Disentangling Neutrino Oscillations

The theory underlying neutrino oscillations has been described at length in the literature. The neutrino state produced by a weak decay is usually portrayed as a linear superposition of mass eigenstates with, variously, equal energies or equal momenta. We point out that such a description is incomplete, that in fact, the neutrino is entangled with the other particle or particles emerging from the decay. We offer an analysis of oscillation phenomena involving neutrinos (applying equally well to neutral mesons) that takes entanglement into account. Thereby we present a theoretically sound proof of the universal validity of the oscillation formulae ordinarily used. In so doing, we show that the departures from exponential decay reported by the GSI experiment cannot be attributed to neutrino mixing. Furthermore, we demonstrate that the `Mossbauer' neutrino oscillation experiment proposed by Raghavan, while technically challenging, is correctly and unambiguously describable by means of the usual oscillation formalae.Comment: 16 page

Constraining CP violation in neutral meson mixing with theory input

There has been a lot of recent interest in the experimental hints of CP violation in B_{d,s}^0 mixing, which would be a clear signal of beyond the standard model physics (with higher significance). We derive a new relation for the mixing parameters, which allows clearer interpretation of the data in models in which new physics enters in M_12 and/or \Gamma_12. Our results imply that the central value of the D\O\ measurement of the semileptonic CP asymmetry in B_{d,s}^0 decay is not only in conflict with the standard model, but in a stronger tension with data on \Delta\Gamma_s than previously appreciated. This result can be used to improve the constraint on \Delta\Gamma or A_SL, whichever is less precisely measured.Comment: 5 pages, 2 figures, informed of prior derivation of eq. (21), title modifie

1/m_Q Corrections to the Heavy-to-Light-Vector Transitions in the HQET

Within the HQET, the heavy to light vector meson transitions are systematically analyzed to the order of 1/m_Q. Besides the four universal functions at the leading order, there are twenty-two independent universal form factors at the order of 1/m_Q. Both the semileptonic decay B->\rho which is relevant to the |V_{ub}| extraction, and the penguin induced decay B -> K^* which is important to new physics discovering, depend on these form factors. Phenomenological implications are discussed.Comment: RevTeX, 9 pages, no figure

Corrections of Order ΛQCD2/mc2\Lambda^2_{QCD}/m^2_c to Inclusive Rare B Decays

We calculate nonperturbative ${\cal O}(\Lambda^2_{QCD}/m^2_c)$ corrections to the dilepton invariant mass spectrum and the forward-backward charge asymmetry in $B\to X_se^+e^-$ decay using a heavy quark expansion approach. The method has recently been used to estimate long-distance effects in $B\to X_s\gamma$. We generalize this analysis to the case of nonvanishing photon invariant mass, $q^2\not= 0$, relevant for the rare decay mode $B\to X_se^+e^-$. In the phenomenologically interesting $q^2$ region away from the $c\bar c$ resonances, the heavy quark expansion approach should provide a reasonable description of possible nonperturbative corrections. In particular this picture is preferable to the model-dependent approach relying on the tails of Breit-Wigner resonances, which has been employed so far in the literature to account for these effects. We find that the ${\cal O}(\Lambda^2_{QCD}/m^2_c)$ corrections to the dilepton invariant mass spectrum and to the forward-backward asymmetry in $B\to X_se^+e^-$ amount to several percent at most for $q^2/m^2_b < 0.3$ and $q^2/m^2_b > 0.6$. The ${\cal O}(\Lambda^2_{QCD}/m^2_c)$ correction to the $B\to X_s\gamma$ decay rate is also computed and found to be +3%, which agrees in magnitude with previous calculations. Finally, we comment on long-distance effects in $B\to X_s\nu\bar\nu$, which in this case are extremely suppressed due to the absence of virtual photon contributions.Comment: Latex, 15 pages, 3 figures (included

Non-perturbative Effects in B→Xsl+l−B\to X_sl^+l^-

The rare decay $B\to X_sl^+l^-$ provides excellent prospects for precision tests of Standard Model flavour dynamics. The process can be computed in perturbation theory with small uncertainty. However, in order to ensure a reliable theoretical prediction, also potentially important effects from non-perturbative QCD have to be controlled with sufficient accuracy. The present article summarizes recent developments related to this topic.Comment: Invited Talk presented at the QCD Euroconference 98, Montpellier, 2-8 July 1998, 7 pages, 1 figur

B -> K^* gamma from D -> K^* l nu

The B -> K^* gamma branching fraction is predicted using heavy quark spin symmetry at large recoil to relate the tensor and (axial-)vector form factors, using heavy quark flavor symmetry to relate the B decay form factors to the measured D -> K^* l nu form form factors, and extrapolating the semileptonic B decay form factors to large recoil assuming nearest pole dominance. This prediction agrees with data surprisingly well, and we comment on its implications for the extraction of |Vub| from B -> rho l nu.Comment: 10 page

New Physics with earliest LHC data

We investigate which new physics models could be discovered in the first year of the LHC. Such a “Supermodel” is a new physics scenario for which the LHC sensitivity with only 10 pb−1 useful luminosity is greater than that of the Tevatron with 10 fb−1. The simplest supermodels involve s-channel resonances in the quark-antiquark and especially in the quark-quark channels. We concentrate on easily visible final states with small standard model backgrounds, and suggest simple searches, besides those for Z states, which could discover new physics in early LHC data

Relativistic quantum theories and neutrino oscillations

Neutrino oscillations are examined under the broad requirements of Poincar\'e-invariant scattering theory in an S-matrix formulation. This approach can be consistently applied to theories with either field or particle degrees of freedom. The goal of this paper is to use this general framework to identify all of the unique physical properties of this problem that lead to a simple oscillation formula. We discuss what is in principle observable, and how many factors that are important in principle end up being negligible in practice.Comment: 21 pages, no figure

Combining exclusive semi-leptonic and hadronic B decays to measure |V_ub|

The Cabibbo-Kobayashi-Maskawa matrix element |V_ub| can be extracted from the rate for the semi-leptonic decay B -> pi + l + antineutrino_l, with little theoretical uncertainty, provided the hadronic form factor for the B -> pi transition can be measured from some other B decay. In here, we suggest using the decay B -> pi J\psi. This is a color suppressed decay, and it cannot be properly described within the usual factorization approximation; we use instead a simple and very general phenomenological model for the b d J\psi vertex. In order to relate the hadronic form factors in the B -> pi J\psi and B -> pi + l + antineutrino_l decays, we use form factor relations that hold for heavy-to-light transitions at large recoil.Comment: Latex, 7 pages, no figure