9 research outputs found
Supersymmetric Large Extra Dimensions and the Cosmological Constant Problem
This article briefly summarizes and reviews the motivations for - and the
present status of - the proposal that the small size of the observed Dark
Energy density can be understood in terms of the dynamical relaxation of two
large extra dimensions within a supersymmetric higher-dimensional theory.Comment: Talk presented to Theory Canada I, Vancouver, June 2005. References
added in V
Oxidised cosmic acceleration
We give detailed proofs of several new no-go theorems for constructing flat
four-dimensional accelerating universes from warped dimensional reduction.
These new theorems improve upon previous ones by weakening the energy
conditions, by including time-dependent compactifications, and by treating
accelerated expansion that is not precisely de Sitter. We show that de Sitter
expansion violates the higher-dimensional null energy condition (NEC) if the
compactification manifold M is one-dimensional, if its intrinsic Ricci scalar R
vanishes everywhere, or if R and the warp function satisfy a simple limit
condition. If expansion is not de Sitter, we establish threshold
equation-of-state parameters w below which accelerated expansion must be
transient. Below the threshold w there are bounds on the number of e-foldings
of expansion. If M is one-dimensional or R everywhere vanishing, exceeding the
bound implies the NEC is violated. If R does not vanish everywhere on M,
exceeding the bound implies the strong energy condition (SEC) is violated.
Observationally, the w thresholds indicate that experiments with finite
resolution in w can cleanly discriminate between different models which satisfy
or violate the relevant energy conditions.Comment: v2: corrections, references adde
Measurement of B0 ---> D(*)+ D*- branching fractions and B0 ---> D*+(s) D*- polarization with a partial reconstruction technique
We present a study of the decays B0->D_s(*)+D*-, using 20.8 fb-1 of e+e-
annihilation data recorded with the BABAR detector. The analysis is conducted
with a partial reconstruction technique, in which only the D_s(*)+ and the soft
pion from the D*- decay are reconstructed. We measure the branching fractions
BR(B0->D_s+D*-) = (1.03 +/- 0.14 +/- 0.13 +/- 0.26)% and BR(B0->D_s*+D*-) =
(1.97 +/- 0.15 +/- 0.30 +/- 0.49)%, where the first error is statistical, the
second is systematic, and the third is the error due to the D_s+->phi pi+
branching fraction uncertainty. From the B0->D_s*+D*- angular distributions, we
measure the fraction of longitudinal polarization Gamma_L/Gamma = (51.9 +/- 5.0
+/- 2.8)%, which is consistent with theoretical predictions based on
factorization.Comment: 9 pages, 4 postscript figues, submitted to Physical Review D (Rapid
Communications
Measurement of the CKM matrix element |V(ub)| with B ---> rho e nu decays
We present a measurement of the branching fraction for the rare decays B->rho
e nu and extract a value for the magnitude of Vub, one of the smallest elements
of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix. The results are given for
five different calculations of form factors used to parametrize the hadronic
current in semileptonic decays. Using a sample of 55 million BBbar meson pairs
recorded with the BABAR detector at the PEP-II e+e- storage ring, we obtain
Br(B0->rho- e+ nu)=(3.29 +-0.42 +-0.47 +-0.60) x 10^-4 and |Vub|=(3.64 +-0.22
+-0.25 +0.39-0.56)x10^-3, where the uncertainties are statistical, systematic,
and theoretical, respectively.Comment: Submitted to Phys. Rev. Let
Measurement of the branching fraction and CP violating asymmetries in neutral B decays to D*+- D-+
We present measurements of the branching fraction and CP-violating
asymmetries for neutral B decays to D*+-D-+. The measurement uses a data sample
of approximately 88 million Y(4S) --> B Bbar decays collected with the BABAR
detector at the SLAC PEP-II asymmetric-energy B factory. We measure the
branching fraction to be (8.8 +- 1.0 +- 1.3) x 10^-4 and the time-integrated
CP-violating asymmetry between the rates to D*+D- and D*-D+ to be A = -0.03 +-
0.11 +- 0.05. We also measure the time-dependent CP-violating asymmetry
parameters to be S-+ = -0.24 +- 0.69 +- 0.12, C-+ = -0.22 +- 0.37 +- 0.10 for B
--> D*-D+ and S+- = -0.82 +- 0.75 +- 0.14$, C+- = -0.47 +- 0.40 +- 0.12 for B
--> D*+D-. In each case the first error is statistical and the second error is
systematic.Comment: 7 pages, 3 figures, published as Phys. Rev. Lett 90 (2003) 22180
Measurement of the branching fraction for inclusive semileptonic B meson decays
A largely model-independent measurement of the inclusive electron momentum
spectrum and branching fraction for semileptonic decays of B mesons is
presented based on data recorded at the Upsilon(4S) resonance with the BABAR
detector. Backgrounds from secondary charm decays are separated from prompt B
decays using charge and angular correlations between the electron from one B
meson and a high momentum electron tag from the second B meson. The resulting
branching fraction is BR(B -> X e nu) = (10.87 +-0.18(stat)+-0.30(syst))%.
Based on this measurement we determine the CKM matrix element |V_cb|
Measurement of the branching fraction for inclusive semileptonic B meson decays
A largely model-independent measurement of the inclusive electron momentum
spectrum and branching fraction for semileptonic decays of B mesons is
presented based on data recorded at the Upsilon(4S) resonance with the BABAR
detector. Backgrounds from secondary charm decays are separated from prompt B
decays using charge and angular correlations between the electron from one B
meson and a high momentum electron tag from the second B meson. The resulting
branching fraction is BR(B -> X e nu) = (10.87 +-0.18(stat)+-0.30(syst))%.
Based on this measurement we determine the CKM matrix element |V_cb|