Large CP-violating Effects Research Articles

Predicting the values of the leptonic CP violation phases in theories with discrete flavour symmetries

Using the fact that the neutrino mixing matrix U=Ue†Uν, where Ue and Uν result from the diagonalisation of the charged lepton and neutrino mass matrices, we consider a number of forms of Uν associated with a variety of discrete symmetries: i) bimaximal (BM) and ii) tri-bimaximal (TBM) forms, the forms corresponding iii) to the conservation of the lepton charge L′=Le−Lμ−Lτ (LC), iv) to golden ratio type A (GRA) mixing, v) to golden ratio type B (GRB) mixing, and vi) to hexagonal (HG) mixing. Employing the minimal form of Ue, in terms of angles and phases it contains, that can provide the requisite corrections to Uν so that reactor, atmospheric and solar neutrino mixing angles θ13, θ23 and θ12 have values compatible with the current data, including a possible sizable deviation of θ23 from π/4, we discuss the possibility to obtain predictions for the CP violation phases in the neutrino mixing matrix. Considering the “standard ordering” of the 12 and the 23 rotations in Ue and following the approach developed in [1] we derive predictions for the Dirac phase δ and the rephasing invariant JCP in the cases of GRA, GRB and HG forms of Uν (results for the TBM and BM (LC) forms were obtained in [1]). We show also that under rather general conditions within the scheme considered the values of the Majorana phases in the PMNS matrix can be predicted for each of the forms of Uν discussed. We give examples of these predictions and of their implications for neutrinoless double beta decay. In the GRA, GRB and HG cases, as in the TBM one, relatively large CP violation effects in neutrino oscillations are predicted (|JCP|∼(0.031–0.034)). Distinguishing between the TBM, BM (LC), GRA, GRB and HG forms of Uν requires a measurement of cos⁡δ or a relatively high precision measurement of JCP.

Less space for a new family of fermions

We investigate the experimentally allowed parameter space of an extension of the standard model (SM3) by one additional family of fermions. Therefore we extend our previous study of the CKM like mixing constraints of a fourth generation of quarks. In addition to the bounds from tree-level determinations of the 3$\times$3 CKM elements and FCNC processes ($K$-, $D$-, $B_d$-, $B_s$-mixing and the decay $b \to s \gamma$) we also investigate the electroweak $S$, $T$, $U$ parameters, the angle $\gamma$ of the unitarity triangle and the rare decay $B_s \to \mu^+ \mu^-$. Moreover we improve our treatment of the QCD corrections compared to our previous analysis. We also take leptonic contributions into account, but we neglect the mixing among leptons. As a result we find that typically small mixing with the fourth family is favored, but still some sizeable deviations from the SM3 results are not yet excluded. The minimal possible value of $V_{tb}$ is 0.93. Also very large CP-violating effects in $B_s$ mixing seem to be impossible within an extension of the SM3 that consists of an additional fermion family alone. We find a delicate interplay of electroweak and flavor observables, which strongly suggests that a separate treatment of the two sectors is not feasible. In particular we show that the inclusion of the full CKM dependence of the $S$ and $T$ parameters in principle allows the existence of a degenerate fourth generation of quarks.

Formula omitted], [formula omitted] and new physics

We consider the New-Physics (NP) solution to the polarization puzzle in B→ϕK∗ decays. We note that any such solution must reproduce the data in Bd0→ϕKS, where there are disagreements with the standard model in CP-asymmetry measurements. We examine 10 NP operators, of S/P, V/A and T variety. We find that, as long as Bd0→ϕKS exhibits large CP-violating effects, no single operator can explain the observations in both B→ϕK∗ and Bd0→ϕKS. For 2-NP-operator solutions, there are four possibilities, all of S/P type, which are presently allowed. We discuss ways of distinguishing among these solutions in the future. Models which contain only V/A operators, such as those with supersymmetry or extra Z′ bosons, cannot explain both Bd0→ϕKS and B→ϕK∗ data. On the other hand, the two-Higgs-doublet model, which has only S/P operators, is favored.

CP-violating Higgs boson mixing in chargino production at the muon collider

We study the pair-production of charginos in the CP-violating Minimal Supersymmetric Standard Model at center-of-mass energies around the heavy neutral Higgs boson resonances. If these resonances are nearly degenerate, as it can happen in the Higgs decoupling limit, radiatively induced scalar-pseudoscalar transitions can be strongly enhanced. The resulting mixing in the Higgs sector leads to large CP-violating effects, and a change of their mass spectrum. For longitudinally polarized muon beams, we analyze CP asymmetries which are sensitive to the interference of the two heavy neutral Higgs bosons. We present a detailed numerical analysis of the cross sections, chargino branching ratios, and the CP observables. We obtain sizable CP-asymmetries, which would be accessible in future measurements at a muon collider. Especially for intermediate values of the parameter \tan\beta, where the largest branching ratios of Higgs bosons into charginos are expected, this process allows to analyze the Higgs sector properties and its interaction to supersymmetric fermions.

Dirac leptogenesis and anomalous U(1)

We consider Dirac leptogenesis in supersymmetric theories where the supersymmetry breaking is transmitted to the observable sector by an anomalous U(1) symmetry. This kind of supersymmetry breaking is known to provide a solution to the μ problem and avoid large CP-violation effects. The asymmetries generated by the decays of heavy leptons do not suffer from wash-out due to the equilibration of left- and right-handed neutrinos thanks to the extreme smallness of the neutrino masses. The model ties up the smallness of the neutrino masses and the out-of-equilibrium nature of the heavy lepton decays with no tension with the overproduction of gravitinos.

Measuring the weak phaseγin color allowedB→DKπdecays

We present a method to measure the weak phase gamma in the three-body decay of charged B mesons to the final states D K pi0. These decays are mediated by interfering amplitudes which are color-allowed and hence relatively large. As a result, large CP violation effects that could be observed with high statistical significance are possible. In addition, the three-body decay helps resolve discrete ambiguities that are usually present in measurements of the weak phase. The experimental implications of conducting these measurements with three-body decays are discussed, and the sensitivity of the method is evaluated using a simulation.

Possible large directCPviolations in charmlessBmeson decays: Summary report on the PQCD method

We discuss the perturbative QCD approach for the exclusive two body B-meson decays to light mesons. We briefly review its ingredients and some important theoretical issues on factorization approach. We show numerical results which are compatible with present experimantal data for the charmless B-meson decays. Specailly we predict the possibility of large direct CP violation effects in $B^0 \to \pi^{+}\pi^{-}$ $(23\pm7 %)$ and $B^0\to K^{+}\pi^{-}$ $(-17\pm5%)$. In the last section we investigate two methods to determine the weak phases $\phi_2$ and $\phi_3$ from $B \to \pi\pi,K\pi$ processes. We obtain bounds on $\phi_2$ and $\phi_3$ from present experimental measurements.

Flavor-conservingCPphases in supersymmetry and implications for exclusiveBdecays

We study rare exclusive B decays based on the quark-level transition b->s(d)l^+l^-, where l=e or mu, in the context of supersymmetric theories with minimal flavour violation. We present analytic expressions for various mixing matrices in the presence of new CP-violating phases, and examine their impact on observables involving B and \bar{B} decays. An estimate is obtained for CP-violating asymmetries in B->K^(*)l^+l^- and B->rho(pi)l^+l^- decays for the dilepton invariant mass region 1.2 GeV < M_{l^+l^-}< M_{J/psi}. As a typical result, we find a CP-violating partial width asymmetry of about -6% (-5%) in the case of B->pi (B->rho) in effective supersymmetry with phases of O(1), taking into account the measurement of the inclusive b->s gamma branching fraction. On the other hand, CP asymmetries of less than 1% are predicted in the case of B->K^(*). We argue that it is not sufficient to have additional CP phases of O(1) to observe large CP-violating effects in exclusive b->s(d)l^+l^- decays.

CP violation and the CKM angle γ from angular distributions of untagged Bs decays governed by [formula omitted

We demonstrate that time-dependent studies of angular distributions for B s decays caused by b → cu s quark-level transitions extract clearly and model-independently the CKM angle γ. This CKM angle could be cleanly determined from untagged B s decays alone, if the lifetime difference between the B s mass eigenstates B s L and B s H is sizable. The time dependences for the relevant tagged and untagged observables are given both in a general notation and in terms of linear polarization states and should exhibit large CP-violating effects. These observables may furthermore provide insights into the hadronization dynamics of the corresponding exclusive B s decays, thereby allowing tests of the factorization hypothesis.

Electroweak chiral Lagrangian andCP-violating effects in technicolor theories

We estimate the CP-violating WW\ensuremath{\gamma} and WWZ anomalous form factors, arising from CP-violating interactions in extended technicolor theories, and discuss their future experimental detectability. The electric dipole moment of the W boson is found to be as large as \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}21}$ e cm. We connect the CP-odd WW\ensuremath{\gamma} and WWZ couplings to the corresponding CP-violating electroweak chiral Lagrangian operators. The electric dipole moments of the neutron and the electron in technicolor theories are estimated to be as large as \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}26}$ and \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}29}$ cm, respectively. We also suggest the potential to observe large CP-violating technicolor effects in the decay t\ensuremath{\rightarrow}b+${\mathit{W}}^{+}$.

Neutrino mass physics

It is shown that, even if right-handed currents exist, the observation of ν → ν oscillation would imply not only that neutrinos are their own antiparticles but also that they have mass. If neutrinos are their own antiparticles, then there can be large CP-violating effects in the leptonic sector even if only two of the lepton generations mix appreciably. However, the nature of the CP-violating signals can be constrained by CPT invariance. In general, neutrinos can have transition electromagnetic dipole moments, and, if they are not their own antiparticles, non-transition moments as well. The role of neutrino-electron scattering in bounding these moments, and the implications for radiative neutrino decay, and for the solar neutrino flux, are discussed.

CP violation in the lepton sector with small neutrino masses

Small, even vanishing neutrino masses are consistent with large CP violation effects in the leptonic sector. As an example, and a proof of existence of this situation, we present a model based on the SU(2) L × SU(2) R × U(1) gauge symmetry, where the fermion content has been Extended to include a gauge singlet lepton S L. Interesting features of this model (which should be seen as a mere example) are: (1) neutrino masses can either vanish or be in the range where the Mikheyev-Smirnov-Wolfenstein (MSW) mechanism for the solar neutrino puzzle is operative, and (2) CP violation effects in the lepton sector are manifestly large and therefore accessible to current experiments. In particular, it is found that the electron electric dipole moment, d rme , can be of order 10 −24 e·cm; if generation mixing is negligible, the μ longitudinal polarization, P rmL , in the decay K L → μ μ can be in the range 10 −10−10 −3.

Searching for possible large CP-violation effects in neutral-charm-meson decays.

Possible large CP-violation effects in the partial-decay-rate asymmetries for the ${D}^{0}$-D\ifmmode\bar\else\textasciimacron\fi{} $^{0}$ system are discussed. All possible nonleptonic two-body final states are studied. It turns out that ${D}^{0}$\ensuremath{\rightarrow}${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${K}^{+}$, ${\ensuremath{\pi}}^{0}$${K}^{0}$, ${\ensuremath{\pi}}^{0}$\ensuremath{\eta}, ${\ensuremath{\pi}}^{0}$\ensuremath{\omega}, ${K}^{+}$${K}^{\mathrm{\ensuremath{-}}}$, \ensuremath{\varphi}${K}^{0}$ are the most promising channels. If the ${D}^{0}$-D\ifmmode\bar\else\textasciimacron\fi{} $^{0}$ mixing is on \ensuremath{\sim}1% level, ${10}^{4}$--${10}^{6}$ ${D}^{0}$D\ifmmode\bar\else\textasciimacron\fi{} $^{0}$ pairs would be enough for testing these channels.