118710763
Lepton Flavour Violation Theory
I discuss theoretical and phenomenological aspects of flavour violation in charged lepton transitions. This includes minimal extensions of the Standard Model within effective-theory approaches, as well as an incomplete selection of concrete new physics models.
17293706
A diquark model for baryons containing one heavy quark
We present a phenomenological ansatz for coupling a heavy quark with two light quarks to form a heavy baryon. The heavy quark is treated in the heavy mass limit, and the light quark dynamics is approximated by propagating scalar and axial vector ‘diquarks’. The resulting effective lagrangian, which incorporates heavy quark and chiral symmetry, describes interactions of heavy baryons with Goldstone bosons in the low energy region. As an application, the Isgur-Wise form factors are estimated.
17368261
Factorization of heavy to light form-factors in soft collinear effective theory
Abstract Heavy-to-light transition form factors at large recoil energy of the light meson have been conjectured to obey a factorization formula, where the set of form factors is reduced to a smaller number of universal form factors up to hard-scattering corrections. In this paper we extend our previous investigation of heavy-to-light currents in soft-collinear effective theory to final states with invariant mass Λ 2 as is appropriate to exclusive B meson decays. The effective theory contains soft modes and two collinear modes with virtualities of order m b Λ (“hard-collinear”) and  Λ 2 . Integrating out the hard-collinear modes results in the hard spectator-scattering contributions to exclusive B decays. We discuss the representation of heavy-to-light currents in the effective theory after integrating out the hard-collinear scale, and show that the previously conjectured factorization formula is valid to all orders in perturbation theory. The naive factorization of matrix elements in the effective theory into collinear and soft matrix elements may be invalidated by divergences in convolution integrals. In the factorization proof we circumvent the explicit regularization of endpoint divergences by a definition of the universal form factors that includes hard-collinear, collinear and soft effects.
119204322
Patterns of flavour violation in the presence of a fourth generation of quarks and leptons
We calculate a number of observables related to particle-antiparticle mixing and the branching ratios for the most interesting rare and CP-violating K and B decays in the Standard Model (SM3) extended by a fourth generation of quarks and leptons (SM4). A model-independent parametrisation of these observables in terms of gauge-independent functions is adopted, which is useful for studying the breaking of the universality between K, Bd and Bs systems through non-minimal flavour violating interactions. We calculate first the mass differences ΔMi in the neutral K and B systems, the mixing-induced CP asymmetries $ {S_{\psi {K_S}}} $, Sψϕ, $ {S_{\phi {K_S}}} $, $ {S_{\eta '{K_S}}} $ and εK. Subsequently, a detailed analysis of $ {K^{+} } \to {\pi^{+} }\nu \bar{\nu } $, $ {K_L} \to {\pi^0}\nu \bar{\nu } $, Bs,d → μ+μ−, $ B \to {X_{s,d}}\nu \bar{\nu } $, KL → π0ℓ+ℓ−, B → Xsγ and B → Xs,dℓ+ℓ− is presented, and also ε′/ε is considered. For some of these observables the departures from SM3 predictions can still be spectacular.We discuss how the new mixing parameters (3 angles, 2 CP phases) can be determined using the flavour observables in question. We identify the different hierarchical structures in the SM4 flavour mixing matrix, allowed by phenomenological and theoretical constraints, and define the corresponding generalised Wolfenstein expansion. Most importantly, we show how the characteristic patterns of correlations among the considered flavour observables allow to distinguish this New Physics scenario from supersymmetric flavour models, the Littlest Higgs model with T-parity and the Randall-Sundrum model with custodial protection. Of particular importance are the correlations involving Sψϕ, $ {S_{\phi {K_S}}} $, $ {\text{Br}}\left( {{K^{+} } \to {\pi^{+} }\nu \bar{\nu }} \right) $, $ {\text{Br}}\left( {{K_L} \to {\pi^0}\nu \bar{\nu }} \right) $ and Br(Bs,d → μ+μ−), which could in principle rule out the SM4. Interestingly ε′/ε turns out to be suppressed below the data for large positive values of Sψϕ unless the relevant hadronic matrix elements differ strongly from the large N results. The important role of ε′/ε in bounding large enhancements of rare K decay branching ratios is reemphasised. We also show how the existing anomalies in the unitarity triangle fits as well as in Sψϕ and $ {S_{\phi {K_S}}} $ can be simultaneously explained in the SM4 scenario.
119307893
The impact of a 4th generation on mixing and CP violation in the charm system
We study $$ {D^0} - {\overline D^0} $$ mixing in the presence of a fourth generation of quarks. In particular, we calculate the size of the allowed CP violation which is found at the observable level well beyond anything possible with CKM dynamics. We calculate the semileptonic asymmetry aSL(D) and the mixing induced CP asymmetry ηfSf (D) which are correlated with each other. We also investigate the correlation of ηfSf (D) with a number of prominent observables in other mesonic systems like ε′/ε, Br(KL → π0$$ \nu \overline \nu $$), Br(K+ → π+$$ \nu \overline \nu $$), Br(Bs → μ+μ-), Br(Bd → μ+μ-) and finally Sψϕ(Bs) in the Bs system. We identify a clear pattern of flavour and CP violation predicted by the SM4 model: While simultaneous large 4G effects in the K and D systems are possible, accompanying large NP effects in the Bd system are disfavoured. However this behaviour is not as pronounced as found for the LHT and RSc models. In contrast to this, sizeable CP violating effects in the Bs system are possible unless extreme effects in ηfSf (D) are found, and Br(Bs → μ+μ-) can be strongly enhanced regardless of the situation in the D system. We find that, on the other hand, Sψϕ(Bs) > 0.2 combined with the measured ε′/ε significantly diminishes 4G effects within the D system.
118537993
B-meson light-cone distribution amplitude: Perturbative constraints and asymptotic behavior in dual space
Based on the dual representation in terms of the recently established eigenfunctions of the evolution kernel in heavy-quark effective theory, we investigate the description of the B-meson light-cone distribution amplitude (LCDA) beyond tree-level. In particular, in dual space, small and large momenta do not mix under renormalization, and therefore perturbative constraints from a short-distance expansion in the parton picture can be implemented independently from non-perturbative modelling of long-distance effects. It also allows to (locally) resum perturbative logarithms from large dual momenta at fixed values of the renormalization scale. We construct a generic procedure to combine perturbative and non-perturbative information on the B-meson LCDA and compare different model functions and the resulting logarithmic moments which are the relevant hadronic parameters in QCD factorization theorems for exclusive B-meson decays.
53502912
Remote atomic clock synchronization via satellites and optical fibers
Abstract. In the global network of institutions engaged with the realization of International Atomic Time (TAI), atomic clocks and time scales are compared by means of the Global Positioning System (GPS) and by employing telecommunication satellites for two-way satellite time and frequency transfer (TWSTFT). The frequencies of the state-of-the-art primary caesium fountain clocks can be compared at the level of 10−15 (relative, 1 day averaging) and time scales can be synchronized with an uncertainty of one nanosecond. Future improvements of worldwide clock comparisons will require also an improvement of the local signal distribution systems. For example, the future ACES (atomic clock ensemble in space) mission shall demonstrate remote time scale comparisons at the uncertainty level of 100 ps. To ensure that the ACES ground instrument will be synchronized to the local time scale at the Physikalisch-Technische Bundesanstalt (PTB) without a significant uncertainty contribution, we have developed a means for calibrated clock comparisons through optical fibers. An uncertainty below 40 ps over a distance of 2 km has been demonstrated on the campus of PTB. This technology is thus in general a promising candidate for synchronization of enhanced time transfer equipment with the local realizations of Coordinated Universal Time UTC. Based on these experiments we estimate the uncertainty level for calibrated time transfer through optical fibers over longer distances. These findings are compared with the current status and developments of satellite based time transfer systems, with a focus on the calibration techniques for operational systems.