arXiv subjects

Olcyr Sumensari

Publications and source records attributed to Olcyr Sumensari.

At least 19 recordsLinked to original sources

arXiv2026

Challenging Majorana neutrino effects in $B\to K^{(\ast)}\nu\nu$ and $K\to \pi\nu\nu$ decays

We investigate the contributions of Lepton Number Violating (LNV) effective operators to the rare decays $B\to K^{(\ast)}\nu\nu$ and $K\to \pi\nu\nu$. Such operators can modify the kinematic distributions of these processes, providing distinctive probes of physics beyond the Standard Model. Through a renormalization-group analysis, we show that the Standard Model Effective Field Theory (SMEFT) operators responsible for these effects are subject to stringent indirect constraints from neutrino physics. In particular, we find that the mild excess reported by Belle-II in the $B^+\to K^+\nu\nu$ channel cannot be explained by LNV SMEFT operators without introducing significant fine-tuning in neutrino masses. We then show that these constraints can be evaded in the SMEFT minimally extended by a light right-handed neutrino, allowing for sizable effects in rare meson decays. Finally, we explore the implications of this viable scenario for low-energy processes, including neutrinoless double-beta decays.

hep-ph↗

arXiv2024

On the EFT validity for Drell-Yan tails at the LHC

In this article, we examine the validity range of the Effective Field Theory (EFT) description of high-energy Drell-Yan processes at the LHC. To this purpose, we consider explicit mediators that contribute to these processes in the $s$- and $t$-channels, comparing their effects in Drell-Yan distributions with the ones obtained by matching onto the corresponding EFT. We determine the conditions for the EFT results to accurately describe these scenarios. In particular, we explore the impact of including dimension-eight $(d=8)$ operators in the faster convergence of the EFT series, at the analytical and numerical level, considering contributions to the cross section up to the square of $d=8$ EFT operator insertions. Moreover, we discuss the possible implications of clipping LHC data and illustrate results for a specific New-Physics scenario motivated by low-energy flavor data.

hep-ph↗

arXiv2024

Lepton flavor violation in exclusive $b\to d\ell_i\ell_j$ and $b\to s\ell_i\ell_j$ decay modes

We discuss the exclusive lepton flavor violating (LFV) decays modes based on $b\to d\ell_i\ell_j$ and $b\to s\ell_i\ell_j$ by considering the ground state mesons and baryons. After spelling out the expressions for such decay rates in a low energy effective theory which includes generic contributions arising from physics beyond the Standard Model (BSM), we show that the experimental bounds on meson decays can be used to bound the corresponding modes involving baryons. We find, for example, $\mathcal{B}(Λ_b\to Λμτ)\lesssim 4\times 10^{-5}$. We also consider two specific models and constrain the relevant LFV couplings by using the low energy observables. In the first model we assume the Higgs mediated LFV and find the resulting decay rates to be too small to be experimentally detectable. We also emphasize that the regions favored by the bounds $\mathcal{B}(h\toμτ)^\mathrm{Atlas}$ and $\mathcal{B}(h\to eτ)^\mathrm{Atlas}$ are not compatible with $\mathcal{B}(μ\to eγ)^\mathrm{MEG}$ to $1σ$. In the second model we assume LFV mediated by a heavy $Z'$ boson and find that the corresponding $b$-hadron branching fractions can be $\mathcal{O}(10^{-6})$, thus possibly within experimental reach at LHCb and Belle~II.

hep-ph↗

arXiv2024

Looking for New Physics Through the Exclusive $b\to sν\barν$ Modes

The Belle-II experiment has recently measured $\mathcal{B}(B^+\to K^+ν\barν)$, which appears to be almost $3σ$ larger than its Standard Model (SM) prediction. In this talk, I will critically revisit the status of the SM predictions for the $B\to K^{(\ast)}ν\barν$ decays, and discuss the interpretation of the recent Belle-II measurement in terms of a general Effective Field Theory, as well as concrete models of physics beyond the SM.

hep-ph↗

arXiv2024

Positivity in Amplitudes and Quantum Entanglement

We explore the connection of positivity of the imaginary part of forward elastic amplitudes for perturbative scattering with consistency of the entanglement generated by the S-matrix, for states with arbitrary internal quantum numbers such as flavor. We also analyze "disentanglers," certain highly entangled initial states for which the action of the S-matrix is to decrease subsystem entanglement. As a by-product, we develop a framework based on wave packets to regularize the spacetime divergences that appear in the plane-wave derivation of the $2\to2$ entanglement expression.

hep-th↗

arXiv2024

Probing Lepton Flavor Violation in Meson Decays with LHC Data

In this letter, we use LHC data from the Drell-Yan processes $pp\to\ell_i\ell_j$ (with $i\neq j$) to derive model-independent upper limits on lepton-flavor-violating meson decays. Our analysis is based on an Effective Field Theory (EFT) approach and it does not require a specific assumption regarding the basis of effective operators. We find that current LHC data (140~$\mathrm{fb}^{-1}$) already provides competitive limits on $B(B\to πe τ)$ and $B(B\to πμτ)$ with respect to the ones obtained through experimental searches at the $B$-factories. Moreover, we derive upper limits on several decays that have not been searched for experimentally yet, such as $D^0\to eτ$ in the charm sector, and various semileptonic decays such as $B\to ρμτ$, $B_s\to K μτ$ and $B_s\toϕμτ$. Lastly, we discuss the validity of the EFT description of LHC data and the impact of loop corrections in our analysis.

hep-ph↗

arXiv2024

Understanding the first measurement of $\mathcal{B}(B\to K ν\barν)$

Recently, Belle II reported on the first measurement of $\mathcal{B}(B^\pm\to K^\pm ν\barν)$ which appears to be almost $3σ$ larger than predicted in the Standard Model. We point out the important correlation with $\mathcal{B}(B\to K^{\ast} ν\barν)$ so that the measurement of that decay mode could help restraining the possible options for building the model of New Physics. We then try to interpret this new experimental result in terms of physics beyond the Standard Model by using SMEFT and find that a scenario with coupling only to $τ$ can accommodate the current experimental constraints but fails in getting a desired $R_{D^{(\ast )}}^\mathrm{exp}/R_{D^{(\ast )}}^\mathrm{SM}$, unless one turns the other SMEFT operators that are not related to $b\to s\ell\ell$ or/and $b\to sνν$.

hep-ph↗

arXiv2023

New Physics Searches at Kaon and Hyperon Factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

hep-ph↗

arXiv2023

Revisiting $B\to K^{(\ast)} ν\barν$ decays in the Standard Model and beyond

In this letter we revisit the Standard Model predictions for $\mathcal{B}(B\to K^{(\ast)}ν\barν)$ and discuss the opportunities that open up when combining its partial decay rate with that of $B\to K^{(\ast)}\ell\ell$. In the Standard Model a suitable ratio of these two modes can be used to extract $C_9^\mathrm{eff}$, which is essential for a reliable phenomenological analysis of the $B\to K^{(\ast)}\ell\ell$ angular observables. The same ratio also proves to be more sensitive to the presence of New Physics in many plausible extensions of the Standard Model. We also suggest that the separate measurement of $\mathcal{B}(B\to Kν\barν)$ for high and for low $q^2$'s can be helpful for testing the assumed shape of the vector form factor, because the lattice QCD data are obtained at high $q^2$'s, whereas the low $q^2$ region is obtained through an extrapolation.

hep-ph↗

arXiv2023

Drell-Yan Tails Beyond the Standard Model

We investigate the high-$p_T$ tails of the $pp\to \ell ν$ and $pp \to \ell \ell$ Drell-Yan processes as probes of New Physics in semileptonic interactions with an arbitrary flavor structure. For this purpose, we provide a general decomposition of the $2\to2$ scattering amplitudes in terms of form-factors that we match to specific scenarios, such as the Standard Model Effective Field Theory (SMEFT), including all relevant operators up to dimension-$8$, as well as ultraviolet scenarios giving rise to tree-level exchange of new bosonic mediators with masses at the TeV scale. By using the latest LHC run-II data in the monolepton ($eν$, $μν$, $τν$) and dilepton ($ee$, $μμ$, $ττ$, $eμ$, $eτ$, $μτ$) production channels, we derive constraints on the SMEFT Wilson coefficients for semileptonic four-fermion and dipole operators with the most general flavor structure, as well as on all possible leptoquark models. For the SMEFT, we discuss the range of validity of the EFT description, the relevance of $\mathcal{O}(1/Λ^2)$ and $\mathcal{O}(1/Λ^4)$ truncations, the impact of $d=8$ operators and the effects of different quark-flavor alignments. Finally, as a highlight, we extract for several New Physics scenarios the combined limits from high-$p_T$ processes, electroweak pole measurements and low-energy flavor data for the $b\to cτν$ transition, showing the complementarity between these different observables. Our results are compiled in {\tt HighPT}, a package in {\tt Mathematica} which provides a simple way for users to extract the Drell-Yan tails likelihoods for semileptonic effective operators and for leptoquark models.

hep-ph↗

arXiv2023

On the impact of meson mixing on $B_s\toϕee$ angular observables at low $q^2$

Decays based on the $b\to sγ$ transition are expected to yield left-handed photons in the Standard Model, but could be particularly sensitive to New Physics contributions modifying the short-distance Wilson coefficients $\mathcal{C}_7$ and $\mathcal{C}_{7'}$ defined in the low-energy Effective Field Theory. These coefficients can be determined by combining observables of several modes, among which $B_s\toϕee$ at low $q^2$, in a kinematic range where the photon-pole is dominant. We investigate the impact of $B_s-\bar{B}_s$ mixing on the angular observables available for this mode, which induces a time-dependent modulation governed by interference terms between mixing and decay that are sensitive to the moduli and phases of $\mathcal{C}_7$ and $\mathcal{C}_{7'}$. These interference terms can be extracted through a time-dependent analysis but they also affect time-integrated observables. In particular, we show that the asymmetries $A_T^{(2)}$ and $A_T^{(\text{Im});CP}$ receive terms of potentially similar size from mixing-independent and mixing-induced terms, and we discuss how the constraints coming from the angular analysis of $B_s\toϕee$ at low $q^2$ should be interpreted in the presence of mixing.

hep-ph↗

arXiv2022

High-energy frontier of the muon g-2 at a muon collider

The long-standing muon g-2 anomaly can be explained by heavy new physics particles through chirally enhanced contributions. It has been recently proposed that a muon collider running at center-of-mass energies of several TeV could test these new physics scenarios in a model-independent way, through the study of high-energy processes such as mu+ mu- --> h gamma. In this work, we validate these findings, based on effective field theories, by considering selected renormalizable simplified models and by computing this one-loop process in full generality. Furthermore, we explore the interplay of direct and indirect high-energy searches to pin down the details of the underlying new physics model accommodating the muon g-2 anomaly.

hep-ph↗

arXiv2022

HighPT: A Tool for high-$p_T$ Drell-Yan Tails Beyond the Standard Model

HighPT is a Mathematica package for the analysis of high-energy data of semileptonic transitions at hadron colliders. It allows to compute high-$p_T$ tail observables for semileptonic processes, i.e. Drell-Yan cross sections, for dilepton and monolepton final states at the LHC. These observables can be calculated at tree level within the Standard Model Effective Field Theory, including the relevant operators up to dimension eight to ensure a consistent description of the cross section including terms of $\mathcal{O}(\Lambda^{-4})$ in the cutoff scale $\Lambda$. For New Physics models with new mediators that can be resolved at LHC energies, HighPT can also account for the full propagation effects of these new bosonic states at tree level. Using the available data from the high-$p_T$ tails in the relevant LHC run-II searches by the ATLAS and CMS collaborations, HighPT can also construct the corresponding likelihoods for all possible flavors of the leptonic final states. As an illustration, we derive and compare constraints on Wilson coefficients at different orders in the Effective Field Theory expansion, and we investigate lepton flavor violation for the $S_3$ leptoquark model. The HighPT code is publicly available at https://github.com/HighPT/HighPT.

hep-ph↗

arXiv2022

On a model with two scalar leptoquarks -- $R_2$ and $S_3$

We discuss a model that can accommodate the $B$-physics anomalies, based on combining two scalar leptoquarks, $R_2$ and $S_3$, of mass $\mathcal{O}(1\,\mathrm{TeV})$, and that we proposed in our previous paper. We update the analysis of its parameter space and show that a model remains viable and consistent with a number of low energy and high energy flavor physics constraints. Since the model predicts a non-zero New Physics phase, we discuss the possibility to test its contribution to the neutron electric dipole moment and to the angular distributions of the exclusive $b\to cτ\bar ν$ decays. We find that the model can provide a significant enhancement to $\mathcal{B}(B\to K^{(\ast)}νν)$ and provides both the upper and lower bounds to $\mathcal{B}(B\to K^{(\ast)}μτ)$.

hep-ph↗

arXiv2022

Triple-leptoquark interactions for tree- and loop-level proton decays

We study the impact of triple-leptoquark interactions on matter stability for two specific proton decay topologies that arise at the tree- and one-loop level if and when they coexist. We demonstrate that the one-loop level topology is much more relevant than the tree-level one when it comes to the proton decay signatures despite the usual loop-suppression factor. We subsequently present detailed analysis of the triple-leptoquark interaction effects on the proton stability within one representative scenario to support our claim, where the scenario in question simultaneously features a tree-level topology that yields three-body proton decay $p\to e^+ e^+ e^-$ and a one-loop level topology that induces two-body proton decays $p\to π^0 e^+$ and $p\to π^+ \barν$. We also provide a comprehensive list of the leading-order proton decay channels for all non-trivial cubic and quartic contractions involving three scalar leptoquark multiplets that generate triple-leptoquark interactions of our interest, where in the latter case one of the scalar multiplets is the Standard Model Higgs doublet.

hep-ph↗

arXiv2021

Prospects for $B_{c}^+\to τ^+ ν_τ$ at FCC-ee

This paper presents the prospects for a precise measurement of the branching fraction of the leptonic $B_{c}^+\to τ^+ ν_τ$ decay at the Future Circular Collider (FCC-ee) running at the $Z$-pole. A detailed description of the simulation and analysis framework is provided. To select signal candidates, two Boosted Decision Tree algorithms are employed and optimised. The first stage suppresses inclusive $b\bar{b}$, $c\bar{c}$, and $q\bar{q}$ backgrounds using event-based topological information. A second stage utilises the properties of the hadronic $τ^{+} \to π^+ π^+ π^- \barν_τ$ decay to further suppress these backgrounds, and is also found to achieve high rejection for the $B^+\to τ^+ ν_τ$ background. The number of $B_{c}^+\to τ^+ ν_τ$ candidates is estimated for various Tera-$Z$ scenarios, and the potential precision of signal yield and branching fraction measurements evaluated. The phenomenological impact of such measurements on various New Physics scenarios is also explored.

hep-ex↗

arXiv2021

Leptoquarks and Real Singlets: A Richer Scalar Sector Behind the Origin of Dark Matter

We investigate scenarios with $\mathcal{O}(1\mathrm{\,TeV})$ scalar leptoquarks that act as portals between the Standard Model and Dark Matter. We assume that Dark Matter is a scalar singlet $S$ which couples to a scalar leptoquark $Δ$ and the Higgs boson via the terms in the scalar potential. In addition, the leptoquark is endowed with Yukawa couplings to quarks and leptons that may address the anomalies in $B$ meson decays. We consider the $SS$ annihilation cross sections to estimate the Dark Matter relic abundance and explore the interplay between astrophysical, collider and flavour physics bounds on such models. In the heavy Dark Matter window, $m_S > m_Δ$, the leptoquark portal becomes the dominant mechanism to explain the Dark Matter abundance. We find that the leptoquark Yukawa couplings, relevant for quark and lepton flavour physics, are decoupled from the dark matter phenomenology. By focussing on a scenario with a single leptoquark state, we find that relic density can only be explained when both $Δ$ and $S$ masses are lighter than $\mathcal{O}(10\mathrm{\,TeV})$.

hep-ph↗

arXiv2021

New Physics effects in leptonic and semileptonic decays

We discuss the possibilities of extracting the constraints on New Physics by using the current data on the leptonic and semileptonic decays of pseudoscalar mesons. In doing so we use a general low energy Lagrangian that besides the vector and axial operators also includes the (pseudo-)scalar and tensor ones. In obtaining constraints on New Physics couplings we combine the experimental information concerning several decay modes with the accurate lattice QCD results for the hadronic matrix elements. We propose to study new observables that can be extracted from the angular analysis of the semileptonic decays and discuss their values both in the Standard Model and in some specific scenarios of physics beyond the Standard Model.

hep-ph↗