NMSSM and seesaw physics at LHC

We consider extensions of the next-to-minimal supersymmetric model (NMSSM) in which the observed neutrino masses are described in terms of effective dimension six (or seven) rather than dimension five operators. All such operators respect the discrete symmetries of the model. The new particles associated with the double (or triple) seesaw mechanism can have sizable couplings to the known leptons, even with a TeV seesaw scale. In the latter case some of these new short-lived particles could be produced and detected at the LHC.     

Massless gauge bosons other than the photon

Gauge bosons associated with unbroken gauge symmetries, under which all standard model fields are singlets, may interact with ordinary matter via higher-dimensional operators. A complete set of dimension-six operators involving a massless U(1) field, gamma('), and standard model fields is presented. The mu-->egamma(') decay, primordial nucleosynthesis, star cooling, and other phenomena set lower limits on the scale of chirality-flip operators in the 1-15 TeV range if the operators have coefficients given by the corresponding Yukawa couplings. Simple renormalizable models induce gamma(') interactions with leptons or quarks at two loops, and may provide a cold dark matter candidate.     

A novel string-derived $Z^\prime$ with stable proton,light neutrinos and R-parity violation

The standard model indicates the realization of grand unified structures in nature, and it can only be viewed as an effective theory below a higher energy cutoff. While the renormalizable standard model forbids proton decay mediating operators due to accidental global symmetries, many extensions of the standard model introduce such dimension 4, 5 and 6 operators. Furthermore, quantum gravity effects are expected to induce proton instability, indicating that the higher energy cutoff scale must be above 10¹⁶ GeV. Quasi-realistic heterotic string models provide the arena to explore how perturbative quantum gravity affects the particle physics phenomenology. An appealing explanation for the proton longevity is provided by the existence of an Abelian gauge symmetry that suppresses the proton decay mediating operators. Additionally, such a low scale U(1) symmetry should feature the following: it should allow for the suppression of the left-handed neutrino masses by a seesaw mechanism; allow for fermion Yukawa couplings to the electroweak Higgs doublets; be anomaly free; and finally be family universal. These requirements render the existence of such U(1) symmetries in quasi-realistic heterotic string models highly non-trivial. We demonstrate the existence of a U(1) symmetry that satisfies all of the above requirements in a class of left–right symmetric heterotic string models in the free fermionic formulation. The existence of the extra in the energy range accessible to future experiments is motivated by the requirement of adequate suppression of proton decay mediation. We further show that, while the extra U(1) forbids dimension 4 baryon number violating operators, it allows dimension 4 lepton number violating operators and R-parity violation.     

Electroweak chiral Lagrangian for left–right symmetric models: The matter sector

The matter sector of electroweak chiral Lagrangian up to dimension four operators for left–right symmetric models with a neutral light Higgs is provided. The connection of these operators to Yukawa couplings, anomalous gauge couplings and parameters in the matter sector of conventional electroweak chiral Lagrangian is made. It is shown that there exists proper parameter space to loosen constraint for the mass of right handed gauge boson from the mass difference of neutral K meson.     

Electroweak baryogenesis from late neutrino masses

Electroweak baryogenesis, given a first-order phase transition, does not work in the standard model because the quark Yukawa matrices are too hierarchical. On the other hand, the neutrino mass matrix is apparently not hierarchical. In models with neutrino mass generation at low scales, the neutrino Yukawa couplings lead to large CP violation in the reflection probability of heavy leptons by the expanding Higgs bubble wall, and can generate the observed baryon asymmetry of the universe. The mechanism predicts new vectorlike leptons below the TeV scale and sizable mu --> e processes.     

Electroweak Chiral Lagrangian for Neutral Higgs Boson

A neutral Higgs boson is added into the traditional electroweak chiral Lagrangian by writing down all possible high dimension operators. The matter part of the Lagrangian is investigated in detail. We find that if Higgs field dependence of Yukawa couplings can be factorized out, there will be no flavour changing neutral couplings; neutral Higgs can induce coupling between light and heavy neutrinos.     

Effective-Lagrangian approach to γγ → WW I: Couplings and amplitudes

We consider the gauge-boson sector of a locally SU(2) × U(1) invariant effective Lagrangian with ten dimension-six operators added to the Lagrangian of the standard model. These operators induce anomalous three- and four-gauge-boson couplings and an anomalous γγH coupling. In the framework of this effective Lagrangian we calculate the helicity amplitudes and differential and total cross sections for the process γγ → WW at a photon collider. We give relations between different parts of the amplitudes that show which linear combinations of anomalous couplings are measurable in this reaction. The transformation properties of the differential cross section under CP are discussed. We find that three linear combinations of CP-conserving and of CP-violating couplings can be measured independently of the photon polarization in γγ → WW. M. Pospischil: now at CNRS UPR 2191, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.     

General description of new physics in t,b and boson interactions and its unitarity constraints

We list all possible dim = 6 CP conserving and SU(3) × SU(2) × U(1) gauge invariant interactions, which could be generated in case no new particles would be reachable in the future Colliders, and the only observable New Physics would be in the form of new interactions affecting the scalar sector and the quarks of the third family. These interactions are described by operators involving the standard model scalar field, the quarks of the third family and the gauge bosons. Subsequently, we identify those operators which do not contribute to LEP1 (and lower energy) observables at tree level and are not purely gluonic. Since present measurements do not strongly constrain the couplings of these operators, we derive here the unitarity bounds on them. Finally, in order to get a feeling on the possible physical meaning of the appearance of any of these operators, we identify the operators generated in a class of renormalizable dynamical models which at the TeV scale, are fully described by the SU(3) × SU(2) × U(1) gauge group.     

Effective-Lagrangian approach to γγ→WW II: Results and comparison with e+e-→WW

We present a study of anomalous electroweak gauge-boson couplings that can be measured in e⁺e^- and γγ collisions at a future linear collider like ILC. We consider the gauge-boson sector of a locally SU(2)×U(1) invariant effective Lagrangian with ten dimension-six operators added to the Lagrangian of the standard model. These operators induce anomalous three-gauge-boson and four-gauge-boson couplings and an anomalous γγH coupling. We calculate the reachable sensitivity for the measurement of the anomalous couplings in γγ→WW. We compare these results with the reachable precision in the reaction e⁺e^-→WW on the one hand and with the bounds that one can obtain from high-precision observables in Z decays on the other hand. We show that one needs both the e⁺e^- and the γγ modes at an ILC to constrain the largest possible number of anomalous couplings and that the Giga-Z mode offers the best sensitivity for certain anomalous couplings.     

Two loop electroweak corrections from heavy fermions to b→s+γ

Applying an effective Lagrangian method and an on-shell scheme, we analyze the electroweak corrections to the rare decay b→, s+γ from some special two loop diagrams in which a closed heavy fermion loop is attached to the virtual charged gauge bosons or Higgs. At the decoupling limit where the virtual fermions in the inner loop are much heavier than the electroweak scale, we verify the final results satisfying the decoupling theorem explicitly when the interactions among Higgs and heavy fermions do not contain the nondecoupling couplings. Adopting the universal assumptions on the relevant couplings and mass spectrum of new physics, we find that the relative corrections from those two loop diagrams to the SM theoretical prediction on the branching ratio of B → Xsγ can reach 5% as the energy scale of new physics ANp=200 GeV.     

Azimuthal angular dependence of decay lepton in e^+ e^- \to t \bar{t}

We discuss top quark production and its subsequent decay as used for searching new physics at lepton colliders. The angular dependence of the decay leptons is calculated including both QCD corrections and anomalous couplings. The off-diagonal spin basis for the top and anti-top quarks is shown to be useful to probe the anomalous couplings. Received: 11 August 2000 / Published online: 27 November 2000     

Renormalization of the neutrino mass operators in the multi-Higgs-doublet standard model

We derive the renormalization group equations (RGE) for the flavor coupling matrices of the effective dimension-five operators which yield Majorana neutrino masses in the multi-Higgs-doublet standard model; in particular, we consider the case where two different scalar doublets occur in those operators. We also write down the RGE for the scalar-potential quartic couplings and for the Yukawa couplings of that model, in the absence of quarks. As an application of the RGE, we consider two models which, based on a - interchange symmetry, predict maximal atmospheric neutrino mixing, together with U _e3 = 0, at the seesaw scale. We estimate the change of those predictions due to the evolution of the coupling matrices of the effective mass operators from the seesaw scale down to the electroweak scale. We derive an upper bound on that change, thereby finding that the radiative corrections to those predictions are in general negligible.Received: 30 September 2004, Published online: 11 January 2005PACS: 11.10.Hi, 14.60.Pq, 12.60.Fr, 11.30.Hv     

Perturbative Power Counting,Lowest-Index Operators and Their Renormalization in Standard Model Effective Field Theory

We study two aspects of higher dimensional operators in standard model effective field theory.We first introduce a perturbative power counting rule for the entries in the anomalous dimension matrix of operators with equal mass dimension.The power counting is determined by the number of loops and the difference of the indices of the two operators involved,which in turn is defined by assuming that all terms in the standard model Lagrangian have an equal perturbative power.Then we show that the operators with the lowest index are unique at each mass dimension d,i.e.,(H~?H)~(d/2)for even d≥4,and(L~TεH)C(L~TεH)~T(H~?H)~((d-5)/2)for odd d≥5.Here H,L are the Higgs and lepton doublet,andε,C the antisymmetric matrix of rank two and the charge conjugation matrix,respectively.The renormalization group running of these operators can be studied separately from other operators of equal mass dimension at the leading order in power counting.We compute their anomalous dimensions at one loop for general d and find that they are enhanced quadratically in d due to combinatorics.We also make connections with classification of operators in terms of their holomorphic and anti-holomorphic weights.     

Deep inelastic scattering as a probe of new hadronic mass scales

We present the general form for deep-inelastic cross sections obtained from all SU(3) × SU(2) × U(1) invariant operators of dimension six or less. The operators of dimension six generate corrections to the predictions of the standard model, which serve as a probe of a possible new mass-scale Λ and other new physics.     

Anomalous gauge-boson couplings and the Higgs-boson mass

We study anomalous gauge-boson couplings induced by a locally SU(2) × U(1) invariant effective Lagrangian containing ten operators of dimension six built from boson fields of the standard model (SM) before spontaneous symmetry breaking (SSB). After SSB some operators lead to new three- and four-gauge-boson interactions, some contribute to the diagonal and off-diagonal kinetic terms of the gauge bosons, to the kinetic term of the Higgs boson and to the mass terms of the W and Z bosons. This requires a renormalisation of the gauge-boson fields, which, in turn, modifies the charged- and neutral-current interactions, although none of the additional operators contain fermion fields. Also the Higgs field must be renormalised. Bounds on the anomalous couplings from electroweak precision measurements at LEP and SLC are correlated with the Higgs-boson mass m_H. Rather moderate values of anomalous couplings allow m_H up to 500 GeV. At a future linear collider the triple-gauge-boson couplings and ZWW can be measured in the reaction . We compare three approaches to anomalous gauge-boson couplings: the form-factor approach, the addition of anomalous-coupling terms to the SM Lagrangian after and, as outlined above, before SSB. The translation of the bounds on the couplings from one approach to another is not straightforward. We show that it can be done for the process by defining new effective and ZWW couplings.Received: 8 June 2004, Revised: 26 January 2005, Published online: 8 June 2005     

Two-photon exchange contributions to elastic ep scattering in the non-local field formalism

We construct a non-local gauge-invariant Lagrangian to model the electromagnetic interaction of the proton. The Lagrangian includes all allowed operators with dimension up to five. We compute the two-photon exchange contribution to elastic electron–proton scattering using this effective non-local Lagrangian. The one-loop calculation in this model includes the standard box and cross box diagram with the standard on-shell form of the hadron electromagnetic vertices. Besides this we find an extra contribution, which depends on an unknown constant. We use experimentally extracted form factors for our calculation. We find that the correction to the reduced cross section is slightly non-linear as a function of the photon longitudinal polarization ε. The non-linearity seen is within the experimental error bars of the Rosenbluth data. The final result completely explains the difference between the form factor ratio G_E/G_M extracted by Rosenbluth separation technique at SLAC and polarization transfer technique at JLAB.     

Emission pattern of high-energy pions: A new probe for the early phase of heavy-Ion collisions

Recent results from CLEO on B-->Kpi indicate that the phase gamma may be substantially different from that obtained from other fit to the KM matrix elements in the standard model. We show that gamma extracted using B-->Kpi,pipi is sensitive to new physics occurring at loop level. It provides a powerful method to probe new physics in electroweak penguin interactions. Using effects due to anomalous gauge couplings as an example, we show that within the allowed ranges for these couplings information about gamma obtained from B-->Kpi,pipi can be very different from the standard model prediction.     

Flavor changing neutral currents in the Lee–Wick Standard Model

Recently an extension of the Standard Model (the Lee–Wick Standard Model) based on ideas of Lee and Wick (LW) was introduced. It does not contain quadratic divergences in the Higgs mass and hence solves the hierarchy puzzle. The LW Standard Model contains new heavy LW-resonances at the TeV scale that decay to ordinary particles. In this Letter we examine in more detail the flavor structure of the theory. We integrate out the heavy LW-fermions at tree level and find that this induces flavor changing Z-boson couplings. However, these flavor changing neutral currents are acceptably small since they are automatically suppressed by small Yukawa couplings. This is the case even though the theory does not satisfy the principle of minimal flavor violation. New couplings of the charged W-bosons to quarks and leptons are also induced. We also integrate out the LW–Higgs and examine the four-fermion operators induced.     

Effective field theory: A modern approach to anomalous couplings

We advocate an effective field theory approach to anomalous couplings. The effective field theory approach is the natural way to extend the standard model such that the gauge symmetries are respected. It is general enough to capture any physics beyond the standard model, yet also provides guidance as to the most likely place to see the effects of new physics. The effective field theory approach also clarifies that one need not be concerned with the violation of unitarity in scattering processes at high energy. We apply these ideas to pair production of electroweak vector bosons.     

Black hole evaporation with separated fermions

In models with a low quantum gravity scale, fast proton decay can be avoided by localizing quarks and leptons to separated positions in an extra 1/TeV sized dimension with gauge and Higgs fields living throughout. Black holes with masses of the order of the quantum gravity scale are therefore expected to evaporate nonuniversally, preferentially radiating directly into quarks or leptons but not both. Should black holes be copiously produced at a future hadron collider, we find the ratio of final state jets to charged leptons to photons is 113:8:1, which differs from previous analyses that assumed all standard model fields live at the same point in the extra dimensional space.