0000000000147675
AUTHOR
Francisco J. Botella
Tree-level flavor-changing neutral currents in theBsystem: FromCPasymmetries to rare decays
corresponding to 0.59 ≤ sin(2�) ≤ 0.82, which is cer- tainly outside the 1� Babar range but not outside the world average. This potential discrepancy is at the ori- gin of several papers (6) studying the implications of a small aJ/ in the search of new physics. In this paper, we analyze the implications of this situ- ation for a realistic model, obtained with the only addi- tion of an isosinglet down vector-like quark (7) to the SM spectrum. This model naturally arises, for instance, as the low-energy limit of an E6 grand unified theory. At a more phenomenological level, models with isosinglet quarks provide the simplest self-consistent framework to study deviations of 3 ×3 unitarity of the…
ϵ′/ϵ effects from time integrated coherent decays of in a φ-factory
We study the ϵ′/ϵ-effects from time integrated coherent decays of the K0 − K0-system in a φ-factory. A complete set of observables is presented. We paid special attention to backgrounds effects coming from the C = + state, both for Re(ϵ′/ϵ) and Im(ϵ′/ϵ).
B Physics: CP Violation Beyond the SM
We analyse the present experimental evidence for a complex CKM matrix, even allowing for New Physics contributions to ϵK, aJ/ΨKS%, ΔMBd, ΔMBs, and the ΔI=1/2 piece of and B→ρπ. We emphasize the crucial r\^{o}le played by the angle γ in both providing irrefutable evidence for a 3×3 complex CKM matrix and placing constraints on the size of NP contributions. It is shown that even if one allows for New Physics a real CKM matrix is excluded at a 99.92% C.L., and the probability for the phase γ to be in the interval [−170∘:−10∘]∪[10∘:170∘] is 99.7%. Large value of the phase χ, e.g. of order λ, is only possible in models where the unitarity of the 3×3 Cabibbo-Kobayashi-Maskawa matrix is violated t…
P-odd observables at the upsilon peak
We study the $\gamma$-Z interference in the process $e^+ e^-\to \Upsilon \to \tau^+ \tau^-$ as a means to measure the neutral current coupling of the b-quark. The helicity amplitudes are calculated from resonant and background diagrams and the spin density matrix of the final state is discussed. The spin analyzer of the $\tau$'s is illustrated with the decays $\pi \nu$ and $\rho \nu \to (\pi \pi) \nu$. With $10^8 \Upsilon$ a sensitivity to $g_V^b$ of a few per cent could be reachable.
Minimal Flavour Violation and Multi-Higgs Models
We propose an extension of the hypothesis of Minimal Flavour Violation (MFV) to general multi-Higgs models without the assumption of Natural Flavour Conservation (NFC) in the Higgs sector. We study in detail under what conditions the neutral Higgs couplings are only functions of V-CKM and propose a MFV expansion for the neutral Higgs couplings to fermions
Singlet Heavy Fermions as the Origin of B Anomalies in Flavour Changing Neutral Currents
We show that a simple extension of the Standard Model involving the introduction of vector-like quarks and heavy neutrinos, provides an explanation of the so called B-anomalies in $b\to s\ell\bar\ell$ transitions. Vector-like quarks can explain, in the context of a discrete flavour symmetry, all the relevant characteristics of the Cabibbo-Kobayashi-Maskawa sector. It is in this framework that we study the requirements on the masses of the vector like quarks and the heavy neutrinos leading to viable models with sufficient deviations of lepton flavour universality and which simultaneously avoid too large Flavour Changing Neutral Current effects. Related predictions on $b\to d\ell\bar\ell$ and…
Unitarity Triangles and the Search for New Physics
Assuming that the Kobayashi-Maskawa mechanism gives the dominant contribution to CP violation at low energies, we propose a novel way of testing the flavour sector of the Standard Model which has the potencial for discovering New Physics. Using 3 x 3 unitarity of the V_{CKM} matrix and choosing a complete set of rephasing invariant phases, we derive a set of exact relations in terms of measurable quantities, namely moduli of V_{CKM} and arguments of rephasing invariant quartets. These tests complement the usual analysis in the \rho, \eta plane and, if there is New Physics, may reveal its source.
Natural quasi-alignment with two Higgs doublets and RGE stability
In the context of two Higgs doublet models, we study the conditions required in order to have stable quasi-alignment in flavour space. We show that stability under the RGE imposes strong constraints on the flavour structure of the Yukawa couplings associated to each one of the Higgs doublets. In particular, we find a novel solution, where all Yukawa couplings are proportional to the so-called democratic matrix. This solution is rather unique, since it is the only stable solution which is a good starting point for reproducing the observed pattern of quark masses and mixing. We also show that this stable solution can be obtained by imposing on the Lagrangian a $Z_3 \times Z^\prime_3$ flavour …
Invariant approach to flavor-dependent CP-violating phases in the MSSM
We use a new weak basis invariant approach to classify all the observable phases in any extension of the Standard Model (SM). We apply this formalism to determine the invariant CP phases in a simplified version of the Minimal Supersymmetric SM with only three non-trivial flavour structures. We propose four experimental measures to fix completely all the observable phases in the model. After these phases have been determined from experiment, we are able to make predictions on any other CP-violating observable in the theory, much in the same way as in the Standard Model all CP-violation observables are proportional to the Jarlskog invariant.
Dynamical zeros in neutrino-electron elastic scattering at leading order
We show the existence of dynamical zeros in the helicity amplitudes for neutrino-electron elastic scattering at lowest order in the standard theory. In particular, the $\lambda=1/2$ non-flip electron helicity amplitude in the electron antineutrino process vanishes for an incident neutrino energy $E_{\nu}=m_{e}/(4sin^{2}\theta_{W})$ and forward electrons (maximum recoil energy). The rest of helicity amplitudes show kinematical zeros in this configuration and therefore the cross section vanishes. Prospects to search for neutrino magnetic moment are discussed.
Two-Higgs leptonic minimal flavour violation
We construct extensions of the Standard Model with two Higgs doublets, where there are flavour changing neutral currents both in the quark and leptonic sectors, with their strength fixed by the fermion mixing matrices $V_{CKM}$ and $V_{PMNS}$. These models are an extension to the leptonic sector of the class of models previously considered by Branco, Grimus and Lavoura, for the quark sector. We consider both the cases of Dirac and Majorana neutrinos and identify the minimal discrete symmetry required in order to implement the models in a natural way.
Tree-level flavor-changing neutral currents in the B system: From CP asymmetries to rare decays
Tree-level flavor-changing neutral currents (FCNC) are characteristic of models with extra vectorlike quarks. These new couplings can strongly modify the B/sup 0/ CP asymmetries without conflicting with low-energy constraints. In the light of low CP asymmetry in B to J/ psi K/sub S/, we discuss the implications of these contributions. We find that even these low values can be easily accommodated in these models. Furthermore, we show that the new data from B factories tend to favor an O(20) enhancement of the b to dll transition over the SM expectation. (25 refs).
New Physics and Evidence for a Complex CKM
We carefully analyse the present experimental evidence for a complex CKM matrix, even allowing for New Physics contributions to $\epsilon_{K}$, $a_{J/\Psi K_S}$, $\Delta M_{B_{d}}$, $\Delta M_{B_{s}}$, and the $\Delta I=1/2$ piece of $B\to\rho\rho$ and $B\to\rho\pi$. We emphasize the crucial r\^ ole played by the angle $\gamma$ in both providing irrefutable evidence for a complex CKM matrix and placing constraints on the size of NP contributions. It is shown that even if one allows for New Physics a real CKM matrix is excluded at a 99.92% C.L., and the probability for the phase $\gamma$ to be in the interval $[-170^\circ;-10^\circ]\cup [10^\circ;170^\circ]$ is 99.7%.
Novel T-Violation observable open to any pair of decay channels at meson factories
Quantum entanglement between the two neutral mesons produced in meson factories has allowed the first indisputable direct observation of Time Reversal Violation in the time evolution of the neutral meson between the two decays. The exceptional meson transitions are directly connected to semileptonic and CP eigenstate decay channels. The possibility of extending the observable asymmetries to more decay channels confronts the problem of the “orthogonality condition”, which can be stated with this tongue-twister: Given a decay channel f , which is the decay channel f′f′ such that the meson state not decaying to f′f′ is orthogonal to the meson state not decaying to f? In this Letter we propose …
CPT Violation in $\boldsymbol{B^0_s}$--$\boldsymbol{\bar B^0_s}$ mixing and the measurement of CP Violation in $\boldsymbol{B_s\to K^+K^-}$
A simple analysis of time-dependent $B_s\to K^+K^-$ transitions, based on recent results from the LHCb experiment, is presented. The benefits of adopting a fully consistent theoretical description of the $B^0_s$--$\bar B^0_s$ mixing are stressed. It is shown that bounds on CPT violation in the $B^0_s$--$\bar B^0_s$ system can be consistently obtained and that direct CP violation in $B_s\to K^+K^-$ can be robustly established, even in the presence of CPT violation in the mixing.
Small violations of 3 × 3 unitarity, the phase inB0s–B̄0smixing and visiblet → cZdecays at the LHC
We show that it is possible to accommodate the observed size of the phase in Bs0?s0 mixing in the framework of a model with violation of 3 ? 3 unitarity. This violation is associated to the presence of a new Q = 2/3 isosinglet quark T, which mixes both with t and c and has a mass not exceeding 500 GeV. The crucial point is the fact that this framework allows for ? ? arg(?VtsVcbV*tbV*cs) of order ?, to be contrasted with the situation in the Standard Model, where ? is constrained to be of order ?2. We point out that this scenario implies rare top decays t?cZ at a rate observable at the LHC and |Vtb| significantly different from unity. In this framework, one may also account for the observed …
A novel kind of neutrino oscillation experiment
A novel method to look for neutrino oscillations is proposed based on the elastic scattering process $\bar{\nu}_{i} e^{-}\rightarrow \bar{\nu}_{i} e^{-}$, taking advantage of the dynamical zero present in the differential cross section for $\bar{\nu}_{e} e^{-}\rightarrow \bar{\nu}_{e} e^{-}$. An effective tunable experiment between the "appearance" and "disappearance" limits is made possible. Prospects to exclude the allowed region for atmospheric neutrino oscillations are given.
Novel T-violation observable open to any decay channel at meson factories
Two genuine Quantum phenomena: Entanglement and Filtering Measurement are at the origin of the first direct observation of Time-Reversal-Violation in the time evolution of the B neutral meson system by BaBar. The used meson transitions are directly connected to semileptonic and CP-eigenstate decay channels. We analyse the possibility of extending the observable asymmetries to more decay channels. We propose an alternative T-Violation Asymmetry in the meson factories which allows its opening to any pair of decay channels. The new asymmetry needs also the measurement of the time dependent total survival probability of the initial tagged states. By combining several asymmetries these total sur…
Physical constraints on a class of two-Higgs doublet models with FCNC at tree level
We analyse the constraints and some of the phenomenological implications of a class of two Higgs doublet models where there are flavour-changing neutral currents (FCNC) at tree level but the potentially dangerous FCNC couplings are suppressed by small entries of the CKM matrix V. This class of models have the remarkable feature that, as a result of a discrete symmetry of the Lagrangian, the FCNC couplings are entirely fixed in the quark sector by V and the ratio v 2/v 1 of the vevs of the neutral Higgs. The discrete symmetry is extended to the leptonic sector, so that there are FCNC in the leptonic sector with their flavour structure fixed by the leptonic mixing matrix. We analyse a large n…
ɛ-type contribution to baryon asymmetry from colored Higgs triplets
In scenarios where the cosmological baryon asymmetry is generated in the decay of heavy colored Higgs triplets at the one-loop level (at least two triplets are needed), it is shown that in addition to the conventional triangle loop ({epsilon}{prime}-type effect), a new kind of diagram must be considered. This new type of diagram has its origin in the mixing of the two Higgs fields ({epsilon}-type effect). The mixing of the two Higgs fields violates {ital CP} provided they have at least two common decay channels. For small mixing angles, the new contribution can be bigger than the conventional one.
Reparametrization invariance ofBdecay amplitudes and implications for new physics searches inBdecays
When studying $B$ decays within the standard model (SM), it is customary to use the unitarity of the CKM matrix in order to write the decay amplitudes in terms of only two of the three weak phases which appear in the various diagrams. Occasionally, it is mentioned that those two weak phases can be used in order to describe any decay amplitude, even beyond the standard model. Here we point out that, when describing a generic decay amplitude, the two weak phases can be chosen completely at will, and we study the behavior of the decay amplitudes under changes in the two weak phases chosen as a basis. Of course, physical observables cannot depend on such reparametrizations. This has an impact o…
The size of and physics beyond the Standard Model
Abstract We analyse the allowed range of values of χ , both in the Standard Model and in models with new physics, pointing out that a relatively large value of χ , e.g., of order λ , is only possible in models where the unitarity of the 3 × 3 Cabibbo–Kobayashi–Maskawa matrix is violated through the introduction of extra Q = 2 / 3 quarks. We study the interesting case where the extra quark is an isosinglet, determining the allowed range for χ and the effect of a large χ on various low-energy observables, such as CP asymmetries in B meson decays. We also discuss the correlated effects which would be observable at high energy colliders, like decays t → c Z , modifications of the cross section …
mixing in the weak-gauged U(4)L⊗U(4)R chiral lagrangian model
Abstract The D0– D 0 mixing is analyzed in a weak gauged U(4)L⊗U(4)R chiral lagrangian model where the electroweak interaction is introduced as a gauge theory over the meson degrees of freedom. This model allows a particular realization of the G.I.M. mechanism and then could be useful in the study of processes where G.I.M. suppression is effective. As a test of the model we have also analyzed the K0– K 0 mixing. We find ΔmK in good agreement with the experimental result and we show that the D0– D 0 mixing is very much suppressed in agreement with previous estimates in the Heavy Quark expansion framework.
Constraining models with vector-like fermions from FCNC in K and B physics
In this work, we update the constraints on tree level FCNC couplings in the framework of a theory with n isosinglet vector-like down quarks. In this context, we emphasize the sensitivity of the B -> J/psi K_S CP asymmetry to the presence of new vector-like down quarks. This CP asymmetry, together with the rare decays B -> X_{s,d} l bar{l} and K -> pi nu bar{nu} are the best options to further constrain the FCNC tree level couplings or even to point out, in the near future, the possible presence of vector-like quarks in the low energy spectrum, as suggested by GUT theories or models of large extra dimensions at the TeV scale.
Measurements of new physics inB→ππdecays
If new physics (NP) is present in B{yields}{pi}{pi} decays, it can affect the isospin I=2 or I=0 channels. In this paper, we discuss various methods for detecting and measuring this NP. The techniques have increasing amounts of theoretical hadronic input. If NP is eventually detected in B{yields}{pi}{pi}--there is no evidence for it at present--one will be able to distinguish I=2 and I=0, and measure its parameters, using these methods.
How sensitive to FCNC can $B^0$ CP asymmetries be?
We show that the study of CP asymmetries in neutral B-meson decays provides a very sensitive probe of flavour-changing neutral currents (FCNC). We introduce two new angles, $\alpha_{SM}$ and $\beta_{SM}$, whose main feature is that they can be readily obtained from the measurement of the CP asymmetries $a_{J/\psi K_s}$, $a_{\pi^+ \pi^-}$ and the ratio $R_u \equiv|V_{ud}V_{ub}^*|/|V_{cd}V_{cb}^*|$, providing a quantitative test of the presence of new physics in a model-independent way. Assuming that new physics is due to the presence of an isosinglet down-type quark, we indicate how to reconstruct the unitarity quadrangles and point out that the measurements of the above asymmetries, within …
Invariants and flavour in the general Two Higgs Doublet Model
The flavour structure of the general Two Higgs Doublet Model (2HDM) is analysed and a detailed study of the parameter space is presented, showing that flavour mixing in the 2HDM can be parametrized by various unitary matrices which arise from the misalignment in flavour space between pairs of various Hermitian flavour matrices which can be constructed within the model. This is entirely analogous to the generation of the CKM matrix in the Standard Model (SM). We construct weak basis invariants which can give insight into the physical implications of any flavour model, written in an arbitrary weak basis (WB) in the context of 2HDM. We apply this technique to two special cases, models with MFV…
CP violation and limits on New Physics including recent B-s measurements
We analyse present constraints on the SM parameter space and derive, in a model independent way, various bounds on New Physics contributions to $B_d^0$--$\bar B_d^0$ and $B_s^0$--$\bar B_s^0$ mixings. Our analyses include information on a large set of asymmetries, leading to the measurement of the CKM phases $\gamma$ and $\bar\beta$, as well as recent data from D0 and CDF related to the $B_s^0$--$\bar B_s^0$ system such as the measurement of $\Delta M_{B_s}$, $A_{SL}$ and $\Delta\Gamma_{s}^{CP}$. We examine in detail several observables such as the asymmetries $A_{sl}^d$, $A_{SL}$, the width differences $\Delta\Gamma_{d}$ and $\Delta\Gamma_{s}^{CP}$ and discuss the r\^ole they play in estab…
Electron and muon $g-2$ anomalies in general flavour conserving two Higgs doublets models
In general two Higgs doublet models (2HDMs) without scalar flavour changing neutral couplings (SFCNC) in the lepton sector, the electron, muon and tau interactions can be decoupled in a robust framework, stable under renormalization group evolution. In this framework, the breaking of lepton flavour universality (LFU) goes beyond the mass proportionality, opening the possibility to accommodate a different behaviour among charged leptons. We analyze the electron and muon $(g-2)$ anomalies in the context of these general flavour conserving models in the leptonic sector (g$\ell$FC). We consider two different models, I-g$\ell$FC and II-g$\ell$FC, in which the quark Yukawa couplings coincide, res…
Vacuum Induced CP Violation Generating a Complex CKM Matrix with Controlled Scalar FCNC
We propose a viable minimal model with spontaneous CP violation in the framework of a two Higgs doublet model. The model is based on a generalised Branco–Grimus–Lavoura model with a flavoured Z2 symmetry, under which two of the quark families are even and the third one is odd. The lagrangian respects CP invariance, but the vacuum has a CP violating phase, which is able to generate a complex CKM matrix, with the rephasing invariant strength of CP violation compatible with experiment. The question of scalar mediated flavour changing neutral couplings is carefully studied. In particular we point out a deep connection between the generation of a complex CKM matrix from a vacuum phase and the ap…
Vector-like quarks and New Physics in the flavour sector
We present a detailed analysis of recent flavour data in the framework of a simple extension of the Standard Model, where a Q = 2/3 vector-like isosinglet quark is added to the spectrum. Constraints from all the relevant quark flavour sectors are used. Important deviations from Standard Model expectations in different observables such as the semileptonic asymmetry in Bd decays, AdSL, the time-dependent CP asymmetry in Bs ? J/??, and rare decays such as K+ ? ?+? can be obtained.
Flavour Conservation in Two Higgs Doublet Models
In extensions of the Standard Model with two Higgs doublets, flavour changing Yukawa couplings of the neutral scalars may be present at tree level. In this work we consider the most general scenario in which those flavour changing couplings are absent. We re-analyse the conditions that the Yukawa coupling matrices must obey for such \emph{general flavour conservation} (gFC), and study the one loop renormalisation group evolution of such conditions in both the quark and lepton sectors. We show that gFC in the leptonic sector is one loop stable under the Renormalization Group Evolution (RGE) and in the quark sector we present some new Cabibbo like solution also one loop RGE stable. At a pheno…
The Hunt for New Physics in the Flavour Sector with up vector-like quarks
We analyse the possible presence of New Physics (NP) in the Flavour Sector and evaluate its potential for solving the tension between the experimental values of $\AJPKs$ and $\BTNu$ with respect to the Standard Model (SM) expectations. Updated model independent analyses, where NP contributions are allowed in Bd - anti-Bd and Bs - anti-Bs transitions, suggest the need of New Physics in the $bd$ sector. A detailed analysis of recent Flavour data is then presented in the framework of a simple extension of the SM, where a $Q=2/3$ vector-like isosinglet quark is added to the spectrum of the SM. Special emphasis is given to the implications of this model for correlations among various measurable …