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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.

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.

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.

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).

There is a widely held belief that conformal field theories (CFTs) require zero beta functions. Nevertheless, the work of Jack and Osborn implies that the beta functions are not actually the quantites that decide conformality, but until recently no such behavior had been exhibited. Our recent work has led to the discovery of CFTs with nonzero beta functions, more precisely CFTs that live on recurrent trajectories, e.g., limit cycles, of the beta-function vector field. To demonstrate this we study the S function of Jack and Osborn. We use Weyl consistency conditions to show that it vanishes at fixed points and agrees with the generator Q of limit cycles on them. Moreover, we compute S to third order in perturbation theory, and explicitly verify that it agrees with our previous determinations of Q. A byproduct of our analysis is that, in perturbation theory, unitarity and scale invariance imply conformal invariance in four-dimensional quantum field theories. Finally, we study some properties of these new, "cyclic" CFTs, and point out that the a-theorem still governs the asymptotic behavior of renormalization-group flows. © 2013 SISSA.

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.

The running of quantum field theories can be studied in detail with the use of a local renormalization group equation. The usual beta-function effects are easy to include, but by introducing spacetime-dependence of the various parameters of the theory one can efficiently incorporate renormalization effects of composite operators as well. An illustration of the power of these methods was presented by Osborn in the early 90s, who used consistency conditions following from the Abelian nature of the Weyl group to rederive Zamolodchikov's c-theorem in d = 2 spacetime dimensions, and also to obtain a perturbative a-theorem in d = 4. In this work we present an extension of Osborn's work to d = 6 and to general even d. We compute the full set of Weyl consistency conditions, and we discover among them a candidate for an a-theorem in d = 6, similar to the d = 2, 4 cases studied by Osborn. Additionally, we show that in any even spacetime dimension one finds a consistency condition that may serve as a generalization of the c-theorem, and that the associated candidate c-function involves the coefficient of the Euler term in the trace anomaly. Such a generalization hinges on proving the positivity of a certain "metric" in the space of couplings. © 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 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.