Search

A relation between the radii and masses of the quarks and leptons is established for each fermion generation. Kinematical calculations provide a proof of the essential stability of the proton at rest within the standard model together with conditions for the reaction p → uuu + e- + ve with a uuu composite state as a byproduct. The Koide relation reduces the scaling to a single number, and a theoretical explanation is given in terms of graded symmetries. The values of the masses of the each of the quarks are derived through nonperturbative infinite-genus effects. [ABSTRACT FROM AUTHOR]

The quartification model is an S U (3) 4 extension with a bi-fundamental fermion sector of the well-known S U (3) 3 bi-fundamentalfication model. An alternative "flipped" version of the quartification model is obtained by rearrangement of the particle assignments. The flipped model has two standard (bi-fundamentalfication) families and one flipped quartification family. In contrast to traditional product group unification models, flipped quartification stands out by featuring leptoquarks and thus allows for new mechanisms to explain the generation of neutrino masses and possible hints of lepton-flavor non-universality. [ABSTRACT FROM AUTHOR]

We suggest a simple relation between the quark and the lepton mixing within the framework of type-I seesaw mechanism. We show that within our ansatz the empirical King–Mohapatra–Smirnov relation, which suggests a connection between the CKM and PMNS mixing where | V 13 PMNS | ≈ sin θ C / 2 , can be derived. This is possible within a restricted region of the Dirac and Majorana mass parameters. [ABSTRACT FROM AUTHOR]

Motivated by the study of heavy–light meson production within the framework of heavy quark effective theory (HQET) factorization, we extend the factorization formalism for a rather complicated process W + → B +ℓ+ℓ− in the limit of a nonzero invariant squared mass of the dilepton, q 2, at the lowest order in 1/ mb up to |$\mathcal {O}(\alpha _s)$|⁠. The purpose of the current study is to extend the HQET factorization formula for the W + → B +ℓ+ℓ− process and subsequently compute the form factors for this channel up to next-to-leading-order corrections in α s . We explicitly show that the amplitude of the W + → B +ℓ+ℓ− process can also be factorized into a convolution between the perturbatively calculable hard-scattering kernel and the nonperturbative yet universal light-cone distribution amplitude (LCDA) defined in HQET. The validity of the HQET factorization depends on the assumed scale hierarchy mW ∼ mb ≫ ΛQCD. Within the HQET framework, we evaluate the form factors associated with the W + → B +ℓ+ℓ− process, providing insights into its phenomenology. In addition, we also perform an exploratory phenomenological study on W + → B +ℓ+ℓ− by employing an exponential model for the LCDAs for the B + meson. Our findings reveal that the branching ratio for W + → B +ℓ+ℓ− is below 10−10. Although the branching ratios are small, this channel in high-luminosity LHC experiments may serve to further constrain the value of λ B . [ABSTRACT FROM AUTHOR]

We study the charged LFV μ decays such as μ → e γ, μ → eee, and μ − e Ti with a vector leptoquark (U 3) by considering the constraints from non-standard neutrino interaction (NSI) sector parameter ϵ e μ . We consider that these NSIs are attributed to the presence of leptoquarks to account for the difference in the experimental observations of δ CP measurement by NOvA and T2K. In our study, we obtained the branching ratios with uncertainties for three decay modes: B (μ → e γ) ≤ 4.6 − 2.6 + 3.8 × 10 − 18 , B (μ → eee) ≤ 9.57 − 5.37 + 7.43 × 10 − 21 , B μ → e Ti ≤ 6.89 − 3.89 + 5.61 × 10 − 19. Our results show an improvement in the current limits, which can be explored in future experiments. [ABSTRACT FROM AUTHOR]

We investigate the radiative QED corrections to the lepton (L = e, μ and τ) anomalous magnetic moment due to the contributions of diagrams with insertions of the photon vacuum polarisation operator consisting solely of four closed lepton (l = e, μ and τ) loops. Moreover, we focus on specific operators with two loops formed by leptons L of the same type as the external one, the other two formed by leptons ℓ different from L. The approach is essentially based on the employment of the Mellin–Barnes representation of the x -parametrization of the corresponding Feynman diagrams. This allows one to obtain, for the first time, exact analytical expressions for the radiative corrections of the tenth order w.r.t. the electromagnetic coupling constant e. Analytically, the radiative corrections are expressed in terms of the ratio r = m ℓ / m L of the internal to external lepton masses. The dependence on r is investigated numerically in the whole interval of r, 0 < r < ∞. To make comparisons with earlier published results possible, our exact analytical expressions are expanded as r → 0 and r → ∞ and compared with the corresponding asymptotic expansions known in the literature. [ABSTRACT FROM AUTHOR]

In the model [J. Ganguly and R. S. Hundi, Chinese Phys. C 46, 103101 (2022).], the neutrino mixing has been explained in a type II seesaw scenario with generalized CP symmetries. The neutrino mass matrix has μ − τ symmetric nature. As neutrino oscillation data suggests neutrino mixing can deviate from μ − τ symmetry, in this work, deviation from μ − τ symmetric mass matrix is shown by breaking the generalized CP symmetry explicitly by a small amount in the Yukawa Lagrangian which actually shows that atmospheric mixing angle can deviate from maximal value. As a phenomenological implication, branching ratios of the lepton flavor violating decays have been studied, which occurs by the triplet Higgs, by writing down the full scalar potential and then finding the mass eigenstates of the scalars. We have studied the implications of neutrinoless double beta decay within our model. [ABSTRACT FROM AUTHOR]

We review aspects of the modular invariance approach to the flavour problem. Harald Fritzsch was among the first to realise the existence and the fundamental nature of the quark and lepton flavour problems in particle physics, that symmetries may be the key to the solution(s) of these problems and to propose in 1978 and 1979 a solution to the quark flavour problem in the form of the Fritzsch quark mass matrices with texture zeros. After introducing the general ingredients of the modular invariance approach, we describe the formalism that allows to construct models in which fermion (charged-lepton and quark) mass hierarchies follow solely from the properties of the modular forms, avoiding the fine-tuning of the constant parameters present in the fermion mass matrices and the need to introduce extra fields. Focusing on the lepton sector, we show how the indicated formalism can be used in lepton flavour models to obtain the charged lepton mass hierarchies without parameter fine-tuning. Only a very limited number of models satisfy the non-fine-tuning requirement in explaining the observed fermion mass hierarchies. We review next the general conditions under which also the peculiar pattern of Pontecorvo, Maki, Nakagawa and Sakata (PMNS) lepton mixing consisting of two large and one small angles can be reproduced without fine-tuning. We then give an example of a phenomenologically viable "minimal" modular lepton flavour model in which both the lepton mixing and charged lepton mass hierarchies are generated without fine-tuning. We conclude by listing some of the open questions and problems in the modular invariant approach to the flavour problem. [ABSTRACT FROM AUTHOR]

We discuss aspects of a promising top-down origin of flavor symmetries in particle physics. Modular transformations originating from string theory dualities are shown to play a crucial role. We introduce the notion of an "eclectic" flavor scheme that unifies traditional flavor symmetries, modular symmetries and -transformations. It exhibits the phenomenon of "Local Flavor Unification" with enhanced flavor symmetries at fixed points or lines in moduli space. Successful fits of masses and mixing angles of quarks and leptons are found in the vicinity of these points and lines. [ABSTRACT FROM AUTHOR]

We review the experimental status of searches for lepton-flavour violation in the charged sector. We give an overview of searches for lepton-flavour violation in purely leptonic decays, hadron decays, and decays of heavy bosons. We focus on the most stringent constraints on lepton-flavour violating processes in these areas and give prospects for ongoing and future experiments. [ABSTRACT FROM AUTHOR]

The upcoming European Spallation Source (ESS) will soon provide the most intense neutrino source in the world. We propose the Search for Hidden Neutrinos at the ESS (SHiNESS) experiment, highlighting its unique opportunities to search for the existence of sterile neutrinos across a wide range of scales: anomalous oscillations at short baselines; non-unitarity mixing in the active neutrino sector; or an excess of events with multiple leptons in the final state, produced in the decay of heavy neutrinos. The baseline design of the detector comprises an active volume filled with 42 ton of liquid scintillator, located 25 m far from the ESS beam target. We show that SHiNESS will be able to considerably improve current global limits for the three cases outlined above. Although in this work we focus on new physics in the neutrino sector, the proposed setup may also be used to search for signals from weakly interacting particles in a broader context. [ABSTRACT FROM AUTHOR]

In this paper we investigate how well the nature of heavy neutral leptons can be determined at a future lepton collider, after its potential discovery. Considered in a simplified model are prompt decays of the neutrino in the mass range from 100 GeV to 10 TeV. We study event selection and application of multivariate analyses to determine whether such a newly discovered particle is of the Dirac or Majorana nature. Combining lepton charge and kinematic event variables, we find that the nature of a heavy neutrino, whether it is a Dirac or a Majorana particle, can be determined at 95% C.L. almost in the whole discovery range. We will briefly speculate about other than the studied channels and the robustness of this statement in more general models of heavy neutral leptons, particularly on the complementarity of high-energy electron-positron vs. muon colliders on resolving the flavor structure of heavy neutrinos. [ABSTRACT FROM AUTHOR]

We present an exact evaluation of the two-photon exchange contribution to the elastic lepton-proton scattering process at low-energies using heavy baryon chiral perturbation theory. The evaluation is performed including next-to-leading order accuracy. This exact analytical evaluation contains all soft and hard two-photon exchanges and we identify the contributions missing in a soft-photon approximation approach. We evaluate the infrared divergent four-point box diagrams analytically using dimensional regularization. We also emphasize the differences between muon-proton and electron-proton scatterings relevant to the MUSE kinematics due to lepton mass differences. [ABSTRACT FROM AUTHOR]

After three generations of quarks-leptons and Higgs boson have been confirmed, we research some possible development directions of particle physics. First, particles of three generations are extended. Second, the hadronic theory must precision quantification such as heavy flavor hadrons and the lifetime formula, etc. Third, various unifications of interactions are discussed. Fourth, some basic principles (Pauli Exclusion Principle, duality, uncertainty principle, etc.) are probably violated under some cases. Fifth, Santillli, Penrose, et al., proposed some new mathematical methods. Sixth, particle astrophysics, the negative matter as unified dark matter and dark energy, and the extensive quantum theory are searched. [ABSTRACT FROM AUTHOR]

We perform a collider search for fatjet signals originating from boosted heavy neutral and charged leptons with masses between a few hundred GeV to a TeV. These heavy leptons originate from the decay of heavy gauge bosons with masses above 4 TeV in a left-right symmetric extension of the Standard Model (SM), which considers a universal seesaw mechanism for the generation of all the SM fermion masses. The fatjet signals arise naturally in this model due to the presence of heavy seesaw partners of the SM fermions which decay to SM gauge bosons carrying large boosts. We employ substructure based variables lepton sub-jet fraction (LSF) and lepton mass drop (LMD) together with kinematic variables of fatjets to look for fatjet signals associated with non-isolated leptons. These variables help in reducing the SM backgrounds while retaining enough statistics for signal events, which leads to a robust discovery potential at the high-luminosity Large Hadron Collider (HL-LHC). [ABSTRACT FROM AUTHOR]

The document is a correction notice for a journal article titled "Observation of four-top-quark production in the multilepton final state with the ATLAS detector." The corrections involve changes to figures, tables, and corresponding numbers in the text, specifically related to systematic uncertainties. These corrections impact the limits on the top-quark Yukawa coupling, Higgs oblique parameter, and EFT operators. The document provides more accurate and updated information for researchers studying particle physics. [Extracted from the article]

We study lepton flavour universality violation in SM boson decays in low-scale seesaw models of neutrino mass generation, also addressing other electroweak precision observables. We compute the electroweak next-to-leading order corrections, which turn out to be important – notably in the case of the invisible decay width of the Z boson, for which the corrections can be as large as the current experimental uncertainty. As a well-motivated illustrative study case, we choose a realisation of the Inverse Seesaw mechanism, and discuss the complementary role of lepton flavour conserving, lepton flavour violating and precision observables, both in constraining and in probing such models of neutrino mass generation. Our findings suggest that invisible Z decays are especially important, potentially at the origin of the most stringent constraints for certain regimes of the Inverse Seesaw (while complying with charge lepton flavour violation and other electroweak precision tests). We also discuss the probing power of the considered observables in view of the expected improvement in experimental precision at FCC-ee. [ABSTRACT FROM AUTHOR]

This talk summarizes a new understanding of the cosmological constant problem, which essentially relies on a phase-space-like computation of the vacuum energy, both in the realm of quantum field theory coupled to gravity, and in the realm of a consistent formulation of a quantum theory of gravity and matter, such as string theory, combined with central properties of gravitational entropy as captured by the Bekenstein bound. This new understanding of the vacuum in a quantum theory of gravity and matter sheds light on the Higgs mass as well as the masses of quarks and leptons. [ABSTRACT FROM AUTHOR]

This article is based on the study of pure leptonic decays of charged pseudoscalar mesons taking nonuniversality into account. We calculate the branching ratios of the processes π ±, K±, D±, Ds±, b±. For the search for new physics (NP), we examine the discrepancies between theoretical and experimental results. The discrepancies are possibly due to massive neutrinos, processed massless in the Standard Model (SM), and universal coupling of leptons. We focus on the non-universality of leptons in order to find the bounds on Non-Standard Interaction (NSI) parameters ε. We use charge current like NSI and conclude that these decays could provide strong constraints on the NSI parameter. [ABSTRACT FROM AUTHOR]

In the framework of the MSSM extension with local gauged baryon and lepton numbers (BLMSSM), we calculate the muon anomalous magnetic dipole moment (MDM) and lepton (e, μ, τ) electric dipole moment (EDM), and discuss how the muon MDM and lepton EDM depend on the parameters within the mass insertion approximation. Among many parameters, tan β , g L , m L and μ H are more sensitive parameters for a μ BL . Considering the experimental limitations, our best numerical result of a μ BL is around 2.5 × 10−9, which can well compensate the departure between the experiment data and standard model (SM) prediction. The CP violating phases in BLMSSM are more than those in the MSSM, including new parameters θ μ L and θ L . They can give large contributions, which play an important role in exploring the source of CP violation and probing new physics beyond SM. [ABSTRACT FROM AUTHOR]

The framed standard model (FSM), constructed to explain, with some success, why there should be three and apparently only three generations of quarks and leptons in nature falling into a hierarchical mass and mixing pattern,10 suggests also, among other things, a scalar boson U, with mass around 17 MeV and small couplings to quarks and leptons,11 which might explain9 the g − 2 anomaly reported in experiment.12 The U arises in FSM initially as a state in the predicted "hidden sector" with mass around 17 MeV, which mixes with the standard model (SM) Higgs h W , acquiring thereby a coupling to quarks and leptons and a mass just below 17 MeV. The initial purpose of this paper is to check whether this proposal is compatible with experiment on semileptonic decays of Ks and Bs where the U can also appear. The answer to this we find is affirmative, in that the contribution of U to new physics as calculated in the FSM remains within the experimental bounds, but only if m U lies within a narrow range just below the unmixed mass. As a result from this, one has an estimate m U ∼ 1 5 –17 MeV for the mass of U, and from some further considerations the estimate Γ U ∼ 0. 0 2 eV for its width, both of which may be useful for an eventual search for it in experiment. If found, it will be, for the FSM, not just the discovery of a predicted new particle, but the opening of a window into a whole "hidden sector" containing at least some, perhaps even the bulk, of the dark matter in the universe. [ABSTRACT FROM AUTHOR]

We perform a detailed study of the b → c τν and b → sl + l − processes in a minimal flipped 331 model based on the SU (3) C × SU (3) L × U (1) X gauge symmetry. The non-universal SU (3) L × U (1) X symmetry in the lepton sector gives rise to non-universal neutral and charged currents involving heavy non-SM gauge bosons and SM leptons that yield radiative contributions to the b → s, b → c, s → u , and d → u transitions arising from one-loop-level penguin and box diagrams. We find that the observables related to these transitions agree with their experimental values in a region of parameter space that includes TeV-scale exotic up-type quarks, within the reach of the Large Hadron Collider. [ABSTRACT FROM AUTHOR]

In this work, we study the neutrino mixing sum rules arising from discrete symmetries and the class of Littlest Seesaw (LS) neutrino models. These symmetry-based approaches all offer predictions for the cosine of the leptonic CP phase  cos δ  in terms of the mixing angles,  θ 13 ,  θ 12 ,  θ 23 , while the LS models also predict the sine of the leptonic CP phase  sin δ , as well as making other predictions. In particular, we study the solar neutrino mixing sum rules, arising from charged lepton corrections to tri-bimaximal (TB), bimaximal (BM), golden ratio (GR) and hexagonal (HEX) neutrino mixing, and the atmospheric neutrino mixing sum rules, arising from preserving one of the columns of these types of mixing—for example, the first or second column of the TB mixing matrix (TM1 or TM2)—and we confront them with an up-to-date global fit of the neutrino oscillation data. We show that some mixing sum rules, such as an atmospheric neutrino mixing sum rule arising from a version of neutrino golden ratio mixing (GRa1), are already excluded at 3 σ , and we determine the remaining models allowed by the data. We also consider the more predictive LS models (which obey the TM1 sum rules and offer further predictions) based on constrained sequential dominance CSD(n) with  n ≈ 3 . We compare for the first time the three cases  n = 2.5 ,  n = 3  and  n = 1 + 6 ≈ 3.45 , which are favored by theoretical models, using a new type of analysis to accurately predict the observables  θ 12 ,  θ 23  and  δ. We study all the above approaches, solar and atmospheric mixing sum rules and LS models, together so that they may be compared and to give an up-to-date analysis of the predictions of all of these possibilities, when confronted with the most recent global fits. [ABSTRACT FROM AUTHOR]

Searches for new physics (NP) at particle colliders typically involve multivariate analysis of kinematic distributions of final state particles produced in a decay of a hypothetical NP resonance. Since the pair-production cross-sections mediated by such resonances are strongly suppressed by the NP scale, this analysis becomes less relevant for NP searches for masses of the BSM resonance above 1 TeV. On the other hand, t-channel processes are less sensitive to the mass of the virtual mediator and therefore larger phase-space can be potentially probed as well as the couplings between the NP particles and the Standard Model fields. The fact that transitions between different generations of quarks and leptons may exist, the potential of the search presented in this article can be used, as a reference guide, to enlarge significantly the scope of searches performed at the LHC to flavour off-diagonal channels, in a theoretically consistent approach. In this work, we study non-resonant production of scalar leptoquarks which have been proposed in the literature to provide a potential avenue for radiative generation of neutrino masses, accommodating as well the existing flavour physics data. Final states involving just two muons at the LHC (μ+μ−), are used as a well-motivated case study. [ABSTRACT FROM AUTHOR]

In this work, we obtain the current limits on the pair production of vectorlike leptons decaying to a Standard Model gauge boson and a lepton in the second generation using the Run-2 data at the LHC. Since there is no dedicated search out of Run-2 data, we recast the ATLAS analyses searching for the type-III seesaw heavy leptons in the multi-lepton channels. There is no limit for the SU(2)L singlet vectorlike lepton beyond about 100 GeV, while the limit is about 780 GeV for the doublet one. Thus, dedicated searches for the vectorlike leptons are necessary, especially for the singlet one. We also study the general cases of the vectorlike lepton decays and future sensitivities at the HL-LHC. [ABSTRACT FROM AUTHOR]

The CMS experiment at CERN has reported a possible signal for a resonance at 146 GeV decaying into the eμ final state which, presently, is the only experimental hint for lepton flavour violation in any low- and high-energy experiment. The Froggatt-Nielsen mechanism naturally predicts the existence of new scalars, the flavons, with flavour off-diagonal couplings. We study this framework in the context of the CMS result and find that the minimal, purely leptophilic model is too restricted to match the claimed signal. Thereafter we show how models with additional flavon couplings to quarks can explain the claimed signal while satisfying all the existing constraints on lepton flavour violation. [ABSTRACT FROM AUTHOR]

We propose a deep learning-based search strategy for pair production of doubly charged scalars undergoing three-body decays to W + t b ¯ in the same-sign lepton plus multi-jet final state. This process is motivated by composite Higgs models with an underlying fermionic UV theory. We demonstrate that for such busy final states, jet image classification with convolutional neural networks outperforms standard fully connected networks acting on reconstructed kinematic variables. We derive the expected discovery reach and exclusion limit at the high-luminosity LHC. [ABSTRACT FROM AUTHOR]

The NA62 experiment collected the world's largest dataset of charged kaon decays in 2016–2018, leading to the first measurement of the branching ratio of the ultra-rare decay, based on 20 candidates. The radiative kaon decay () is studied with the data recorded in 2017–2018, achieving the most precise measurements of the branching ratio and -asymmetry. Preliminary results from an analysis of the flavour-changing neutral current decay led to the most precise determination of the form-factor parameters and using data collected in 2017–2018. New preliminary results are obtained from an analysis of the decay using data collected in 2016–2018 with a minimum-bias trigger, leading to an unprecedented sensitivity. This analysis can be naturally extended to search for the , process, where is a short-lived axion-like particle. The NA62 dataset is exploited to search for light feebly interacting particles (heavy neutral leptons) in Kaon decays. Dedicated trigger lines are employed to collect di-lepton final states, which allowed establishing new stringent upper limits on the rates of lepton flavour and lepton number violating kaon decays. NA62 can also be run as a beam-dump experiment, by removing the Kaon production target and moving the upstream collimators into a "closed" position. Analyses of the data taken in beam-dump mode are performed to search for visible decays of exotic mediators, with a particular emphasis on Dark Photon Models. [ABSTRACT FROM AUTHOR]

An explanation using nonlocal quantum electrodynamics (QED) for lepton g − 2 anomalies is provided that is a simple extension of the standard model. This solution is based on the same gauge symmetry as QED without introducing any new particles and interactions. The correlation functions in the nonlocal strength tension and lepton–photon interaction make it possible to explain the discrepancies of both Δ a μ and Δ a e . With the same approach, the discrepancy of the anomalous magnetic moment of τ leptons from the standard model is estimated in the range from 1.19 × 10−5 to 3.21 × 10−3, which is covered by the current experimental uncertainty. [ABSTRACT FROM AUTHOR]

Leptoquarks (LQ s) are hypothetical particles that appear in various extensions of the Standard Model (SM), that can explain observed differences between SM theory predictions and experimental results. The production of these particles has been widely studied at various experiments, most recently at the Large Hadron Collider (LHC), and stringent bounds have been placed on their masses and couplings, assuming the simplest beyond-SM (BSM) hypotheses. However, the limits are significantly weaker for LQ models with family non-universal couplings containing enhanced couplings to third-generation fermions. We present a new study on the production of a LQ at the LHC, with preferential couplings to third-generation fermions, considering proton-proton collisions at s = 13 TeV and s = 13.6 TeV . Such a hypothesis is well motivated theoretically and it can explain the recent anomalies in the precision measurements of B -meson decay rates, specifically the R D (∗) ratios. Under a simplified model where the LQ masses and couplings are free parameters, we focus on cases where the LQ decays to a τ lepton and a b quark, and study how the results are affected by different assumptions about chiral currents and interference effects with other BSM processes with the same final states, such as diagrams with a heavy vector boson, Z ′ . The analysis is performed using machine learning techniques, resulting in an increased discovery reach at the LHC, allowing us to probe new physics phase space which addresses the B -meson anomalies, for LQ masses up to 5.00 TeV , for the high luminosity LHC scenario. [ABSTRACT FROM AUTHOR]

Hard exclusive reactions initiated by pion or photon beams within the near-backward kinematical regime specified by the small Mandelstam variable - u can be studied to access pion-to-nucleon and photon-to-nucleon transition distribution amplitudes (TDAs). Checking the validity of collinear factorized description of pion and photon induced reactions in terms of TDAs allows to test the universality of TDAs between the space-like and time-like regimes that is the indispensable feature of the QCD collinear factorization approach. In this short review, we consider the exclusive pion- and photo-production off nucleon of a highly virtual lepton pair (or heavy quarkonium) in the near-backward region. We first employ a simplistic cross channel nucleon exchange model of pion-to-nucleon TDAs to estimate the magnitude of the corresponding cross sections for the kinematical conditions of J-PARC. We then illustrate the flexibility of our approach by building a two parameter model for the photon-to-nucleon TDAs based on recent results for near threshold J / ψ photoproduction at JLab and provide our estimates for near-backward J / ψ photoproduction and timelike Compton scattering cross sections for the kinematical conditions of JLab and of future EIC and EIcC. [ABSTRACT FROM AUTHOR]

In recent times, there have been several observations suggesting deviations from lepton universality in semileptonic decays of B mesons. These deviations have been noticed both in the neutral-current transitions (b → s l l) and charged-current transitions (b → c l ν ̄ l ). Motivated by these intriguing findings, we investigate the semileptonic decays involving the quark-level transitions of b → c l ν ̄ l . To explore the presence of new physics, we adopt a model-independent approach and analyze the processes Λ b → Λ c τ ν ̄ τ , B c + → η c τ + ν τ and B → D ∗ ∗ τ ν ̄ τ , where D ∗ ∗ = D 0 ∗ , D 1 ∗ , D 1 , D 2 ∗ represent the four lightest excited charm mesons. Considering a comprehensive effective Hamiltonian, we perform a global fit using various sets of new coefficients and incorporate measurements of R D , R D ∗ , R J ∕ ψ , P τ D ∗ , as well as the upper limit on the branching ratio of B c + → τ + ν τ . Subsequently, we examine the impact of constrained new couplings on the branching ratios, forward–backward asymmetry parameters, lepton nonuniversality (LNU) ratios, as well as lepton and hadron polarization asymmetries in these decay modes. [ABSTRACT FROM AUTHOR]

We discuss the process , where N is a heavy Majorana neutrino and . Large cross sections are expected for these processes at high center-of-mass energies, which can be reached at future lepton–lepton colliders. The Monte Carlo simulation of the studied processes is produced within the framework of the seesaw type-I model, where the Majorana neutrinos (or heavy neutral leptons, HNL), are introduced in the standard leptonic sector. Recently the possibility to search for the direct HNL production was studied in the process with the subsequent decay . In this paper we investigate an alternative process with the lepton number violation by two units. The similar processes appear in collisions with the same-sign beams, or . The cross sections of the processes under consideration are enhanced by the soft photon exchange in the t-channel. We calculate the cross sections for the signals and potential Standard Model backgrounds for the beam collisions at the 1 TeV center-of-mass energy and the collisions at 3 and 10 TeV. Due to the diagrams with soft t-channel photons and respective interference the promptly emitted leptons are produced in the direction close to the corresponding beam. These leptons will be lost in the beam pipe or badly measured by forward detectors. However, the signal events can be well separated from backgrounds using the rest of the event containing the particles. Finally, the expected upper limits on the mixing parameters as a function of M(N) are calculated. [ABSTRACT FROM AUTHOR]

Lepton flavor universality exists in the Standard Model, and hence any observation of the violation of this universality will be a hint for new physics. Recent experimental searches for processes violating this symmetry have attracted much attention among theorists and experimentalists alike. In recent years, such hints have been observed in flavor changing neutral current weak processes such as b → s l l and charged current weak processes such as b → c l ν processes by collider experiments like Belle, Belle II, BaBar, LHCb, ATLAS, and CMS collaborations, where b , s , c are the bottom, strange, and charm quarks, respectively, and l , ν stand for lepton and the corresponding lepton neutrino, respectively. This article is a review of some of the interesting anomalies observed in the B-sector and includes decays of B s mesons. [ABSTRACT FROM AUTHOR]

We investigate a local SU(3)F flavour symmetry for its viability in generating the masses for the quarks and charged leptons of the first two families through radiative corrections. Only the third-generation fermions get tree-level masses due to specific choice of the field content and their gauge charges. Unprotected by symmetry, the remaining fermions acquire non-vanishing masses through the quantum corrections induced by the gauge bosons of broken SU(3)F. We show that inter-generational hierarchy between the masses of the first two families arises if the flavour symmetry is broken with an intermediate SU(2) leading to a specific ordering in the masses of the gauge bosons. Based on this scheme, we construct an explicit and predictive model and show its viability in reproducing the realistic charged fermion masses and quark mixing parameters in terms of not-so-hierarchical fundamental couplings. The model leads to the strange quark mass, ms ≈ 16 MeV at MZ, which is ~2.4σ away from its current central value. Large flavour violations are a generic prediction of the scheme which pushes the masses of the new gauge bosons to 103 TeV or higher. [ABSTRACT FROM AUTHOR]

A search is performed for a heavy particle decaying into different-flavour, dilepton final states, using 139 fb−1 of proton-proton collision data at s = 13 TeV collected in 2015–2018 by the ATLAS detector at the Large Hadron Collider. Final states with electrons, muons and hadronically decaying tau leptons are considered (eμ, eτ or μτ). No significant excess over the Standard Model predictions is observed. Upper limits on the production cross-section are set as a function of the mass of a Z′ boson, a supersymmetric τ-sneutrino, and a quantum black-hole. The observed 95% CL lower mass limits obtained on a typical benchmark model Z′ boson are 5.0 TeV (eμ), 4.0 TeV (eτ), and 3.9 TeV (μτ), respectively. [ABSTRACT FROM AUTHOR]

Motivated by a dynamical enhancement of the electromagnetic corrections by a power of ΛQCD/mb in Bd,s→ μ+μ− at next-to-leading order (NLO), we extend the QED factorization effects on the leptonic B meson decays with light muon leptons to tauonic final states, Bd,s→ τ+τ−, using soft-collinear effective theory (SCET). This extension is necessary owing to the appearance of the large τ mass, which will lead to different power counting in SCET and also different results. We provide a complete NLO electromagnetic corrections to Bd,s→ τ+τ−, which include hard functions and hard-collinear functions below the bottom quark mass scale μb. The power enhanced electromagnetic effects from hard-collinear contributions on Bd,s→ μ+μ− discussed before also exist in Bd,s→ τ+τ−. However the logarithm term arising from contributions of hard-collinear photon and lepton virtualities for Bd,s→ τ+τ− is not large as it is in muon case due to the hard-collinear scale of τ mass, which lead to only approximately 0.04% QED corrections to the branching fraction of Bd,s→ τ+τ− compared with overall reduction about 0.5% in Bd,s→ μ+μ−. [ABSTRACT FROM AUTHOR]

The rare decays, K+→π+νν¯, B+→π+νν¯ and D+→π+νν¯, are investigated in the frame work of nonstandard neutrino interactions (NSI). It is claimed that NSI are arising due to non-universality of the leptons and bounds on NSI parameters ϵll‧uL are determined. For this purpose, the branching ratios (Br) of these processes with in the Standard Model (SM) and beyond the SM are calculated by applying the non-universality of the leptons. The NSI in K+→π+νν¯ and B+→π+νν¯ proceed with u quark in the loop while other two with d quark in the loop. Very stringent 1 σ level constrains on non-standard parameters (ϵττuL and ϵτl‧uL) are pointed out. [ABSTRACT FROM AUTHOR]

Motivated by a dynamical enhancement of the electromagnetic corrections by a power of ΛQCD/mb in Bd,s→ μ+μ− at next-to-leading order (NLO), we extend the QED factorization effects on the leptonic B meson decays with light muon leptons to tauonic final states, Bd,s→ τ+τ−, using soft-collinear effective theory (SCET). This extension is necessary owing to the appearance of the large τ mass, which will lead to different power counting in SCET and also different results. We provide a complete NLO electromagnetic corrections to Bd,s→ τ+τ−, which include hard functions and hard-collinear functions below the bottom quark mass scale μb. The power enhanced electromagnetic effects from hard-collinear contributions on Bd,s→ μ+μ− discussed before also exist in Bd,s→ τ+τ−. However the logarithm term arising from contributions of hard-collinear photon and lepton virtualities for Bd,s→ τ+τ− is not large as it is in muon case due to the hard-collinear scale of τ mass, which lead to only approximately 0.04% QED corrections to the branching fraction of Bd,s→ τ+τ− compared with overall reduction about 0.5% in Bd,s→ μ+μ−. [ABSTRACT FROM AUTHOR]

In this paper, we elaborate on the new understanding of the cosmological constant and the gauge hierarchy problems in the context of string theory in its metastring formulation, based on the concepts of modular spacetime and Born geometry. The interplay of phase space (and Born geometry), the Bekenstein bound, the mixing between ultraviolet (UV) and infrared (IR) physics and modular invariance in string theory is emphasized. This new viewpoint is fundamentally rooted in quantum contextuality and not in statistical observer bias (anthropic principle). We also discuss the extension of this point of view to the problem of masses of quarks and leptons and their respective mixing matrices. [ABSTRACT FROM AUTHOR]

In this work, we report on the sensitivity potential of complementary muon-on-target experiments to new physics using a scalar boson benchmark model associated with charged lepton flavor violation. The NA64 μ experiment at CERN uses a 160-GeV energy muon beam with an active target to search for excess events with missing energy and momentum as a probe of new physics. At the same time, the proton beam at Fermilab, which is used to produce the neutrino beam for the Deep Underground Neutrino Experiment (DUNE), will also produce a high-intensity muon beam dumped in an absorber. Combined with the liquid argon near detector, the system could be used to search for similar scalar boson particles with a lower-energy but higher-intensity beam. We find that both NA64 μ and DUNE could cover new, unexplored parts of the parameter space of the same benchmark model, providing a complementary way to search for new physics. [ABSTRACT FROM AUTHOR]

Inspired by recent anomalies associated with the b hadron decays, a theoretical investigation on B d (s) ∗ → D d + (D s +) τ − v ̄ τ decays has been performed in W ′ model and scalar leptoquark model. To implicate these models, new coupling parameters are fixed by χ 2 fitting using recent experimental results from b → c τ v ̄ τ transition as constraints. We have estimated branching fraction, lepton flavor universality (LFU) parameter, forward–backward asymmetry and lepton-spin asymmetry in the standard model (SM) as well as above two new physics (NP) models. Except lepton-spin asymmetry, significant deviations from the SM predictions are observed in W ′ model for both channels. In comparison to other observables, lepton-spin asymmetry shifts slightly from the SM in scalar leptoquark model. Our results may be helpful to the experimental communities to explore these decays and W ′ boson and leptoquark at the colliders. [ABSTRACT FROM AUTHOR]