Universality Violation Research Articles

Corrigendum

Koehler, M. J., Arnold, B., Greenhalgh, S. P., Boltz, L. O., & Burdell, G. P. (2017). A taxonomy approach to studying how gamers review games. Simulation & Gaming, 48(3). doi:10.1177/1046878117703680 The above article has been revised as follows: listed author, “George P. Burdell” has been removed, including the references to author affiliation and author biography originally included for Burdell. It was brought to the attention of the journal that this reference is not to an actual person, and therefore no contributions were made by George P. Burdell. Corresponding author, Dr. Matthew Koehler, responded to the Publisher’s queries about Burdell by stating Dr. Koehler added the reference to the fictitious co-author with the intent of creating an “academic Easter-egg” for readers. Dr. Koehler further provided assurances that no similar assertions were made that impacted the data and findings of the article. Given the unusual nature of this event, the Editors and Publisher wanted to include an additional comment on behalf of the journal. Knowingly providing false information in relation to an article, including the authorship of the article, is a universal violation of the codes of ethics authors are expected to follow, including COPE standards. Further, signing a contract that includes information the author knows to be false is a violation of ethics codes and may additionally raise legal issues such as breach of warranties. Simulation & Gaming, like all scholarly journals, relies on authors to provide truthful information. The Editors have spent significant time considering the potential harm of “pranks”, however innocently intended, on the credibility of the journal, and more generally, on the credibility of scholarly research. To have value and usefulness to society, the scholarly research system must be trustworthy. The journal’s aim is to publish articles that contribute to the development of knowledge around simulation and gaming methodologies, including the practical application of this knowledge to real-world problems. Any compromise of the journal’s credibility that might impair this aim clearly is of serious concern to us, and we deeply regret the publication of inaccurate information in the journal.

High- $$p_T$$ p T dilepton tails and flavor physics

We investigate the impact of flavor-conserving, non-universal quark-lepton contact interactions on the dilepton invariant mass distribution in p~p rightarrow ell ^+ ell ^- processes at the LHC. After recasting the recent ATLAS search performed at 13 TeV with 36.1 fb^{-1} of data, we derive the best up-to-date limits on the full set of 36 chirality-conserving four-fermion operators contributing to the processes and estimate the sensitivity achievable at the HL-LHC. We discuss how these high-p_T measurements can provide complementary information to the low-p_T rare meson decays. In particular, we find that the recent hints on lepton-flavor universality violation in b rightarrow s mu ^+ mu ^- transitions are already in mild tension with the dimuon spectrum at high-p_T if the flavor structure follows minimal flavor violation. Even if the mass scale of new physics is well beyond the kinematical reach for on-shell production, the signal in the high-p_T dilepton tail might still be observed, a fact that has been often overlooked in the present literature. In scenarios where new physics couples predominantly to third generation quarks, instead, the HL-LHC phase is necessary in order to provide valuable information.

Semileptonic B -physics anomalies: A general EFT analysis within U(2)n flavor symmetry

We analyse the recent hints of Lepton Flavor Universality violations in semi-leptonic $B$ decays within a general EFT based on a $U(2)^n$ flavor symmetry acting on the light generations of SM fermions. We analyse in particular the consistency of these anomalies with the tight constraints on various low-energy observables in $B$ and $\tau$ physics. We show that, with a moderate fine-tuning, a consistent picture for all low-energy observables can be obtained under the additional dynamical assumption that the NP sector is coupled preferentially to third generation SM fermions. We discuss how this dynamical assumption can be implemented in general terms within the EFT, and we identify a series of observables in $\tau$ decays which could provide further evidences of this NP framework.

Lepton-flavor universality violation in RK and {R}_{D^{{}_{left(ast right)}}} from warped space

Some anomalies in the processes b → sℓℓ (ℓ = μ, e) and bto cell {overline{nu}}_{ell } (ℓ = τ, μ, e), in particular in the observables RK and {R}_{D^{{}_{left(ast right)}}} , have been found by the BaBar, LHCb and Belle collaborations, leading to a possible lepton flavor universality violation. If these anomalies were confirmed they would inevitably lead to physics beyond the Standard Model. In this paper we try to accommodate the present anomalies in an extra dimensional theory, solving the naturalness problem of the Standard Model by means of a warped metric with a strong conformality violation near the infra-red brane. The RK anomaly can be accommodated provided that the left-handed bottom quark and muon lepton have some degree of compositeness in the dual theory. The theory is consistent with all electroweak and flavor observables, and with all direct searches of Kaluza-Klein electroweak gauge bosons and gluons. The fermion spectrum, and fermion mixing angles, can be reproduced by mostly elementary right-handed bottom quarks, and tau and muon leptons. Moreover the {R}_{D^{{}_{left(ast right)}}} anomaly requires a strong degree of compositeness for the left-handed tau leptons, which turns out to be in tension with experimental data on the {g}_{tau_L}^Z coupling, possibly unless some degree of fine-tuning is introduced in the fixing of the CKM matrix.

Assessing lepton-flavour non-universality from B → K*ℓℓ angular analyses

The recent years of activity at the LHC have brought to light several anomalies in exclusive semileptonic b → sℓ+ℓ− decays. Even though the latest model independent analyses are pointing to sizable New Physics contributions to different Wilson coefficients (especially C9), the possibility of interpreting these results unambiguously in terms of New Physics is spoilt by non-perturbative QCD corrections entering at amplitude level. In this proceeding, we present a brief summary of the latest results of our global fits. Also, the origin of the above mentioned QCD corrections, plus their interplay with possible New Physics contributions, is shortly reviewed. A discussion about the properties of the observable RK leads to the central part of this work: the proposal of a new set of observables able to test for lepton-flavour universality violation, where hadronic uncertainties cancel (in the Standard Model). To conclude, the properties of these observables are analysed within the Standard Model as well as within several New Physics benchmark scenarios.

Status of the Brightarrow K^*mu ^+mu ^- anomaly after Moriond 2017

Motivated by recent results by the ATLAS and CMS collaborations on the angular distribution of the B rightarrow K^* mu ^+mu ^- decay, we perform a state-of-the-art analysis of rare B meson decays based on the b rightarrow s mu mu transition. Using standard estimates of hadronic uncertainties, we confirm the presence of a sizeable discrepancy between data and SM predictions. We do not find evidence for a q^2 or helicity dependence of the discrepancy. The data can be consistently described by new physics in the form of a four-fermion contact interaction (bar{s} gamma _alpha P_L b)(bar{mu }gamma ^alpha mu ). Assuming that the new physics affects decays with muons but not with electrons, we make predictions for a variety of theoretically clean observables sensitive to violation of lepton flavour universality.

Y and \u03c8 leptonic decays as probes of solutions to the R(D(*)) puzzle

Experimental measurements of the ratios Rleft({D}^{left(ast right)}right)equiv frac{Gamma left(Bto {D}^{left(*right)}tau vright)}{Gamma left(Bto {D}^{left(*right)}ell vright)}left(ell =e,mu right) show a 3.9σ deviation from the Standard Model prediction. In the absence of light right-handed neutrinos, a new physics contribution to b → cτν decays necessarily modifies also boverline{b}to {tau}^{+}{tau}^{-} and/or coverline{c}to {tau}^{+}{tau}^{-} transitions. These contributions lead to violation of lepton flavor universality in, respectively, Y and ψ leptonic decays. We analyze the constraints resulting from measurements of the leptonic vector-meson decays on solutions to the R(D(*)) puzzle. Available data from BaBar and Belle can already disfavor some of the new physics explanations of this anomaly. Further discrimination can be made by measuring Y(1S, 2S, 3S) → ττ in the upcoming Belle II experiment.

R(D) and R(D*) anomalies and their phenomenological implications

Recently, BaBar, Belle and LHCb have found hints of lepton flavour universality violation in B→D(⁎)τν‾τ decays, i.e., the measured ratios R(D(⁎))=B(B→D(⁎)τν‾τ)/B(B→D(⁎)ℓν‾ℓ)(ℓ=e/μ) show a combined 3.8 σ deviation from the SM predictions. In this talk, we will discuss two possible solutions to the observed R(D) and R(D*) anomalies: one with an EW-scale charged scalar and the other with a TeV-scale scalar leptoquark transforming as (3, 1, −13) under the SM gauge group. Their phenomenological implications for the other decays are also briefly discussed.

A flavor-safe composite explanation of RK

In these proceedings we discuss a flavor-safe explanation of the anomaly found in RK=B(B→Kμ+μ−)/B(B→Ke+e−) by LHCb, within the framework of composite Higgs models. We present a model featuring a non-negligible degree of compositeness for all three generations of right-handed leptons, which leads to a violation of lepton-flavor universality in neutral current interactions while other constraints from quark- and lepton-flavor physics are met. Moreoever, the particular embedding of the lepton sector considered in this setup provides a parametrically enhanded contribution to the Higgs mass that can weak considerably the need for ultra-light top partners.

Neutrino mixing and RK anomaly in U(1)X models: a bottom-up approach

We identify a class of U(1)X models which can explain the RK anomaly and the neutrino mixing pattern, by using a bottom-up approach. The different X-charges of lepton generations account for the lepton universality violation required to explain RK . In addition to the three right-handed neutrinos needed for the Type-I seesaw mechanism, these minimal models only introduce an additional doublet Higgs and a singlet scalar. While the former helps in reproducing the quark mixing structure, the latter gives masses to neutrinos and the new gauge boson Z′. Our bottom-up approach determines the X-charges of all particles using theoretical consistency and experimental constraints. We find the parameter space allowed by the constraints from neutral meson mixing, rare b → s decays and direct collider searches for Z′. Such a Z′ may be observable at the ongoing run of the Large Hadron Collider with a few hundred fb−1 of integrated luminosity.

Consequences of R-parity violating interactions for anomalies in {bar{B}}rightarrow D^{(*)} tau {bar{nu }} and brightarrow s mu ^+mu ^-

We investigate the possibility of explaining the enhancement in semileptonic decays of {bar{B}} rightarrow D^{(*)} tau {bar{nu }}, the anomalies induced by brightarrow smu ^+mu ^- in {bar{B}}rightarrow (K, K^*, phi )mu ^+mu ^- and violation of lepton universality in R_K = mathrm{Br}({bar{B}}rightarrow K mu ^+mu ^-)/mathrm{Br}({bar{B}}rightarrow K e^+e^-) within the framework of R-parity violating MSSM. The exchange of down type right-handed squark coupled to quarks and leptons yields interactions which are similar to leptoquark induced interactions that have been proposed to explain the {bar{B}} rightarrow D^{(*)} tau {bar{nu }} by tree level interactions and brightarrow s mu ^+mu ^- anomalies by loop induced interactions, simultaneously. However, the Yukawa couplings in such theories have severe constraints from other rare processes in B and D decays. Although this interaction can provide a viable solution to the R(D^{(*)}) anomaly, we show that with the severe constraint from {bar{B}} rightarrow K nu {bar{nu }}, it is impossible to solve the anomalies in the brightarrow s mu ^+mu ^- process simultaneously.

Impact of lepton flavor universality violation on CP-violation sensitivity of long-baseline neutrino oscillation experiments

The observation of neutrino oscillation as well as the recent experimental results on lepton flavor universality (LFU) violation in B meson decays are indications of new physics beyond the standard model. Many theoretical models, which are introduced in the literature as an extension of SM to explain these observed deviations in LFU, lead to a new kind of interactions, the so-called non-standard interaction (NSI) between the elementary particles. In this paper, we consider a model with an additional Z' boson (which is quite successful in explaining the observed LFU anomalies) and analyze its effect in the lepton flavor violating (LFV) B_drightarrow tau ^pm e^mp decay modes. From the present upper bound of the B_drightarrow tau ^pm e^mp branching ratio, we obtain the constraints on the new physics parameters, which are related to the corresponding NSI parameters in the neutrino sector by SU(2)_L symmetry. These new parameters are expected to have potential implications in the neutrino oscillation studies and in this work we investigate the possibility of observing the effects of these interactions in the currently running and upcoming long-baseline experiments, i.e., NOnu A and DUNE, respectively.

Probing lepton flavour (universality) violation at NA62 and future kaon experiments

Recent results from the LHC’s first run have revealed intriguing departures from lepton flavour universality in the semi-leptonic decays of B-mesons. We discuss the complementary role that rare kaon decays can provide in testing new physics explanations of these flavour anomalies. In the framework of minimal flavour violation, we relate the chiral low-energy constants involved in and with the new physics Wilson coefficients of the b → s effective Hamiltonian. We comment on the determination of these low-energy constants at NA62 and future kaon experiments, as well as the required improvements in sensitivity necessary to test the B-physics anomalies in the kaon sector.

Rare B Decays And Lepton Flavour Universality Tests at LHCb

In the lepton sector the Standard Model incorporates both lepton-flavour and lepton-number universality. In a generic New Physics scenario this is not necessarily the case and these symmetries need to be experimentally tested. Numerous searches have failed to find any signs of Lepton Flavour Violation (LFU) or Lepton Flavour Universality Violation (LFUV). New Physics could, however, generate LFUV in the heavy flavour sector where the existing experimental constraints are weaker. Recent searches at LHCb focus on precisely this unexplored territory by studying the B decays involving b → cτυ and b → sl+l− transitions. Several theoretically and experimentally clean observables, such as R(D*) or R(K), diverge from the Standard Model predictions and could be the first signs of LFUV.

A violation of universality in anomalous Fourier's law.

Since the discovery of long-time tails, it has been clear that Fourier’s law in low dimensions is typically anomalous, with a size-dependent heat conductivity, though the nature of the anomaly remains puzzling. The conventional wisdom, supported by renormalization-group arguments and mode-coupling approximations within fluctuating hydrodynamics, is that the anomaly is universal in 1d momentum-conserving systems and belongs in the Lévy/Kardar-Parisi-Zhang universality class. Here we challenge this picture by using a novel scaling method to show unambiguously that universality breaks down in the paradigmatic 1d diatomic hard-point fluid. Hydrodynamic profiles for a broad set of gradients, densities and sizes all collapse onto an universal master curve, showing that (anomalous) Fourier’s law holds even deep into the nonlinear regime. This allows to solve the macroscopic transport problem for this model, a solution which compares flawlessly with data and, interestingly, implies the existence of a bound on the heat current in terms of pressure. These results question the renormalization-group and mode-coupling universality predictions for anomalous Fourier’s law in 1d, offering a new perspective on transport in low dimensions.

Phenomenology of an SU(2) × SU(2) × U(1) model with lepton-flavour non-universality

We investigate a gauge extension of the Standard Model in light of the observed hints of lepton universality violation in $b \to c \ell \nu$ and $b \to s \ell^+ \ell^-$ decays at BaBar, Belle and LHCb. The model consists of an extended gauge group $\mathrm{SU(2)}_{1} \times \mathrm{SU(2)}_{2} \times \mathrm{U(1)}_Y$ which breaks spontaneously around the TeV scale to the electroweak gauge group. Fermion mixing effects with vector-like fermions give rise to potentially large new physics contributions in flavour transitions mediated by $W^{\prime}$ and $Z^{\prime}$ bosons. This model can ease tensions in $B$-physics data while satisfying stringent bounds from flavour physics, tau decays, and electroweak precision data. Possible ways to test the proposed new physics scenario with upcoming experimental measurements are discussed. Among other predictions, the lepton flavour violating ratios $R_M$, with $M = K^*, \phi$, are found to be reduced with respect to the Standard Model expectation $R_M \simeq 1$.

Lμ−Lτ theory of Higgs flavor violation and (g−2)μ

Several experiments reported hints for the violation of lepton flavor or lepton flavor universality in processes involving muons. Most prominently, there is the hint for a non-zero rate of the flavor violating Higgs decay $h \to \tau\mu$ at the LHC, as well as the hint for lepton flavor universality violation in rare $B$ meson decays at LHCb. In addition, also the long standing discrepancy in the anomalous magnetic moment of the muon motivates new physics connected to muons. A symmetry which violates lepton flavor universality, is $L_\mu-L_\tau$: the difference of muon-number and tau-number. We show that adding vector-like fermions to a $L_\mu-L_\tau$ theory generates naturally an effect in the anomalous magnetic moment of the muon and $h\to\tau\mu$, while effects in other $\tau \to \mu$ transitions are systematically suppressed by symmetry arguments. We find that if $L_\mu-L_\tau$ is gauged it is possible to also accommodate the discrepant $b\to s\mu\mu$ data while predicting a $\tau\to3\mu$ and a modified $h\to\mu\mu$ rate within reach of upcoming experiments.

Confronting lepton flavor universality violation in B decays with high- p T tau lepton searches at LHC

We confront the indications of lepton flavor universality (LFU) violation observed in semi-tauonic $B$ meson decays with new physics (NP) searches using high $p_T$ tau leptons at the LHC. Using effective field theory arguments we correlate possible non-standard contributions to semi-tauonic charged currents with the $\tau^+ \tau^-$ signature at high energy hadron colliders. Several representative standard model extensions put forward to explain the anomaly are examined in detail: (i) weak triplet of color-neutral vector resonances, (ii) second Higgs doublet and (iii) scalar or (iv) vector leptoquark. We find that, in general, $\tau^+ \tau^-$ searches pose a serious challenge to NP explanations of the LFU anomaly. Recasting existing 8 TeV and 13 TeV LHC analyses, stringent limits are set on all considered simplified models. Future projections of the $\tau^+ \tau^-$ constraints as well as caveats in interpreting them within more elaborate models are also discussed.

Assessing lepton-flavour non-universality from B →K ∗ ℓℓ angular analyses

The B → K ∗ μμ decay exhibits deviations with respect to Standard Model expectations and the measurement of the ratio R K hints at a violation of lepton-flavour universality in B → Kll transitions. Both effects can be understood in model-independent fits as a short-distance contribution to the Wilson coefficient C 9μ , with some room for similar contributions in other Wilson coefficients for b → sμμ transitions. We discuss how a full angular analysis of B → K ∗ ee and its comparison with B → K ∗ μμ could improve our understanding of these anomalies and help confirming their interpretation in terms of short-distance New Physics. We discuss several observables of interest in this context and provide predictions for them within the Standard Model as well as within several New Physics benchmark scenarios. We pay special attention to the sensitivity of these observables to hadronic uncertainties from SM contributions with charm loops.

Proton fragmentation functions considering finite-mass corrections

We present new sets of proton fragmentation functions describing the production of protons from the gluon and each of the quarks, obtained by a global fit to all relevant data sets extracted from the single-inclusive electron-positron annihilation. Our analysis is in good agreement with $e^+e^-$ annihilation data. We also impose the finite-mass effects of proton in our calculations, a topic with a very little attention paid to in the literatures. Proton mass effects turn out to be appreciable for the gluon and light quark fragmentation functions, so the inclusion of finite-mass effects tends to improve the overall description of the data by reducing the minimized $\chi^2$ values, significantly. As an application, we also apply the extracted fragmentation functions to make our predictions for the scaled-energy distribution of protons inclusively produced in top quark decays at next-to-leading order, relying on the universality and scaling violations of fragmentation functions.