Search

Abstract We consider the possibility that the neutral-current B anomalies are due to radiative corrections generated by Yukawa interactions of quarks and leptons with new vector-like quark and lepton electroweak doublets and new Standard Model singlet scalars. We show that the restricted interactions needed can result from an underlying Abelian family symmetry and that the same symmetry can give rise to an acceptable pattern of quark and charged lepton masses and mixings, providing a bridge between the non-universality observed in the B-sector and that of the fermion mass matrices. We construct two simple models, one with a single singlet scalar in which the flavour changing comes from quark and lepton mixing and one with an additional scalar in which the flavour changing can come from both fermion and scalar mixing. We show that for the case the new quarks are much heavier than the new leptons and scalars the B anomalies can be due to box diagrams with couplings in the perturbative regime consistent with the bounds coming from $$ {B}_s-{\overline{B}}_s $$ B s − B ¯ s , $$ K-\overline{K} $$ K − K ¯ and $$ D-\overline{D} $$ D − D ¯ mixing as well as other lepton family number violating processes. The new states can be dark matter candidates and, in the two scalar model with a light scalar of O(60) GeV and vector-like lepton of O(100) GeV, there can be a simultaneous explanation of the B-anomalies, the muon anomalous magnetic moment and the dark matter abundance.

We briefly comment on the paper by Albaladejo et al. [arXiv:1709.09101],rejecting its conclusions.

Tests of lepton-universality as rate ratios in b→sℓℓ transitions can be predicted very accurately in the Standard Model. The deficits with respect to expectations reported by the LHCb experiment in muon-To-electron ratios of the B→K(∗)ℓℓ decay rates thus point to genuine manifestations of lepton nonuniversal new physics. In this paper, we analyze these measurements in the context of effective field theory. First, we discuss the interplay of the different operators in RK and RK∗ and provide predictions for RK∗ in the Standard Model and in new-physics scenarios that can explain RK. We also provide approximate numerical formulas for these observables in bins of interest as functions of the relevant Wilson coefficients. Secondly, we perform frequentist fits to RK and RK∗. The Standard Model disagrees with these measurements at 3.7σ significance. We find excellent fits in scenarios with combinations of O9(10)ℓ=s γμbLℓγμ(γ5)ℓ operators, with pulls relative to the Standard Model in the region of 4σ. An important conclusion of our analysis is that a lepton-specific contribution to O10 is important to understand the data. Under the hypothesis that new-physics couples selectively to the muons, we also present fits to other b→sμμ data with a conservative error assessment and comment on more general scenarios. Finally, we discuss new lepton universality ratios that, if new physics is the origin of the observed discrepancy, should contribute to the statistically significant discovery of new physics in the near future.

The gauging of the lepton flavour group is considered in the Standard Modelcontext and in its extension with three right-handed neutrinos. The anomalycancellation conditions lead to a Seesaw mechanism as underlying dynamics forall leptons; requiring in addition a phenomenologically viable setup leads toMajorana masses for the neutral sector: the type I Seesaw Lagrangian in theStandard Model case and the inverse Seesaw in the extended model. Within theminimal extension of the scalar sector, the Yukawa couplings are promoted toscalar fields in the bifundamental of the flavour group. The resultinglow-energy Yukawa couplings are proportional to inverse powers of the vacuumexpectation values of those scalars; the protection against flavour changingneutral currents differs from that of Minimal Flavor Violation. In all cases,the $\mu-\tau$ flavour sector exhibits rich and promising phenomenologicalsignals.

We investigate the decays of the excited (bq[over ¯]) mesons as probes of the short-distance structure of the weak ΔB=1 transitions. These states are unstable under the electromagnetic or strong interactions, although their widths are typically suppressed by phase space. Compared to the pseudoscalar B meson, the purely leptonic decays of the vector B^{*} are not chirally suppressed and are sensitive to different combinations of the underlying weak effective operators. An interesting example is B_{s}^{*}→ℓ^{+}ℓ^{-}, which has a rate that can be accurately predicted in the standard model. The branching fraction is B∼10^{-11}, irrespective of the lepton flavor and where the main uncertainty stems from the unmeasured and theoretically not well known B_{s}^{*} width. We discuss the prospects for producing this decay mode at the LHC and explore the possibility of measuring the B_{s}^{*}→ℓℓ amplitude, instead, through scattering experiments at the B_{s}^{*} resonance peak.

The model-independent parametrization for exclusive hadronic form factors commonly used for semileptonic decays is generalized to allow for the inclusion of above-threshold resonant poles of known mass and width. We discuss the interpretation of such poles, particularly with respect to the analytic structure of the relevant two-point Green's function in which they reside. Their presence has a remarkably small effect on the parametrization, as we show explicitly for the case of D→πe+νe.

Abstract: We derive the decay rate of an unstable phase of a quantum field theory in the presence of an impurity in the thin-wall approximation. This derivation is based on the how the impurity changes the (flat spacetime) geometry relative to case of pure false vacuum. Two examples are given that show how to estimate some of the additional parameters that enter into this heterogeneous decay rate. This formalism is then applied to the Higgs vacuum of the Standard Model (SM), where baryonic matter acts as an impurity in the electroweak Higgs vacuum. We find that the probability for heterogeneous vacuum decay to occur is suppressed with respect to the homogeneous case. That is to say, the conclusions drawn from the homogeneous case are not modified by the inclusion of baryonic matter in the calculation. On the other hand, we show that Beyond the Standard Model physics with a characteristic scale comparable to the scale that governs the homogeneous decay rate in the SM, can in principle lead to an enhanced decay rate.

Abstract: Anomalies in semileptonic B-meson decays present interesting patterns that might be revealing the shape of the new physics to come. Under the assumption that neutrino and charged lepton mass terms are the only sources of flavor violation and given the hierarchy between the two, we find that charged lepton universality violation without charged lepton flavor violation naturally arises. This can account for a deficit of B+ → K+μμ over B+ → K+ee decays with new physics coupled predominantly to muons and a new physics scale of a few TeV. A generic prediction of this scenario is a large enhacement of tauonic B decay rates that, in particular, could accommodate an excess in B → D(∗)τ ν. For the most part, the study is carried out in an effective field theory framework with an underlying SU(2)L × U(1)Y symmetry that emphasizes the model-independent correlations between low- and high-energy observables. As an example, a connection between B-decays and top physics is pointed out. To complement the discussion, all possible (spin 0 and 1) leptoquark models are matched to the low-energy field theory so that the effective analysis can be used to survey these candidates for new physics.

New physics effects in B decays are routinely modeled through operators invariant under the strong and electromagnetic gauge symmetries. Assuming the scale for new physics is well above the electroweak scale, we further require invariance under the full standard model gauge symmetry group. Retaining up to dimension-six operators, we unveil new constraints between different new physics operators that are assumed to be independent in the standard phenomenological analyses. We illustrate this approach by analyzing the constraints on new physics from rare Bq (semi-)leptonic decays.

New physics effects in B decays are routinely modeled through operators invariant under the strong and electromagnetic gauge symmetries. Assuming the scale for new physics is well above the electroweak scale, we further require invariance under the full standard model gauge symmetry group. Retaining up to dimension-six operators, we unveil new constraints between different new physics operators that are assumed to be independent in the standard phenomenological analyses. We illustrate this approach by analyzing the constraints on new physics from rare Bq (semi-)leptonic decays.

We perform an isospin analysis of B decays to two pseudoscalars. The analysis extracts appropriate Cabbibo-Kobayashi-Maskawa matrix elements and short distance loop factors to allow for comparison of nonperturbative QCD effects in the reduced matrix elements of the amplitudes. In decays where penguin diagrams compete with tree-level diagrams we find that the reduced matrix elements of the penguin diagrams, which are singlets or doublets under isospin, are significantly enhanced compared with the triplet and fourplet contributions of the weak Hamiltonian. This similarity to the ΔI=12 rule in K→ππ decays suggests that, more generally, processes mediated by Hamiltonians in lower-dimensional isospin representations see enhancement over higher-dimensional ones in QCD. © 2014 American Physical Society.

We present a sum rule for Higgs fields in general representations under SU(2) L × U(1) Y that follows from the connection between the Higgs couplings and the mechanism that gives the electroweak bosons their masses, and at the same time restricts these couplings. Sum rules that follow from perturbative unitarity will require us to include singly and doubly charged Higgses in our analysis. We examine the consequences of these sum rules for Higgs phenomenology in both model independent and model specific ways. The relation between our sum rules and other works, based on dispersion relations, is also clarified. © 2014 The Author(s).

We analyze the Type-II two Higgs doublets model in light of the newly discovered Higgs-like particle with mass 125 GeV. The observed 125 GeV particle is identified with the light CP-even Higgs boson in the two Higgs doublets model. We study the parameter space of the model consistent with the Higgs data, branching ratio of B̄ → X s γ as well as precision electroweak measurements. We also incorporate theoretical constraints - perturbativity of the couplings and vacuum stability, in our study. We find that only a small parameter space of the model remains viable. The phenomenology of the heavy Higgs bosons in the surviving parameter space is studied. © 2013 SISSA, Trieste, Italy.

We show that the three-body decays of the resonance recently discovered at the LHC are potentially sensitive to efects of new physics. Even if the fully integrated partial decay widths are consistent with the minimal Standard Model there is information that is lost upon integration, which can be uncovered in the diferential decay widths. oncentrating on the decay h→Zll, we identify the regions in the three-body phase space in which these efects become especially pronounced and could be detected in future experiments. © SISSA 2013.

We present an example of a limit cycle, i.e., a recurrent flow-line of the beta-function vector field, in a unitary four-dimensional gauge theory. We thus prove that beta functions of four-dimensional gauge theories do not produce gradient flows. The limit cycle is established in perturbation theory with a three-loop calculation which we describe in detail. © 2012 SISSA, Trieste, Italy.

We develop a formalism for constructing the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix and neutrino masses using an expansion that originates when a sequence of heavy right handed neutrinos are integrated out, assuming a seesaw mechanism for the origin of neutrino masses. The expansion establishes relationships between the structure of the PMNS matrix and the mass differences of neutrinos, and allows symmetry implications for measured deviations from tri-bimaximal form to be studied systematically. Our approach does not depend on choosing the rotation between the weak and mass eigenstates of the charged lepton fields to be diagonal. We comment on using this expansion to examine the symmetry implications of the recent results from the Daya-Bay collaboration reporting the discovery of a non zero value for θ13, indicating a deviation from tri-bimaximal form, with a significance of 5.2σ.

We explore phenomenological consequences of coupling a non-conformal scale-invariant theory to the standard model. We point out that, under certain circumstances, non-conformal scale-invariant theories have oscillating correlation functions which can dramatically modify standard model processes. We dub this scenario cyclic unparticle physics, or simply cyclunparticle physics. We compute phase spaces and amplitudes associated with final state cyclunparticle and cyclunparticle exchange, respectively. We show detailed formulae in a simple example. © 2012.

We show that the anomalously large top quark forward-backward asymmetry observed by CDF and DØ can naturally be accommodated in models with flavor-violating couplings of a new massive spin-2 state to quarks. Regardless of its origin, the lowest-order couplings of a spin-2 boson to fermions are analogous to the coupling of the graviton to energy/momentum, leading to strong sensitivity of the effects associated with its virtual exchange to the energy scales at hand. Precisely due to this fact, the observed dependence of the asymmetry on the tt invariant mass fits nicely into the proposed framework. In particular, we find a vast parameter space which can lead to the central value for the observed forward-backward asymmetry in the high mass bin. © 2012 SISSA.

We carry out a three-loop computation that establishes the existence of scale without conformal invariance in dimensional regularization with the MS scheme in unitary theories in d = 4 - ε spacetime dimensions. We also comment on the effects of scheme changes in theories with many couplings, as well as in theories that live on non-conformal scale-invariant renormalization group trajectories. Stability properties of such trajectories are analyzed, revealing both attractive and repulsive directions in a specific example. We explain how our results are in accord with those of Jack & Osborn on a c-theorem in d = 4 (and d = 4-ε) dimensions. Finally, we point out that limit cycles with turning points are unlike limit cycles with continuous scale invariance. © 2012 SISSA.

We present the theoretical underpinnings of scale without conformal invariance in quantum field theory. In light of our results the gradient-flow interpretation of renormalization-group (RG) flow is challenged, due to deep connections between scaleinvariant theories and recurrent behaviors in the RG. We show that, on scale-invariant trajectories, there is a redefinition of the dilatation current that leads to generators of dilatations that generate dilatations. Finally, we develop a systematic algorithm for the search of scale-invariant trajectories in perturbation theory. © SISSA 2012.

We discuss the phenomenology of effective field theories with new scalar or vector representations of the Standard Model quark avor symmetry group, allowing for large avor breaking involving the third generation. Such field content can have a relatively low mass scale ≲ TeV and O(1) couplings to quarks, while being naturally consistent with both avor violating and avor diagonal constraints. These theories therefore have the potential for early discovery at LHC, and provide a avor safe \tool box" for addressing anomalies at colliders and low energy experiments. We catalogue the possible avor symmetric representations, and consider applications to the anomalous Tevatron t t̄ forward backward asymmetry and Bs mixing measurements, individually or concurrently. Collider signatures and constraints on avor symmetric models are also studied more generally. In our examination of the t t̄ forward backward asymmetry we determine model independent acceptance corrections appropriate for comparing against CDF data that can be applied to any model seeking to explain the t t̄, forward backward asymmetry. © 2011 SISSA.

Electroweak precision data constraints on avor symmetric vector fields are determined. The avor multiplets of spin one that we examine are the complete set of fields that couple to quark bi-linears at tree level while not initially breaking the quark global avor symmetry group. Flavor safe vector masses proximate to, and in some cases below, the electroweak symmetry breaking scale are found to be allowed. Many of these fields provide a avor safe mechanism to explain the tt forward backward anomaly, and can simultaneously significantly raise the allowed values of the Standard Model Higgs mass consistent with electroweak precision data. © SISSA 2011.

We give an explicit example of a model in D=4-ε space-time dimensions that is scale but not conformally invariant, is unitary, and has finite correlators. The invariance is associated with a limit cycle renormalization group (RG) trajectory. We also prove, to second order in the loop expansion, in D=4-ε, that scale implies conformal invariance for models of any number of real scalars. For models with one real scalar and any number of Weyl spinors we show that scale implies conformal invariance to all orders in perturbation theory. © us-gov 2011.

We consider for the first time flavor changing neutral currents (FCNC's) in the infall stage of stellar collapse. We take as an example R-Parity violating interactions of the minimal standard supersymmetric model involving neutrinos and quarks. However, our considerations extend to other kinds of flavor changing neutrino reactions as well. We examine non-forward neutrino scattering processes on heavy nuclei and free nucleons in the supernova core. This investigation has led to four principal original discoveries/products: (1) first calculation of neutrino flavor changing cross sections for spin 1/2 (e.g., free nucleon) and spin 0 nuclear targets; (2) discovery of nuclear mass number squared (A2) coherent amplification of neutrino-quark FCNC's; (3) analysis of FCNC-induced alteration of electron capture and weak/nuclear equilibrium in the collapsing core; and (4) generalization of the calculated cross sections (mentioned in 1) for the case of hot heavy nuclei to be used in collapse/supernova and neutrino transport simulations. The scattering processes that we consider allow electron neutrinos to change flavor during core collapse, thereby opening holes in the Ve sea, which allows electron capture to proceed and results in a lower core electron fraction Ye. A lower Ye implies a lower homologous core mass, a lower shock energy, and a greater nuclear photo-disintegration burden for the shock. In addition, unlike the standard supernova model, the core now could have net muon and/or tau lepton numbers. These effects could be significant even for supersymmetric couplings below current experimental bounds. © 2005 Elsevier B.V. All rights reserved.

The Proceedings of the 2003 SLAC Workshops on flavor physics with a highluminosity asymmetric e+e- collider. The sensitivity of flavor physics tophysics beyond the Standard Model is addressed in detail, in the context of theimprovement of experimental measurements and theoretical calculations.