Effective field theory (EFT) approaches are widely used at the LHC, such that it is important to study their validity, and ease of matching to specific new physics models. In this paper, we consider an extension of the SM in which a top quark couples to a new heavy scalar. We find the dimension six operators generated by this theory at low energy, and match the EFT to the full theory up to NLO precision in the simplified model coupling. We then examine the range of validity of the EFT description in top pair production, finding excellent validity even if the scalar mass is only slightly above LHC energies, provided NLO corrections are included. In the absence of the latter, the LO EFT overestimates kinematic distributions, such that over-optimistic constraints on BSM contributions are obtained. We next examine the constraints on the EFT and full models that are expected to be obtained from both top pair and four top production at the LHC, finding for low scalar masses that both processes show similar exclusion power. However, for larger masses, estimated LHC uncertainties push constraints into the non-perturbative regime, where the full model is difficult to analyse, and thus not perturbatively matchable to the EFT. This highlights the necessity to improve uncertainties of SM hypotheses in top final states.
In view of the observed strong hierarchy of quark masses, we propose a new description of flavor mixing which is particularly suited for models of quark mass matrices based on flavor symmetries. The necessary and sufficient conditions for CP violation are clarified. The emergence of CP violation is primarily linked to a large phase difference (near 90^{\circ}) in the light quark sector. The unitarity triangle is determined by the mass ratios of the light quarks. We conclude that the unitarity triangle should be close or identical to a rectangular triangle, and CP violation is maximal in this s…
Predictions for the Standard Model Effective Field Theory at the next-to-leading order accuracy in QCD, including parton-shower effects, have started to become available in the MadGraph5_aMC@NLO framework. In this talk we summarize some recent results for $t\bar t$, single top, $t\bar tZ/γ$, and $t\bar tH$ production channels at dimension six.
For the purpose of deriving the observed nearly tribimaximal neutrino mixing, a possible yukawaon model in the quark sector is investigated. Five observable quantities (2 up-quark mass ratios and 3 neutrino mixing parameters \sin^2 2θ_{atm}, \tan^2θ_{solar} and |U_{13}|) are excellently fitted by two parameters (one in the up-quark sector and another one in the right-handed Majorana neutrino sector).
An analysis is given of the chromoelectric dipole moment of quarks and of the neutron in an MSSM extension where the matter sector contains an extra vectorlike generation of quarks and mirror quarks. The analysis includes contributions to the CEDM from the exchange of the $W$ and the $Z$ bosons, from the exchange of charginos and neutralinos and the gluino. Their contribution to the EDM of quarks is investigated. The interference between the MSSM sector and the new sector with vectorlike quarks is investigated. It is shown that inclusion of the vectorlike quarks can modify the quark EDMs in a …
The discovery of hadronic states beyond the conventional two-quark meson and three-quark baryon picture in the last two decades is one of the most amazing accomplishments in fundamental physics research. Many experiments contributed to this field despite of the original goals of the design. We review the experimental progress on the study of the quarkoniumlike states -- states with at least one heavy quark-antiquark pair and possible light quarks, also known as XYZ states. We give a general review and then focus on the new experimental results on the X(3872) and its bottom-quark partner X_b, t…
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. Spe…
Universidad de Córdoba（科尔多瓦大学）；Universitat d’Alacant（阿利坎特大学）；University of Glasgow（格拉斯哥大学）；IFIC, Universitat de València and CSIC（巴伦西亚大学与西班牙国家研究委员会联合物理研究所）
We demonstrate that flavour-changing neutral currents in the top sector, mediated by leptophilic scalars at the electroweak scale, can easily arise in scenarios of new physics, and in particular in composite Higgs models. We moreover show that such interactions are poorly constrained by current experiments, while they can be searched for at the LHC in rare top decays and, more generally, in the channels $pp\to tS(S)+j$, with $S\to\ell^+\ell^-$. We provide dedicated analyses in this respect, obtaining that cut-off scales as large as $Λ\sim$ 90 TeV can be probed with an integrated luminosity of …
A preliminary determination of the Dirac phase in the PMNS matrix is $\dell\approx -\fracπ{2}$. A rather accurately determined Jarlskog invariant $J$ in the CKM matrix is close to the maximum. Since the phases in the CKM and PMNS matrices will be accurately determined in the future, it is an interesting problem to relate these two phases. This can be achieved in a families-unified grand unification if the weak CP violation is introduced spontaneously {\it à la} Froggatt and Nielsen at a high energy scale, where only one meaningful Dirac CP phase appears.
We present a framework for carrying out global analyses of the Standard Model Effective Field Theory: SMEFiT. This approach is based on the Monte Carlo replica method, widely used in the case of NNPDF fits of the proton structure, for deriving a faithful estimate of the experimental and theoretical uncertainties. As a proof of concept of the SMEFiT methodology, we present a study of the constraints on the SMEFT provided by top quark production measurements from the LHC. We derive bounds for the 34 degrees of freedom relevant for the interpretation of the LHC top quark data and compare these bo…
Results obtained in recent years in the strange quark sector of chiral perturbation theory are reviewed and the theoretical relevance of this sector for probing the phase structure of QCD at zero temperature with respect to the variation of the number of massless quarks is emphasized.
We present discovery limits for heavy quarks in the Bestest Little Higgs model via pair production at the LHC running at $\sqrt{s} = 7 \mathrm{TeV}$. We study pair produced heavy top-like quarks decaying to $b\bar{b}W^+W^-$ and $t\bar{t}ZZ$ final states and singly produced heavy top-like quarks via t-channel $W$ exchange. These results are compared to currently available limits on heavy top-like quark cross sections from CMS (with 1.14 fb$^{-1}$ integrated luminosity) for two scenarios of Yukawa couplings. We find that the CMS data limits the mass of the lightest top partner to larger than 413…
The residual $\mathbb Z^{23}_2$ ($\mathbb Z^{μτ}_2$) and $\mathbb Z^{12}_2$ ($\mathbb Z^s_2$ or $\overline{\mathbb Z}^s_2$) symmetries can not only apply to the lepton sector, but also explain the mainly $1$--$2$ mixing in the quark sector. With both up and down quarks subject to the same $\mathbb Z^{23}_2$ symmetry, which interchanges the second and third generations, the $1$--$3$ and $2$--$3$ mixing angles in CKM vanish while the Cabibbo angle is dictated by two residual $\mathbb Z^{12}_2$ symmetries. It turns out that the quark-lepton complementarity conditions are natural consequences of u…
I survey the characteristics of hadron colliders as tools to investigate top-quark physics and to explore the 1-TeV scale of electroweak symmetry breaking.
The large number of top quarks produced at the LHC and possible future hadron colliders allows to study rare decays of this particle. In many well motivated models of new physics, for example in non-minimal composite-Higgs models, the existence of scalar singlets can induce new flavor-violating top decays surpassing the Higgs contribution by orders of magnitude. We study the discovery prospects of rare top decays within such models and develop new search strategies to test these interactions in top pair-produced events at the LHC. We demonstrate that scales as large as $10$--$50$ TeV can be pr…
We present how to further the search for Lorentz and CPT violation in the top-quark sector after the first measurement in this sector by D0. We compute the Lorentz-violating matrix element for top pair production via gluon fusion, which allows a similar but more precise measurement at the LHC. For CPT violation, we analyze single-top production, derive the modified matrix elements, and predict possible signals.
In this article we aim to estimate the bounds on the noncommutative scale $Λ_{NC}$ and to extract the 95% exclusion contours for some $θ_{μν}$ components using the recent measurements of the top quark width and the $W$ boson polarization in top pair events from CDF experiment at Tevatron.
We derive a tree-level heavy quark effective Lagrangian keeping particle-antiparticle mixed sectors allowing for heavy quark-antiquark pair annihilation and creation. However, when removing the unwanted degrees of freedom from the effective Lagrangian one has to be careful in using the classical equations of motion obeyed by the effective fields in order to get a convergent expansion on the reciprocal of the heavy quark mass. Then the application of the effective theory to such hard processes should be sensible for special kinematic regimes as for example heavy quark pair production near thres…
The democracy of quark flavors is a well-motivated flavor symmetry, but it must be properly broken in order to explain the observed quark mass spectrum and flavor mixing pattern. We reconstruct the texture of flavor democracy breaking and evaluate its strength in a novel way, by assuming a parallelism between the Q=+2/3 and Q=-1/3 quark sectors and using a nontrivial parametrization of the flavor mixing matrix. Some phenomenological implications of such democratic quark mass matrices, including their variations in the hierarchy basis and their evolution from the electroweak scale to a superhig…
We discuss the sensitivity of the processes $e^+e^-\to t\bar t$ and $e^+e^-\to b\bar b$ to special sets of operators describing residual New Physics effects. Experimental data in this sector together with those expected in the bosonic sector should allow to constrain possible New Physics schemes with effective scales in the 10 TeV range.
We study the CP violation of universal seesaw model, especially its quark sector. The model is based on SU(2)_L \times SU(2)_R \times U(1)_{Y^\prime}. In order to count the number of parameters in quark sector, we use the degree of freedom of weak basis transformation. For N(3)-generation model, the number of CP violating phase in quark sector is identified as 3N^2-3N+1 (19). We also construct nineteen CP violating weak basis invariants of Yukawa coupling matrices and SU(2) singlet quark mass matrices in the three-generation universal seesaw model. The quark interaction terms induced by neutra…
Models with extended quark sector affect the CP asymmetry in the $B\to ψK_{S}$ decay, $a_{ψK_{S}}$, in two ways: First, the top-mediated box diagram is not necessarily the only important contribution to $B-\bar{B}$ mixing. Second, the $3\times 3$ CKM matrix is no longer unitary. We analyze the constraints that follow from the CDF measurement, $a_{ψK_{S}} =0.79^{+0.41}_{-0.44}$, on the mixing parameters of extended quark sectors. Most noticeably, we find significant constraints on the phase of the relevant flavor changing $Z$ coupling in models with extra down quarks in vector-like representati…
The top quark data in the lepton plus $τ$ channel offers a viable probe for the charged Higgs boson signal. We analyse the recent Tevatron collider data in this channel to obtain a significant limit on the $H^\pm$ mass in the large $\tanβ$ region.
We study the physics of Kaluza-Klein (KK) top quarks in the framework of a non-minimal Universal Extra Dimension (nmUED) with an orbifolded (S1/Z2) flat extra spatial dimension in the presence of brane-localized terms (BLTs). In general, BLTs affect the masses and the couplings of the KK excitations in a non-trivial way including those for the KK top quarks. On top of that, BLTs also influence the mixing of the top quark chiral states at each KK level and trigger mixings among excitations from different levels with identical KK parity (even or odd). The latter phenomenon of mixing of KK levels…
A pseudo-Goldstone boson for {\it quintessence} is known to require the decay constant $F_q\sim M_P$ and the height of the potential $(0.003 {\rm eV})^4$, and hence the pseudo-Goldstone boson mass of order $10^{-33}$ eV. The model-dependent axion in some superstring models is suggested as a good candidate for the quintessence. We realize this idea with a hidden-sector gauge group $SU(3)_H\times U(1)_H$. The hidden-sector instanton contribution to the quintessence potential is suppressed by the almost massless hidden-sector quarks. The model-independent axion is the QCD axion required for the s…
I discuss the issue of quark-hadron duality in the system of heavy-light quark mesons. As an example, I consider a correlator of two currents comprising heavy quark operators, and I compare the OPE expression with the result obtained by a complete insertion of hadronic states. After a smearing procedure, OPE and hadronic spectral functions agree with each other. However, the local behaviour of the two functions is different, and the difference manifests itself in a term which is absent in the OPE.
In the simplest examples of models with a discrete quark-lepton symmetry, an electroweak symmetry breaking sector with more than one Higgs doublet is necessary to obtain the correct mass relations between quarks and leptons. A two Higgs doublet model has flavour-nonconserving Yukawa couplings, which are proportional to the masses of the quark-lepton symmetric partners of the fermions. We describe how flavour changing leptonic decays can occur, with branching ratios not far beyond that currently measureable, enabling investigation of the phenomenology of such models.
Recently, using specific Weak Basis transformations, Y. Giraldo [Phys. Rev. D 86, 093021 (2012)] has constructed some texture 5 and 4 zero quark mass matrices and examined their compatibility with the quark mixing data. In this comment, we have re-analyzed these to bring forth certain important issues regarding their viability which need to be taken note of.
In view of the observed strong hierarchy of quark masses, we discuss a new description of flavor mixing which is particularly suited for models of quark mass matrices based on flavor symmetries. The necessary and sufficient conditions for CP violation are clarified. The emergence of CP violation is primarily linked to a large phase difference (near 90^{\circ}) in the light quark sector. The unitarity triangle is determined by the mass ratios of the light quarks. We conclude that the unitarity triangle should be close or identical to a rectangular triangle, and CP violation is maximal in this s…
A convergence of the valence quark self-energies in the 1S, 2S, $1P_{1/2}$, $1P_{3/2}$ orbits induced by pion and gluon field configurations, is shown in the frame of a relativistic chiral quark model. It is shown that in order to reach a convergence, one needs to include contribution of the intermediate quark and anti-quark states with the total momentum up to $j=25/2$. It is argued that a restriction to the lowest mode when estimating the self-energy is not good approximation.
An overview over recent spectroscopy results in comparison with data is given. We focus on the exotica Z_b(10610), Z_b(10650) and Y_b(10890) in the bottom sector and discuss a possible connection to the exotica in the charm sector, namely to the resonances Y_c(4260) and Z_c(3900). Furthermore, future prospects for the determination of the nature of Y_b(10890) are outlined.
Minimal Flavor Violation in the up-type quark sector leads to particularly interesting phenomenology due to the interplay of flavor physics in the charm sector and collider physics from flavor changing processes in the top sector. We study the most general operators that can affect top quark properties and $D$ meson decays in this scenario, concentrating on two CP violating operators for detailed studies. The consequences of these effective operators on charm and top flavor changing processes are generically small, but can be enhanced if there exists a light flavor mediator that is a Standard …
The small quark mixing, described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix in the Standard Model, may be a clue to reveal new physics around the TeV scale. We consider a simple scenario that extra particles in a hidden sector radiatively mediate the flavor violation to the quark sector around the TeV scale and effectively realize the observed CKM matrix. The lightest particle in the hidden sector, whose contribution to the CKM matrix is expected to be dominant, is a good dark matter (DM) candidate, so we focus on the contribution, and discuss the DM physics. In this scenario, there is an …
Stimulated by the recent attention given to the texture zeros found in the quark mass matrices sector of the Standard Model, an analytical method for identifying (or to exclude) texture zeros models will be implemented here, starting from arbitrary quark mass matrices and making a suitable weak basis transformation, we are be able to find equivalent quark mass matrix. It is shown that the number of non-equivalent quark mass matrix representations is finite. We give exact numerical results for parallel and non-parallel four-texture zeros models. We find that some five-texture zeros Ans$\ddot{\t…
The top quark data in the lepton plus $τ$ channel offers a viable probe for the charged Higgs boson signal. We have analysed the recent Collider Detector at Fermilab (CDF) data in this channel to obtain a significant limit on the $H^\pm$ mass in the large $\tanβ$ region.
The Higgs sector of the U(1)-extended supersymmetric model is studied with great detail. We calculate the masses of the Higgs bosons at the one-loop level. We also calculate at the one-loop level the gluon-involving processes for the productions and decays of the scalar Higgs bosons of the model at the energy of the CERN Large Hadron Collider (LHC), where the radiative corrections due to the loops of top, bottom, and exotic quarks and their scalar partners are taken into account. We find that the exotic quark and exotic scalar quarks in the model may manifest themselves at the LHC, since the p…
We study the static gluon and quark propagator of the Hamiltonian approach to Quantum Chromodynamics in Coulomb gauge in one-loop Rayleigh--Schrödinger perturbation theory. We show that the results agree with the equal-time limit of the four-dimensional propagators evaluated in the functional integral (Lagrangian) approach.
The most popular way to present mixing matrices of quarks (CKM) and leptons (PMNS) is the parametrization with three mixing angles and one CP-violating phase. There are two major options in this kind of parametrizations, one is the original Kobayashi-Maskawa (KM) matrix, and the other is the Chau-Keung (CK) matrix. In a new proposal by Frampton and He, a unitarity boomerang is introduced to combine two unitarity triangles, and this new presentation displays all four independent parameters of the KM parametrization in the quark sector simultaneously. In this paper, we study the relations betwee…
In this talk I discuss the role of heavy quarks in new physics searches with tau leptons. I focus on new physics effects associated to the scalar sector which are naturally enhanced for the heaviest fermions due to the large hierarchy of the fermion masses. I will discuss two topics within this context: lepton flavour violation in the $τ- \ell$ ($\ell=e,μ$) sector and violations of lepton universality in tauonic $B$ decays.
A chiral quark model is described which is regularized in terms of Lorentz invariant non-local interactions. The model is regularized to all loop orders and it ensures the proper quantization of the baryon number. It sustains bound hedgehog solitons which, after suitable centre of mass corrections, can adequately describe the nucleon.
We review the potential of the LHC to detect a very light CP-odd Higgs boson of the NMSSM, $a_1$, through its direct production in association with a bottom-quark pair at large tan$β$. We also review the LHC discovery potential of the two lightest CP-even Higgs states, decaying into two lighter Higgs states or into the lightest CP-odd Higgs state and the $Z$ gauge boson.
We propose a dynamical scenario beyond the standard model, in which the radiative correction to the Higgs mass parameter is suppressed due to a large anomalous dimension induced through a conformal invariant coupling with an extra gauge sector. Then the anomalous dimension also suppresses the Yukawa couplings of the Higgs field. However, the large top Yukawa coupling can be generated effectively through mixing among top quarks and the fermions of the conformal gauge sector. This scenario is found to predict a fairly heavy Higgs mass of about 500 GeV. We present an explicit model and show consi…
The simplest noncompact group SU(1,1),when introduced as a symmetry group of the generations of quarks and leptons in the framework of a vector-like theory, gives an excellent viewpoint on low energy physics. The minimal setup of the scheme, however, gives phenomenologically unacceptable prediction on the Yukawa coupling matrices. This suggests the higgs sector has richer structure than we expect from the success of MSSM. The natural extension of the scheme, which has doubled structure in the higgs sector, is formulated. The framework admits this extension in a restrictive way. The possible pa…
A striking manifestation of CP violation in the electroweak symmetry breaking sector would be the existence of neutral Higgs boson(s) with undefined CP parity. We analyse signatures of such a boson, with a mass of about 300 GeV or larger, produced in high energy proton-proton collisions at LHC energies in its top-quark antitop-quark decay channel. The large irreducible $t\bar t$ background is taken into account. We propose, both for the dilepton and the lepton + jets decay channels of $t\bar t$, several correlations and asymmetries with which (Higgs sector) CP violation can be traced. We show …
Here we show that the Weak Basis Transformation is an appropriate mathematical tool that can be used to find texture zeros in the quark mass matrix sector of the Standard Model. So, starting with the most general quark mass matrices and taking physical data into consideration, is possible to obtain more than three texture zeros by any weak basis transformation. Where the most general quark mass matrices considered in the model, were obtained through a special weak basis wherein the mass matrix $M_u$~(or $M_d$) has been taken to be diagonal and only the matrix $M_d$~(or $M_u$) is considered to …
In Little Higgs models a collective symmetry prevents the higgs from acquiring a quadratically divergent mass at one loop. We have previously shown that the couplings in the Littlest Higgs model introduced to give the top quark a mass do not naturally respect the collective symmetry. We extend our previous work showing that the problem is generic: it arises from the fact that the would be collective symmetry of any one top quark mass term is broken by gauge interactions.
In this work we study the properties of hadronic molecules in the heavy-quark sector. These have become increasingly important since from the beginning of this century a large number of states have been measured that for different reasons do not fit the predictions of simple quark models. In particular we discuss two candidates in the open charm sector, $D_{s0}^*(2317)$ and $D_{s1}(2460)$, and two candidates in the bottomonium sector, $Z_b(10610)$ and $Z_b(10650)$. Theorists have proposed different explanations for these states including tetraquarks, hybrids, hadro-quarkonia and, subject of th…
We explain all features of lepton and quark mixing in a scenario with the flavor symmetry Delta (384) and a CP symmetry, where these are broken in several steps. The residual symmetry in the neutrino and up quark sector is a Klein group and CP, while a Z_3 and a Z_{16} symmetry are preserved among charged leptons and down quarks, respectively. If the Klein group in the neutrino sector is further broken down to a single Z_2 symmetry, we obtain predictions for all lepton mixing parameters in terms of one real quantity, whose size is determined by the value of the reactor mixing angle. The Dirac …
We present a novel framework for carrying out global analyses of the Standard Model Effective Field Theory (SMEFT) at dimension-six: SMEFiT. This approach is based on the Monte Carlo replica method for deriving a faithful estimate of the experimental and theoretical uncertainties and enables one to construct the probability distribution in the space of the SMEFT degrees of freedom. As a proof of concept of the SMEFiT methodology, we present a first study of the constraints on the SMEFT provided by top quark production measurements from the LHC. Our analysis includes more than 30 independent me…
A study on effective anomalous interactions up to dimension 5 of the top quark with the electroweak gauge bosons is made in the non-linear Chiral Lagrangian approach. Bounds on the anomalous dimension four terms are obtained from their contribution to low energy data. Also, the potential contribution to the production of top quarks at hadron colliders (the Tevatron and the LHC) and the electron Linear Collider from both dimension 4 and 5 operators is analysed.
We study the effects of a vector-like SU(2) quark doublet as a fourth generation. In this model we examine the chiral structure and the FCNC in the quark sector by using radiative B meson decays in the allowed region for parameters from $R_b = {Γ_{qq}}/{Γ_{had.}}$. We compute the ratio $R = {Br (b \to d γ)}/{Br (b \to s γ)}$ in the model which realizes a different chiral structure as well as FCNC. The constraints has been extracted from the experimental results of B meson decays, the $T_{new}$ parameter of oblique corrections and $R_b$. Under the natural assumption that the violation of the $V…
We present a broad study of collider processes that embed $2 \to 2$ scattering amplitudes involving top quarks in the Electroweak sector. We parametrise the modified interactions using the Standard Model Effective Field Theory framework and discuss how the New Physics effects lead to unitarity violating behaviour at the amplitude level. For each scattering amplitude we compute the helicity amplitudes in the high energy limit paying special attention to the effects of the higher dimensional operators. We also discuss whether and to what extent the unitarity violating effects are retained in phy…
We examine the origin of possible failures of the quark-hadron local duality. In particular, we consider a correlator of two currents comprising heavy quark operators, and compare the evaluation by the Operator Product Expansion with the result obtained inserting an infinite set of hadronic states, in the N_c to infinity limit. Whereas the smeared spectral functions agree with each other, their local behaviour is different. The difference manifests itself in the form of a term O(Lambda/epsilon) (epsilon being the residual energy) that is not present in the expansion in powers of Lambda/epsilon…
We study direct searches of additional Higgs bosons in multi-top-quarks events at the LHC Run-II, its luminosity upgraded version with 3000 fb$^{-1}$, and the International Linear Collider (ILC) with the collision energy of 1 TeV. Additional Higgs bosons are predicted in all kinds of extended Higgs sectors, and their detection at collider experiments is a clear signature of the physics beyond the standard model. We consider two Higgs doublet models with the discrete symmetry as benchmark models. If these additional Higgs bosons are heavy enough, the decay modes including top quarks can be domi…
An origin of flavor mixings in quark and lepton sectors is still a mystery, and a structure of the flavor mixings in lepton sector seems completely different from that of quark sector. In this letter, we point out that the flavor mixing angles in quark and lepton sectors could be unified at a high energy scale, when neutrinos are degenerate. It means that a minimal flavor violation at a high energy scale can induce a rich variety of flavor mixings in quark and lepton sectors at a low energy scale through quantum corrections.
We present an $S_3$-invariant extension of the SM which is able to account for the mixing both in the quark and the lepton sector. We focus here on the quark sector and present different realizations of the model, according to how many Higgs fields are involved. We then confront the models with the up-to-date values of masses and mixing in the quark sector.
