><mi>V</mi><mrow><mi>c</mi><mi>b</mi></mrow></msub><mo>|</mo></math> compatible with the inclusive value. However, this comes at the expense of creating tensions with differential <math><mi>B</mi><mo>→</mo><msup><mi>D</mi><mo>*</mo></msup><mo>ℓ</mo><mi>ν</mi></math> distributions (with light leptons). In this article, we explore the implications of using the dispersive matrix method form factors, in light of the recent Belle (II) measurements of the longitudinal polarization fraction of the <math><msup><mi>D</mi><mo>*</mo></msup></math> in <math><mi>B</mi><mo>→</mo><msup><mi>D</mi><mo>*</mo></msup><mo>ℓ</mo><mi>ν</mi></math> with light leptons, <math><msubsup><mi>F</mi><mi>L</mi><mo>ℓ</mo></msubsup></math>, and the forward-backward asymmetry, <math><msubsup><mi>A</mi><mi>FB</mi><mo>ℓ</mo></msubsup></math>. We find that the dispersive matrix approach predicts a Standard Model value of <math><msubsup><mi>F</mi><mi>L</mi><mo>ℓ</mo></msubsup></math> that is in significant tension with these measurements, while mild deviations in <math><msubsup><mi>A</mi><mi>FB</mi><mo>ℓ</mo></msubsup></math> appear. Furthermore, <math><msubsup><mi>F</mi><mi>L</mi><mo>ℓ</mo></msubsup></math> is very insensitive to new physics such that the latter cannot account for the tension between dispersive matrix predictions and its measurement. While this tension can be resolved by deforming the original dispersive matrix form factor shapes within a global fit, a tension in <math><mi>R</mi><mo>(</mo><msup><mi>D</mi><mo>*</mo></msup><mo>)</mo></math> reemerges. As this tension is milder than for the other form factors, it can be explained by new physics not only in the tau lepton channel but also in the light lepton modes.

Monika Blanke

Andreas Crivellin

Italy

Silvano Simula

France

Ludovico Vittorio

Discriminating <math><mi>B</mi><mo>→</mo><msup><mi>D</mi><mo>*</mo></msup><mo>ℓ</mo><mi>ν</mi></math> form factors via polarization observables and asymmetries

The LHCb Collaboration has recently released a new study of <math><msup><mi>B</mi><mo>+</mo></msup><mo>→</mo><msup><mi>K</mi><mo>+</mo></msup><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math> and <math><mi>B</mi><mo>→</mo><msup><mi>K</mi><mrow><mo>*</mo><mn>0</mn></mrow></msup><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math> (<math><mo>ℓ</mo><mo>=</mo><mi>e</mi></math>, <math><mrow><mi>μ</mi></mrow></math>) decays, testing lepton universality with unprecedented accuracy using the whole Run 1 and 2 dataset. In addition, the CMS Collaboration has reported an improved analysis of the branching ratios <math><msub><mi>B</mi><mrow><mo>(</mo><mi>d</mi><mo>,</mo><mi>s</mi><mo>)</mo></mrow></msub><mo>→</mo><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></math>. While these measurements offer, per se, a powerful probe of new physics, global analyses of <math><mi>b</mi><mo>→</mo><mi>s</mi><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math> transitions also rely on the assumptions about nonperturbative contributions to the decay matrix elements. In this work, we perform a global Bayesian analysis of new physics in (semi)leptonic rare <math><mi>B</mi></math> decays, paying attention to the role of charming penguins which are difficult to evaluate from first principles. We find data to be consistent with the Standard Model once rescattering from intermediate hadronic states is included. Consequently, we derive stringent bounds on lepton universality violation in <math><mo>|</mo><mi>Δ</mi><mi>B</mi><mo>|</mo><mo>=</mo><mo>|</mo><mi>Δ</mi><mi>S</mi><mo>|</mo><mo>=</mo><mn>1</mn></math> (semi)leptonic processes.

Marco Ciuchini

Enrico Franco

United States

Ayan Paul

Luca Silvestrini

Mauro Valli

Constraints on lepton universality violation from rare <math><mi>B</mi></math> decays

Measurements of the branching ratios of <math><mi>B</mi><mo>→</mo><msup><mi>D</mi><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mi>τ</mi><mover><mi>ν</mi><mo>¯</mo></mover><mo>/</mo><mi>B</mi><mo>→</mo><msup><mi>D</mi><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mo>ℓ</mo><mover><mi>ν</mi><mo>¯</mo></mover></math> and <math><msub><mi>B</mi><mi>c</mi></msub><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><mi>τ</mi><mover><mi>ν</mi><mo>¯</mo></mover><mo>/</mo><msub><mi>B</mi><mi>c</mi></msub><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><mo>ℓ</mo><mover><mi>ν</mi><mo>¯</mo></mover></math> by the BABAR, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio <math><msub><mi>Λ</mi><mi>b</mi></msub><mo>→</mo><msub><mi>Λ</mi><mi>c</mi></msub><mi>τ</mi><mover><mi>ν</mi><mo>¯</mo></mover><mo>/</mo><msub><mi>Λ</mi><mi>b</mi></msub><mo>→</mo><msub><mi>Λ</mi><mi>c</mi></msub><mo>ℓ</mo><mover><mi>ν</mi><mo>¯</mo></mover></math> shows a relative deficit in taus. In this paper, we critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible (within <math><mn>2</mn><mi>σ</mi></math> or <math><mn>1.5</mn><mi>σ</mi></math>, depending on the <math><mi>R</mi><mo>(</mo><msub><mi>Λ</mi><mi>c</mi></msub><mo>)</mo></math> normalization to light lepton channels). While this inconsistency could be a statistical fluctuation, further measurements are required in order to converge to a coherent pattern of experimental results.

Japan

China

Teppei Kitahara

Ryoutaro Watanabe

Impact of <math><msub><mi>Λ</mi><mi>b</mi></msub><mo>→</mo><msub><mi>Λ</mi><mi>c</mi></msub><mi>τ</mi><mi>ν</mi></math> measurement on new physics in <math><mi>b</mi><mo>→</mo><mi>c</mi><mi>l</mi><mi>ν</mi></math> transitions

The LHCb experiment has recently presented new results on Lepton Universality Violation (LUV) in  $$B \rightarrow K^{(*)} \ell ^+ \ell ^-$$  <math> <mrow> <mi>B</mi> <mo>→</mo> <msup> <mi>K</mi> <mrow> <mo>(</mo> <mrow></mrow> <mo>∗</mo> <mo>)</mo> </mrow> </msup> <msup> <mi>ℓ</mi> <mo>+</mo> </msup> <msup> <mi>ℓ</mi> <mo>-</mo> </msup> </mrow> </math>   decays involving  $$K_S$$  <math> <msub> <mi>K</mi> <mi>S</mi> </msub> </math>   in the final state, which strengthen the recent evidence of LUV obtained in  $$B^+ \rightarrow K^{+} \ell ^+ \ell ^-$$  <math> <mrow> <msup> <mi>B</mi> <mo>+</mo> </msup> <mo>→</mo> <msup> <mi>K</mi> <mo>+</mo> </msup> <msup> <mi>ℓ</mi> <mo>+</mo> </msup> <msup> <mi>ℓ</mi> <mo>-</mo> </msup> </mrow> </math>   decays and the previous measurements of  $$B \rightarrow K^{*0} \ell ^+ \ell ^-$$  <math> <mrow> <mi>B</mi> <mo>→</mo> <msup> <mi>K</mi> <mrow> <mrow></mrow> <mo>∗</mo> <mn>0</mn> </mrow> </msup> <msup> <mi>ℓ</mi> <mo>+</mo> </msup> <msup> <mi>ℓ</mi> <mo>-</mo> </msup> </mrow> </math>  . While LUV observables in the Standard Model are theoretically clean, their predictions in New Physics scenarios are sensitive to the details of the hadronic dynamics, and in particular of the charming penguin contribution. In this work, we show how a conservative treatment of hadronic uncertainties is crucial not only to assess the significance of deviations from the Standard Model but also to obtain a conservative picture of the New Physics responsible for LUV. Adopting a very general parameterization of charming penguins, we find that: (i) current data hint at a sizable  $$q^2$$  <math> <msup> <mi>q</mi> <mn>2</mn> </msup> </math>   and helicity dependence of charm loop amplitudes; (ii) conservative NP solutions to B anomalies favour a left-handed or an axial lepton coupling rather than a vector one.

Charming penguins and lepton universality violation in  $$\varvec{b \rightarrow s \ell ^+ \ell ^-}$$  <math> <mrow> <mi>b</mi> <mo>→</mo> <mi>s</mi> <msup> <mi>ℓ</mi> <mo>+</mo> </msup> <msup> <mi>ℓ</mi> <mo>-</mo> </msup> </mrow> </math>   decays

We perform a phenomenological analysis of simplified models of light, feebly interacting particles (FIPs) that can provide a combined explanation of the anomalies in b → sl + l  −  transitions at LHCb and the anomalous magnetic moment of the muon. Different scenarios are categorised according to the explicit momentum dependence of the FIP coupling to the b−s and μ−μ vector currents and they are subject to several constraints from flavour and precision physics. We show that viable combined solutions to the muon g − 2 and flavour anomalies exist with the exchange of a vector FIP with mass larger than 4 GeV. Interestingly, the LHC has the potential to probe this region of the parameter space by increasing the precision of the Z → 4μ cross-section measurement. Conversely, we find that solutions based on the exchange of a lighter vector, in the m  V  &lt; 1 GeV range, are essentially excluded by a combination of B → K+ invisible and W-decay precision bounds.

Luc Darmé

Poland

Kamila Kowalska

Enrico Sessolo

Flavour anomalies and the muon g − 2 from feebly interacting particles

We study renormalizable models with minimal field content that can provide a viable dark matter candidate through the standard freeze-out paradigm and, simultaneously, accommodate the observed anomalies in semileptonic <math><mi>B</mi></math>-meson decays at one loop. Following the hypothesis of minimality, this outcome can be achieved by extending the particle spectrum of the Standard Model either with one vectorlike fermion and two scalars or two vectorlike fermions and one scalar. The dark matter annihilations are mediated by <math><mi>t</mi></math>-channel exchange of other new particles contributing to the <math><mi>B</mi></math> anomalies, thus resulting in a correlation between flavor observables and dark matter abundance. Again based on minimality, we assume the new states to couple only with left-handed muons and second and third generation quarks. Besides an ad hoc symmetry needed to stabilize the dark matter, the interactions of the new states are dictated only by gauge invariance. We present here for the first time a systematic classification of the possible models of this kind, according to the quantum numbers of the new fields under the Standard Model gauge group. Within this general setup we identify a group of representative models that we systematically study, applying the most updated constraints from flavor observables, dedicated dark matter experiments, and LHC searches of leptons and/or jets and missing energy, and of disappearing charged tracks.

Giorgio Arcadi

Lorenzo Calibbi

Federico Mescia

Systematic approach to <math><mi>B</mi></math>-physics anomalies and <math><mi>t</mi></math>-channel dark matter

We study the constraints imposed by perturbative unitarity on the new physics interpretation of the muon <math><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math> anomaly. Within a Standard Model effective field theory approach, we find that scattering amplitudes sourced by effective operators saturate perturbative unitarity at about 1 PeV. This corresponds to the highest energy scale that needs to be probed in order to resolve the new physics origin of the muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> anomaly. On the other hand, simplified models (e.g., scalar-fermion Yukawa theories) in which renormalizable couplings are pushed to the boundary of perturbativity still imply new on-shell states below 200 TeV. We finally suggest that the highest new physics scale responsible for the anomalous effect can be reached in nonrenormalizable models at the PeV scale.

Lukas Allwicher

Luca Di Luzio

Marco Nardecchia

What is the scale of new physics behind the muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math>?