Top flavour signal in thep\bar p collider events—A detailed analysis with flavour creation and excitation models

The single jet electron events recently observed by the UA1 collaboration at the protonantiproton collider are analysed in terms of top flavour production using both flavour creation and excitation mechanisms. A top particle of mass ～ 35 GeV can naturally account for both the event topology (isolated electron coming back to back with a jet) and the neutrinop _T distribution relative to the electron, irrespective of the production mechanism. Each of the two production mechanisms gives an event rate any where between the observed rate and an order of magnitude lower, depending on the model parameters. They can be easily distinguished, however, by studying the jet coming back to back with the electron. It is predicted to be a fat jet containing a top particle for flavour creation and an ordinary narrow jet for flavour excitation. A detailed list of other predictions is given, which can be tested with the available or the forthcoming data. Some of these provide further tests of the top signal irrespective of the production mechanism, while others can discriminate between the two mechanisms as well as between different models for flavour excitation. It is also shown that not only are the available event characteristics naturally explained by top, but they cannot be explained by any other mechanism explored so far.     

Flavour physics and CP violation

It is well known that the study of flavour physics and CP violation is very important to critically test the Standard Model and to look for possible signature of new physics beyond it. The observation of CP violation in kaon system in 1964 has ignited a lot of experimental and theoretical efforts to understand its origin and to look for CP violation effects in other systems besides the neutral kaons. The two B-factories BABAR and BELLE, along with other experiments, in the last decade or so made studies in flavour physics and CP violation a very interesting one. In this article we discuss the status and prospectives of the flavour physics associated with the strange, charm and bottom sectors of the Standard Model. The important results in kaon sector will be briefly discussed. Recently, mixing in the charm system has been observed, which was being pursued for quite some time without any success. The smallness of the mixing parameters in the charm system is due to the hierarchical structure of the CKM matrix. Interestingly, so far we have not found CP violation in the charm system but in the future, with more dedicated experiments at charm threshold, the situation could change. Many interesting observations have been made in the case of bottom mesons and some of them show some kind of deviations from that of the Standard Model expectations which are mainly associated with the b → s flavour changing neutral current transitions. It is long believed that the B _s system could be the harbinger of new physics since it is a system in which both bottom and strange quarks are the constituents. Recently, D0 and CDF announced their result for the B _s mixing which is claimed to be the first possible new physics signature in the flavour sector. We plan to touch upon all important issues pointing out both theoretical and experimental developments and future prospects in this review article.     

Flavoured co-annihilation

In minimal supergravity (mSUGRA) or CMSSM, one of the main co-annihilating partners of the neutralino is the lightest stau, $\tilde{\tau}_1$ . In the presence of flavour violation in the right-handed sector, the co-annihilating partner would be a flavour mixed state. The flavour effect is two-fold: (a) It changes the mass of $\tilde{\tau}_{1}$ , thus modifying the parameter space of the co-annihilation and (b) flavour violating scatterings could now contribute to the cross-sections in the early Universe. In fact, it is shown that for large enough ??~0.2, these processes would constitute the dominant channels in co-annihilation regions. The amount of flavour mixing permissible is constrained by flavour violating ?????? or ????e processes. For ??_RR mass insertions, the constraints from flavour violation are not strong enough in some regions of the parameter space due to partial cancellations in the amplitudes. In mSUGRA, the regions with cancelations within LFV amplitudes do not overlap with the regions of co-annihilations. In non-universal Higgs model (NUHM), however, these regions do overlap leading to significant flavoured co-annihilations. At the LHC and other colliders, these regions can constitute for interesting signals.     

R-parity violation and unification

The reported anomaly in deep-inelastic scattering at HERA has revived interest in the phenomenology of R-parity violation. From the theoretical point of view, the existence of R-violating interactions poses two considerable problems. The first one concerns the flavour structure of the interactions and the origin of an appropriate suppression of flavour-changing neutral-current processes and lepton-family transitions. The second one concerns the way of embedding R-violating interactions in a grand unified theory (GUT) without introducing unacceptable nucleon decay rates. We show that the second problem can be solved by mechanism which is purely group theoretical and does not rely on details of the flavour theory. We construct explicit GUT models in which our mechanism can be realized.     

Measuring and fully testing KM unitarity in\Upsilon (4S) \to B_d \bar B_d decays

It is usually suggested to measure the three angles ?₁, ?₂ and ?₃ of the KM unitarity triangle via the CP asymmetries in the reactionsB _d →ψK _S ,B _d →ππ andB _s →K _S ρ^O respectively. There are obviously many major obstacles to the successful completion of such a program; of those two will be addressed in this note: (i) The CP asymmetry inB _d →ππ could a priori be affected by strong final state interactions that depend on long distance dynamics. (ii) The expected rapid rate of \(B_s - \bar B_s\) oscillations will make it very difficult to measure CP asymmetries inB _s decays. I describe various methods for extracting ?₂ and ?₃ directly from CP asymmetries inB _d decays even in the presence of significant strong final state interactions.     

Spontaneous CP violation in left-right symmetric gauge theories

Motivated by arguments in favour of spontaneous CP violation, we investigate the general conditions imposed by P and CP invariance on the Yukawa couplings in SU(2)_L × SU(2)_R × U(1) gauge theories. A complete discussion of these constraints is presented for two minimal Higgs sectors. In addition to the standard case of manifest CP invariance, we find two phenomenologically interesting models where the P and CP transformations are non-aligned in flavour and Higgs spaces. To a certain extent, P and CP invariance may be responsible for the existence of horizontal symmetries. An intimate connection between CP violation and the general flavour problem emerges.     

Heavy axions from strong broken horizontal gauge symmetry

We study the consequences of the existence and breaking of a Peccei-Quinn symmetry within the context of a dynamical model of electroweak symmetry breaking based on broken gauged flavour symmetries. We perform an estimate of the axion mass by including flavour instanton effects and show that, for low cut-offs, the axion is sufficiently massive to prevent it from being phenomenologically unacceptable. We conclude with an examination of the strong CP problem and show that our axion cannot solve the problem, though we indicate ways in which the model can be extended so that the strong CP problem is solved.     

CP-violation from horizontal interactions

We consider a horizontal SU (3)_H × SU (2)_L × U (1) model in which the Cabibbo mixing and the CP-violation have common origin in the presence of the horizontal interactions. The measure of the CP-violation, which is found to be naturally small, is associated with the horizontal scale.     

Hermitian flavor violation

The fundamental constraint on two Higgs doublet models comes from the requirement of sufficiently suppressing flavor-changing neutral currents. There are various standard approaches for dealing with this problem, but they all tend to share a common feature; all of the Higgs doublets couple very weakly to the first generation quarks. Here we consider a simple two Higgs doublet model which is able to have large couplings to the first generation, while also being safe from flavor constraints. We assume only that there is an SUf(3) flavor symmetry which is respected by the couplings of one of the Higgs doublets, and which is broken by Hermitian Yukawa couplings of the second doublet. As a result of the large permitted couplings to the first generation quarks, this scenario may be used to address the excess in W+dijet events recently observed by CDF at the Tevatron. Moreover, Hermitian Yukawa coupling matrices arise naturally in a broad class of solutions to the strong CP problem, providing a compelling context for the model.     

Models and new phenomenological implications of a class of pseudo-Goldstone bosons

Light pseudo-Goldstone bosons, with mixed CP quantum numbers leading to scalar couplings, can arise naturally in extensions of the standard model. We study several models in detail, including supersymmetric and flavour symmetric theories containing invisible axions and these new objects. They yield new phenomenological implications: (1) potentially detectable long-range forces; (2) quark and lepton masses and mixing angles sensitive to the classical background field; (3) finite gauge-coupling renormalizations in classical fields; and (4) ƒ_axion can be raised to 10¹⁵ GeV by resonant de-excitation. The possibility of experimental detection of variations in masses, charges and mixing angles is discussed in some detail.     

Invariance of Jarlskog Determinant Above the GUT Scale

An asymmetry between the probabilities P(ν _μ →ν _e ) and \(P(\bar {\nu _{\mu }}\rightarrow \bar {\nu _{e}})\) would be direct indication of CP violation at the fundamental level. Planck scale effects on neutrino mixing, we have derived the mixing angles of neutrino flavour due to Planck scale effects. It has been shown that Jarlskog determinant remains nearly invariant above the GUT scale.     

Spontaneous CP violation in a SUSY model with a complex CKM

It is pointed out that the recent measurement of the angle γ   of the unitarity triangle, providing irrefutable evidence for a complex Cabibbo–Kobayashi–Maskawa (CKM) matrix, presents a great challenge for supersymmetric models with spontaneous CP violation. We construct a new minimal extension of the minimal supersymmetric standard model (MSSM), with spontaneous CP breaking, which leads to a complex CKM matrix, thus conforming to present experimental data. This is achieved through the introduction of two singlet chiral superfields and a vector-like quark chiral superfield which mixes with the standard quarks. A Z₃$Z_3$ symmetry is introduced in order to have a potential solution to the strong CP problem.     

Bemerkungen zum Kleinschen Paradoxon

The problem of stationary energy eigenstates of relativistic spin 1/2-particles in external potentials exceeding twice the particles rest mass (Klein's paradox) is investigated, neglecting the interaction of the particles with the radiation field. This corresponds to theH ₀ of the “bound state interaction representation” in quantum electrodynamics. For simplicity, explicit calculations are based on a one dimensional square well potential. In potentials of this type which vanish at infinity and which do not become critically singular at the origin there always exists a stationary ground state of fixed total charge. Though this state, naturally, cannot be attributed to a sharp number of particles, no real paradox occurs.     

A fresh look into the neutron EDM and magnetic susceptibility

We reexamine the estimate of the neutron electric dipole moment (NEDM) from chiral and QCD spectral sum rules (QSSR) approaches. In the former, we evaluate the pion mass corrections which are about 5% of the leading Log results. However, the chiral estimate can be affected by the unknown value of the renormalizaton scale ν  . For QSSR, we analyze the effect of the nucleon interpolating currents on the existing predictions. We conclude that previous QSSR results are not obtained within the optimal choice of these operators, which lead to an overestimate of these results by about a factor 4. The weakest upper bound |θ|?2×¹⁰⁻⁹$|\theta |?2\times {10}^{\mathrm{-9}}$ for the strong CP  -violating angle is obtained from QSSR, while the strongest upper bound |θ|?1.3×¹⁰⁻¹⁰$|\theta |?1.3\times {10}^{\mathrm{-10}}$ comes from the chiral approach evaluated at the scale ν=MN$\nu =M_N$. We also re-estimate the proton magnetic susceptibility, which is an important input in the QSSR estimate of the NEDM.     

Radiative quark masses constrained by the gauge group only

We discuss the possibility of obtaining the observed pattern of quark masses and mixings as a consequence of radiative corrections, gauge invariance and particle content of the theory. We do not allow any kind of additional symmetry, such as family and discrete symmetries. A model based on the gauge groupSU(3)×SU(2) _L ×SU(2) _R ×U(1) _B?L is considered. It turns out that the correct values of quark masses can be reasonably reproduced. The typical strength of the flavour changing couplings of theZ ⁰-boson is however at least one order of magnitude above the experimental upper bounds. A comparison is made with a model in which an additional discrete symmetry is present. In this case flavour changing phenomena can be kept under control.     

Natural suppression of strong P and T non-invariance

In gauge theories with spontaneously broken left-right symmetry, strong P and T non-invariant effects can also be made to vanish naturally in the tree approximation without introducing massless quarks or axions. In a four-flavor SU(2)_L × SU(2)_R × U(1)_L+R model with manifest left-right symmetry, we show that strong CP noninvariance is absent up to the one-loop level and weak CP-violation is of superweak type. Extension to the case of six quarks gives a left-right symmetric generalization of the Kobayashi-Maskawa model without axions.     

Decoupling of heavy quarks in quantum chromodynamics

Decoupling of heavy quarks in quantum chromodynamics (QCD) defined by mass-independent renormalization is investigated. The structure of the relations between the parameters of f flavour QCD and the parameters of the effective f ? 1 flavour QCD below a heavy-quark threshold is discussed to all orders in the loop expansion, and the relations are computed to two-loop approximation for the minimal subtraction schemes (MS) and to one-loop approximation for some Weinberg schemes. These matching relations can be used to systematically determine the renormalization group (RG)-invariant parameters of the effective theory in terms of the RG-invariant parameters of the theory which includes the heavy quark, or vice versa. For the $\text{MS}$ scheme the connection between Λ_{f ? 1} nad Λ_f to two and three loops is given as well as the two-loop connection between the RG-invariant mass parameters of the f ? 1 and f flavour theory. The effect of heavy quarks on the evolution of the QCD coupling is of significance for present QCD phenomenology based on next-to-leading-order perturbation theory. This is illustrated with a few examples within the $\text{MS}$ scheme.     

SupersymmetricSU (11), the invisible axion,and proton decay

We supersymmetrize the very attractive flavour unification modelSU (11). As with other supersymmetric GUTs the gauge hierarchy problem is simplified, but we may also have observable (τ _p ≈10³³ yrs) proton decay. The required split multiplets are obtained by making the adjoint take a particular direction. Supersymmetry is broken softly at the TeV scale. There is a uniqueU(1) _A symmetry, and hence there are no true Nambu-Goldstone bosons. TheU(1) _A is broken at the GUT scale and there result an invisible axion and neutrino masses.     

Solving the SUSY flavour and CP problems with non-Abelian family symmetry and supergravity

Can a theory of flavour capable of describing the spectrum of fermion (including neutrino) masses and mixings also contain within it the seeds for a solution of the SUSY flavour and CP problems? We argue that supergravity together with a non-Abelian family symmetry can completely resolve the SUSY flavour and CP problems in a broad class of theories in which family symmetry and CP is spontaneously broken in the flavon sector. We show that a simple superpotential structure can suppress the F-terms of the flavons and GUT scale Higgs fields and that, if this mechanism is implemented, the resulting flavour and CP violation is suppressed and comfortably within the experimental limits. For illustration, we study a specific model based on SU(3) family symmetry, but similar models based on non-Abelian (continuous or discrete) family symmetry will lead to similar results.     

Neutrino Mass Hierarchy and CP Violation in Long Baseline Neutrino Experiment

We discuss the CP violation in long base line neutrino oscillation experiments. The direct measurement of CP violation is the difference of transitions probability between CP conjugate channels. The sign of Δ ₃₁ is not yet determined, we assume two mass hierarchy conditions, normal (Δ ₃₁>0) and inverted (Δ ₃₁<0). In this paper, we study the CP violation and neutrino mass hierarchy effect in vacuum and matter for long baseline BNL experiments. By an appropriate chose of experimental parameter, neutrino energy and traveled distance. We find that, in matter normal mass hierarchy en-chanced maximum CP violation over their invert mass hierarchy value by 12 %.